Download EARTH SCIENCE, PAGE I. Introduction Earth Science

EARTH SCIENCE, PAGE 1
I. Introduction
Earth Science - study of the Earth and its neighbors in Space
A. Divisions of Earth Science
1. Geology
- the study of the Earth
a. Physical Geology
- study of the Earth's materials, such as minerals and rocks, and the various physical and
chemical changes that occur on its surface and in its interior
b. Historical Geology
- history of the planet and its life forms from its origin to the present
2. Oceanography
- study of the oceans and ocean phenomena
3. Meteorology
- study of the atmosphere and atmospheric phenomena
- includes studies of weather and climate
4. Astronomy
- study of the universe
B. The Earth's Environment
1. Physical Environment
- includes the "nonliving" part of the environment, including water, air, soil and rock, as well as
conditions such as temperature, humidity and sunlight
2. Earth Resources
- usable Earth materials
- includes water and soil, metallic and nonmetallic minerals, and energy resources
a. Renewable Resources
- can be replenished over relatively short time spans
- includes plants and animals for food, natural fibers for clothing, and forest products for lumber
and paper
- also includes renewable energy resources from flowing water, wind and the Sun
b. Nonrenewable Resources
- form or accumulate over such a long time span that they must be considered as fixed in total
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quantity
- include mineral resources (such as metals) and fossil fuels (such as oil, natural gas, and coal)
C. Population Growth
- 2010 estimate of World population is 6.8 billion
- the World's population is expected to reach 9.4 billion by 2050
1. Effect on Resources
- How long will supplies last?
2. Environmental Problems
- overpopulation affects air pollution, acid rain, ozone depletion and global warming
- also with loss of fertile soils due to erosion, disposal of toxic wastes, and contamination and
depletion of water resources
D. The Scientific Method
- means of discovering basic scientific principles
1. Pose a question or problem
2. Collect observations (DATA; "facts")
3. Analyze data
4. Propose hypotheses (tentative explanations)
5. Predict what would happen if hypothesis were true
6. Test predictions and discard incorrect hypotheses (= concept of Multiple Working
Hypotheses)
Null Hypothesis- no systematic relationship exists among the observations
7. Theory
- hypothesis that passes testing and has a good chance of being true
8. Scientific Law
- fundamental principles that are invariably found to be true
9. Model
- a conceptual, graphic, mathematical or physical image that is consistent with the data
a. Conceptual Model
- describes general relationships among components of a system
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b. Graphical Model
- assembles and displays data in an organized and easily-interpreted format
c. Physical Model
- miniaturized version of a system
d. Numerical Model
- consists of mathematical equations that illustrate behavior of a particular physical system;
computerized numerical models are very important for weather forcasting
II. Minerals
A. Minerals
- naturally occurring inorganic solids with definite chemical compositions and crystalline
structure
1. Chemical Composition of Minerals
a. Elements
- fundamental components, cannot be broken down to simpler substances by ordinary chemical
processes
- there are 88 naturally occurring elements
- the 8 most common are Oxygen (O), Silicon (Si), Aluminum (Al), Iron (Fe), Calcium (Ca),
Sodium (Na), Potassium (K) and Magnesium (Mg); comprise 98% of the Earth's Crust
b. Atoms
- fundamental units of elements
Nucleus - positively charged center of mass; includes protons (with mass and a positive charge)
and neutrons (with mass and a neutral charge)
Electrons - with no mass and a negative charge; the number and orientation of electrons
determines chemical behavior
c. Chemical Reactions
- filling of the outer shells of electrons
Ions = charged atoms; atoms with too few or too many electrons; includes cations (positively
charged) and anions (with negative electrical charges)
Ionic Bonding - cations and anions attract one another; Ex. = sodium and chloride join to form
salt
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Covalent Bonding - sharing of electrons between atoms; Ex. = carbon atoms in diamond
Compound - chemical combination of two or more elements
2. Crystal Structure of Minerals
- reflects the orderly arrangement of atoms
3. Physical Properties of Minerals
- use color, streak, hardness, crystal form, cleavage, fracture, luster, specific gravity, magnetism,
chemical reactivity, radioactivity, fluorescence, etc. to identify minerals
- see Mineral Lab
4. Mineral Classification
a. Based on dominant anion present in the Mineral
- including silicates, oxides, sulfides, halides, phosphates, carbonates, native elements and
hydroxides
b. Silicate Minerals
- the most abundant chemical group; constitute about 90% of the Earth's crust
- Silicate Bonding with four oxygen for each silicon (SiO4); bond directions require a tetrahedral
arrangement of the atoms; the tetrahedra may be isolated or form single chains, double chains,
sheets, or frameworks
- the most important silicates in the Earth's crust include feldspars and quartz
5. Mineral Economics
a. Ore
- part of a metal-yielding material that can be economically and legally extracted at a given time;
consists of the ore mineral and waste minerals (gangue)
b. Critical and Strategic Minerals
Critical Minerals - necessary to the economy of a country; no country is self-sufficient in mineral
resources; U. S. must import 50% or more of 24 of its 42 most important nonfuel minerals
Strategic Minerals - fuel or nonfuel minerals vital to the industry and defense of a country (Exs. =
manganese, cobalt, platinum, chromium); often stockpiled to cushion against supply
interruptions and sharp price increases
c. Mining and Processing Minerals
c1. Types of Mining
Surface Mining - remove soil, subsoil, and other strata (i.e., Overburden), and then extract a
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mineral deposit found fairly close to the Earth's surface; usually discard waste material in Spoils
Piles/Tailings
Subsurface Mining - extract a metal ore or fuel resource (Ex. = coal) from a deep underground
deposit
c2. Smelting
- separate desired mineral from the other elements in an ore mineral
c3. Environmental Effects of Mineral Extraction and Processing
- disturbs land, noise pollution, thermal pollution, produces health hazards (solid wastes; air,
water and soil pollution)
- Acid Mine Drainage - occurs when aerobic bacteria produce sulfuric acid from sulfide minerals
in spoils piles
- smelting often results in huge volumes of air pollutants
III. Rocks
- naturally-formed substances composed of minerals or mineraloids (mineraloids have fixed
composition but no crystalline structure)
A. Rock Cycle
- all rocks are continually subject to change and can be transformed into other rocks through
geologic processes
B. Igneous Rocks and Igneous Processes
Igneous Rocks - crystallize directly from magma; are the most abundant rocks within the Earth
(about 95% of all rocks)
1. Magma
- molten rock, often found within a reservoir (magma chamber)
a. Parent Magmas
- most important magmas that form igneous rocks
- include magma of basalt and granite composition
b. Magma Density
- expansion of melted magma creates less density and therefore magma tends to rise within the
Earth
- also will often move toward regions of reduced pressures
c. Crystal Fractionation
- early-formed crystals are removed from remaining magma and are prevented from reacting with
it
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- most important way in which igneous magma composition can be changed
2. Classifying and Naming Igneous Rocks
- igneous rocks are named on the basis of composition and texture
a. Composition
a1. Sialic/Felsic
- rocks rich in silica and aluminum
- sialic (high viscosity, silica-rich) magma with more viscosity (resists flow) and greater
explosiveness
- usually continental crust origin; Exs. = granite, rhyolite
a2. Mafic
- rich in iron and magnesium; ; mafic (silica-poor) magma with lower viscosity and less
explosive eruptions; usually oceanic crust origin; Exs. = basalt, gabbro
a3. Intermediate Composition
- intermediate between felsic and mafic; often found near island arcs and continental margins;
Exs. = andesite, diorite
a4. Ultramafic
- characteristic of mantle rocks
- an example is peridotite
b. Texture
- size, shape and arrangement of igneous particles
- often depends on cooling rate of magma
b1. Extrusive Igneous Rocks
- with rapid cooling and quick solidification of magma
b1a. Glassy Textures
- no crystals, very rapid cooling; Ex. = obsidian
b1b. Aphanitic
- crystals form but are microscopic size
- examples include basalt, andesite, rhyolite
b1c. Porphyritic
- with at least two sizes crystals representing multiple cooling histories
- phenocrysts (larger crystals, due to slower cooling) in finer grained groundmass (smaller
crystals, due to faster cooling)
- Examples = Rhyolite Porphyry, Andesite Porphyry, Basalt Porphyry
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b2. Plutonic/Intrusive Igneous Rocks
- solidify underground and therefore with slower cooling and larger crystals
b2a. Phaneritic
- with larger crystals
- examples include granite, diorite, gabbro, peridotite
3. Magmas and Ore Deposits
Ore - rock in which a valuable or useful mineral occurs in sufficient concentration to be
economic to mine
a. Crystal settling
- dense crystals in igneous magma sink and form layered deposits; Exs. = chromite and platinum
b. Hydrothermal Deposits
- hydrothermal solutions consist of hot, salty water forming a powerful solvent
- hydrothermal solutions are frequently the source of significant ore deposits including copper,
lead, zinc, silver and gold
C. Sedimentary Rocks
- rocks formed from the consolidation of loose sediment, by chemical precipitation, or rocks
consisting of the secretions or remains of organisms
- sedimentary rocks comprise only 5% of the total crustal volume, but constitute about 75% of
the rocks found on the continent's surface
1. Sediment
- unconsolidated accumulation of rock and mineral grains and organic matter that has been
transported and deposited by wind, water, or ice
a. Formation of Sediment is by:
a1. Weathering and Erosion of Preexisting Rocks
- forms clastic (or detrital) rocks
- clastic rocks are classified on the basis of grain size into mudstones/shales, siltstones,
sandstones and breccias/conglomerates
a2. Inorganic Precipitation of Minerals
- chemical sediments form evaporite minerals such as halite and gypsum
a3. Organic Precipitation of Minerals
- sediments precipitated biochemically by organisms, typically forming their shells
- form many limestones and cherts
a4. Conversion of Organic Matter to Rock
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- forms coal deposits
b. Lithification of Sediment
Processes which Turn Sediment to Rock Include:
Compaction of Sediment - reduces pore space ("holes")
Cementation - precipitate dissolved material in the pore spaces (including silica, calcium
carbonate, and iron oxide)
Crystallization - direct precipitation of crystals; often due to loss of solvent resulting from
evaporation
2. Sedimentary Structures
- a megascopic multigranular sedimentary feature, usually best studied in outcrops rather than in
hand specimens
a. Features in Sedimentary Rocks formed during or shortly after Deposition (Primary
Sedimentary Structures)
a1. Bedding/Stratification
- sedimentary layering is due to differences in composition, texture, color and cementation
- sedimentary layers are usually deposited horizontally
a2. Ripple Marks
- small ridges of sediment resembling a ripple of water and formed on the bedding surface of a
sediment
a3. Cross-stratification/Cross-bedding
- layers within a stratified unit that are oriented at an angle to the dominant stratification
- ripple marks and cross-bedding can be used to determine ancient current direction
b. Secondary (Postdepositional or Chemical) Sedimentary Structures
- form after sediment deposition, typically due to the precipitation of minerals dissolved in
groundwater
b1. Nodule
- irregular, round or flat structure formed by filling voids in sediment
b2. Geodes
- hollow, subspherical structures; form around water-filled pocket by crystals growing inward
b3. Concretions
- mineral segregations that replace or force aside the surrounding sediment
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3. Fossils
- remains of ancient organisms
- fossils are most commonly found within sedimentary rocks
4. Sedimentary Ore Deposits
a. Banded Iron Formations (BIFs)
- 2.6 to 1.6 billion year-old layered iron oxides and silicates; probably formed due to
bacteriogenic activity; major source of iron ore
b. Evaporites
- form from the complete evaporation of a solvent
Nonmarine Evaporites are often formed in temporary desert lakes (playas); include borax,
sodium sulfate and sodium carbonate; are very important in the chemical industry
Marine Evaporites form in shallow, restricted seas; include halite (salt) and gypsum (gypsum is
used for building materials, such as sheet rock)
c. Placers
- accumulation of sediment formed by mechanical concentration of heavy mineral particles by
currents (typically streams or waves); sources of gold, tin, platinum, diamonds and other valuable
minerals
d. Fossil Fuels
- remains of plants and animals trapped in sediment that can be used for fuel
d1. Petroleum (Crude Oil)
- gooey liquid consisting of hydrocarbon compounds and small amounts of compounds
containing oxygen, sulfur and nitrogen
- oil is relatively cheap, easily transported, with high net energy yield but may be depleted within
35 to 80 years, releases greenhouse gases and other pollutants (the Greenhouse Effect is an
increase in atmospheric temperature caused by the presence of infrared-absorbing gases)
- 13 countries forming the Organization of Petroleum Exporting Countries (OPEC) with
approximately 60% of oil reserves (Saudi Arabia with over 21%)
- the U. S. has about 1.6% of the total World oil reserves (about 21 billion barrels - Canada has
reserves of 179 billion barrels!); the United States uses over 25% of the World's oil (we use
about 69% of our oil for transportation); U. S. imports about 60% of its oil
d2. Oil Shale
- fine-grained rock containing Kerogen (solid, waxy mixture of hydrocarbon compounds)
- if heated to high temperatures can convert kerogen into a vapor that can be condensed to form a
slow-flowing heavy oil (Shale Oil)
- U. S. has large reserves of Oil Shale but it is expensive, requires large amounts of energy and
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water to process, causes pollution, and mining disturbs land surface
d3. Tar Sand
- mixture of clay, sand, water and tarlike heavy oil (Bitumen)
- Bitumen can be extracted from tar sand by heating, then purified and upgraded to synthetic
crude oil
- requires large amounts of water and energy to process, causes pollution, and mining disturbs
land surface
d4. Natural Gas
- underground deposits of gases consisting of 50% to 90% by weight methane gas and small
amounts of heavier gaseous hydrocarbon compounds such as propane and butane
- is cheaper and with more reserves than oil, cleaner and more efficient burning but must be
converted to highly explosive Liquified Natural Gas (LNG) form for effective transport overseas
and contains greenhouse gases (causes "global warming")
d5. Gas Hydrates (Clathrates)
- icelike compounds composed of water and natural gas (typically methane)
- the solid gas hydrates are typically formed within low-temperature deep ocean sediments
- there may be as many as 20 quadrillion cubic meters (700 quadrillion cubic feet) of gas hydrates
in oceanic sediments (this is double the amount of hydrocarbons in the Earth's coal, oil and
natural gas deposits combined)
- however, there is currently no commercial mining of gas hydrates
d6. Coal
- solid, combustible mixture of organic compounds with 30% to 98% carbon by weight, mixed
with varying amounts of water and small amounts of sulfur and nitrogen compounds
- is formed from buried remains of plants (most coal plants lived in swampy areas associated
with ancient deltas)
- ancient plants were subjected to heat and pressure over millions of years; increasing grade of
coal includes lignite, bituminous, and anthracite coal
- coal supplies 27% of World's commercial energy (especially electricity and steel production)
- can be converted into gaseous or liquid Synfuels (Coal Gasification converts solid coal into
synthetic natural gas, or SNG; Coal Liquefaction converts coal into liquid fuel such as methanol
or synthetic gasoline)
- most abundant fossil fuel but with bad environmental (strip mining, acid rain, etc.) and health
effects (Ex. = Black Lung Disease)
D. Metamorphic Rocks
- rocks derived from pre-existing rocks that changed form in response to changes in temperature,
pressure and the chemical environment
- metamorphism involves "solid state reactions" (chemical reactions in which melting has not
taken place)
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1. Factors that Cause and Influence Metamorphism
a. Temperature
- is especially important for determining composition of metamorphic rocks
Geothermal Gradient - the rate of increase in temperature with depth in the Earth
b. Pressure
b1. Lithostatic Pressure
- rock pressure; confining pressure makes particles become more compact but often causes grain
size to increase
b2. Directed Pressure
- deformation and shear pressures often cause foliation (parallel alignment of linear or planar
minerals or compositional banding) and folding
c. Metasomatism
- introduction of ions in solution into a rock, and the resulting alteration of that rock
- water and carbon dioxide are the most important metasomatic fluids
2. Types of Metamorphism
a. Contact (Thermal) Metamorphism
- alteration of rocks at or near contact with igneous pluton
- temperatures at 300-800°C and pressures at 100-3000 atmospheres
- the area affected by contact metamorphism is termed the Contact Aureole; aureoles seldom
exceed a few hundred meters in thickness
b. Regional Metamorphism
- developed over extensive areas and most often related to Orogenies (mountain-building events)
- caused by combination of heat, lithostatic and directed pressures and chemically active fluids
- with increased metamorphism change shale to Slate -> Phyllite -> Schist -> Gneiss ->
Migmatite (a rock that is intermediate between metamorphic and igneous) -> Granite
c. Impact metamorphism
- due to bolide (meteorite, asteroid, comet) collisions
- common on terrestrial planets and moons (satellites) within the Solar System
IV. Weathering, Soil and Mass Wasting
A. Weathering
- decomposition and disintegration of rocks and minerals at the Earth's surface by mechanical and
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chemical processes
Erosion - removal of weathered rocks and minerals from the place where they formed by moving
water, gravity, wind or glaciers
1. Types of Weathering
a. Mechanical Weathering
- physical degradation of rocks; results in size reduction of particles but no change of chemistry
Frost Wedging - expansion of freezing water in rock fractures; often results in accumulation of
angular debris as Talus Slopes
Abrasion - wearing and grinding of rock against rock; examples include rocks in stream beds,
below glaciers, and rocks sand-blasted by the wind
Organic Activity - "root wedging" of plants growing in rock fractures; bioturbation (disturbing
sediment through the activities of organisms)
Exfoliation - pressure release fracturing due to removal of "overburden" above igneous plutons;
often form concentric fractured layers (Exfoliation Sheets)
b. Chemical Weathering
- breakdown or decomposition of minerals by chemical reaction with water, with other chemicals
dissolved in water, or with gases in the air
- amount of chemical weathering depends primarily on climate influences, including temperature,
amount of water, and amount of vegetation
-Type of parent material also affects weathering
B. Soil
- surface accumulation of weathered rock and organic matter
- also defined as material capable of supporting plant growth
1. Soil Components
a. Mineral Grains - sand to clay size grains
Loam - mixture of sand, clay, and organic matter
b. Organic Material
Litter - organic matter on the surface
Humus - decomposed organic matter in the soil
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2. Soil Profiles
O Horizon - topmost layer, usually dark; mixture of humus and litter
A Horizon - often combined with the O Horizon in classifications (= "Topsoil"); mixture of
humus and minerals; with high density of organisms; Zone of Leaching (rain and organic acids
leach ions; clay and nutrients are removed)
B Horizon - transition between soil and bedrock; zone penetrated by roots; Zone of
Accumulation (clay entrapped and ions are precipitated)
C Horizon - unweathered to slightly weathered rock
- below soil zones may be R or Regolith Horizon (if consolidated on weathered bedrock
underlying the soil)
3. Soil Problems
a. Soil Erosion
- movement of soil components (especially surface-litter and topsoil) from one place to another,
usually by flowing water or wind (especially in areas where vegetation is lost)
- topsoil is eroding faster than it forms in about 1/3 of World's croplands (mostly Asia and
Africa); especially due to overgrazing, deforestation, and unsustainable farming methods
b. Desertification
- conversion of rangeland, rain-fed cropland or irrigated cropland to desert, with a 10% or more
drop in agricultural productivity
- usually due to combination of overgrazing, soil erosion, prolonged drought, and climate change
c. Misuse of Inorganic Fertilizers
- inorganic fertilizers do not add humus to the soil and may result in pollution (especially cultural
eutrophication)
d. Irrigation Misuse
- about 18% of World's land is irrigated; produces about 1/3 World food supply
- improper irrigation leads to accumulation of salts in the soil (Salinization) and raises the water
table to envelop and kill plant roots (Waterlogging)
4. Soil Conservation
- reduce soil erosion and restore soil fertility
a. Reducing Soil Erosion
- use Conservation-tillage farming that disturbs soil as little as possible when planting crops (use
minimum-tillage or no-tillage farming)
- Terrace steeper slopes, Contour Farming gently sloping land, Strip Crop (plant strips of soil-
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saving cover crops between grains, etc.), or by Alley Cropping/Agroforestry (plant crop "alleys"
between trees and shrubs), Gully Reclamation (dam and vegetate gullies), and building
Windbreaks
b. Maintaining and Restoring Soil Fertility
- use organic fertilizer [including animal manure, green manure (vegetation plowed into the soil),
or compost (partially decomposed organic plant and animal matter)] or commercial inorganic
fertilizer (mixtures of plant nutrients such as nitrates, phosphates and potassium)
- use Crop Rotation and alternate planting nutrient-depleting plants (Ex. = corn, tobacco, cotton)
with nutrient-restoring plants (Exs. = legumes, oats, barley, rye, or sorghum)
C. Mass Wasting
- movement of earth material downslope, primarily by gravity
1. Factors that control Mass Wasting
a. Vertical Distance (Relief) and Steepness of Slope
b. Type of Rock and Orientation of Rock Layers
b1. Shear Strength
- resistance to being pulled apart
- massive rock types with high sheer strength; loose regolith with low shear strength
b2. Rock Orientation
- position and orientation of rocks lead to stable or unstable situations
c. Nature of Unconsolidated Debris
Angle of Repose - maximum stable slope angle (for boulders is about 45°; for sand about 35°)
d. Water and Vegetation
- small amounts of water increases shear strength of sediment; large amounts lowers shear
strength of sediments and acts as a lubricant to ease the movement of sediment
2. Classification of Mass Movements
a. Rapid Movement
a1. Slump (Slope failure)
- downward and outward movement of rock or unconsolidated material traveling as a unit
- occurs where original slope is sharply steepened
a2. Rock Slides/Landslides/Rock Avalanches
- sudden, rapid slides of bedrock along planes of weakness
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- the rapid movement may be aided by air trapped beneath the debris, and have been known to
reach speeds in excess of 125 miles per hour
a3. Mudflows and Debris Flows
- well-mixed mass of rock, earth and water that flows down valley slopes with consistency of
newly mixed concrete
- often in arid or semi-arid environments
a4. Talus
- slope built of accumulation of rock fragments at foot of cliff or ridge
b. Slow Movements
b1. Creep
- slow down-slope movement of surface material caused by gravity and moisture
V. Running Water and Groundwater
A. The Hydrologic System
- the system of moving water at the Earth's surface
1. Water returns to the atmosphere by:
a. Evaporation
b. Transpiration
-process by which water is released into the atmosphere by plants
2. Water returns to land by means of precipitation
3. Water is temporarily stored:
a. in bodies of water
b. in glaciers
c. as groundwater
4. Runoff
- water that flows over the land surface
B. Rivers (Fluvial Environments)
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1. River Systems
- a river consists of a main channel and all of the tributaries that flow into it
a. Drainage Basin
- total area that contributes water to a single river system
- is primarily an area of erosion
b. Divide
- a ridge separating two drainage basins
c. Trunk Stream
- forms the transporting system into which tributaries flow
- is an area of erosion and deposition
2. Flow of water in streams is influenced by:
a. Volume of water
Discharge - amount of water passing a given point during a specific interval of time
Perennial Streams - flow continually throughout the year; with substantial input by groundwater
(= base flow)
Intermittent (Ephemeral) Streams - stream through which water flows only part of the time
b. Stream Velocity
- depends on shape and roughness of channel, type of stream pattern, gradient (vertical drop of
stream over a distance; steepest in headwaters and decreases downslope) and volume of water
c. Shape and size of channel
- stream channels adjust shapes to minimize resistance to flow
d. Stream Gradient
- slope of the stream bed (in feet per mile or meters per kilometer)
3. Stream Erosion
- is due to hydraulic action (currents wash sediments downstream), abrasion, and dissolution
4. Stream Deposition
- occurs in the lower reaches of stream systems (in areas of lower gradient)
- most features are formed during flood stages
- depositional features include floodplains, point bars, natural levees and deltas
5. Types of Rivers and Streams
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a. Meandering Rivers
- sinuous stream or river; created in areas of low gradient and where the stream has substantial
base flow (base flow is the amount of water contributed by springs)
b. Braided Rivers
- stream with a complex of converging and diverging channels separated by bars or islands; form
where more sediment is available than can be removed by the discharge of the stream
- braided rivers typically form in semiarid regions, in mountains, in areas with glacial outwash, or
in regions with monsoonal climates
6. Fluvial Features
a. Flood plain
- the flat, occasionally flooded area bordering a stream
b. Meander
- a broad, looping bend in a river
c. Oxbow lake
- a lake fromed in the channel of an abandoned meander
d. Cutbank
- outer bank in the bend of a meandering stream that is the site of maximum erosion
e. Point bar
- a crescent-shaped accumulation of sand and gravel deposited on the inside of a meander bend
f. Natural levee
- a broad, low embankment built up along the banks of a river channel during floods
g. Backswamp
- the marshy area of a flood plain at some distance beyond and lower than the natural levees that
confine the river
7. Deltas
- deposits that form where a stream enters a larger body of water
- often are triangular-shaped due to outward branching of main stream into smaller distributary
channels
- during the constructional phase the delta progrades (builds out), deposits sediment around the
mouth of the channel, and eventually switches distributary channels
- during the destructional, or abandonment, phase the shape of the delta is modified by the action
of waves, tides, and delta subsidence
C. Groundwater
- underground water; constitutes about 70 times the amount of water found in rivers and streams
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1. Groundwater potential
- relative ability of rock or sediment to store underground water
- depends on porosity (the percentage of open space in a rock or sediment); unconsolidated
sediment contains up to 50% porosity; sandstones have about 5-20% porosity
2. Permeability
- speed of groundwater flow through rock; averages 4 centimeters per day or 15 meters per year
3. Vertical Distribution of Groundwater
a. Soil Water Zone (Belt of Soil Moisture)
- Small droplets of water in plant roots
b. Aeration Zone
- below soil water zone
- pores partially filled with "suspended" water
c. Saturation Zone
- beneath zone of aeration
- pores completely filled with groundwater
4. Water Table
- surface between the Zone of Aeration and the Zone of Saturation
a. Recharge
- addition of water to the groundwater reservoir
- height of water table depends on amount of recharge versus amount of groundwater drawn off
by plants and humans
b. Aquifer
- permeable material that carries underground water
Unconfined aquifer - with a "free water table" at atmospheric pressure
Confined aquifer - confined between Aquicludes (impermeable sediment or rock stopping flow
of groundwater); pressure greater than atmospheric pressure; if a well is drilled into confined
aquifer water rises under its own pressure (= Artesian Well)
c. Cone of Depression
- conical depression in water table where groundwater is pumped out at faster rate than can be
recharged
5. Spring
- surface discharge of groundwater
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6. Water Resources and Water Pollution
- only 3% of Earth's water is freshwater, and only about .003% is readily available
a. Sources of Water
a1. Surface Water
- found in streams, lakes, wetlands and artificial reservoirs
- Watershed = land area that delivers surface runoff (water, sediment and dissolved substances)
via small streams to a major stream/river
a2. Groundwater
- most groundwater is used for agricultural irrigation (about 4 times more water is used for
irrigation than for public water supply)
- in many areas groundwater is being removed at a much higher rate than can be replaced through
recharge (Ex. = the Ogallala Aquifer on the U. S. High Plains)
b. Water Resource Problems
b1. Drought
- area does not get enough water due to lower than normal precipitation, higher than normal
temperatures (increase evaporation), or both
- 40% of World population lives in drought-prone areas
- drought effects increased due to population increase, deforestation, desertification, monoculture
(heavy reliance on one type of plant or animal), and politics
b2. Floods
- increased rainfall or rapid snow melt causes river waters to overflow their channel and cover the
Floodplain
- floodplains often support high human populations due to rich soils, abundant water, and ease of
irrigation
- floods more severe where vegetation removed and/or where urbanization increases runoff
- reduce flood risks by channelization (increases flow), artificial levees (build along banks to
prevent overflow), flood control dams, or constructing flood-frequency curves (show how often a
flood of a certain size should happen in order to plan development)
b3. Desalination
- remove dissolved salts from ocean water or brackish (slightly salty) groundwater
- mostly use distillation (evaporate saltwater by heat and condense it to freshwater; very
expensive and produces huge amounts of brine) and reverse osmosis (pump saltwater through a
porous membrane that traps salts)
b4. Water Pollution
- 1.5 billion people in the World do not have safe drinking water
- major types of water pollutants include pathogens (disease-causing organisms), organic wastes
EARTH SCIENCE, PAGE 20
(often depletes oxygen), inorganic chemicals (such as lead and mercury), plant nutrients (lead to
eutrophication), organic chemicals (such as petroleum products, plastics and pesticides),
sediment and suspended matter, and radioactive wastes
b4a. Pollution Sources
Point Source Pollution - discharge pollution from particular sources (discharge from pipes,
ditches or sewers into surface water bodies)
Nonpoint Source Pollution - cannot be traced to any single source (mostly agricultural; worst
water pollution sources)
b4b. Water Pollution Areas
Stream Pollution - flowing streams usually recover rapidly from pollution through dilution and
bacterial decay
Lake Pollution - dilution usually less effective due to water stratification; nitrates and phosphates
from agricultural areas and sewers cause cultural eutrophication (algae bloom and die, using up
lake oxygen)
Groundwater Pollution - slow water movement does not dilute pollution and nondegradable
wastes remain there permanently
Ocean Pollution - is worst around coastal areas (wetlands, estuaries, coral reefs, mangrove
swamps) due to large human populations and often "sluggish" water circulation
b4c. Water Treatment
- pure groundwater requires little treatment
- surface water usually stored in reservoir for several days (suspended matter settles and oxygen
increases), then run water through sand filters, then through activated charcoal, and then
disinfected
D. Karst topography
- areas underlain by carbonate rock (limestone or dolomite) which display features created by
dissolution
1. Types of Karst Features
a. Sinkholes
- irregular depressions formed by dissolution of underlying carbonate rocks
b. Dry Valleys
- areas that lack surface drainage (streams); the surface water quickly flows underground due to
the presence of caverns
EARTH SCIENCE, PAGE 21
c. Tower Karst
- develops in tropical or subtropical regions with thick beds of highly jointed limestone;
groundwater dissolves large amounts of limestone along the joints, leaving the residual towers
(Examples are in southern China and Puerto Rico)
d. Caves (Caverns)
- an underground chamber or series of chambers formed from the dissolution of rocks (typically
carbonates such as limestone or dolomite, but may also be formed within evaporite rocks such as
gypsum)
2. Cave Features
a. Dripstone
- features formed from calcium carbonate dripping off cave ceilings and walls
- the collective term for dripstone features in caves are Speleothems
Types of Speleothems:
Stalactites - extend down from cave ceilings
Stalagmites - grow upward and form by calcium carbonate dripping on floor
Pillars (columns) - form where a stalactite and stalagmite meet
Flowstone (Travertine) - Water dripping down cave walls and across cave floors deposits bands
of calcium carbonate
E. Geysers
- a type of hot spring that intermittently ejects steam and hot water due to the interaction of
groundwater with an underlying heat source
F. Geothermal Energy
- geysers (or drilling into hot springs) may be used to drive turbines to produce electricity
- geothermal energy provides about 1/2 of one percent of the World's energy, but is very
important in some regions (such as Iceland)
VI. Glaciers, Deserts and Wind
A. Glaciers
- systems of flowing ice that originate on land through the accumulation and recrystallization of
snow; therefore more snow must fall each year than is lost by melting and evaporation
1. Formation of Glaciers
EARTH SCIENCE, PAGE 22
a. Stages of ice formation
a1. Snow - "powder"; loose material, with high porosity
a2. Firn/neve - granular ice
a3. Glacial ice - composed of tightly interlocking ice crystals
2. Glacial Zones
a. Zone of Accumulation
- with net gain of ice
b. Zone of Ablation
- where ice leaves the system by melting and evaporation
3. Zones of Glacial Movement
a. Fracture (Brittle) Zone
- upper glacial zone (less than 50 meters thick) that breaks sharply rather than flows (forms
crevasses)
b. Plastic (Flow) Zone
- lower glacial zone (at greater than 50 meters depth) that behaves plastically due to pressure of
overlying ice
4. Types of Glaciers
a. Alpine (Valley) Glaciers
- long, narrow rivers of ice that originate in the snowfields of high mountain ranges and flow
down preexisting stream valleys
- size of alpine glaciers depends upon temperature and amount of precipitation
a1. Erosional Features of Alpine Glaciers Include:
Cirque - an amphitheater-shaped depression at the head of a glacial valley, excavated mainly by
ice plucking and frost wedging
Tarn - small mountain lake within a cirque
Arête - a narrow, sharp ridge separating two adjacent glacial valleys
Horn- A sharp peak formed at the intersection of the headwalls of three or more cirques
EARTH SCIENCE, PAGE 23
U-shaped Glacial Valley- shape of valley in cross-section due to glacial erosion
Hanging Valley - a tributary valley with the floor lying ("hanging") above the valley floor of the
main stream or shore to which it flows; commonly created by deepening of the main valley by
glaciation
Fjord- a glaciated valley flooded by the sea to form a long, narrow, steep-walled inlet
a2. Depositional Features of Alpine Glaciers
Moraine - a general term for a landform composed of till (till is the material deposited by glacial
ice); types of moraines include Terminal, Lateral, Medial and Recessional Moraines
Outwash Plain - the area beyond the margins of a glacier where meltwater deposits sand, gravel,
and mud washed out from the glacier
b. Continental glacier
- thick ice sheet covering large parts of a continent (Exs. = Greenland, Antarctica)
- Continental Glaciers are often with associated:
b1. Icebergs
- floating masses of glacial ice separated and broken away from ice sheets
- Pinnacle Icebergs are typically formed from Alpine Glaciers; Tabular Icebergs are typically
formed from Continental Glaciers
b2. Ice shelves
- floating glacial ice attached to ice sheets
- when Ice Shelves break off in the ocean, they may form huge Ice Islands
b3. Erosional Features of Continental Glaciers
Glacial Striation - a scratch or groove produced on the surface of a rock by a glacier
Kettle - a closed depression in a deposit of glacial drift formed where a block of ice was buried or
partly buried and then melted
b4. Depositional Features of Continental Glaciers
- continental glaciers may form Terminal (End), Recessional and Ground Moraines (these often
produce a landscape of low, gently-rolling hills)
Drumlin - a smooth, glacially streamlined hill that is elongate in the direction of ice movement;
drumlins are usually composed of till
EARTH SCIENCE, PAGE 24
Erratic - a large boulder carried by glacial ice to an area far removed from its point of origin
Esker - a long, narrow, sinuous ridge of stratified glacial drift deposited by a stream flowing
beneath a glacier in a tunnel or in a subglacial stream bed
Loess - unconsolidated, wind-deposited silt and dust derived from glacial regions or deserts
6. Major episodes of Glaciation
- in the Earth's past, great ice sheets have covered large sections of the earth where no ice now
exists (Exs.= PreCambrian, Late Paleozoic and Pleistocene "Ice Ages")
B. Deserts
- areas of low precipitation (less than 25 centimeters/ 10 inches per year)
- deserts are characterized by Internal Drainage (where water flows toward the center of the
desert basin, rather than to the sea)
Semiarid area (Steppe) - with 25-50 centimeters per year precipitation (10-20 inches)
1. Types of Deserts
a. Climatic (Tropical) Deserts
- occur in subtropical latitudes (centered at 30° north and south of the equator)
- formed by atmospheric circulation patterns
b. Topographic (Rain Shadow) Deserts
- deficient in rainfall because either located in the center of continents or cut off from rainbearing winds by high mountains
c. Coastal Deserts
- areas that are arid because they are located at coastlines bordered by cold, moisture-deficient
currents
2. Desert Landforms
- most desert features are formed by the action of water
- deserts are often associated with Basin-and-Range Topography, with bare rock areas along the
ranges, and with alluvial fans, arroyos, dunes and playas toward the center of the basin
a. Depositional Features in Deserts
a1. Dune
- a low mound of fine-grained material that accumulates as a result of sediment transport in a
current system
Eolian Dunes - sand dunes formed by the wind; eolian dunes are often formed in deserts
EARTH SCIENCE, PAGE 25
a2. Playa
- a depression in the center of a desert basin, the site of occasional temporary lakes
a3. Alluvial fan
- a fan-shaped deposit of sediment built by a stream where it emerges from an upland or a
mountain range into a broad valley or plain; common in arid and semi-arid climates but are not
restricted to them
a4. Bajada
- the surface of a system of coalesced alluvial fans
b. Desert Erosional Processes
- erosional features are more common in deserts than depositional features (the dominant features
of deserts are typically bare-rock surfaces, termed Hamadas)
- wind often removes finer-grained material, leaving coarse pebbles and gravel (Desert
Pavement); this gravel may be faceted and polished by the wind to create Ventifacts
Common Erosional Features in Deserts Include:
b1. Stream Features
Arroyo (Wadi) - intermittent desert stream
b2. Flat-Topped Erosional Topography
Plateau - an extensive, flat upland area
Mesa - a flat-topped, steep-sided highland capped with a resistant rock formation; a mesa is
smaller than a plateau but larger than a butte
Butte - a somewhat isolated hill, usually capped with a resistant layer of rock and bordered by
talus; a butte is an erosion remnant of a formerly more extensive slope
VII. Plate Tectonics
A. Continental Drift
1. Alfred Wegener
- German meteorologist and polar explorer (1880-1930)
- set forth Continental Drift theory in 1912, and published "The Origin of Continents and
Oceans" in 1915 (which outlined the evidence for Continental Drift)
2. Wegener's Evidence Included:
EARTH SCIENCE, PAGE 26
a. Fit of Continents
- continental coastlines form a puzzle-like fit (later geoscientists found that edges of continental
shelves form an even better fit)
- Wegener believed that all continents were once joined into a single huge supercontinent
(Pangaea) surrounded by a World ocean (Panthalassa)
- Pangaea broke apart into a northern continent (Laurasia) and southern continent (Gondwana)
b. Fossil Evidence
- distribution of the fossil plant Glossopteris and the reptile Mesosaurus on the Gondwana
continents indicates that they were once joined
c. Paleoclimatology
- distribution of glacial deposits (tillites), ancient deserts and reefs, and coal deposits indicate the
continents were one joined and were at different paleolatitudes
d. Geologic Evidence
- matching of different rock types indicate that the continents were once joined
3. The Demise of Continental Drift Theory
- Wegener believed that the continents were like "boats" (plowing through the ocean basins) or
"sleds" (sliding on top of oceanic rocks), with the continental crust moving upon the mantle
- there is no evidence that the continents moved through or over the ocean basins; the crust and
uppermost mantle are joined together as a rigid unit
B. Earth and Rock Magnetism
- the Earth is analogous to a bar magnet, with a "north" and "south" magnetic pole
- Earth magnetism is believed to be due to movement in the Earth's core
Paleomagnetism - ancient magnetism preserved in iron-rich rocks
1. Magnetic Polarity
- the Earth's magnetic polarity "flips" through time
Normal Magnetic Polarity - the same as today's polarity
Reversed Magnetic Polarity - opposite today's polarity
2. Seafloor Spreading
- the process through which plates diverge and new lithosphere is created at midoceanic ridges
- youngest rocks are nearest to the midoceanic ridges
- during seafloor spreading the polarity of the Earth's magnetic field alternates, which is
preserved as bands of normal and reversed polarity "stripes" in the magnetized basaltic crust
C. Plate Tectonics
- the theory that the Earth is divided into a series of rigid lithospheric plates that can move over
the Earth's surface
EARTH SCIENCE, PAGE 27
1. Types of lithospheric plates
a. Oceanic (Simatic) Plates
- formed from basalt being produced along Rift Zones at mid-oceanic ridges; have high specific
gravity and therefore form basin areas; constitute 71% of Earth's surface
b. Continental (Sialic) Plates
- granitic composition and form continental areas
2. Types of Plate Boundaries
a. Divergent Plate Boundaries
a1. Oceanic Divergent Boundaries
- new simatic oceanic plate material is produced at mid-oceanic ridges through seafloor
spreading
- rates of seafloor spreading average 2-9 centimeters per year as indicated by measurements from
satellites and "laser ranging"
- mid-oceanic ridges constitute a continuous mountain chain that encircles the globe
(approximately 80,000 km long, 1500 km wide, and rises 3 km above the abyssal seafloor)
- age of the ocean floor is determined by radiometric dating of basalt, study of microfossils, and
correlation of magnetic "stripes"; oldest ocean rocks are about 200 million years old
a2. Continental Divergent Boundaries
- continental "breakup" (rifting) produces rift valleys
- rifting produces basalt and igneous rocks of mixed composition
- continued continental divergence often creates a passive continental margin (with wide
continental shelves upon which wedges of land-derived terrigenous sediments are deposited and
carbonate platforms build)
b. Convergent Plate Boundaries
- tectonically active boundaries, typically with relatively narrow continental shelves
b1. Ocean-Ocean Convergent Boundaries
- produces island arc systems (Exs. = Aleutian Islands; Japan) through subduction (oceanic plate
"dives" beneath another oceanic plate)
- island arc systems are typically andesite-rich
Deep-Ocean Trench - a narrow, elongate depression on the seafloor; trenches are formed by
lithospheric plates subducting into the mantle; in the Pacific Ocean many exceed 10,000 meters
(33,000 feet) in depth
b2. Ocean-Continent Convergent Boundaries
- produces magmatic arcs (Ex. = Andes Mountains) by oceanic plate subduction beneath
continental plate
EARTH SCIENCE, PAGE 28
- island and magmatic arcs are areas where oceanic lithospheric plates are being recycled through
subduction
b3. Continent-Continent Convergent Boundaries
- often produces fold mountain belts (Ex. = Himalyas) through suturing of granitic continental
plates
c. Transform Plate Boundaries
- shear boundaries in which plates slide past one another (Ex. = San Andreas Fault, California)
- transform faults offset mid-oceanic ridges at perpendicular angles; develop due to different
rates of seafloor spreading and due to fracturing of a round object (the Earth's surface)
d. Hot Spots and Mantle Plumes
- chains of seamounts and volcanic islands are often formed by lithospheric plates moving over
"fixed" mantle plumes or hot spots
- "weight" of the islands causes isostatic sinking and the formation of flat-topped submarine
guyots and coral atolls
- may show direction of plate movement (Example = Hawaiian Islands)
VIII. Earthquakes and Earth's Interior
Earthquake - perceptible trembling to violent shaking of the ground produced by the sudden
displacement of rocks below the Earth's surface
A. Seismology - study of earthquakes
B. Effects of Earthquakes
1. Fire
- has been the major causes of damage by many earthquakes
2. Damage to Human-Built Structures due to ground movement
3. Destruction by Tsunamis (Seismic Sea Waves) - large ocean wave generated at time of
volcanic eruption or earthquake, which may cause tremendous destruction and death (the 2004
Indonesian tsunami killed more than 230,000!)
4. Landslides caused by earthquakes
C. Interpreting Earthquakes
- locate them and determine their strength
1. Locating Earthquakes
EARTH SCIENCE, PAGE 29
a. Earthquake Focus
- source of given set of earthquake waves
b. Earthquake Epicenter
- area on Earth's surface directly above the focus of an earthquake
2. Earthquake strength
a. Earthquake intensity
- measure of the extent to which human-built structures are damaged
- intensity measured by Mercalli Scale
b. Earthquake magnitude
- measure of the total energy released by an earthquake
-described according to Richter Magnitude Scale
- Each earthquake number represents approximately ten times more amplitude than the
preceeding number and a 32-fold increase in energy!
c. Recording earthquakes
Seismograph - instrument for recording earthquake vibrations
- calculate position of an earthquake by means of Time-Distance Graphs
D. Earth Waves
1. Body Waves - transmit energy through the earth
a. P (Primary) Waves
- earthquake body waves that travel fastest, moving the particles forward and backward
b. S (Shear) Wave
- wave that advances by shearing displacement of the rock
2. Surface Waves
- earthquake waves that travel along the surface
E. Earth Structure
1. Shadow zones
a. P-wave Shadow Zone
- zone between approximately 103° and 143° from earthquake epicenter in which P waves do not
appear
EARTH SCIENCE, PAGE 30
b. S-Wave Shadow Zone
- zone between approximately 103° and 180° from earthquake epicenter in which S waves do not
appear
- shadow zones indicate the presence of the Earth's Core
- the S Wave Shadow Zone indicates that the Earth's core is liquid
2. Earth Discontinuities
a. Gutenberg discontinuity
- boundary between the core and mantle (at 2900 kilometers depth)
b. Mohorovicic Discontinuity
- boundary between the crust and mantle
- 6 km beneath ocean and 30 kilometers beneath continents
IX. Volcanoes and Other Igneous Activity
A. Volcanic Eruptions
1. Magma Viscosity
- magma viscosity is the "stickiness" of the magma
- magmas with higher viscosity are more explosive
The nature of volcanic eruptions are often related to changes in magma viscosity due to:
2. Magma Temperature
- lower temperature magmas have a higher viscosity
3. Magma Composition
- the greater the silica content of a magma, the greater the viscosity
- basalt has about 50% silica; granite has more than 70% silica; therefore rhyolite magmas are
more viscous (and explosive) than basalt magmas
4. Amount of Volatiles
- volatiles are gaseous components of magmas, especially water
- higher water content creates more fluid magmas
B. Volcanic Landforms
1. Lava Structures and Textures
a. Pahoehoe Lava
- lava flow with a smooth, ropy appearance
- develops where there is fluid basaltic lava
EARTH SCIENCE, PAGE 31
- often develop Lava Tubes/Tunnels (horizontal conduits in the interior of lava flows through
which fluid lavas may flow great distances; if the molten lava continues its forward motion,
cave-like voids are left within the Pahoehoe flows)
b. Aa Lava
- jagged, blocky lava
- develops where there is more viscous lava; often vesicular (with holes)
2. Pyroclastic Rocks
- formed from rock and lava fragments (tephra, pyroclasts) derived from an explosive volcanic
eruption; form tuffs and volcanic breccias and agglomerates
3. Volcanoes and their Associated Features
a. Shield Volcanoes
- volcanoes with low, flat, broad profiles
- formed from low viscosity (basaltic) eruptions; Ex. = Hawaiian Island Volcanoes
b. Cinder Cone
- small volcano made of pyroclastic material; usually basalt to andesite composition
- typically symmetrical profile with a relatively steep (about 30°) slope
- grow rapidly (Ex. = Paricutin Volcano, Mexico)
c. Composite Cones (Stratovolcanoes)
- volcanic cone formed from interlayered lava flows and pyroclastic deposits
- mostly formed from andesite lava and pyroclastics
- stratovolcanoes are the most dangerous and destructive volcanoes, due to their explosive nature
(which is caused by their viscous silica-rich magmas that resist flow)
- examples include volcanoes of the Cascade Range in the U. S. Pacific Northwest (Mount St.
Helens, Mount Rainier, Mount Hood), as well as Vesuvius in Italy
d. Calderas
- large, bowl-shaped summit depressions in volcanoes created by collapse or explosion
e. Ash Flows
- mixtures of gas and fine pyroclastic material flows down the sides of volcanoes; ash flows often
form tuffs
Ignimbrites (Nuée Ardentes) - hot (up to 1000°C or more), glowing cloud of volcanic ash and gas
that can rush down slopes of volcanoes at over 100 kms (60 miles) per hour
C. Plutons
- igneous structures formed at depth
- often defined on the basis of morphology and whether the contacts are parallel to the structure
of the adjacent rocks (concordant plutons) or having contacts that cut across or are set an an
EARTH SCIENCE, PAGE 32
angle to the structure of the adjacent rocks (discordant plutons)
1. Types of Plutons
a. Batholith
- massive, discordant pluton, typically composed of granite
- often hundreds of square kilometers in area and averages 10 kms thickness
b. Stock
- similar to a batholith but surface less than 100 square kilometers (less than 35 square miles)
c. Dike
- a tabular discordant pluton
- forms where magma fills in fractures cutting across rocks; occasionally occurs in groups (dike
swarms)
d. Sill
- tabular concordant pluton
- often formed where more fluid magma (ex. = basalt) is injected between rock layers
e. Laccolith
- concordant, mushroom-shaped concordant pluton that domes the country rock above
- often formed from silica-rich magma
X. Mountain Building
A. Mountain Ranges
- linear sets of mountains related by position, direction, age and geologic structure
- are created by linear forces, typically associated with plate tectonic margins
Orogeny - tectonic, plutonic and metamorphic processes involved in mountain building
1. Tectonic Activity associated with Mountain Building
a. Folding and Faulting
- results in rock deformation
b. Volcanic and Plutonic Activity
c. Earthquakes
d. Metamorphism
2. Types of Plate Boundaries
EARTH SCIENCE, PAGE 33
- produce different types of mountains
a. Divergent Plate Boundaries
- tensional activity creates horsts (fault blocks uplifted relative to those on either side) and
grabens (fault blocks dropped relative to the adjacent blocks)
- fault block mountains typically rise sharply from the surrounding terrain; include the Sierra
Nevada of California and the Grand Tetons of Wyoming
b. Transform Plate Boundaries
- shear faults often creates "slivers" of mountain ranges, such as the Coast Ranges in California
c. Convergent Plate Boundaries
- most important orogenic areas
- form several types of distinctive mountain ranges, depending upon the type of plate
convergence
c1. Island Arc Settings
- development of curved island chains created through subduction of oceanic plates (Ex. = JapanType Margins)
c2. Magmatic Arcs
- subduction of oceanic plates beneath continental plates leads to development of andesite
volcanoes (such as those that form the Andes Mountains)
c3. Continental Collision
- convergence and collision of continental plates "sutures" the continents together, forming
mountains such as the Himalayas
B. Stress and Strain
Stress - force applied to an object
Strain - deformation due to stress
1. Factors which control strain in different materials
a. Nature of the Material
- brittle materials (granite, gneiss, quartzite, etc.) act differently than plastic materials (shale,
phyllite, schist, etc.)
b. Temperature
- higher temperatures favor plastic behavior
c. Pressure
- high pressures favor plastic behavior
EARTH SCIENCE, PAGE 34
d. Time
- stress over a long time period favors plastic behavior
C. Structural Geology
- the study of features formed due to rock deformation
1. Structural Attitude
- position in space of rock layers
- Attitude is Defined By:
a. Strike
- direction of a horizontal line in the plane of bedding
b. Dip
- direction in which the rock layer is tilted down from the horizontal; is perpendicular to the
strike; angle between the horizontal plane and the bedding plane
2. Folds
- bends or flexures in rocks created by ductile deformation
a. Parts of a Fold
Limbs (Flanks) - opposite sides of a fold
Fold Axis - line that traces the maximum curvature of a folded layer and separates the two limbs
Axial Plane - imaginary plane which connects the fold axes of each rock layer and divides the
folds symmetrically
b. Major Types of Folds
Anticline - fold in which limbs dip away from one another and away from the fold axis; the
oldest eroded bed is on the inside of the structure
Syncline - fold in which the limbs dip toward one another and toward the fold axis; oldest eroded
bed is on the outside of the structure
Structural Dome - anticline roughly as wide as it is long; dips outward in all directions (oldest
exposed bed on inside)
Structural Basin - syncline roughly as wide as it is long; dips toward central portion of structure
3. Joints and Faults
EARTH SCIENCE, PAGE 35
a. Joint
- break in rock mass with no relative movement of rock on opposite sides of break
b. Fault
- surface of rock rupture where there has been relative movement on opposite sides of the break
b1. Parts of a Fault
Hanging Wall - block involved in fault movement that would hang overhead for a person
standing in tunnel along or across fault
Footwall - block involved in fault movement that would be under feet of person standing in
tunnel along or across a fault
b2. Types of Faults
b2a. Dip-Slip Fault - fault in which displacement is in direction of fault's dip; includes
normal, reverse and thrust faults
Normal Fault - hanging wall moves down relative to footwall
Reverse Fault - hanging wall moves up relative to footwall
Thrust Fault - "low angle reverse fault", in which hanging wall moves up relative to footwall but
dip is gentler (usually less than 20°) than that seen in a reverse fault
b2b. Strike-Slip Faults
- faults with movement parallel to strike
XI. Geologic Time
Stratigraphy - study of rock layers (strata)
- Lithostratigraphy and biostratigraphy have been the major ways in which Relative Geologic
Time (sequencing geologic events) has been established
A. Lithostratigraphy (Physical Stratigraphy)
- defines rock units on the basis of their physical features (i.e. lithologic features)
1. Stratigraphic Laws
a. Superposition
- in series of undisturbed strata, the oldest bed is on the bottom
EARTH SCIENCE, PAGE 36
b. Original Horizontality
- sedimentary units are originally deposited in horizontal layers; if the layers are not horizontal,
the rocks have been deformed
c. Cross-cutting Relationships
- a unit that cuts across another unit is younger than the unit it cuts across
d. Inclusions
- a rock included within another unit is older than that unit
2. Formations
- basic mapping unit in stratigraphy
- formations can be subdivided into Members and combined to form Groups
3. Defining Formal Rock Units
a. Conformities
- contacts between rocks which exhibit continuous depositional histories
b. Unconformities
- gap in rock record due to erosion or nondeposition; often forms contacts between groups or
formations
b1. Angular Unconformity
- surface separating tilted or folded strata from overlying undisturbed strata
b2. Disconformity
-unconformity between essentially parallel strata
b3. Nonconformity
- erosion surface between sedimentary and igneous/metamorphic rocks
4. Correlation
- demonstrating equivalency of stratigraphic units
- Correlation may be established by "walking out" units on surface or "section matching" in the
subsurface, observing their structural or stratigraphic relationships, and by geophysical
techniques (using geophysical well logs or seismic techniques)
B. Paleontology
- study of ancient life
Fossil = any evidence of prehistoric life
1. Fields of Paleontology
EARTH SCIENCE, PAGE 37
a. Paleozoology
- study of fossil animals
a1. Invertebrate paleontology
- study of fossil invertebrates (animals without a vertebral column)
a2. Vertebrate paleontology
- study of fossil vertebrates (animals with a vertebral column)
b. Paleobotany
- study of fossil plants
c. Micropaleontology
- study of small fossils
- microfossils are used extensively in correlation of sedimentary rocks
d. Paleoecology
- study of ancient environments and how ancient creatures relate to their environment and
other organisms
2. Prerequisites/Preferred Conditions for fossilization:
a. Relatively abundant organisms
b. Presence of hard parts
c. Avoid chemical and physical destruction
- rapid burial, typically within a relatively low energy depositional environment
3. Types of Fossil Preservation
a. Unaltered Fossils
a1.Unaltered Soft Parts
- unstable organic compounds are preserved such as carbon, hydrogen and oxygen
- rarely preserved; unaltered soft parts may sometimes be preserved in arid environments,
frozen regions, in waterlogged areas and in amber (fossil tree "sap")
a2. Unaltered Hard parts (Durapartic Preservation)
- relatively rare; preserve "hard parts" as unaltered bone (ex. = La Brea Tar Pits,
California) or shells
b. Altered Fossils
EARTH SCIENCE, PAGE 38
- these are the most typical types of fossil preservation:
b1. "Petrification"
- most petrification is by Cellular Permineralization [percolating groundwater introduces
minerals (ex. = silicates, carbonates, iron compounds, phosphates) into the pore spaces
(especially permineralize calcareous shells with calcite; wood and bone are often
permineralized)]
b2. Carbonization
- volatile components (hydrogen, oxygen, nitrogen) decrease and the outline of the
animals is preserved as a carbon film; often combines with petrification
c. Traces of Animals
c1. Molds and casts
Mold - impression of skeletal (or skin) remains in an adjoining rock
Cast - original skeletal material dissolves and cavity (mold) fills with material
c2. Trace Fossils
- tracks, trails and burrows of organisms
- are very useful since trace fossils were created when the organism was alive (therefore,
trace fossils reflect ancient ecologies and habits of organisms)
c3. Coprolites
- fossil excrement of animals; may contain undigested remains of food
C. Biostratigraphy ("Stratigraphic Paleontology")
- correlating rocks by their fossil content
1. Index Fossils
- fossils useful for correlation
- in order to be a good index fossil, the fossil should have lived during a relatively short time
span, have a wide geographic range, be independent as possible of facies (i.e., found in many
environments), and should have been abundant
2. Biozone
- basic unit of biostratigraphic classification
- Range Zones are established by plotting the stratigraphic range of fossil(s)
3. Major Fossils used in Biostratigraphy
- best are planktonic ("floating") or nektonic ("swimming") forms
D. Absolute (Actual) Dating Techniques
EARTH SCIENCE, PAGE 39
- dates geologic events in terms of years before present
1. Radioactivity
a. Isotopes
- forms of an element with same number of protons, different numbers of neutrons
b. Radioactive Decay
- atoms change to another element by releasing subatomic particles and energy; parent isotope
decays to daughter isotope at a constant rate
c. Radiometric Dating
- measure amount of parent materials relative to their daughter products
Half Life - time required for isotope to decay to half its original amount
Common Isotopes Used for Radiometric Dating Include:
Carbon-14/Nitrogen-14 = Half Life of 5,730 years; used to date organic materials;
typically restricted to objects less than 50 thousand years
Potassium-40/Argon-40 = Half Life of 1.25 billion years; often used to date volcanic
igneous rocks
2. Magnetic Stratigraphy
- uses "Normal" and "Reversed Polarity" Events to construct a Paleomagnetic Polarity Scale,
which is "tied" to absolute dates
E. Geologic Time Scale
- subdivides Earth history into many different units, and provides a framework for arranging
geologic events
The Time Scale is divided into:
1. Eons
- highest ranking time unit
- includes the Phanerozoic and Precambrian (Proterozoic and Archean) Eonothems
2. Eras
- subdivisions of eons
3. Periods
- fundamental units of worldwide Time-Stratigraphic classification
EARTH SCIENCE, PAGE 40
4. Epochs
- next in rank below periods
XII. Earth's Evolution through Geologic Time
A. Solar Nebula Hypothesis
- Solar System probably began as a slowly rotating cloud of gas and dust
- gases and dust condensed and clumped to form planetesimals; planetesimals aggregated to form
planets and their satellites (moons); dates of oldest rocks on the Earth's Moon and the oldest
Meteorites cluster at about 4.6 billion years old
- rocky and metallic material condensed to form planets in the hot inner portion of the Solar
System; lighter gases and ice condensed in the cold outer portions of the Solar Nebula to form
huge planets
- late impact of planetesimals cratered the surfaces of the planets and moons, and may have tilted
the rotational axes of some planets
B. Origin of the Earth and the Archean Eon
1. Archean Eon
- approximately 4.5 billion to 2.5 billion years before the present; the Archean Eon includes
approximately 45% of Earth history
2. Initial Earth Differentiation into Layers
- heat from bolide impacts and radioactive decay produced a molten planet, in which the most
dense material sank toward the center and the least dense rose toward the surface (produced an
iron core and a silicate-rich mantle)
- the less dense silicates floated to the surface, forming a "magma ocean", which cooled to form a
silicate-rich crust (this was a precursor to the oceanic crust of the modern world)
3. The Atmosphere was Formed By:
a. Degassing of Earth's Interior
- volcanic activity produced water vapor, hydrogen, hydrogen chloride, nitrogen, carbon dioxide,
carbon monoxide (and secondary chemical reactions in the atmosphere produced methane and
ammonia)
b. From Comets/"Space Ice"
- comet-like material supplies ammonia, methane, water vapor, etc. to partially create the
atmosphere
c. Photosynthesis
- early photosynthetic organisms, such as blue-green algae (cyanobacteria), create oxygen
- but there was evidently little "free" oxygen present in the Precambrian
EARTH SCIENCE, PAGE 41
4. The Oceans
- the Earth's interior degasses, gases condense in the atmosphere during Earth cooling, and
precipitation forms and falls to Earth to form oceans
- the salinity of the Ocean was created by weathering rocks on land
- seawater has varied little in salinity since the Early Archean
- the Early Archean ocean was probably much warmer than that of today due to the presence of
abundant radioactive elements in the Earth's crust and the "Greenhouse Effect"
C. Origins of the Biosphere
1. Organisms
- ordered (i.e. with cellular organization) living creatures
- "life" is a series of chemical reactions, using carbon-based molecules, by which matter is taken
into a system and used to assist the system's growth and reproduction, with waste products being
expelled
- life forms pass on their organized structure when they reproduce
2. Origins of Life
a. The Earth During the Archean Eon
- conditions favorable for the evolution of life could have existed on Earth as long ago as 4.4 Ga
- hot springs, submarine hydrothermal systems, and heated wind-mixed layers of the oceans may
have been areas where life first evolved
b. Origins of Life
b1. Depends upon the synthesis of Carbon
- once carbon is synthesized, all other biogenic molecules may be formed (Organic Molecules are
complex, carbon-based molecules)
- elements most prominent in organic molecules are carbon, hydrogen, oxygen and nitrogen
b2. Cellular Structure
b2a. Cell
- a "container" filled with organic and inorganic molecules (= Protoplasm)
Cells Contain:
b2b. Proteins
- built from amino acids; proteins are used as "building materials" and for chemical reactions
b2c. Nucleic Acids
- includes Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA); provide information for
the structure of the organism and the means to pass on this information in reproduction
EARTH SCIENCE, PAGE 42
b2d. Organic Phosphorous Compounds
- found in small amounts; transform light or chemical fuel into energy
c. The Formation of Proteins
- mixture of methane, ammonia, hydrogen and water vapor (or nitrogen, carbon dioxide and
water vapor) in the presence of electricity or ultraviolet light leads to the production of amino
acids
- some meteorites also contain amino acids
3. Prokaryotes
- tiny single-celled organisms with their DNA loosely organized within the cell, are not bounded
by a membrane into a nucleus and they lack chromosomes
- are often termed Monerans
- Prokaryotes are often divided into the Archaebacteria (include methanogens and sulfurmetabolizing bacteria) and the Eubacteria (include the "true" bacteria and cyanobacteria)
- life originated at least as early as 3.5 billion years ago, as indicated by (mostly) Eubacteria;
evidence includes algal-produced, dome-like limestone structures (stromatolites), cyanobacteria
microfossils, and carbon deposits with similar chemistry as seen in modern organisms
D. The Proterozoic Eon (Late Precambrian)
- Approximately 2.5 billion to 543 million years before the present
1. Plate Tectonics
- there were no large continents during the Archean and Early Proterozoic
- during the Late Proterozoic (between about 1 billion and 800 million years ago) the plates
sutured together, forming a supercontinent sometimes termed Rodinia
- this "suturing" of plates produced folded rocks and igneous activity, including the igneous and
metamorphic rocks of the Llano Uplift region of Central Texas, which are dated at about 1.1
billion years
2. Life in the Proterozoic
a. Eukaryotes
- single- or multi-celled organisms with chromosomes made of DNA, RNA and proteins
contained within a membrane-bound nucleus; meiosis present (with two consecutive cell
divisions that produce sex cells)
- sexual reproduction provides more variation that may potentially enable the species to better
survive environmental changes
- the Domain Eucarya includes the Kingdoms Protista (Protoctista), Fungi, Plantae (Metaphyta)
and Animalia (Metazoa)
- Eukaryote cell structure probably developed from endosymbiotic prokaryotes living within the
cell membrane of archaebacterial prokaryotes
- oldest known probable eukaryotic algae dates to about 2.1 billion years old
EARTH SCIENCE, PAGE 43
b. Metazoa (Animalia)
- with specialized cells forming tissues (= metazoan organization)
- tissues are united into organs (except in simplest invertebrates)
- the earliest metazoans were the soft-bodied, pancake-like Ediacara Fauna, that absorbed
nutrients directly through the body walls
E. The Paleozoic Era
- Approximately 543 to 248 million years before the present
1. Paleozoic Plate Tectonics and Paleogeography
a. Early Paleozoic
- during the Early Paleozoic the continents were relatively small
c. Late Paleozoic
- by 300 million years ago Gondwana moved northward to collide with Euramerica; this creates a
mountain range in southern Europe, northwestern Africa and in North America (creating the
Appalachian Mountains, Ouachita Mountains, Wichita Mountains, Amarillo Mountains and
Marathon Uplift; it also resulted in the formation of the Midland and Delaware Basins in western
Texas and New Mexico)
- by 270 million years ago, the supercontinent Pangaea was almost completely formed; suturing
created numerous mountain ranges; the result of this mountain-building and the fact that much of
Pangaea was far from moisture-providing oceans led to dry conditions with the formation of huge
dune deposits, extensive red-beds, and evaporites
2. Life of the Paleozoic
a. The "Cambrian Explosion"
- the Cambrian is the earliest period of the Paleozoic
- the first abundant fossils are found in rocks from this period; this rapid diversification may have
been due to improved environmental conditions (the end of "Snowball Earth" and the creation of
warmer seas, more oxygen and the formation of the ozone layer, and larger continental shelves),
and to the development of shells
b. The Origin of Fish
- the oldest-known fish are Cambrian age; they were jawless "agnathans"
- by the Devonian Period (approximately 416-359 million years ago) there were many different
fishes in the seas including armored jawless "agnathan" fish, jawed armor-plated placoderms, and
a wide variety of shark-like and "bony" fishes
- jaws may have been derived from gill arch supports, or as supports for the mouthparts of
agnathan fishes
- the top predators in the Paleozoic seas were huge cephalopods and fish
c. The Origin of Amphibians
EARTH SCIENCE, PAGE 44
- the earliest amphibians (the ichthyostegids) are from Upper Devonian rocks (dated at
approximately 350 million years)
- amphibians evolved from lobe-fined bony fish, which may have left aquatic environments due
to low oxygen content in the water, population pressures (seeking food, competition for space,
breeding sites, and to escape from predators or egg-eaters)
- by Late Paleozoic times (approximately 250 - 300 million years ago) there were many varieties
of both aquatic and terrestrial amphibians
d. Land Plants
- during the Carboniferous Period (Mississippian and Pennsylvanian in North America;
approximately 300-360 million years ago), there were extensive coal swamps with large club
mosses, "horsetails" and tree ferns; these formed the major coal deposits now utilized in the
Northern Hemisphere
- many of these plants became extinct when the Late Paleozoic coal swamp environment
declined, probably due to arid climate changes resulting from the formation of Pangaea
e. Rise of the Reptiles
- the oldest reptiles are of Carboniferous (Mississippian) age (approximately 320 million years
old)
- the success of the reptiles is probably due to the development of the amniote egg (which could
be laid outside of water), and the improvement of feeding and locomotion systems
- important reptile groups of the Late Paleozoic include small- to medium-sized lizard-like
"Parareptiles" and the Synapsids (these include the fin-backed pelycosaurs and the therapsids, or
mammal-like reptiles)
f. The End-Permian Extinction Event (approximately 250 million years ago)
- this was the greatest Phanerozoic extinction event, with some 80 to 85 percent of all species
becoming extinct
- Permian extinctions may have been caused by "stagnating waters" in the Permian seas, by the
formation of Pangaea (which led to less marine shelf area for organisms, and more aridity in the
continental interiors), or from volcanism (global warming from increased carbon dioxide from
the volcanism may have also triggered the melting of methane hydrates on the ocean floor,
producing an enhanced greenhouse effect)
H. The Mesozoic Era
- approximately 248 to 65 million years ago
1. Mesozoic Plate Tectonics and Paleogeography
- during the Early Mesozoic all land masses become united as the supercontinent Pangaea
- Pangaea began rifting by 200 million years ago; the Atlantic Ocean began to form, dividing
Pangaea into a series of basins throughout eastern North America
- by 70 million years ago, Gondwana began rifting to form South America, Africa and India
(Antarctica and Australia remained connected to one another); the separation of continents
caused the oceans to widen
EARTH SCIENCE, PAGE 45
2. Mesozoic Life
a. Mesozoic Marine Life
- Marine Reptiles became the top predators in the seas, including giant marine turtles, the
dolphin-like Ichthyosaurs, giant oceanic crocodiles, the "Loch Ness Monster"-like plesiosaurs,
and giant marine lizards (the Mosasaurs)
b. Land Plants
- "gymnosperms" became the dominant land plants in the Early- to Mid-Mesozoic (including
conifers and cycads)
- during the Late Mesozoic angiosperms (flowering plants) became dominant; these include the
majority of recent plants
c. Land Vertebrates
- during the Early Mesozoic, there were a wide variety of non-dinosaurian "archosaurs" that
dominated land environments
- by 200 million years ago, dinosaurs became the dominant land vertebrates
- saurischian dinosaurs (including the carnivorous theropods and "brontosaur-like" herbivorous
sauropods) dominated during the early Mesozoic but were outnumbered by the ornithischian
dinosaurs during the upper Mesozoic (including the duck-billed ornithopods, the ceratopsians,
the stegosaurs and armored ankylosaurs)
- flying reptiles, the pterosaurs, are found throughout the Mesozoic
- the oldest birds appeared by 150 million years ago
- the earliest mammals appeared during the Early Mesozoic, but these were mostly small and
were relatively insignificant components of Mesozoic faunas
d. The End-Mesozoic Extinction Event
- several groups (including dinosaurs) became extinct at the end of the Cretaceous
(approximately 65 million years ago)
- many scientists believe that a large asteroid (10 to 20 kilometers across) hit the earth, creating a
cloud of dust and something similar to "nuclear winter"
- other scientists believe that "gradual" climate change caused the extinction (major volcanic
eruptions produced greenhouse gases and global warming or modern ocean circulation began
(the "Global Conveyer Belt Model), which brought colder waters to the tropics and changed
climate
I. The Cenozoic Era
- approximately 65 million years ago to present
1. Cenozoic Plate Tectonics
- during the Late Mesozoic and Cenozoic the continents were arranged much like today but were
bunched closer together
- uplift of the Rocky Mountains and Colorado Plateau began about 20 million years ago
- the Cascade Ranges, the volcanic belt in the Pacific Northwest, formed due to the subduction of
the Pacific/Juan de Fuca plate beneath the North American Plate (most of these volcanic
EARTH SCIENCE, PAGE 46
mountains formed within the past 2 million years)
2. Cenozoic Climate
- by 35 million years ago climate became cooler and drier, with expansion of glaciers over
Antarctica; Australia separated from Antarctica and resulted in the formation of the cold
circumpolar current; the psychrosphere (deep, cold ocean currents) formed and climate
deteriorated (it became colder and/or drier)
- at approximately 3.2 million years ago the Ice Age began
3. Cenozoic Life
a. Cenozoic Marine Life
- top predators in the Cenozoic seas were large sharks, large bony fish and marine mammals
(such as toothed whales)
b. Flowering Plants (Angiosperms) Become Dominant
- the deteriorating climates of the Late Cenozoic favored evolution of weeds (the Compositae)
and grasses
- flowering plants, rodents and birds "co-evolved", with the evolution of angiosperms greatly
influencing the evolution of rodents and birds
c. The Placental (Eutherian) Mammals Radiate
- placentals have development taking place in the uterus and the embryo is nourished by tissues
of the placenta (the tissues shed following a birth); the earliest placentals were probably of Late
Mesozoic (Cretaceous) age
- rodents became very abundant during the Cenozoic (they include approximately 40% of all
known modern mammalian species)
- large primitive herbivores were common in the Early Cenozoic (and they persisted on island
continents such as South America and Australia)
- the "odd toed" ungulates (Perissodactyls, including tapirs, rhinoceroses, horses, and the extinct
brontotheres and chalicotheres) and the "even toed" ungulates (Artiodactyls) include pigs,
camels, giraffes, deer, antelope, goats, sheep, cattle and other extinct and modern groups became
the dominant groups of large land herbivores during the Middle- and Late Cenozoic
d. Human Origins
d1. Primates
- usually scansorial ("scurrying"), small- to medium-sized forest-dwelling herbivores or
omnivores
- retain a primitive, generalized skeleton, with five fingers and toes on the hands and feet; trend
toward increasing the mobility of the thumb and big toe; orthograde (upright) posture; typically
cling or sit vertically when resting; locomotion generally quadrupedal
- facial part of skull is reduced in more advanced primates; nasal apparatus generally reduced;
eyes face forward on skull; brain relatively large
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d2. Origin of the Hominoids
- based primarily on DNA evidence, it has been theorized that at approximately 5-6 Ma gorillas,
chimps and hominids (man's family) diverged when climate became cooler, drier and more
seasonal (termed the Messinian Climate Crisis)
- Australopithecines were the first humans (approximately 5.2 to 2.2 million years ago); they
were lightly-built hominids from Africa; they were fully bipedal (they walked upright), but their
brain was chimp-sized
- the earliest Homo (the genus containing modern man) dates at about 2.5 million years ago; this
date also approximately corresponds to the first stone tool culture (the Oldowan Culture)
- humans left Africa by 1.9 million years ago; at approximately the same time large hand-held
stone axes became the dominant tool (the Acheulian Industry) and there was the first deliberate
use of fire (fire provides warmth, is used in hunting, helps protect against predators, and removes
toxins from food)
- there may have been a later dispersal of anatomically modern-looking Homo sapiens from
Africa about 100 thousand years ago; this population may have replaced the older Eurasian
populations (although this is controversial); the appearance of modern Homo sapiens also
corresponds to the development of "punch-struck" stone blade industries, and the first abundant
ceremonial burials, grave goods and art
XIII. The Ocean Floor
A. Features of Ocean Basin Margins
a. Continental Shelves
- submerged continental margins; the shelf edge (Shelf Break) averages 130 meters water depth
b. Reefs
- built by organisms (especially hermatypic corals and their symbiotic algae)
- reefs cover less than 0.25% of the oceans, but contain over 25% of marine fish species
c. Continental Slopes
- sloping areas seaward of continental shelves; averages 4° slope, but vary from 1° to 25°; lower
limit of continental slopes typically extends down to about 2 to 3 kilometers
d. Submarine Canyons
- canyons developed on the continental slope, and to a lesser extent on the continental shelf
- consist of huge, sinuous U-shaped valleys that may be hundreds of kilometers long
- submarine canyons may be formed by turbidity currents (a turbidity current is a density current
that flows as a result of a density contrast; these typically have sediment turbulently suspended
within the current, which flows along the sea floor)
e. Deep Sea Fans
- fan-like structures at lower ends of many canyons; with tremendous volumes of sediments
deposited, often by turbidity currents
EARTH SCIENCE, PAGE 48
B. Classification of Marine Sediments
- Most Sediments in Marine Environments Consist of:
1. Terrigenous Sediments
- particles derived from land as a result of chemical and physical weathering and volcanic
eruptions
- are the dominant particles along continental margins and over much of the deep-ocean basin
- terrigenous sediments are often silica-rich, with abundant quartz and clay
- pelagic sediments consist of fine-grained, clay-sized particles from continental areas that are
transported great distances by winds or ocean currents, and then deposited on the deep ocean
floor
2. Biogenic Sediments (Biogenous Sediments)
- derived from the remains of organisms
Oozes - with 30% or more shells of microorganisms (typically composed of either silica or
calcium carbonate); the type of ooze present depends on the type of organisms present, the
climate, and by the Carbonate Compensation Depth ( (CCD = depth at which carbonate
dissolution equals carbonate production; carbonates are found in shallow water, silicates in
deeper)
XIV. Ocean Water and Ocean Life
A. Seawater Properties and Influences on Ocean Life
1. Composition of sea water
- approximately 96.5% water and averages 3.5% dissolved salts
- 95% of components consist of 6 major elements (Chlorine, Cl; Sodium, Na; Magnesium, Mg;
Sulfur, S; Calcium, Ca; Potassium, K)
- salinity is usually measured in parts per thousand (0/00); averages 35 0/00; varies from 0 to 270
0/00
- organisms internal "salinities" equals surrounding water salinity; if there is a rapid change in
salinity, an organism's cells may not function
2. Physical Properties of Seawater
a. Density and Viscosity
- Density of marine organisms typically equals sea water density
- viscosity influences shape and feeding (oceans have many suspension feeders, largely due to
seawater viscosity)
b. Temperature
EARTH SCIENCE, PAGE 49
- water moderates temperature
- in cold-blooded marine organisms, the rate of biochemical reactions and biological processes is
influenced more by temperature change versus that seen in warm-blooded marine birds and
mammals
c. Dissolved Gases
- oxygen is a biproduct of photosynthesis; there is typically less than 10 parts per million
dissolved oxygen found in seawater (therefore, oxygen content is a dominant limiting factor for
marine organisms)
- carbon dioxide is produced by respiration and burning fossil fuels; it is used by plants (for
photosynthesis) and in building carbonate shells
d. Light
Photic Zone - depth to which sufficient light penetrates for photosynthesis to take place; the
bottom of the photic zone in clear open ocean waters is about 100 to 200 meters
Aphotic Zone - below the photic zone, where photosynthesis does not take place
e. Pressure
- pressure increases approximately one atmosphere every 10 meters water depth
- affects vertical migration of organisms, bacterial decomposition, production of shells (due to
the influences of the CCD, or the Carbonate Compensation Depth)
f. Depth
- deep water stores carbon, nitrate, phosphate
g. Sound Waves
- sound travels at about 1450 to 1550 meters per second in ocean water
- ultrasonic frequencies are used to determine ocean depths, thickness of sediment and location
of underwater objects
B. The Diversity of Ocean Life
1. Oceanic Life Styles
a. Planktonic Organisms (Plankton)
- passively drifting or weakly swimming organisms at the "mercy" of ocean currents
- includes bacteria, phytoplankton (one-celled "plants"), and zooplankton (floating "animals")
b. Nektonic Organisms (Nekton)
- actively swimming, pelagic animals
c. Benthonic Organisms (Benthos)
- bottom-dwelling organisms
EARTH SCIENCE, PAGE 50
2. Ecology
- study of the factors that govern the distribution and abundance of organisms
Ecosystem = organisms and their physical environments
Fauna - animals of an ecosystem
Flora - plants of an ecosystem
Biota = flora + fauna
a. Habitats
- environments inhabited by life
b. Ecological niche
- way in which a species relates to its environment
c. Ecologic Community
- populations of several species living together in a habitat
d. Biodiversity/Biological Diversity
Genetic Diversity = variability in the genetic makeup among individuals within a single species
Species Diversity = variety of species on Earth or the number of species that live together in a
community; tropical climates contain more diverse plant and animal communities
Ecological Diversity = the variety of forests, deserts, grasslands, streams, lakes, wetlands, oceans,
and other biological communities that interact with one another and with their nonliving
environments
e. Species Relationships
e1. Food chains
- sequence of nutritional steps in an ecosystem
Trophic Level - position in food chain
e2. Food webs
- nutritional structure of ecosystem in which more than one species occupies each level
e3. Autotrophs (Producers)
- manufacture their own food; "plants" constitute the lowest (first) trophic level; form base of the
biomass "pyramid" (Biomass = weight of all organic matter contained in organisms)
Photoautotrophs = use solar energy, carbon dioxide and water to produce glucose and oxygen
Chemoautotrophs = convert simple compounds to more complex nutrients in absence of sunlight;
EARTH SCIENCE, PAGE 51
Exs. = bacteria at mid-ocean ridges
e4. Heterotrophs (Consumers)
- feed on other organisms ("animals")
- a lot of energy is lost cycling through higher trophic levels, so heterotrophs are rarer than
autotrophs
Herbivores (Primary Consumers) = feed on producers
Carnivores = feed on other consumers by predation
Omnivores = eat both plants and animals
Detritivores = include Decomposers (convert complex organic molecules to simpler inorganic
compounds; mostly bacteria and fungi) and Detritus Feeders (extract nutrients from partly
decomposed organic matter; include many species of crabs and shrimp, and sea cucumbers;
organisms that consume detritus-coated sediment are termed Deposit Feeders)
Parasites = derive nutrition from other organisms without killing them
f. Primary Productivity
- amount of organic material plants create; most primary productivity is due to the action of
phytoplankton
- there is less primary productivity with less light and less nutrients and "greater depth"
Eutrophic = very productive water; typically found in coastal waters (12% total ocean area)
Oligotrophic = sparsely productive water, characteristic of open ocean areas
XV. The Dynamic Ocean
A. Shorelines and Coastal Processes
- coastal areas are dominated by waves and tides
1. Waves and Tides
a. Waves
- typically, wind-driven waves of water provide most of the energy to modify shorelines
Nearshore Zones include:
Breaker zone - nearshore zone where wave velocity and wavelength decreases; waves become
higher and more asymmetrical
EARTH SCIENCE, PAGE 52
Surf Zone - nearshore zone where over-steepened waves topple over and crash onto the beach
Swash Zone - thin sheet of water moves up the beach face
Backwash Zone - sheet of water moves down the beach face
b. Tides
- produced by a combination of external forces (primarily the attraction of the moon and
centrifugal force of the Earth-Moon system)
- tides affect coasts by initiating a rise and fall in the water level and by generating currents (are
most influential in areas not dominated by waves, such as bays and lagoons)
2. Coastal Landforms
a. Erosional Landforms
- the following landforms develop along rocky shorelines:
a1. Sea Cliff (Wave-Cut Cliff)
- a cliff produced by wave erosion
a2. Headland
- an extension of land seaward from the general trend of the coast; a promontory, cape, or
peninsula
a3. Sea arch
- an arch cut by wave erosion through a headland
a4. Sea stack
- a small, pillar-shaped, rocky island formed by wave erosion through a headland near a sea cliff
b. Depositional Landforms
- the following landforms are typical of sandy shorelines:
b1. Berm
- a nearly horizontal portion of a beach or backshore formed by storm waves
b2. Coastal dunes
- most coastal dunes consist of a veneer of wind-blown sand overlying water-built beach ridges
b3. Features built by Longshore Currents
- near-shore wave refraction creates Longshore Currents (these flow parallel to shore); obliquelybreaking waves also move Beach Drift (transported sand and pebbles) in a zig-zag manner down
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the beach
Types of Features Created by Longshore Currents Include:
Offshore Bar - an offshore, submerged, elongate ridge of sand or gravel built on the sea floor by
waves and currents
Spit - a sandy bar projecting from the mainland into open water; formed by deposition of
sediment moved by longshore drift
Barrier island - an elongate island of sand or gravel formed parallel to a coast
Beach - a deposit of wave-washed sediment along a coast between the landward limit of wave
action and the outermost breakers
c. Tidal Inlet
- a waterway from open water to a lagoon
4. Lagoon
- a shallow body of seawater separated from the open ocean by a barrier island or reef
5. Estuary
- a funnel-shaped inlet of the sea that is formed when a rise in sea level or subsidence of land
causes the mouth of a river to be flooded
- lagoons and estuaries are very important marine ecosystems, as they are rich in nutrients and
marine life
B. Ocean Surface Currents
1. Formation of Surface Currents
- ocean currents are wind-driven circulation that involves water between the surface and 300 to
1000 meters depth
- most surface currents flow in closed loops (Gyres); flow clockwise in Northern Hemisphere;
surface currents usually restricted to upper few hundred meters
2. Upwelling
- surface water is deflected offshore and is replaced by deeper water
- approximately 90% of the World's productive fisheries are in upwelling areas
C. Deep Ocean Currents
- water movement in surface currents is mostly horizontal, but deep ocean currents have both
horizontal and vertical flow
1. Causes of Deep ocean currents
- dense waters at the ocean surface are due to evaporation (with greater salinity), cooling,
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freezing sea water (greater salinity), and where wind-driven surface water moves to regions
where mixing and sinking are possible
- denser water will sink until it reaches level at which density equals that of surrounding water
2. The Global Conveyer Belt
- the integrated system of surface and deep-ocean currents
- appears to influence climate (Europe may be warmer than it should be, in part because freezing
of sea ice in the North Atlantic releases latent heat)
XVI. The Atmosphere: Composition, Structure and Temperature
The Atmosphere - the envelope of gases and tiny, suspended particles encircling the Earth
A. Meteorology
- study of the atmosphere and weather processes
B. Weather
- the state of the atmosphere at a given time and place
C. Climate
- sum of all statistical weather information that helps describe a region
Climatology - the study of climate
D. Subdividing the Atmosphere
1. By Homogeneity
a. Homosphere
- lower 80 km of atmosphere where gases mix; gases mostly nitrogen (78%) and oxygen (21%);
also argon (0.93%), carbon dioxide (0.035%) and aerosols (minute liquid and solid particles)
b. Heterosphere
- above 80 km where gases are stratified; consists mostly of oxygen and nitrogen
2. By Temperature
a. Troposphere
- lowest layer; up to approximately 18 km (equator) or 8 km (poles)
- the troposphere is where most of the weather occurs
- temperature usually decreases with altitude; upper boundary = Tropopause
b. Stratosphere
- from tropopause to approximately 50 km
EARTH SCIENCE, PAGE 55
- temperature does not change to about 20 km (= isothermal); temperature increases above this to
Stratopause
c. Mesosphere
- up to approximately 80 km; temperature decreases upward; upper boundary = Mesopause
d. Thermosphere
- above 80 km
- temperature is isothermal to approximately 90 km, then increases (temperature highly variable)
3. Ionosphere
- located primarily in thermosphere
- with high concentration of ions (charged atomic particles), especially in the lower thermosphere
- Affects Include:
a. "bounces" AM radio waves
b. produces Aurora Borealis (northern lights) and Aurora Australis (southern lights)
- produced where solar wind (charged subatomic particles) deflects Earth's magnetic field into a
magnetosphere, excites atoms and produces radiation (forms mostly blue-green lights)
- especially important when the Sun produces abundant solar flares
E. Radiation
1. Solar Radiation
a. Electromagnetic radiation emitted by Sun's surface
- usually described by wavelength (distance between wave crests) and wave frequency (number
of crests/troughs that pass per time unit)
- primarily ultraviolet (UV; 9%), visible light (45%) and infrared (IR; 46%)
b. Global Radiation Balance
- total energy absorbed by Earth equals total energy emitted by Earth-atmosphere back to space
2. Global Insolation
- incoming solar radiation
- the amount of insolation depends primarily on the latitude and seasons
F. Earth's Motions in Space
1. Axis of Rotation
a. Earth rotates on its axis (counterclockwise; 15° per hour = time zones) and revolves about the
sun (counterclockwise in approximately 365 1/4 days)
EARTH SCIENCE, PAGE 56
b. The Earth's axis is inclined 23 1/2° from the perpendicular, and "always" points to the North
Star
G. The Seasons
- due to angle Earth tilts toward and away from the sun
- If sun is directly overhead, solar rays are most concentrated and less atmosphere traversed
- air temperature usually lags 1-2 months behind periods of minimum and maximum solar
radiation
1. Equinox
a. Earth's axis at a 90° angle with a line drawn to the sun
b. Noon sun directly overhead at Equator and at horizon at the Poles
c. Day and night are equal length
d. Vernal (Spring) Equinox
- on or about March 21
e. Autumnal (Fall) Equinox
- on or about September 22
2. Solstice
a. Points farthest from Equator at which Noon Sun is directly overhead (subsolar point) = 23
1/2° North (Tropic of Cancer) and 23 1/2° South latitude (Tropic of Capricorn)
b. Points from the Equator at which Noon Sun is at the horizon = 66 1/2° North and South
latitude; define the Arctic and Antarctic Circles
c. Summer Solstice
- on or about June 22; Northern hemisphere tipped toward sun; noontime rays of sun have
greatest poleward displacement (23.5°)
d. Winter Solstice
- on or about December 22; Southern hemisphere tipped toward sun
- In Northern Hemisphere intensity of light from the sun is at a minimum
H. Heat and Temperature
1. Kinetic Energy
- energy of motion
EARTH SCIENCE, PAGE 57
a. Heat
- total kinetic energy of atoms or molecules composing a substance
b. Heat Transport
b1. Conduction
- kinetic energy transferred due to atom/molecule collision
- substances (solid, liquid, gas) in contact
b2. Convection
- kinetic energy transferred due to fluid motion (due to the movement of gases or liquids)
Sensible Heating - heat transported by conduction plus convection
b3. Radiation
- electromagnetic waves traveling at speed of light
- can travel through a vacuum
- primary way Earth-atmosphere system gains heat from sun and loses heat into space
c. Temperature
- average kinetic energy of atoms or molecules composing a substance or the degree of molecular
activity of a substance
2. Temperature Scales
a. Fahrenheit (°F)
- boiling point of water at sea level at 212°F; freezing point 32°F
b. Celsius (formerly Centigrade)
- boiling point at 100°C; freezing point 0°C
c. Kelvin
- number of degrees above absolute zero (= temperature at which molecular motion stops;
= -273.15°C)
3. Temperature Conversion Formulas
°F = (1.8 X °C) + 32°
°C = (°F - 32°) X 0.56
°K = °C + 273.15
4. Thermometers
- used to measure temperature
EARTH SCIENCE, PAGE 58
- thermometers should be protected from direct or reflected light (measure air temperature)
5. Isotherm
- a line on a weather map connecting points of equal air temperature
XVII. Moisture, Clouds and Precipitation
A. Humidity
- amount of water vapor in the air
1. Atmospheric humidity
- capacity of air to hold water vapor
Saturated air = contains maximum amount of water vapor for a given temperature (saturation
point)
2. Relative Humidity
- ratio of water vapor in air to maximum allowable amount for a given temperature
- relative humidity is varied by (1) adding moisture by evaporation or transpiration (2) changing
the temperature (warmer air can hold greater moisture than cooler air)
- relative humidity is measured by psychrometers or hygrometers
B. Condensation
1. Dew Point
- temperature where air becomes saturated with water vapor
2. Condensation occurs if temperature falls below dew point
- the amount of condensation depends on how much the air is cooled below the dew point
- warm air has a greater potential for precipitation than cooler air (warmer air holds more water
vapor)
- a suitable surface (hygroscopic nuclei) must be present upon which condensation forms
C. Flow of energy from Earth's surface to Atmosphere is by:
1. Sensible Heating (23%)
- by conduction/convection
2. Latent Heating (77%)
Latent heat = stored-up energy in water vapor
a. Energy is stored during evaporation, released during condensation (Latent Heat of
Vaporization)
EARTH SCIENCE, PAGE 59
b. Energy is stored during melting, released during freezing (Latent Heat of Fusion/Melting)
c. Energy is stored when ice transforms directly to vapor, released when vapor transforms
directly to ice (Latent Heat of Sublimation)
D. Adiabatic Processes
- cooling or warming an air parcel by moving it vertically; when air rises and expands it cools;
when it subsides and compresses it warms
- adiabatic processes are the major cause of temperature change in large air masses that move
vertically
1. Stable air
- Parcel of air resists upward vertical movement
- cooler than surrounding air (sinks to original position)
- cool surface air will not rise
2. Unstable Air
- warm air rises until it reaches an altitude with the same temperature
Atmospheric Instability is enhanced by:
a. Intense solar heating warms air from below
b. Heating of air mass from below as it traverses a warm surface
c. Forceful Lifting of Air Including:
c1. Orographic Lifting
- sloping terrain (Ex.= mountains) act as barriers to flow of air and forces air to ascend; the moist
air expands, cools and condenses, producing substantial rainfall (Ex. = windward side of the
Cascade Range, Oregon and Washington State)
- air on leeward side of mountains loses moisture (creates Rain Shadow Deserts; Ex.= Great
Basin Desert of U.S.)
c2. Frontal Wedging
- cool air acts as a barrier over which warmer, lighter air rises
- frontal wedging is responsible for most precipitation in many areas
c3. Upward movement of air due to Convergence (air flowing together); often associated with
forceful lifting
c4. Radiation cooling from tops of clouds that are trapping heat below may cause instability in
the cloud; produce many nocturnal thunderstorms
EARTH SCIENCE, PAGE 60
E. Low Level Saturation Processes
- takes place at Earth surface where relative humidity is 100% due to cooling
- causes dew, frost or fog
1. Dew and Frost
- due primarily to nocturnal radiational cooling (surface emits infrared radiation)
a. Dew
- water droplets formed by condensation at the surface
b. Frost
- water vapor deposited as ice crystals where air temperature is less than 0°C
2. Fog
- cloud layer in contact with Earth's surface
- restricts visiblity to 1 km or less (otherwise is termed mist)
a. Radiation fog
- fog produced over land when radiational cooling reduces the air temperature at (or below) its
dew point (calm, humid air overlies a chilled land surface)
- is also termed "ground fog" or "valley fog"
- usually occurs over marshy areas or wet soils
b. Advection fog
- warm, humid air moves over a chilled surface (land or water)
- most common when warm, humid air is forced over a cold ocean current
c. Steam Fog
- cold air moves over warm water and evaporates it; looks like rising streamers; common over
lakes on autumn mornings
F. Clouds
1. Cloud Dynamics
a. Unstable Air Rises due to convection, orographic uplift, convergence of air, or lifting along
fronts
b. Rising air expands (decreasing pressure) and cools due to adiabatic processes
c. If water vapor is present, condensation begins when the dew point is reached
Convective Condensation Level (CCL) - altitude at which condensation begins to occur through
EARTH SCIENCE, PAGE 61
convection; coincides with the altitude of the cloud base
- hygroscopic nuclei must be present for condensation to take place (hygroscopic nuclei have a
chemical affinity for water molecules)
d. condensed particles form a cloud
e. Water droplets and ice particles remain suspended due to air resistance and upward moving
air in the cloud
G. Precipitation
- water in solid or liquid form that falls to the Earth
1. The Bergeron Process
- probably the major precipitation process at mid-latitudes
- Both ice crystals and supercooled water droplets are present in clouds with a temperature of
approximately -10 to -20°C
- Water droplets evaporate (higher vapor pressure) and water vapor deposited on ice crystals
(which grow)
- ice crystals fall into the lower atmosphere and melt (if they don't melt, it snows); some
evaporate when they encounter drier air, some may reach the Earth's surface
2. Forms of Precipitation
a. Drizzle
- 0.2-0.5 mm water droplets that drift slowly to surface
- associated with fog and stratus clouds
b. Rain
- most common type of precipitation
- 1-8 mm diameter (but rarely exceed 2 mm diameter)
- often start as snowflakes or hail in cumulonimbus or nimbostratus clouds
c. Freezing Rain/Freezing Drizzle
- water condenses in warmer atmosphere above and then freezes at the ground
- may produce hazardous glaze
d. Sleet (Ice Pellets)
- transparent/translucent ice less than 5 mm in diameter
- raindrops form in atmosphere and fall into lower air with freezing temperature (usually due to
upper air inversion)
e. Snow
- water vapor deposits directly as solid six-sided crystal
- most common just north of center of low pressure; warm moist air overrides colder air located
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north of the low
Blizzard - a violent and extremely cold wind laden with dry snow picked up from the ground
f. Hail
- large ice pellets (5-190 mm in diameter); with concentric milky rings (rapid freezing)
alternating with clear rings (slow freezing)
- due to cycling pellets in large updrafts and downdrafts in mature cumulonimbus clouds
- commonly produced by thunderstorms 15 km or more in height
3. Measuring Precipitation
- Measure in units of depth per unit of time
a. Rain
a1. Standard Rain Gauge
- with cone-shaped funnel at top to resolve rainfall to increments of 0.01 inches
a2. Tipping Bucket Rain Gauge
- with two small, free-swinging containers that collect 0.01 inches of rainfall each and alternately
spill their contents and recorded
a3. Weighing Bucket Rain Gauge
- with continuously recording scale that calibrates the weight of rainwater or other precipitation
as water depth
b. Snow
- measure depth each 24-hour period or depth on ground at observation time
- sometimes measure meltwater equivalent (meltwater averages 1/10 snow depth)
H. Atmospheric Optics
The Most Common Types of Atmospheric Optical Phenomena Include:
1. Halo
- ring of light around the Sun or Moon due to refraction of sunlight by tiny ice crystals suspended
in cirriform clouds
2. Rainbow
- arc of concentric colored bands due to refraction and internal reflection of sunlight by raindrops
- in order to observe a rainbow, you must be looking at a distant rain shower with the sun at your
back
- a Primary Rainbow exhibits brilliant colors, with each individual raindrop reflecting/refracting
a particular color
EARTH SCIENCE, PAGE 63
- Secondary Rainbows are larger and usually much fainter than primary rainbows; they appear
above the primary rainbow and are created where the sunlight enters the raindrops at an angle
that allows the light to make two internal reflections in each drop
3. Mirages
- an optical effect of the atmosphere caused by refraction in which the image of an object appears
displaced from its true position
a. Inferior Mirage
- a mirage in which the image appears below the true location of the object
- hotter air near the ground causes light to be bent upward (includes the classic "desert mirage")
b. Superior Mirage
- a mirage in which the image appears above the true location of the object
- cooler air near the ground causes light to be bent downward; typically created in polar regions
or over cool ocean surfaces [may cause objects such as ships to appear to be suspended above the
horizon (termed looming)]
XVIII. Air Pressure and Wind
A. Atmospheric pressure
Pressure - force per unit area of surface confining a fluid
1. At sea level atmospheric pressure is about 14.7 pounds per square inch
Millibar (mb) = conventional air pressure unit
- atmospheric pressure typically ranges from 970mb to 1050mb
2. Rate of decreasing pressure much greater at low altitudes than at higher altitudes
- at 16 km atmospheric pressure is approximately 10% sea level pressure
3. Standard Atmosphere
- mean vertical profiles of temperature, pressure and density within the atmosphere
- average atmospheric temperature is 59°F; average atmospheric pressure is 1013.25 mb
4. Pressure at a given location changes constantly (during a single day and between seasons)
5. Influences on Atmospheric Pressure
EARTH SCIENCE, PAGE 64
a. Temperature
- air heating increases distance between molecules, therefore less air density and less air pressure
b. Humidity
- the greater the water vapor, the less the density (the molecular weight of water is less than dry
air)
c. Therefore, cold and dry air has greater atmospheric pressure than warm, humid air
- Therefore, during air mass advection there is a change in air pressure
B. Weather Maps and Pressure
1. Isobars
- lines on a map connecting equal pressures
Air Pressure Tendency = change of air pressure with time
2. High Pressure ("H" or "HIGH")
- pressure higher than surrounding areas
- usually fair weather system
3. Low Pressure ("L" or "LOW")
- low pressure
- falling pressure; usually stormy weather system
C. Measuring Atmospheric Pressure
1. Barometers
- measure atmospheric pressure
a. Mercurial barometer
- at sea level, a column of mercury is about 29.92 inches or 760 mm high
- with falling air pressure, there will be a drop in the level of mercury
b. Aneroid barometer
- a nonliquid barometer; it is less precise than a mercury barometer but more mobile and easier to
use
c. Barograph
- aneroid barometer that records data
D. The Wind
1. Atmospheric Motion is due to:
EARTH SCIENCE, PAGE 65
a. Gravity
- "heavy" air (such as cold, dry air) flows "downhill"
- the effects of gravity are proportional to the mass of the air parcel (the larger the air parcel, the
greater the effect of gravity)
b. Pressure
b1. Air moves from High Pressure to Low Pressure Areas
- the pressure differences are due to unequal surface heating
b2. Pressure Differences Cause the Wind to Blow
- isobar spacing indicates the amount of pressure change over a given distance (termed the
Pressure Gradient); more closely-spaced isobars indicate a steeper pressure gradient and greater
wind velocity
c. Coriolis Effect
- free-moving objects (Ex.= wind) are deflected from a straight-line path due to Earth's rotation
- deflection is to the right in the Northern Hemisphere, and to the left in the Southern Hemisphere
- the effect is greatest at the poles and nonexistent at the equator
- Deflection amount depends on wind speed (stronger winds have greater deflection)
E. Wind Measurement
1. Wind Direction
- determined by wind vanes and wind socks
- direction from which the wind is blowing
2. Wind Speed
- measured by cup anemometer (cups spin) or hotwire anemometer (wind cools hot wire)
F. Highs and Lows
1. Types
a. Cyclone
- in Northern Hemisphere counterclockwise winds moving around a center of low pressure
b. Anticyclone
- in Northern Hemisphere clockwise winds moving around a center of high pressure
c. Trough
- isobars curve to form an elongate region of low pressure with cyclonic flow
d. Ridge
- isobars curve to form an elongate region of high pressure with anticyclonic flow
EARTH SCIENCE, PAGE 66
2. the wind direction for cyclones/anticyclones is opposite in the Southern Hemisphere
G. Convective circulation (thermal circulation)
- Due to unequal heating of atmosphere
1. Two winds develop (one high level, one low level) blowing in opposite directions
2. Convective System
- with rising air over one area (warm, less dense air) and sinking air over other areas (cooler,
more dense air)
H. Planetary-Scale Circulation
- large-scale wind systems of planet
1. General circulation
Semipermanent Pressure Systems - global-scale persistent cyclones and anticyclones; change
seasonally; include subtropical anticyclones, equatorial trough and subpolar lows
a. Equatorial Trough/Doldrums/ Intertropical Convergence Zone (ITCZ)
- equatorial
- light, variable winds; Coriolis force weakest
- equatorial regions have maximum insolation; the warm, moist air rises, cools, and produces
heavy precipitation
b. Hadley Cell
- rising equatorial air moves poleward, deflected eastward due to Coriolis force
- the air cools, descends, creating a zone of high pressure
- the descending air is dry, resulting in large continental deserts at 25-30° latitude
- there are light winds over the oceans due to the near-constant high pressure (this region is
termed the "Horse Latitudes" or Subtropical High Pressure Belt)
- the air then moves poleward or toward the equator
c. Trade winds
- surface air in the Hadley cell that moves toward the equator; with persistent winds
- Coriolis deflection results in Northeast Trades (Northern Hemisphere) and Southeast Trades
(Southern Hemisphere)
d. Westerlies
- 35° to 60° North and South latitude
- descending air in the Hadley cell reaches the surface, and then moves poleward
- deflected by the Coriolis force to the northeast (Northern Hemisphere) and southeast (Southern
Hemisphere), but the direction is often variable due to influences from polar air
EARTH SCIENCE, PAGE 67
- disrupted by land in the Northern Hemisphere, but the Southern Hemisphere has strong winds
e. Subpolar Lows/Cyclones
- at approximately 60° north and south latitude
- including Aleutian Low (North Pacific) and Icelandic Low (North Atlantic)
- low pressure belt surrounds Antarctica
f. Polar Easterlies
- well defined in Southern Hemisphere over Antarctica
- in Northern Hemisphere the wind directions are variable and regionally-developed
Polar Front = where surface westerlies meet and override polar easteries; often cause Synopticscale storms
g. Polar Anticyclones
- centered over poles
- year-round in the Southern Hemisphere; develop over continents in winter in the Northern
Hemisphere
- upper air flow in mid- to polar-latitudes is westerly
- Global Circulation Patterns shift toward the poles in spring and equator in autumn
I. Local and Regional Circulation Systems
1. Monsoon winds
a. best developed over south/southeast Asia and Africa
b. Seasonal Changes
b1. Summer
- low pressure over Afghanistan and eastward with warm, humid air; moves northward into Asia
- air rises over land, causes precipitation (especially on the Indian subcontinent)
- occurrence, duration, and intensity varies from year to year
b2. Winter
- air from Siberian High flows southward across Asia
- dry air picks up moisture across ocean; with rain on western mountain slopes of Pacific Islands
2. Land and Sea (or Lake) Breezes
a. Daytime
- land heats more rapidly than water
- air over land expands and rises, causes low pressure
- opposite occurs over water and thermal cell develops, produces a pressure gradient
- wind blows from water to land; produces a Sea (or Lake) Breeze and higher relative humidity
EARTH SCIENCE, PAGE 68
b. Nighttime
- opposite conditions from daytime with wind blowing from land toward water, produces a Land
Breeze
3. Lake-Effect Snows
- local snowfall downwind from open lake
a. Occurrence
- often in autumn/early winter with mild lake surface temperature
- arctic air mass evaporates water, clouds develops and snows
- best developed over hilly terrain, in regions where there is a large lake-land temperature
difference, and where lakes have a large fetch (amount of lake surface over which wind blows)
b. Snowbelts
- downwind areas affected by lake-effect snows
c. Snowbursts
- extreme lake-effect snowfall
4. Urban Heat Island Effect
- urban areas with higher temperature due to more heat sources, better heat conduction by
asphalt, etc. and low evapotranspiration
- best developed where synoptic-scale winds are weak
5. Dust Devils (Whirlwinds)
- swirling mass of dust due to intense solar heating of dry surface areas, producing atmospheric
instability and rising, spinning columns of air
J. Jet Stream
- zone(s) of very high speed wind, typically forming at the tropopause (between 10 and 15
kilometers altitude, but may also occur at higher and lower altitudes)
- due to unequal heating of poles versus equator
- the Polar Front Jet Stream (Polar Jet) is the most important feature of upper atmosphere
circulation; it is at approximately 35°N during winter with wind speed up to 350 km/hr; it may
split, creating northern and southern branches
- in summer, the Polar Front Jet Stream is at approximately 50° north latitude and with an
average velocity of approximately 65 km/hr
- the jet stream may have both horizontal divergence and convergence aloft (divergence aids
cyclone development; convergence with anticyclones)
- upper level atmospheric circulation can enhance (or suppress) weather events
K. El Niño/Southern Oscillation (ENSO)
- develops where the air pressure gradient of Indonesia/Australia versus the tropical eastern
Pacific weakens, and the trade winds die; warm surface waters in the Pacific move eastward
EARTH SCIENCE, PAGE 69
- El Niño events cause higher sea-surface temperatures and suppress upwelling (which may result
in the collapse of fisheries)
- usually lasts a few months
La Niña = opposite conditions (with strong trade winds); may also cause mid-latitude weather
extremes
XIX. Weather Patterns and Severe Storms
Synoptic-Scale Weather - the typical weather map scale that shows features such as high-and
low-pressure areas and fronts over a distance spanning a continent
A. Air Masses
- body of air with uniform temperature and moisture over large area
1. Characteristics
a. may cover large part of continent
b. with distinctive temperature and humidity characteristics
c. Acquire properties of region over which it occurs or slowly passes
d. Move from one region to another due to barometric pressure changes
2. Classification of Air Masses is Based Upon:
a. Latitudinal position
- determines thermal properties
b. Underlying surface
- determines moisture content
c. Combinations of thermal and humidity properties result in defining approximately 6 major air
masses
3. North American Air Masses (learn from Power Point slide)
a. Invasion of Continental Arctic (cA) air produces severe cold wave
- originates over Siberia, Arctic Basin, Greenland and northern Canada
b. Continental Polar (cP) air originates in northern Canada
c. Maritime Polar (mP) air originates over north Pacific, Bering Strait and north Atlantic
EARTH SCIENCE, PAGE 70
d. Maritime Tropical (mT) air originates mainly from the Gulf of Mexico (often termed "Gulf
Air"); also from the Pacific southwest of Baja, California ("Pacific Air") and the Atlantic Ocean
east of Florida
e. Continental Tropical (cT) air originates over northern Mexico and southwestern U.S.
(Arizona-Texas)
f. there is no direct influence of Maritime Equatorial (mE) air in North America
B. Weather Fronts
- boundaries separating air masses of different types
1. General Features
a. air masses do not easily mix
b. Air on either side of front and along front is in motion
c. Boundary always slopes upward over colder air
d. fronts are associated with trough development, wind shift and surface convergence
2. Cold front
a. cold air mass invades a region occupied by a less cold air mass
b. cold air forms a wedge, pushing the warm air up
- the "Blunt" leading edge lifts the warmer air, often resulting in thunderstorms (with
development of cumulonimbus clouds)
c. Cold Fronts are usually narrow and fast-moving (about twice as fast as warm fronts)
- Squall Line = band of intense thunderstorms at or ahead of front
d. Front passage causes a drop in temperature and humidity, and a shift in wind direction
e. Symbol = triangle-shaped points
3. Warm Front
a. warm air mass moves into a region of colder air
b. warm air slides up over the cold air
- the frontal surface is broad and gently sloping
- there is often steady, prolonged precipitation
EARTH SCIENCE, PAGE 71
- Freezing rain may develop if the cold lower air mass is below freezing
c. Warm Fronts tend to be wide and slow-moving
d. Passage of front causes gradually rising temperature and the wind shifts
e. Symbol
- semicircles extending into cooler air
4. Occluded Front
- type of precipitation depends on stability of the warm air
Symbol = triangles and semicircles on same side of line
- the most common type of occlusion is Cold-Type Occlusion [where cold air wedges under
warm and cool air masses, and the warm air mass is lifted off the ground (Occluded)]
5. Stationary Front
- front between air masses that have stalled
a. Stalling may occur due to:
- Presence of mountains
- Weather front parallels jet stream
b. the Front is oriented east-west, with strong southerly and northerly flow towards the front
c. Precipitation is often due to warm moist air overrunning cold air
- produces widespread cloudiness, drizzle, light rain, light snow
d. Symbol
- triangular points on one side and semicircles on other
C. Extratropical/Midlatitude Cyclones
- low pressure systems
- principle weather-maker at mid-latitudes
1. Development of Midlatitude Cyclones
- mid-latitude cyclones form along the Polar Front
- a cold front develops west of a center of low pressure, and a warm front develops toward the
east
- the cold front overtakes the warm front, resulting in occlusion
- the type of precipitation often depends on the position within the wave cyclone
2. Storm tracks
- usually move toward the east in the Northern Hemisphere
- Midlatitude Cyclones may originate in eastern North America and cross the north Atlantic to
EARTH SCIENCE, PAGE 72
northern Europe OR originate in far eastern Asia and cross the north Pacific to Alaska and the
northwest North American coast
D. Thunderstorms
- mesoscale weather system due to strong convection currents
- reach to great altitudes within the troposphere
1. Life Cycle
- form in intense thermal/convection cells
- air rises in small parcels, condenses, and forms a cumulus cloud at the CCL (Convective
Condensation Level)
- with more condensation, latent heat is released, and the cloud builds higher to create a
cauliflower-like Cumulus Congestus cloud
- this leads to tremendous updrafts and instability (the updraft prevents raindrops and ice crystals
from falling)
- cooling and subsidence of air leads to the formation of downdrafts and results in the
development of Thunderstorm Cells
- Ice crystals/snow begins to melt and forms rain (often intense)
- late mature stage with anvil-shaped Cumulonimbus clouds with tops up to 60,000 feet (may be
associated with heavy rains, lightning, hail, flash floods and tornadoes)
- with less precipitation and less latent heat, the updraft disappears and the cloud dissipates
3. Thunderstorm Hazards
a. Lightning
- visible electric discharges produced by thunderstorms
a1. Formation
- in general, lower part of thundercloud with negative charge, upper part with positive charge
(with huge electrical potential); probably due to interaction between graupel/ice pellets and ice
crystals
- induces positive charge on surface and on objects beneath thunderstorm
- Discharge (Lightning) is initiated as a Stepped Leader Stroke (there is a discharge of electrons
that rush toward the cloud base and then toward the ground in a series of steps, each about 50 to
100 meters long); the stepped leader is typically invisible to the human eye
- as the stepped leader approaches the ground, a current of positive charge starts upward from the
ground to meet it; after they meet, electrons flow to the ground and a much larger
Return/Streamer Stroke surges upward to the cloud
- the leader-and-stroke process is typically repeated several times along the ionized channel at
intervals of about four-hundredths of a second (the subsequent leaders are termed Dart Leaders);
typically there are 3 or 4 leaders per lightning flash
- the lightning continues until the electrical potential is reduced
a2. Types of Lightning
EARTH SCIENCE, PAGE 73
Forked Lightning - cloud-to-ground lightning that exhibits downard-directed crooked branches;
this is the most common type of lightning
Ribbon Lightning - lightning that appears to spread horizontally into a ribbon of parallel
luminous streaks when strong winds are blowing parallel to the observer's line of sight
Ball Lightning - a rare form of lightning that consists of a reddish, luminous ball of electricity or
charged air
Sheet Lightning - occurs when the lightning flash is not seen, but the flash causes the cloud (or
clouds) to appear as a diffuse luminous white sheet
Heat Lightning - distant lightning that illuminates the sky, but is too far away for its thunder to be
heard
a3. Protection against Lightning
- kills about as many people as tornadoes and floods
- Warning - hair often stands on end before lightning hits you; if hair stands on end crouch as low
as possible
- Dangerous Areas - under tall trees, on hilltops, open water, golf courses and golf carts, wire
fences, tractors; also telephones, TV, water pipes, metal appliances, sinks, bathtubs
- Lightning Safety - avoid areas mentioned above (automobiles and metal buildings usually safe;
also lighting rods work!)
a4. Thunder
- lightning discharge heats air up to 54,000°F
- air expands rapidly, producing shock waves which produce tremendous sound
- the sound of thunder travels at about 330 meters per second (1100 feet per second), so it takes
the sound of thunder about 5 seconds to travel one mile
b. Microbursts
- a strong localized downdraft (downburst) less than 4 kilometers (2.5 miles) wide that occur
beneath thunderstorms; winds up to 168 mph; duration less than 10 minutes
- microbursts trigger Wind Shear (an abrupt change in wind speed and direction); wind shear is
dangerous to aircraft because there is a sudden loss of lift and a subsequent decrease in the
performance of the aircraft
c. Straight-Line Winds
- damaging winds associated with downbursts from severe thunderstorms; wind speed may
exceed 90 knots
E. Tornado
- very intense, highly localized cyclonic vortex associated with cumulonimbus clouds
Funnel Cloud - a tornado whose circulation has not reached the ground
EARTH SCIENCE, PAGE 74
1. Characteristics
a. Small diameter [most are between 100 to 600 meters wide (300-2000 feet), although the
largest ones have diameters exceeding 1600 meters (one mile)]
b. Averages 20 to 40 knots forward speed
c. Very high winds (but most wind speeds are less than 125 knots, and few exceed 220 knots)
- pressure changes up to 200 mb
d. Duration usually short (but can be several hours)
e. Generally move east or northeast (Northern Hemisphere)
f. Most common over larger continents during warmer weather
g. Can be Very Destructive
- until recently, tornado destruction was measured by the Fujita Tornado Intensity Scale [F-Scale;
classified as weak (F0,F1), strong (F2,F3) or violent (F4,F5)]; in U.S. approximately 2/3 are
Weak; approximately 2/3 total fatalities in Violent
- on February 1st, 2007 the Enhanced Fujita Scale (EF Scale) was introduced in the U.S., as
meteorologists believed that the wind speeds in the original F Scale were over-estimated
2. Tornado Association
a. In the United States:
- two-thirds occur during the warmest hours of the day
- three-fourths occur from March to July
- the greatest number of tornadoes in the U. S. occurs in Tornado Alley (on the Great Plains,
from Texas to Nebraska)
- others tornadoes are associated with hurricanes (about one-fourth of the hurricanes in the U. S.
produce tornadoes)
b. Spring Maximum
- during the Spring, there may be a steep lapse rate (the air is warm near the ground, and cold
above); this creates a very unstable situation in the atmosphere (this is especially characteristic of
Tornado Alley tornadoes)
- approximately 80% of North American tornadoes are associated with Mid-Latitude Cyclones
(especially fronts between mP or cP air and mT air)
c. Tornadoes and Thunderstorms
- tornadoes are typically associated with Supercell Thunderstorms (very energetic thunderstorms
with updraft speeds exceeding 150 miles per hour)
- for Tornadoes on the Great Plains (see my power point slide), a typical situation is when (at the
EARTH SCIENCE, PAGE 75
surface) an open-wave middle latitude cyclone with cold, dry air is moving in behind a cold
front, and warm, humid air is pushing northward from the Gulf of Mexico behind a warm front;
above the warm surface air a wedge of warm, moist area is streaming northward; directly above
the moist layer is a wedge of colder, drier air moving in from the southwest; higher up (500 mb
level) a trough of low pressure exists to the west of the surface low and higher (at the 300 mb
level) the polar front jet stream swings over the region (this provides an area of divergence that
initiates surface convergence and rising air; the stage is set for the development of severe storms
- in order to form a tornado, the updraft must rotate; this rising, spinning column of air 5 to 10
kilometers across is termed a Mesocyclone
- the mesocyclone narrows and spirals downward as a funnel (this narrowing increases the wind
speed, creating a Tornado Cyclone)
- air rushes into the low-pressure vortex from all directions; it expands, cools, and if sufficiently
moist it condenses into a visible cloud (the Funnel Cloud)
- the air beneath the funnel is drawn into the core; it cools rapidly and condenses, and the funnel
cloud descends toward the surface
d. Observing Tornadoes
- the first sign that a thunderstorm may give birth to a tornado are rotating clouds at the base of
the storm (if the area of rotation in the cloud lowers, it becomes a Wall Cloud)
- usually within the wall cloud, a smaller funnel extends toward the surface (sometimes it can't be
seen because of the intensity of falling rain or dust)
- tornadoes may have a distinctive roar ("like a thousand freight trains") that can be heard for
several kilometers (but other tornadoes are silent!)
- tornadoes often with mammatus cloud formation (they look like pouches hanging from the
underside of the cloud)
- on conventional radar, the circulation of tornadoes is indicated by a hook-shaped pattern; on
Doppler Radar the speed at which precipitation is moving horizontally toward or away from the
radar can be calculated
3. Tornado Watches and Warnings
a. Tornado Watch
- a forecast issued to alert the public that tornadoes may develop within a specified area
b. Tornado Warning
- a warning is issued when a tornado has actually been observed, either visually or on a radar
screen
- it is also issued when the formation of tornadoes is imminent
3. Tornado Damage is due to:
a. High winds
b. Strong Updraft
EARTH SCIENCE, PAGE 76
c. Subsidiary Vortices
- Suction Vortices are small, rapidly rotating whirls perhaps 10 meters in diameter that are found
within large tornadoes
4. Tornado Safety
a. Seek secure shelter (avoid wide-roof buildings)
b. Go to small room in interior
c. Avoid windows
d. If outdoors lie in ditch
e. Avoid mobile homes
- account for about 45% of fatalities
5. Waterspouts
- tornado-like disturbance that occurs over ocean or large lake
F. Tropical Cyclones
- are also termed Hurricanes (Atlantic and eastern Pacific), Typhoons (western Pacific Ocean), or
Cyclones (Indian Ocean and Australia)
1. Origin
a. Originate only at latitudes of approximately 4° to 20°
b. Originate only over water
- Sea-surface temperature at least 80°F through 200 meters (600 foot) water depth
- die quickly if move over cold water or land
c. Usually originate in the Easterly Waves (disturbances in the trade winds)
- Center of low pressure forms in the wave trough, and the low pressure deepens rapidly
2. Hurricane Developmental Sequence
a. Tropical Disturbance
- no strong winds or closed isobars
b. Tropical Depression
- with one or more closed isobars; winds 37-63 km/hr (23-39 mph)
c. Tropical Storm
- distinct coriolis rotation around central low pressure with several closed isobars around it;
EARTH SCIENCE, PAGE 77
winds 63 to 119 km/hr (39-74 mph)
d. Hurricane
- pronounced rotation around eye (air sinks in center of eye); spiralling air around it with winds
greater than 119 km/hr; often moves west, then north, then northeast (due to coriolis effect and
jet stream influence); radar shows spiral bands of heavy rainfall
3. Hurricane Destruction
- the peak month in the Atlantic and Gulf of Mexico is September
a. High winds (up to 250 km/hr or more)
b. Flooding due to heavy rains
c. Storm surge
- flooding due to a combination of low pressure and high winds; storm surges are especially bad
in high tides
d. Measured by Saffir-Simpson Hurricane Intensity Scale
- include Categories 1 through 5, with those above a 3 classified as Major (includes about 20% of
hurricanes)
- the Saffir-Simpson Scale measures central pressure, wind speed, storm surge potential and
potential for property damage
e. Naming Hurricanes
- since 1978 (eastern Pacific) and 1979 (North Atlantic) hurricane names have been alternately
assigned male and female names
- a storm only gets a name when it reaches tropical storm strength
- if a storm has caused great damage, its name is retired for at least ten years
4. Hurricane Safety
a. Obey warnings
Hurricane Watch = indicates that a hurricane poses a threat to an area (often within several days)
and residents of the watch area should be prepared
Hurricane warning = hurricane conditions are expected in 24 hours or less
- Evacuate if requested
b. Enter hurricane season prepared with plywood/wood, radio with batteries, flashlight,
nonperishable foods and water
c. avoid low-lying areas, mobile homes
EARTH SCIENCE, PAGE 78
d. listen for tornado warnings
XX. World Climates and Global Climate Change
A. Climate
- average weather over time plus seasonal distribution of weather plus extremes in weather
behavior
- described by normals, means and extremes of temperature, precipitation, wind, etc.
1. Climatic Norm/Normal
- average plus extremes for a locality, usually over 30 years
2. Climatic Anomalies
- departures from long-term climatic averages
- upper air westerlies determine weather extremes (very cold temperature; drought, etc.)
B. Global Patterns of Climate
1. Temperature
- mean annual isotherms approximately parallel latitude
- January and July are the coldest and warmest months
- there is a larger shift of isotherms over land than water
2. Precipitation
- global mean annual precipitation = rain + melted snow
- tends to be zonal (east-west) pattern
- rain more reliable in maritime climates, less in continental
Equator = trade winds converge and with abundant rain
Tropical Monsoon Circulation = shifts of ITCZ and subtropical highs
Subtropics (20-35°) = with subtropical anticyclones and deserts
- at 35-40° with influence by prevailing westerlies and subtropical anticyclones; west side of
continents with moist winters and dry summers; east side with little variation in rain throughout
the year
- Poleward of 40° with less precipitation; with more rain during the summer
C. Air Pollution
Pollution - atypical contribution of substances to the environment
EARTH SCIENCE, PAGE 79
1. Types of Pollutants
a. Oxides of Carbon
a1. Carbon Dioxide (CO2)
- released through respiration, burning fossil fuels, brush fires, volcanoes
- carbon dioxide is a "greenhouse" gas (the Greenhouse Effect is an increase in atmospheric
temperature caused by the presence of infrared-absorbing gases)
a2. Carbon Monoxide (CO)
- released by burning fossil fuels and slash and burn agriculture
- causes drowsiness, slows reflexes, may kill you (especially in tunnels and parking garages)
b. Hydrocarbons
- volatile organic compounds
- often smog-forming and/or carcinogenic (cancer-causing)
b1. Methane (CH4)
- most from anaerobic decay and natural gas
- methane is also a "greenhouse" gas
b2. Vegetation Emissions
- may help form smog
b3. Motor Vehicle Emissions
- with many types of hydrocarbons
b4. Tobacco Smoke
c. Oxides of Nitrogen
- produced by soil bacteria, burning fossil fuels, motor emissions
- nitrogen dioxide (NO2) causes heart, lung, liver and kidney damage; bronchitis and pneumonia
- nitric oxides may also form nitric acid (contributing to the formation of acid rain) and smog
- Acid Rain (also termed Acid Precipitation) is where natural precipitation becomes acidic after
reacting with air pollutants
d. Sulfur Compounds
- produced by volcanoes, anaerobic decay, burning fossil fuels (especially coal and oil), smelting
sulfides, auto emissions
- may form sulfuric acid (causing acid rain)
- sulfur compounds may also cause respiratory problems
e. Photochemical Smog
- autos make oxides of nitrogens and hydrocarbons, combine with sunlight
EARTH SCIENCE, PAGE 80
- produce ozone, formaldehyde, ketones and PAN (peroxyacetyl nitrates)
- causes respiratory damage
- ozone also damages crops and trees, degrades rubber and fabrics
f. Aerosols
- suspended particulates
f1. Dust
- most by soil erosion
f2. Soot
- carbon particles
- incomplete combusion of fossil fuels and refuse
f3. Fungal Spores and Pollen
- often cause allergic reactions
f4. Many Others produced by mining, milling and manufacturing
- examples = asbestos fibers, pesticides, fertilizer dust
2. Air Pollution Episodes
- atmospheric conditions inhibit dilution of air pollutants, causing health-hazards
a. Wind Speed
- if wind speed doubles, it cuts air pollutants by one-half
- air pollution episodes greater at center of anticyclone, or where greater surface roughness
(buildings, etc.)
b. Atmospheric Stability
- enhances air pollution episodes
Subsidence Temperature Inversion - due to stalled anticyclone and subsiding air (forms a "lid",
termed Fumigation)
c. Air Pollution Potential
- increases with above conditions, also with high topographic relief
- in western U.S. air quality usually worst in winter, in eastern U.S. in Fall
- during pollution episodes advisories issued based on PSI (Pollution Standards Index = for 6
pollutants including carbon monoxide, sulfur dioxide, nitrogen dioxide, particulate matter, ozone
and lead)
3. Natural Cleansing Processes
a. Dry Deposition
- includes Impaction (particulates stick to buildings, etc.) and gravitational settling
EARTH SCIENCE, PAGE 81
b. Precipitation Scavenging
- by hygroscopic nuclei
- precipitation scavenging is the most important natural cleansing process, removing as much as
70% of the aerosols from the air
4. Ozone Shield
- absorbs UV light (especially important is UV-B = biologically effective radiation; causes skin
cancer)
a. Chlorofluorocarbons (CFC's)
- used in refrigeration and foams (insulation, fast food packages); formerly in aerosol sprays
- CFC's break down to chlorine in the upper atmosphere, which destroys ozone
b. Antarctic Ozone Hole
- ozone depleted during Southern Hemisphere "Spring" (September-October)
- by CFC's(?); also due to Circumpolar Vortex keeping warmer air out and greater catalytic
reactions
C. Weather Analysis and Forecasting
1. The National Weather Service
- Congress established U.S. Weather Bureau in 1890 (now the National Weather Service; NWS)
- an agency of NOAA (National Oceanic and Atmospheric Administration)
a. NWS Surface Weather Observations
- approximately 1000 weather stations (and others)
- provide data for weather map preparation and forecasting
- reports every 3 hours sky condition (cloud type, sky cover), visibility, air temperature, dewpoint, barometric pressure, wind speed and direction, weather occurrences
- data transmitted electronically to other NWS stations and numerous other facilities
b. NWS Upper-Air Observations
Radiosondes - instrument packages with radio transmitters carried aloft by hydrogen (or helium)
balloons; transmit soundings (continuous altitude measurements of temperature, pressure and
humidity) to ground stations
- vertical Air temperature, pressure and relative humidity monitored twice daily (0000 GMT and
1200 GMT)
c. Weather Radar
- NWS with approximately 120 radar stations
c1. Conventional radar
EARTH SCIENCE, PAGE 82
- time interval between emission and reception of signal (Radar Echo) gives distance to
precipitation; larger drops and hailstones with greatest reflectivity
- PPI (Plan-Position Indicator) Radar - sweeps horizontally up to 250 mile radius
- RHI (Range-Height Indicator) Radar - scans up to determine thunderstorm types
- conventional radar units use PPI and RHI modes
c2. Doppler Radar
- can determine motion of precipitation (and air circulation pattern!) within a weather system
based on frequency shift between outgoing and returning radar
d. Weather Satellites
- typically measure the heat produced by the land, sea surfaces and cloud tops by measuring
infrared radiation
d1. Polar-Orbiting Satellites
- low orbit; moves pole-to-pole; moves over same spot twice daily
d2. Geosynchronous/Geostationary Satellites
- scans same region all the time
2. Weather Maps
a. Station Model
- uses symbols to indicate weather conditions at a locality
b. Surface Weather Maps
b1. Synoptic Weather Charts
- weather maps that provide a summary of weather data
- Surface Synoptic Weather Maps are drawn every 3 hours for North America and 6 hours for
Northern Hemisphere
b2. Prognosis Chart (Prog Chart)
- predicts what weather will be like in the (near) future
c. Upper-Air Weather Maps
- radiosonde data plotted on constant-pressure surfaces (500-mb, etc.)
- draw "contour maps" twice daily
- useful for finding upper-level steering winds (jet stream at 250- and 300-mb), troughs and
ridges
3. Weather Prediction
a. Numerical Weather Forecasting
- computer programmed with numerical model of atmosphere
EARTH SCIENCE, PAGE 83
- predicts weather for next 12, 24, 36 and 48 hours
- AWIPS (Advanced Weather Interactive Processing System) has data communications, storage,
processing and display capabilities to help individual forecasters to assimilate and analyze data
b. Special Forecast Centers
b1. National Hurricane Center (NHC)
- Coral Gables, Florida
- also Central Pacific Hurricane Center, Honolulu, Hawaii
- goal to provide 12 hours daylight warning to coastal residents
- tracks hurricanes, predicts storm surge
b2. Storm Prediction Center (SPC) and National Severe Storms Laboratory (NSSL)
- in Norman, Oklahoma
- monitors severe thunderstorms, tornadoes and blizzards and conducts severe weather research
b3. Long-Range Forecasting
- Long Range Prediction Branch of Climate Analysis Center (Camp Springs, Maryland) provides
30- and 90-day "outlooks" that identify expected positive and negative anomalies (departure from
average)
- also looks at Teleconnections (long-range changes in widely separated regions; Ex. = ENSO)
XXI. Origins of Modern Astronomy
A. Coordinate Systems
- systems in which numbers are used to give the locations of bodies or events
1. Coordinates
- set of numbers used to locate something
- must agree on a Zero Point, the spot from which the coordinates are measured
2. Terrestrial Coordinate System
- system used to locate places on the Earth
- the Zero Point is located on the equator, directly south of Greenwich, England
a. Longitude
- describes distance east or west from the zero point
- angle, measured east or west, around the equator from the point where the Prime Meridian
intersects the equator
- Prime Meridian (at 0° longitude) is the longitude line passing through Greenwich, England; at
180° East and West Longitude is the International Dateline
b. Latitude
EARTH SCIENCE, PAGE 84
- angle measured north or south from the equator
- Equator is at 0° latitude; North and South Pole at 90°N and 90°S latitude respectively
B. The Celestial Sphere
- the imaginary sphere surrounding the Earth upon which celestial bodies appear to carry out their
motions
1. Angular Measurement
- used to describe the positions and sizes of objects seen in the sky
a. Degrees
- one degree is 1/360 of a circle
- the most commonly used system for measuring angles uses degrees
- at arms length your index finger is about 1° across, your fist about 10° across the knuckles, and
your outstretched hand about 18° across from the tip of your thumb to the tip of your little finger
b. Minute of arc
- is 1/60 of a degree
- some planets have angular sizes almost as large as a minute of arc
c. Second of Arc
- 1/60 of a minute
- equals the angular diameter of a penny at a distance of 4 kilometers (2.5 miles)
- angular sizes of stars are all smaller than 1 second of arc
2. The Horizon System
- coordinate system used to locate the positions of objects in the sky, using altitude and azimuth
as coordinates
a. Zenith
- point on the celestial sphere directly above your head
b. Celestial Horizon
- the great circle dividing the celestial sphere into an upper (visible) and lower (invisible) half
- the celestial horizon is situated 90° from the Zenith
c. Meridian
- circle on the celestial sphere that passes from the south celestial pole to the north celestial pole
and passes through the observer's zenith
- north and south points on the observer's horizon occur where the meridian crosses the horizon
- celestial equator is the circle midway between the north and south celestial poles; it divides the
celestial sphere into northern and southern halves
d. Altitude
- angular distance above the celestial horizon
EARTH SCIENCE, PAGE 85
- the horizon has an altitude of 0° and the zenith has an altitude of 90°
e. Azimuth
- angular distance measured eastward from north around the celestial horizon to the point directly
below the chosen position on the celestial sphere
- the azimuth of the east point on the celestial horizon is 90°, the south point is 180°, and the
west point 270°
- altitude and azimuth of a star depend on the time and the location where the observation is
made
C. Diurnal (Daily) Motion
- daily motion of the stars is westward on a circle that is centered on the North Celestial Pole
(situated about 3/4° from Polaris, the North Star)
- pattern of diurnal motion makes it look as if the celestial sphere is rotating on an axis passing
through the celestial poles
- motion appears to be counterclockwise if facing north and clockwise if facing south
1. Equatorial System
- coordinate system used to describe the angular location of astronomical objects
- uses right ascension and declination as coordinates
a. Declination
- north-south coordinate equal to the angular distance of a star from the celestial equator
- declination is measured in degrees, minutes, and seconds of arc
b. Right Ascension
- angular distance measured eastward along the celestial equator from the Vernal Equinox to the
point on the celestial equator nearest the star's position
- Vernal Equinox is the location of the Sun on the celestial sphere on the first day of spring
- right ascension is measured in hours, minutes and seconds (one hour equals 15 degrees)
c. Locating a Star using the Equatorial System
- right ascension (or hour angle) and declination are used to locate stars in the equatorial system,
which resembles the terrestrial system of longitude and latitude
- use Star Catalogues to find a particular star to observe
D. Motions of the Planets
1. Rotation and Revolution
a. Rotation
- the turning of a body, such as a planet, on its axis
b. Revolution
- the motion of a body in orbit around another body or a common center of mass
EARTH SCIENCE, PAGE 86
2. Prograde versus Retrograde Motion
a. Prograde (Direct) Motion
- when a planet moves eastward with respect to the stars
b. Retrograde Motion
- when a planet appears to reverse its direction of motion and move westward with respect to the
stars
- Synodic Period of a Planet is the interval of time in which episodes of retrograde motion occur
3. Conjuction and Opposition
a. Conjunction
- time when a planet is nearly aligned with the Sun
- for Mercury and Venus, retrograde motion can only take place when the planet appears to pass
near the Sun in the sky (near every other conjunction)
b. Opposition
- when the planet is opposite the Sun in the sky
- retrograde motion for all planets (except Mercury and Venus) happens when planets are at
opposition
4. Elongation
- the apparent angular distance of an object from the Sun, measured between 0° and 180° east or
west of the Sun
- the Inferior Planets, Mercury and Venus, are best observed near their Greatest Elongations
E. Keeping Time
- time keeping is based primarily on celestial events
1. The Ecliptic
- the path that the Sun appears to follow among the stars
a. Zodiacal Constellations
- the constellations through which the Sun appears to move during a year
- includes Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus,
Gemini, Cancer and Leo
b. Year
- time it takes the Sun to move through the zodiacal constellations and return to the same spot on
the celestial sphere (complete one circle around the Zodiac)
- the year is 365.242199 days or 365 days, 5 hours, 48 minutes and 46 seconds long
2. The Seasons
EARTH SCIENCE, PAGE 87
- the seasons are due to the angle the Earth tilts toward and away from the Sun (see the
discussion in the Meteorology Section)
3. The Month
- interval from New Moon to New Moon
- therefore about 12 lunar cycles per year and 12 months
- Julian Calendar made months 30 or 31 days long; Roman politics resulted in the formulation of
our current Calendar
- Religious Calendars (such as the Muslim and Jewish) are based primarily on lunar cycles
4. Days of the Week
- seven days probably due to 7 visible objects in sky seen by ancient peoples that move with
respect to stars (Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn)
- weekdays named primarily for astronomical objects or ancient gods
5. The Day
- time from sunrise to sunrise
- approximately 24 hours (Mean Solar Day)
- Mean Solar Time is time kept according to the average length of the Solar Day (24 hours)
6. Time Zones
- regions of the Earth, roughly 15° wide in longitude, where everyone keeps the same standard
time
- Earth has 24 time zones of one hour each
a. U.S. with Eastern, Central, Mountain, and Pacific Standard Time Zones
- when you move West to East add an hour; East to West subtract
b. Daylight Savings Time
- set clocks ahead of Standard time; provides more recreation hours and saves energy
- Spring forward (2nd Sunday in March at 2 A.M.) and Fall back (first Sunday in November at 2
A.M.)
c. International Date Line
- at 180 degrees longitude where day shifts
d. Universal Time (UT)
- time kept in the time zone containing longitude 0 (through Greenwich, U.K.); provides a
"standard" World time
7. Daylight Length
- due to Earth's tilted rotational axis
a. Northern Hemisphere with sunshine more direct in Summer than Winter; therefore longer
day
EARTH SCIENCE, PAGE 88
b. Equinoxes
- with Northern and Southern Hemispheres equally lit and day/night of equal length everywhere
on Earth
8. A.M. and P.M.
- noon sun lies overhead (at the meridian) at noon
a. Antemeridian (A. M.) - sun lies before (ante) the meridian
b. Postmeridian (P. M.) - sun lies past (post) the meridian
9. Calendars
a. In order for seasons not to get out of sequence with calendar add one day every fourth year
(Leap Year)
b. Gregorian Calendar
- because the Tropical Year is shorter than 365 1/4 days, Century Years are not leap years unless
they can be evenly divided by 400 (1900 was not a leap year, but 2000 was)
c. B. C. and A. D.
B. C. - before Christ
A. D. - anno Domini, "in the year of our Lord"
- another system uses BCE (Before the Common Era) and CE (Common Era)
XXII. Touring Our Solar System
A. The Planets
1. The Terrestrial Planets
- small, dense "rocky" planets; lie in inner part of Solar System; not much hydrogen and helium;
few satellites
a. Mercury
- smallest terrestrial planet (approximately 40% larger than the Earth's Moon), and closest to the
Sun
- essentially no atmosphere, with temperatures ranging from -280°F to 800°F
- heavily cratered due to bolide (asteroid, comet) impacts (indicates that no modern geologic
activity is present; the largest crater is the Caloris Basin); with prominent fault lines (scarps),
probably due to the planet cooling and shrinking; ancient lava flows cover most of the surface of
EARTH SCIENCE, PAGE 89
Mercury
b. Venus
- similar to Earth in size and geologic composition; often one of the brightest objects in the sky
- atmosphere is 96% carbon dioxide, creating a runaway Greenhouse Effect (temperatures up to
900°F); thick clouds of sulfuric acid cover the planet
- rotates once every 243 days; with a retrograde (reverse) rotation (possibly due to collision with
a large planetesimal) and very weak magnetic field (due to slow rotation)
- surface mostly low, gently-rolling plains; surface features appear to be young, developed
primarily due to volcanic activity
c. Earth
- radius is 6400 kms (4000 miles); rotates on it's axis in 24 hrs; Axis tilted at 23.5° (causes
seasons); revolves around the sun in 365.2422 days; gyrates around it's axis (precession) in
26,000 years; one satellite (the Moon)
- Seismic (earthquake) waves indicate that the Earth can be divided into a thin crust of silicate
rocks; a mantle of heavier, relatively "solid" silicates; a liquid outer core of iron and nickel; and a
solid inner core of iron and nickel
- internal convection of the Earth causes shift of the Earth's crust and uppermost mantle (Plate
Tectonics), which creates the major geologic and topographic features of Earth
- 71% of surface is covered by oceans; only planet known to support life
d. Mars
- approximately 1/2 Earth diameter with 1/10th Earth's mass; red color
- atmosphere is 95% carbon dioxide, but only 1/100th density of Earth's atmosphere; average
surface temperature is -67°F
- large polar icecaps are present, mostly made of water ice
- poles bordered by immense deserts with sand dunes; has a few large volcanic peaks [(Olympus
Mons is 25 kms (16 miles) tall!)]; a large rift valley (the Valles Marineris) is 5000 kms (3000
miles) long and 10 kms (6 miles) deep!
- with indications of 4 billion year-old stream beds, large lakes, and small oceans (indicates that
Mars was warmer in the geologic past, probably due to the Greenhouse Effect)
- 2 irregular-shaped moons/satellites (Deimos and Phobos)
- a Martian meteorite has yielded possible indications of life, but this is highly controversial
2. The Jovian Planets
- giant planets consisting primarily of hydrogen, helium, methane and ammonia gases and liquids
(and water); low density; ring systems and many moons present
a. Jupiter
- largest planet (about 10 times diameter of Earth, with a mass greater than all other planets
combined); rotates in 9.9 hours; with intense radiation and a very strong magnetic field (about
20,000 times stronger than the Earth's)
- hydrogen, helium, ammonia and methane atmosphere; interior mostly metallic liquid hydrogen,
with a rocky core
EARTH SCIENCE, PAGE 90
- with high- and low-atmospheric pressure bands; create jet streams that flow in opposite
directions, which cause the formation of atmospheric vortices (the best example is the Great Red
Spot)
- small ring system made of rock dust
- with approximately 63 moons (Io spews molten sulfur!; Europa may have liquid oceans!)
b. Saturn
- second largest planet; rotates in about 10.7 hours
- atmosphere and internal composition is similar to that of Jupiter; produces more heat internally
than receives from the sun (due to helium condensation)
- surrounded by thousands of rings of water ice (made out of particles a few centimeters to
several meters across); ring system created by broken-up satellites, asteroids and comets
- approximately 56 moons; the moon Enceladus appears to erupt water from its interior, which
covers and freezes over old craters
c. Uranus
- with blue-green color due to methane-rich atmosphere (atmosphere also contains hydrogen);
most of planet composition is water, ammonia and methane surrounding a rocky core
- the axis of rotation is practically in the plane of its orbit (i.e., Uranus is "laying on its side",
possibly due to collision with a large planetesimal); odd axis of rotation causes unusual
atmospheric circulation
- dark and thin rings, probably carbon-rich
- approximately 27 small moons; one of the moons (Miranda) has a messed up appearance,
possibly due to collision with a planetesimal
d. Neptune
- appears blue or blue-green in telescopes (like Uranus with atmospheric methane, and with a
similar internal composition and structure)
- atmosphere with distinctive cloud belts; formerly with an Earth-size Great Dark Spot (it has
since disappeared); also with rings (probably made of ice and carbon particles); approximately 13
moons
B. The Earth's Moon
- the Moon is Earth's Satellite
1. Origin of the Earth's Moon
- probably formed when a Mars-sized body collided with the Earth, splashing material into orbit
- the Moon is not a chunk of Earth; it formed almost entirely from the mantle of the impacting
body (which accounts for the differing proportions of iron and magnesium versus the Earth)
- this material coalesced to form the Moon (which has a feldspar-rich outer layer and very small
metallic core)
- the core material of the impacting planet combined with the Earth's core
2. Characteristics
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a. Size
- approximately 1/4 diameter of Earth and with approximately 1/6 its gravity
b. Revolves around Earth and rotates on its axis approximately 29 1/2 days; only 1 side is
visible to the Earth (this is due to "tidal braking" by the Earth, which slowed the Moon's spin to
make it synchronous with the orbital motion around the Earth)
c. Topography
- there has been no atmosphere or tectonic activity on the Moon for billions of years; therefore,
the surface has remained unaltered except for impact features
c1. Craters
- shallow depressions due to bolide (i.e., comet, asteroid, meteorite) impacts; many craters are
surrounded by Rays (material thrown from craters)
- the Moon's surface is covered with shattered rock (Regolith) due to bolide impacts
c2. Mountains/Highlands
- as high as 20,000 feet; formed 3.9 - 4.4 billion years ago; made from anorthosites (rocks rich in
calcium and aluminum silicates)
c3. Maria/Plains
- flat areas (filled craters) covered with basalt lava; formed 3.8 - 3.1 billion years ago
c4. Rilles
- lunar valleys; probably formed by ancient lava flows or due to crustal cracking
3. Phases of the Moon
a. New and Full Moon
- the Earth, Moon and Sun are aligned
b. 1st and 3rd Quarters
- the Moon, Sun and Earth are perpendicular
4. Eclipses
- darkening of one celestial body by another
a. Solar Eclipse
- the Moon passes between the Earth and the Sun, thereby totally or partially obscuring Earth's
view of the Sun
- in order for a Solar Eclipse to occur, the Moon is at or near new phase and is in or near the
ecliptic plane
b. Lunar Eclipse
- the Earth passes between the Moon and the Sun, thereby totally or partially obscuring Earth's
EARTH SCIENCE, PAGE 92
view of the Moon
- in order for a Lunar Eclipse to occur, the Moon is at or near full phase and is on or near the
ecliptic plane
D. Other Features of the Solar System
1. Minor Planets (Dwarf Planets)
a. Pluto
- completes highly elliptical orbit (which is out of the ecliptic plane) in approximately 248 years;
axis of rotation nearly lies in it's orbital plane
- made of rock mixed with ices (water, nitrogen, methane)
- Pluto and it's "moon" Charon are now considered to be "Minor Planets"; they are probably
remnant planetesimals from the birth of the Solar System
2. Comets
- icy bodies (mostly water and carbon dioxide/carbon monoxide ice) less than 10 kilometers
across
- the comet nucleus consists of ice and gases; as comets approach the Sun they begin to vaporize
to form a Coma (cloud of gases) and a tail [(a dust tail due to radiation ("sunlight") pressure, and
a gas tail due to the Solar Wind (charged particles coming from the Sun)]; the tail always faces
away from the Sun
- comets are possibly derived from the "Oort Cloud", which surrounds the Solar System
3. Asteroids
- irregular-shaped rocky or metallic bodies with diameters from a few meters to 1000 kilometers
- most orbit Sun within the Asteroid Belt between Mars and Jupiter
- an asteroid may have struck Earth at the end of the Cretaceous Period (approximately 65
million years ago), stirred up dust and created fires, initiated a "nuclear winter" and caused mass
extinctions (including the dinosaurs); evidence of this "bolide impact" includes the "iridium
layer" and presence of "shocked quartz"
4. Meteors
Meteoroids = small space particles with elliptical orbits around the sun
Meteors = fall through the Earth's atmosphere ("shooting stars"; consist mostly of icy particles
from comets); Meteor Showers occur when the Earth passes through clumps of material left by
comets
Meteorites = iron, stony (silica-rich), or stony-iron particles that hit the ground; most formed
from broken-up asteroids/planetesimals or material left over from formation of the Solar System
XXIII. Light, Astronomical Observations, and the Sun
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A. Waves
- a wave is composed of a regular series of disturbances that move through a medium or through
empty space
1. Description of Waves
- a wave is described by its length (wavelength), rate at which its crests pass (frequency), and the
energy flux that the wave carries (energy flux = rate at which the wave carries energy through a
given area)
2. Electromagnetic Waves
- consist of oscillating magnetic and electric fields moving at the speed of light (speed of light
equals 3 X 108 m/s or 186,000 miles per second)
- electromagnetic waves differ in wavelength and frequency (the Electromagnetic Spectrum);
waves with small wavelengths (such as gamma rays) have high frequencies, whereas waves with
large wavelengths (such as radio waves) have low frequencies
3. The Doppler Effect
- change in the measured wavelength and frequency of a wave
- the Doppler Effect occurs when the source and observer of the wave are moving toward or
away from each other; the change in wavelength is proportional to the speed of the source
relative to the observer
4. Photons
- massless particles of electromagnetic energy; the energy of a photon is proportional to its
frequency
- light behaves both as waves and as particles
B. Light Collection and Detection
1. Optical Telescopes
- use lenses and mirrors to bring light to a focus
- the lens or mirror used to focus the light is called the Objective of the telescope
a. Refracting Telescopes (Refractors)
Refraction - bending of light when it passes from one material into another
- in refracting telescopes the objective is a lens; the size of a refracting telescope is the diameter
of the light-collecting lens
- the World's largest refractor is the 40-inch (1.02 meter) telescope of the Yerkes Observatory,
Wisconsin (built before 1900)
b. Reflecting Telescopes (Reflectors)
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Reflection - bouncing of a wave from a surface
- in Reflecting Telescopes the objective is a mirror
- the size of a reflecting telescope refers to the diameter of its mirror
- reflecting telescopes are preferred in astronomy because refracting telescopes cannot have any
internal imperfections in the lens, reflecting telescopes only have to have one lens surface ground
and polished (makes it easier and much less expensive to manufacture), and the weight of a large
refracting lens produces distorted images (reflecting lenses are supported along their entire back
surface and therefore do not warp as much)
2. Detectors
- once light has been brought to a focus, it is measured by a detector
These include:
a. Photography
- when telescopes are used in photography they operate like a camera, except the objective of the
telescope replaces the camera lens
- long exposure times are needed to capture images of astronomical objects that may be 100
million times too faint to be seen with the naked eye
b. CCDs
- a Charge Coupled Device (CCD) is a collection of photo-sensitive devices laid out in a
miniaturized pattern that resembles a chessboard; each piece of the pattern is known as a picture
element (Pixel); the amount of electric charge buildup on each pixel is recorded and stored
electronically so that it can be displayed or analyzed later using a computer
c. Spectroscopy
- the recording and analysis of spectra; in spectroscopy the light is dispersed according to
wavelength
- astronomers often measure the shapes and strengths of absorption and emission lines of atoms
and molecules to learn about important properties of celestial objects such as chemical makeup,
motion, and magnetic fields
Spectrograph - device used to produce and record a spectrum
3. Optical Observatories
a. Quality of Observing
- depends on many factors such as the amount of clear weather, the transparency and steadiness
of the atmosphere, and the darkness of the sky at night
- clearest locations tend to be in dry or desert regions (such as in the southwestern United States,
Chile, Australia) or on mountains which rise above low-lying clouds (such as on Mauna Kea,
Hawaii)
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Light Pollution - light from large population centers increases the brightness of the night sky,
making it more difficult to observe faint objects
Seeing - blurring of an image caused by turbulence in the atmosphere (effects of seeing are least
noticeable where the air isn't very turbulent, such as on isolated mountain tops)
Adaptive Optics - using a flexible mirror on a telescope that has actuators to move a small
segment of the mirror up and down as much as 1000 times per second to correct for distortion
due to atmospheric turbulence
b. Modern Observatories
- Kitt Peak National Observatory in Arizona, Mauna Kea in Hawaii (probably the best observing
site), McDonald Observatory in West Texas, the European Southern Observatory and Cerro
Tololo Inter-American Observatory in Chile are some of the most important
4. Space Observatories
- because the Earth's atmosphere is opaque to most of the electromagnetic spectrum, it is
important to carry telescopes above the atmosphere where they can observe in the gamma ray, Xray, ultraviolet and infrared parts of the spectrum
5. Radio Telescopes
-most radio telescopes are reflectors, using metallic conducting surfaces as mirrors to reflect
radio waves to a focus; the radio waves brought to a focus can be measured using an antenna
(which operates somewhat like an automobile radio antenna)
- because they are used at long wavelengths, even the largest radio telescopes have poor angular
resolution (the largest radio dish at Arecibo, Puerto Rico is 305 m across with a circumference of
about 1 kilometer!); interferometery is used to obtain high angular resolution, where signals from
widely separated radio dishes are combined to produce the resolution of a single telescope
C. Our Sun: Local Star
1. Internal Structure
a. Central Temperature and Pressure
- central temperature of the Sun is about 15.6 million K
- gas in the Sun's core is compressed to about 150,000 kg/m3 (about 150 times the density of
water)
- the Sun's energy is produced by the fusion of hydrogen into helium in the Sun's core
- almost all of the Sun's energy is produced in the inner 25% of the Sun's radius (about 1.5% of
the Sun's volume)
b. Sun's Surface
- hydrogen constitutes about 71% of the gases (at the Sun's center hydrogen is only about 34%)
- hydrogen has been used as fuel by the Sun for most of the 4.6 billion years the Sun has existed,
and slightly more than half of the hydrogen at the Sun's center has been consumed
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2. The Outer Layers of the Sun
- the outer layers are the only ones that emit radiation that reaches Earth
- the deepest layer we see is the photosphere, above which is the chromosphere and corona
(which extends into interplanetary space to form the solar wind)
a. The Photosphere
- the layer that we see in visible images of the Sun
- the Sun's surface shows a pattern of bright and dark markings (Granules), which are rising
columns of hot gas about 1000 kilometers across that last about 15 minutes
b. Sunspots and Solar Magnetism
Sunspot - region of the Sun's photosphere that appears darker than its surroundings because it is
cooler; the inner darkest part of the sunspot is the Umbra, the outer part is the penumbra;
sunspots tend to occur in groups (Sunspot Groups) and the area around the sunspot group (the
Active Region) has many solar flares and other indications of activity
- regions of strong magnetic fields are concentrated in sunspot groups; the large magnetic fields
in sunspots inhibit convection and reduce the flow of energy to the Sun's surface
The Sunspot Cycle- the number of sunspots increases and decreases during an 11-year Sunspot
Cycle (although there have been long periods of time in which very few spots have been seen on
the Sun); the Sunspot Cycle and the pattern of magnetic polarities in sunspots are probably due to
the differential rotation of the Sun, that stetches and twists magnetic field lines
c. The Chromosphere
- a tenuous region of gas that lies just above the photosphere
- most of the chromospheric gas is in the form of rapidly rising jets of gas (Spicules), which
shoot upward at about 25 kilometers per second (50,000 miles per hour) and last for about 5
minutes
d. The Corona
- outermost layer of the Sun's atmosphere, within which the temperature is millions of kelvins;
the high temperature of the corona is probably due to heating by waves that move into the corona
along magnetic field lines
- Prominences are clouds of relatively cool gas that extend upward into the corona; large
prominences erupt about once or twice a day, blasting gas outward into space (Coronal Mass
Ejections)
- Flares are explosive releases of the Sun's magnetic energy; high-energy radiation and energetic
particles are both produced by flares
e. The Solar Wind
- the flow of coronal gas into interplanetary space; the magnetic field lines in the solar wind
remain attached to the Sun, so the rotation of the Sun (once every 27 days) stretches the field
lines into a spiral pattern; the solar wind reaches the Earth in about 4 days
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- the Heliosphere is the region of space affected by the solar wind; it extends about 100
Astronomical Units
- Note: one Astronomical Unit, or AU, is the distance from the Earth to the Sun, about 150
million kilometers or 93 million miles
XXIV. Beyond Our Solar System
A. Star Names
Stars are named by:
1. Ancient Sources
- typically use names from Latin, Greek or Arabic
- Arabic names often have prefix “al”
2. Using Constellation Names
- for brighter stars often pair a Greek letter with the name of the constellation in which the star is
found; stars are designated in roughly descending order of brightess with  brighter than ; 
brighter than , etc. (Ex. = Sirius, the brightest star in the constellation Canis Major, is
designated  Canis Major )
3. Star Catalogs
- the existence of numerous star catalogs has led to the same star given several names, sometimes
a confusing situation
B. Determining Star Distances
1. Parallax
- the apparent change in the direction of a star resulting from viewing it from different places on
the Earth’s orbit around the Sun
- all stellar parallaxes are less than one second of arc, so in order to get precise measurements
astronomers measure positions of a nearby star relative to more distant stars that lie in the same
direction
2. Units of Measurement
- distances of stars are often measured in light years (the distance light travels in a year; 9.46 X
1015m; about 9.46 trillion kilometers or 5.88 trillion miles) OR Parsecs (pc; the distance at which
a star has a parallax of 1 second of arc; one parsec equals 3.09 X 1016m or 3.2616 light years);
one kiloparsec, or kpc, is 1000 parsecs or 3260 light years
3. Standard Candles
- an astronomical body in which the luminosity is known, allowing its distance to be determined
by measuring its apparent brightness (Exs. = Cepheid variable stars, supernovas)
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C. Brightness of Stars
1. Stellar Magnitude
a. Apparent Magnitude
- system devised by Ptolemy to describe the apparent brightness of stars (the observed brightness
as viewed from Earth)
- in the magnitude system objects brighter than the brightest stars are given negative magnitudes,
whereas faint objects have large positive magnitudes; each additional magnitude corresponds to a
decrease in brightness by a factor of 2.512
b. Absolute Magnitude
- the apparent magnitude a star would have it were at a distance of ten parsecs; absolute
magnitude measures the star’s intrinsic brightness (i.e. the luminosity)
- apparent magnitude and absolute magnitude are related to each other through the distance to the
star
D. Stellar Color and Temperature
1. Very Hot Stars with temperatures above 30,000 K emit most of their energy in the form of
short wavelength light, and therefore appear blue
2. Stars with surface temperatures between 5,000 and 6,000 K appear yellow (like our Sun)
3. Stars with surface temperatures less than 3,000 K appear red
E. Binary Star Systems
- two stars revolving around a common center of mass under their mutual gravitational attraction
Multiple Star Systems - consist of close binary pairs orbited, at a much greater distance, by other
binary pairs or single stars
- at least 85% of all stars are members of binary or multiple star systems
F. Interstellar Matter
- makes up about 20% of the Galaxies' visible mass
Nebulae - clouds of gas and dust seen in visible light; constitute important parts of the Milky
Way
1. Interstellar Gas
- about 99% of the matter in interstellar space is gaseous (mostly hydrogen and helium)
Emission nebula - gas glows in the visible part of the spectrum
2. Interstellar Dust
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- consists of small bits of solid material, mostly less than a millionth of a meter in size
- most interstellar dust particles form in the atmospheres of cool giant and supergiant stars; the
core of the particle is made of silicate or carbon soot, around which a mantle of water, ammonia,
methane, and other icy material slowly grows
a. Dark (Absorption) Nebula
- dense interstellar cloud containing enough dust and gas to block out the light of background
stars (dust appears as dark spot against emission nebula)
- the dimming of background stars gives the appearance of a region with no stars
b. Reflection Nebulae
- a cloud of interstellar gas and dust that is luminous because the dust it contains reflects the light
of a nearby star; often appear blue
c. Diffuse Interstellar Dust
- dims and reddens the light from distant stars
- dimming is due to scattering of light and absorption
- scattered light appears as a general glow in the galaxy
G. Star Formation
- stars form inside relatively dense concentrations of interstellar gas and dust (Molecular Clouds)
1. Protostars
- stars in the process of formation; density increases fastest at the center of a collapsing cloud
core and produces a protostar; when it becomes opaque the protostar stops collapsing and begins
to accumulate infalling material; it contracts slowly until its central temperature becomes hot
enough for hydrogen fusion to take place; the rotation of a cloud core causes infalling matter to
accumulate in a rotating, nebular disk
2. Main Sequence Stars
- period of time in which the star is consuming hydrogen in its core; most visible stars are on the
main sequence
a. Variety of Main Sequence Stars
- although all main sequence stars generate energy by the fusion of hydrogen into helium in their
cores, they differ from one another in mass, size, temperature, luminosity, and internal structure
- massive main sequence stars are larger, hotter, and more luminous than the Sun, whereas lowmass main sequence stars are smaller, cooler and dimmer than the Sun
b. Main Sequence Lifetime
- length of time a star spends consuming hydrogen in its core
- the temperature and luminosity of a star change relatively little while it is on the main sequence
- the main sequence lifetime of a star is proportional to its mass and inversely proportional to its
luminosity (however, the luminosity increases as mass increases, so the most massive main
sequence stars have the briefest lives)
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3. Star Death
- depends on the star's mass
- higher mass stars have shorter lifetimes
a. Low Mass Stars
- mass less than 1.5 stellar masses (1 Stellar Mass = mass of our Sun)
- the Evolution of Low Mass stars is as follows:
Main Sequence - hydrogen "burns" in core (hydrogen fuses to helium); core hydrogen is
eventually consumed
Red Giant - hydrogen "burns" outside the core (in the Shell Source), pressure pushes outward and
the star expands; core contracts, heats and ignites helium (Helium Flash)
Yellow Giant - many swell and shrink rhythmically (they "pulsate" to form "variables" or
"pulsating stars")
Red Giant - helium burns in shell; outer layers ejected to form "Planetary Nebula"
Core begins to cool to become a White Dwarf (a dense star whose radius is about the same as
Earth's but whose mass is comparable to the Sun; one teaspoon of White Dwarf would weigh
about 5 tons!; White Dwarfs have no energy generation)
b. High Mass Stars
- mass more than 1.5 stellar masses
- the Evolution of High Mass stars is as follows:
Main Sequence - hydrogen "burns" in core (hydrogen fuses to helium); core hydrogen is
eventually consumed
Yellow Supergiant - helium "burns" in core; star begins to pulsate
Red Supergiant - heavier elements "burn" in a series of shells in the star's core
Buildup of iron core, eventually collapses to form a Supernova Explosion; the remnant may be a
Neutron Star or Black Hole
- Neutron Star (forms from collapse of stars from 1.5 to 3 solar masses; a very dense, compact
star composed primarily of neutrons; one teaspoon of Neutron Star would weigh 100 Million
Metric Tons!)
- conservation of angular momentum may accelerate the rotation rates of neutron stars to 1,000
times per second; beams of radiation are emitted that sweep across space (these rapidly-rotating
EARTH SCIENCE, PAGE 101
neutron stars are termed Pulsars)
- Black Hole (created from collapse of stars that are greater than 3 stellar masses; an object
whose gravitational attraction is so strong that it prevents light or any radiation or material body
from leaving its "surface"; these are formed by the collapse of super-massive stars after a
supernova explosion); they may be detected where x-rays are created when "companion stars" are
drawn into the Black Hole
H. Galaxies
- a massive system of billions of stars held together by their mutual gravity
- galaxies are found in groupings (Galaxy Clusters), which group into even larger units
(Superclusters)
1. The Milky Way
- a band of light that consists of a vast system of stars, the Milky Way Galaxy (which is our
galaxy)
- the visible portion of the Milky Way has a diameter of approximately 25,000 parsecs (75,000
light years) and contains about 200 billion stars
a. Milky Way Subdivisions
a1. Nuclear bulge
- in center of galaxy; is obscured by interstellar dust, but can be mapped in the infrared and radio
parts of the spectrum
- densely packed old stars and interstellar gas and dust
- Galactic Nucleus in center; approximately 4 parsecs across; produces tremendous amount of
energy (probably due to a central black hole)
a2. Galactic Disc
- thin, phonograph record-shaped part outside the bulge
- with young stars and interstellar gas and dust
- the disc of the Milky Way probably has spiral arms
a3. Galactic Halo
- flattened spheroid surrounding disc
- made of scattered older stars and hot interstellar matter
a4. Galactic Corona (Dark Halo)
- made of non-luminous material (also no radio waves, x-rays, infrared!) with approximately ten
to one hundred times the mass of the combined size of the nucleus, disc and halo
- consists of "Dark Matter" (nonluminous matter that is detected only by its gravitational
influence)
b. The Milky Way is probably a Spiral Galaxy
- we lie about two-thirds of the way from the center of the disk, on one of the arms
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2. Types of Galaxies
Hubble Classification System - formulated by Edwin Hubble; divides galaxies into different
classes (Hubble Types) according to their shapes
a. Elliptical Galaxies
- the most numerous galaxies; are spherical or egg-shaped; with little gas and dust (and therefore
few "young stars" are present)
b. Spiral Galaxies
- disk-like galaxies, with arms of young stars and gas winding out from the nucleus; both old and
young stars are present in Spiral Galaxies
c. Irregular Galaxies
- irregular-shaped galaxies, with large amounts of gas and dust and many young stars
3. Active Galaxies
- in at least 10% of galaxies, the centers emit abnormally large amounts of energy from a tiny
region in their core; possibly created by huge amounts of matter being drawn into a central black
hole
- include Quasars (Quasi-Stellar Objects, or QSOs), peculiar galaxies that represent the farthest
(oldest) known objects in the universe; study of quasars may reveal the early history of galaxies
in the Universe
4. Clusters of Galaxies
- a group of galaxies held together by their mutual gravitational attraction (the Local Group
consists of approximately 2 dozen galaxies nearest to, and including, the Milky Way)
- there are also "cluster of clusters", forming a supercluster
- clusters and superclusters are arranged in patterns of sheets that surround voids, within which
few galaxies can be found
I. Cosmology
- study of the universe
1. Origin of The Universe
- the universe is believed to be approximately 10 - 20 billion years old
Age Estimation is Based Upon:
a. Star Observations
- observation of star clusters and interpretation of nucleosynthesis (study of element formation,
especially in massive stars) estimates that age of universe is from about 15 to 20 billion years old
b. Hubble's Law (Law of Redshifts)
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- the velocities at which galaxies move away from us are proportional to their distance from us;
more and more remote galaxies will have greater and greater speeds of recession
- based on the Law of Redshifts, it is believed that the universe is 10 to 20 billion years old
(recent studies indicate possibly 13.7 billion years old)
b1. According to Hubble's Law, the universe is expanding
b2. At the "beginning of time" all energy and matter in the universe was crowded together at a
single point
b3. The Big Bang
- the event that created the Universe; it generated the expanding motion that we observe today
Cosmic Microwave Background Radiation is spread uniformly over the entire sky; it represents
light from the Big Bang; it is seen in all directions but comes from such a great distance that it is
redshifted by a factor of 1100 (and is therefore seen as radio waves); the background radiation is
strong evidence that the Universe began with a Big Bang
Inflationary Models of the Universe suggest that the Universe may have originated in a "False
Vacuum", in which gravity was a repulsive force (at this time the Universe would have been
trillions of times smaller than a proton, but negative gravity "inflated" the Universe, cooled it,
and released huge amounts of energy which became the Big Bang)
- Inflationary Models suggest that there are not several independent forces in the universe (these
are aspects of a single unified force; Grand Unified Theory, or GUTs)
b4. Sequence of Events in the Big Bang
- during the first few minutes of the Big Bang some hydrogen was fused to helium, but the
Universe quickly became too cool for such fusion actions to occur
- the rate of cooling increased, and after about 300,000 years protons were able to capture
electrons to form hydrogen (this is termed Recombination); recombination left the gas of the Big
Bang neutral
- the first stars and galaxies began forming within one billion years after the Big Bang; the
violent burst of star formation caused ultraviolet photons to ionize the gases (termed
Reionization); the first stars were very massive, very luminous, and very short lived (astronomers
looking at quasars can see evidence of this reionization)
2. Universe Expansion or Collapse?
- older theories stated that the total matter and energy of the universe creates gravitation, which
will slow the expansion of the universe through time
- however, recent studies indicate that the rate of expansion is actually increasing, which
suggests the existence of an unknown force (Dark Energy); dark energy may account for threefourths of the total mass-energy of the universe
"Open Universe" - the universe will continue to expand forever [occurs if average density is less
than critical density (critical density is density that is great enough to cause gravitational collapse
EARTH SCIENCE, PAGE 104
of the universe)]
"Closed Universe" - if dark matter (matter in the universe that cannot be detected thus far) is
enough so that the universe will eventually reverse itself and compress all matter and energy in
the "Big Crunch"
"Flat Universe" - the density of the Universe equals the critical density
"Oscillating Universe" - with big bang, big crunch, big bang, big crunch, etc., etc.