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*Prior to 18th century Archbishop Usher, of Ireland in 1864;
> New Testament. Earth was formed October 23 4004 B.C.E
*Steno (~ 1650) found clues indicating Earth
- Observed marine fossils high in the Apennines.
- Reasoned were from and ancient sea.
- Lithification & uplift suggested long periods time.
*Hutton (1726-97) Scottish physician and farmer.
- Called the father of modern geology.
- First to articulate the principle of “uniformitarianism”.
*Uniformitarianism Processes seen today same as those in past.
- Geologic change very slow; large changes require time.
*Lyell (1830-33) Set up by Lyell for deciphering Earth History.
-Used to establish relative ages of Earth materials.
-Basis: uniformitarianism and Steno’s rules
*Uniformitarianism We can observe lava flowing and cooling into solid rock. Ancient
lave flows the products of volcanic eruptions.
*Original Horizontality ediments settle out of fluid by gravity.
-Causes sediments to accumulate horizontally. Sediment accumulation not favored on
a slope. tilted sedimentary rocks must be deformed
*Superposition -In an undeformed sequence of layered rocks:
-Younger strata are on top; older strata below.
*Lateral Continuity Strata form laterally extensive horizontal sheets.
-Subsequent erosion dissects continuous layers. Flat-lying rock layers unlikely been
disturbeted
*Cross-cutting Relations Younger features truncate, cross across older features.
Faults, dikes etc., must be younger than the material that is faulted, intruded or
eroded. A volcano cannot intrude rocks not there.
*Consider block of geologic history. Folded beds. Intrusions. Granite.
Basalt dike. A fault. Easily deciphered.
*Principle Fossil Succession. Fossils often preserved in sedimentary rock. Fossils are
time markers for relative age-dating.
-Fossils speak of past depositional enviro.
*Fossil succession: species evolve, die out First appearance, range, extinction used for
dating. Fossils succeed one another in a known order. Time period is recognized by
fossil content.
*Fossil range – first and last appearance. Each fossil has unique range.
- Range overlap narrows time. -Index fossils diagnostic a particular time.
-Fossils correlate strata. Locally Regionally Globally
*GAPS IN RECORD Unconformity is a gap in rock record, from:
-Non-deposition. Erosion.-There are three types. Angular unconformity.
Nonconformity. Disconformity.
*Angular Hutton’s Unconformity: Siccar Point Scotland.
Missing time – 50 million years.
*Nonconformity -Igneous/metamorphic rocks capped by sedimentary
*Disconformity – parallel strata bounding nondeposition.
*FORMATIONS Earth History: Grand Canyon Earth history recorded in sedimentary
strata. Formations can be correlated over long distances
* William Smith in 1793 recognized strata could be matched over large distances.
Made the first geologic map. Geologic Maps Portray the distribution of rock units On
Earth’s surface. Based on the Formation.
*THE GEOLOGIC COLUMN Composite column Composite stratigraphic column
constructed.
*Geologic Time and Life Life first appeared on Earth ~ 3.8 Ga. Consisted of
anaerobic single celled organisms. O2 from cyanobacteria built up in tmosphere by 2
Ga Around 700 Ma multicelluer life evolved.
*Geologic Time and Life Around 542 marks first appearance hard shells. Shells
increased fossil preservation. Life diversified rapidly in the Cambrian explosion.
*DETERMINING RADIOMATRIC AGE. Radioactive Decay
Decay progresses along a decay chain. decay created unstable elements that also
decay. Decay proceeds to a stable element endpoint.
- Parent Isotope – isotope that undergoes decay.
- Daughter isotope – the product of this decay.
Radioactive Decay: Isotopes
-Isotopes – elements that have a varying number of neutrons.
Isotopes have similar but different mass numbers.
- Stable – isotopes never change (i.e. 13C).
- Radioactive isotopes that spontaneously decay
Radioactive Decay: Half-Life
Half-life (t1/2) – time for half of unstable parent nuclei to decay. Half-life is
characteristic of each isotope.
- After one t1/2 one half of the original parent remains.
- After three t1/2 one eighth of the original parent remains.
- As parent decays daughter “grows in”.
*Radiometric Dating: Geochronology
* Age of mineral determined by:
- Measuring ratio of parent to daughter isotopes.
- Calculating amount of time by using known t1/2
* Geochronology requires analytical precision.
Radiometric dates give time a mineral began to preserve all atoms of parent and
daughter isotopes. Requires cooling below a “closure Temperature.” If Rock reheated
the clock can be reset.
*Igneous/Metamorphic rocks the best for dating the Geologic Column
NUMERICAL AGE: GEOLOGIC COLUMN
* Geochronolgy less useful for sediments. However can be bracketed by numerical
dates Yields age ranges that Narrow as data accumulates.
*WHAT IS THE EARTH’S AGE? Initial Estimates Before radiometric dating age
estimates varied widely From 20 Ma - earth Cooling. From 90 Ma – ocean
salinization.
*Uniformitarianism and evolution argued much older 100ma .
*Best Estimate -Oldest rocks on Earth’s surface are 3.96 Ga.
Zircon’s in ancient sandstones give 4.1 -4.2 Ga.
Age of Earth is 4.67 Ga from: Meteorites. Moon Rocks.
*Earth Has a History. Geologic materials record conditions and change.
Earth consists of systems that interact and evolve.
- Continents grow and migrate.
- Ocean Basins orm and grow.
- Species arise, fluorish and become extinct.
*Orogeny. Paleoclimate..Paleomagnetic location. Location and arrangement of
continents. Not Easy to Decipher
*Record of conditions events in past incomplete.
-Younger rocks more abundant than older rocks.
- Sediment deposition not continuous.
- Erosion removes sediment, destroys rock.
- Subduction removes much of record
*Orogens are laboratories for studying the past.
- Deposition into foreland basins. Uplift and expose rocks.
- Igneous activity, metamorphism, deformation alter record
*Paleoclimatology – study of past climates.
- Greenhouse Earth. Snowball Earth. Indicators of past climate:
- Tropical – coral reefs. Subtropical – deserts. Polar – glacial deposits.
* Ocean Basins -Seafloor rocks and sediment record age. Magnetic anoms give
relative position continents. Paleomagnetism gives past latitude. Abyssal sediments
give much detailed information.
* Fossil Record :Sedimentary rocks contain fossils.
Type and geographic distribution of organisms changed through time.
Some species indicate specific conditions. Sudden catastrophic
changes in record indicate catastrophic events
* THE HADEAN EAON Hell-like (Hadean): Moon (4.6 – 3.8Ga)
Earth formed 4.57 GA based on radiometric analysis of planetesimal fragment
meteorites. Very early Earth had a partially molten surface.
Differentiated to core, mantle and crust by 4.5 Ga.
Collisions with Mars sized protoplanet ~ 4.4 Ga:
- Ejected mantle and crust into space. Coalesced to produced moon.
Intense meteorite bombardment 4.0 – 3.9 Ga.
* Hadean Atmosphere-Earth’s atmosphere very different from now.
- Probably formed by “outgassing” during differentiation/ volcanism.
- Humans and most modern life forms could not have survived Earth’s early
volcanism because of lack of oxygen.
*Formation of Oceans -First oceans formed as rain from the sky. Liquid water
required cooling of the surface. First evidence of oceans from marine seds ~ 3.85 Ga
*ARCHEAN EON. Beginning (3.8 – 2.5 Ga)
Based on first abundance of crustal rocks (3.85 Ga). Plate tectonics began during or
just before Archean.
*Cratons - Broad low areas continental lithosphere.
- Expose or have bedrock > 1 Ga Consist of orogens and blocks.
Consist of: -Shields broad lowland areas exposed rock.
- Platforms broad regions shallow water sedimentary rock over basement.
*Increase in Volume Continental Crust increased dramatically.
- 85% of modern continents present by the end of Archean.
Indicates full development of plate tectonic processes.
*First Life - Oldest undisputed fossils - ~3.2 Ga
Possibly as old as 3.8 Ga. Photosynthesis occurred by 2.7 Ga.
Evidence: Fossils. Biomarkers. Carbon isotope ratio.
> Organisms preferentially incorporate 12C compared to 13C
*PROTEROZOIC EON - early life (2.5 Ga – 542 Ma)
Cratons reached modern abundance by accretion.
Several rounds of super continent rifting and assembly.
Oxygen rose form <1% to ~ 12% ~ 2.0 Ga.
*Evolution of Life Life developed slowly. Eukaryotes (bacteria containing nuclei)
evolved ~ 2.7 – 2.1 Ga. Muticellular life
forms evolved between 1 G and 750 Ma. Large life forms
leaving recognizable fossils evolved around 620 Ma
*Proterozoic Atmsophere Atmospheric Oxygen:
- Rose slowly from ~ 1% at 2.4 Ga to ~ 3% at 1.8 Ga.
Little change form 1.8 Ga to 0.8 Ga.
- Rose rapidly from 3% at 0.8 Ga to ~ 12% at 542 Ma.
*The Snowball Earth Near 600 - 700 Ma glaciers over most of the Earth.
Cause is not known. Oceans were nearly completely frozen over.
Many life forms became extinct. Volcanic activity and greenhouse effect ended it.
*THE PHANEROZOIC EON visible life (542Ma – present)
Defined by widespread divers fossils of skeletal or other durable remains.
*Divided into 3 eras:Paleozoic(542-252 Ma)Cezozoic(251-65 Ma)Cenozoic (65-now)
*Early Paleozoic – 542 – 448 Ma
Shallow epi-continental seas, platform deposits. Rifting created:
New ocean basins. Siberian Craton. North America and Greenland
(Laurentia). South america, Africa, India and Australia (Gondwana).
Middle Plaleozoic – 448 – 359 Ma Biological Diversification
New ecological niches result landmass breakup? Epi-continental sea rich in life.
Conondonts, Trilobites, hard shelled forms abundant. extinctions.
*Middle Paleozoic – Life Arrives on Land. Around 420 Ma – life emerges from the
sea. Adapt to living on land.Land plants developed:
- Protective tissues. Vascular systems, Seeds. Atmospheric O2 rose > 30%.
- Crustaceans, spiders, insects evolved. Amphibians evolved lungs
*Late Paleozoic, 359 - 251 Ma Global cooling starts beginning Carboniferous. End of
Permian continents coalesced to form super continent Pangea. Tremendous adapation
to living on land Trees resembling Pines and palms. Reptiles evolved rapidly.
Late Paleozoic – Permian Mass Extincion Nearly 95% of marine species killed off..
Thought to be a result of extended eruption of vast basalts in Siberia Increased dust.
Increased acidity of atmosphere and water due to gasses erupted.
*MEZOZOIC ERA Breakup of Pangea 251 – 65 Ma Pangea breaks up: modern
features begin to appear. Late Triassic rifting of Pangea formed deep basins. *
Western margin of North America changed from passive margin to active
convergent margin. *Jurassic – rifting matures into a proto-Atlantic Ocean. *
Gondwana breaks up Mesozoic – Biological Evolution. Mesozioc – the age of the
Dinosaurs.
*Triassic – (251 to 200Ma) Rapid evolution of species after Permian extinction.
Swimming reptiles evolved.
*Late Triassic:1st dinosaurs. Earliest ancestors of mammals. Mesozoic – Biological
Evolution.
*Jurrasic – (220 – 145 Ma) Evolution of large creatures. Dinasours. Modern fish.
*Cretaceous (145 – 65) Grasses
*Mesozoic – North America Interior largely submerged beneath shallow sea.
Southern and eastern coast were passive margins and accumulated thick sediments
Major orogenies occurred in the west at different times with different styles.
*Mesozoic – the Cretaceous Plate tectonic activity increased. Seafloor spread at much
higher rates than today. Sea level rose as ridge volume increased. Vast eruptions of
submarine basalt produced.
*THE CENOZOIC ERA (65 – 0 Ma) *The Cretaceous-Tertiary Boundary
Widespread extinctions species at end Cretaceous.
Disappearances included: All Dinosaurs. 75% of plant species.
Most plankton species. World sediments showed: Iridium layer at 65 Ma horizons.
Iridium found only in meteorites. Extinction due to 13 km wide meteorite.
*Final Breakup of Gondwana .Australia rifted from Antarctica. Greenland rifted form
North America. Continental collision: Italy, Turkey, Iran, India collided with Eurasia.
Forms Alpine-Himalayan orogen, longest on Earth.
*Development of Primates - Widespread grasses. Rapid diversification of mammals.
Giant mammals: Mammoths, beaver, bears, sloths.
Giant mammals went extinct ~ 10 Ka. Human genus of primates: 2.4 Ma. Earliest
known use of tolls: Homo rectus; 1.6 Ma Modern Humans evolved about 200 Ka
*Cooling Climate throughout Cenozoic Ice Sheets increased during the Cenozoic:
Glaciers formed and have remained on Antarctica. Beginning at 2 Ma northern
hemisphere glaciation has occurred more than 20x.
*The Pleistocene Ice Ages Sea floor dropped exposing sea floor of between Alaska
and Russia.
*Human migrate long the coast to North America. Last ice terminated suddenly at 11
Ka yielding present interglacial period (Holecne).
*Energy Human consumption of energy grown steadily.
Americans consume 110 times as much as early humans.
*SOURCES OF ENERGY Five Fundamental Sources
Energy stored in chemical bonds. Nuclear Fusion (Sun). Energy from Earth’s
interior. Pull of Gravity. Nuclear fission.
*Sources of Energy: Solar Energy produced by Fusion in the Sun’s Interior Heat and
light are radiated out form the Sun. Tiny portion of output reaches Earth. Solar energy
can be used by humans. Conversion into electricity by photovoltaic cells.
Conversion into heat. Humans cannot control fusion.
*Sources of Energy: Gravity. Moon power. Gravitational pull of moon causes tides.
Tidal flow in oceans can be harnessed. Gravity pulls water downhill. Energy can be
extracted from dams by turbines. Hydroelectric power. Fluids in complex motion.
Energy can be extracted form air and ocean currents. Wind power.
*Sources of Energy: Fossil Fuels Oil, natural gas, coal derived living organisms.
These materials have energy stored in H-C bonds: Created by photosynthesis; solar
energy from past. Thus, oil, gas and coal represent “fossilized sunshine.”
*Sources of Energy: Nuclear Fission Certain radioactive atoms can be broken apart
(fission). Fission yields tremendous energy. Nuclear power plants use fission of
uranium to create electricity.
*OIL AND GAS Depends on them. Oil and gas (hydrocarbons) complex organic
molecules. Were produced by once living creatures.
May consist only of H and C. Many types. - Occur as complex mixtures.
Compounds separated by refining Oil and Gas Genesis
Oil and gas derived from plankton/marine algae. Dead plankton and alga sink.
Organic material accumulates offshore as fine mud. Under anoxic conditions, material
is preserved. Lithification forms a dark shale, petroleum source rock
Hydrocarbon Systems
* Oil and gas preservation is geologically rare. A known supply of oil is called an oil
reserve. Oil reserves are geographically limited. 60% world reserves in the Persian
Gulf South Atlantic deep water, Arctic new exploration areas.
*Creation of a Resevoir: Requires four features: Source rock. Usually an organic rich
shale. Migration pathway. Fractures and/or bedding porosity. Reservoir rock.
Permeable or can be fractured. A trap. Features must develop in specific order.
*Reservoir Rocks and Migration. Reservoir rocks store and transmit oils and gas.
Porosity is the open space in rock that stores fluid. Permeability - ease of fluid
movement thru pore spaces. > Low – small well yields.
> High – large well yields.
*OIL EXPLORATION, PRODUCTION : Oil Discovery . Oil seeps had been used for
millennia. First oil well drilled Titusville, Pennsylvania 1859 Wells allowed fast
removal from ground Oil was available consumption boomed. Within decade 1000’s
wells drilled. Oil Exploration: Seismic Reflection . Sound “bounces off” contrast
between layers..Allows geologists look for traps without drilling. Seismic surveys
conducted on land and as sea. One of the disciplines of geophysics.
*Exploration: Diamond Bit Drilling
Rapid circulation of high-density drilling mud. Lifts cutting to the ground surface.
Reduces the risk of blowouts. Cools the drill bit. Oil Production
*Primary recovery. Uses reservoir fluid pressure and pumping to extract oil. Can
only recover ~ 30% of oil.
*Secondary recovery. Uses fluids (steam, CO2) to heat, “thin” and push oil Hydraulic
fracturing – increases permeability. Can only recover ~ 20% more of the oil.
*ALTERNATIVE HYDROCARBONS -Natural Gas – Short Chain Hydrocarbons.
Methane, ethane,proposane, butane and others.
Form at temperatures just above the oil window. Natural gas more abundant than oil;
a cleaner fuel. Now being drilled fROm shale using “fracking”. Oil Shale: Abundant
Kerogen. Source rock not reached the oil window. Burning transforms kerogen into
liquid hydrocarbon.
*Tar sands – heavy residual petroleum found sand. eavy oil is residue of former oil
field. * Gas hydrates methane (CH 4) in cage of ice. CH4
from decomposition of organic matter. Forms in cold water depths > 300 m More
than all other reservoirs combined
*Other Alternative Hydrocarbons COAL: ENERGY FROM SWAMPS
*Coal Black, brittle, carbon rich, sedimentary rock. Produced from burial and
heating of vegetation. Around 60% of world reserves formed in the Carboniferous
(354 – 286 Ma). Important energy source and CO2emitter
*Coal Formation -Vegetation accumulates in anoxic (O2poor) setting Absence of O2
retards decay organic matter. Common depositional environments yielding
coal:Marine Deltas. Tropical coastal wetlands. Area subsides vegetation buried under
sediments.
Coal Formation -Compaction decay turn plant debris into peat.
Peat is ~ 50% carbon. Peat is easily cut dries and burned.
Burial several km increased heat, alters peat. H,N and S expelled as gases; C content
increases. At 70% carbon, material becomes coal.
*Coal Mining Geologists look for specific sedimentary sequences deposited in
shallow marine coastal environment Typically occurs thin beds. To be mined must be:
Not too deep. Have a thick enough
bed (>1 m thick) Mined underground. Dangerous, expensive.
Strip mined. Environmentally dangerous.
*Coal Mining . Coal deposits are found world wide. US, Canada vast bituminous and
lignite coals. Mined by stripping. Open pit or
underground.
*NUCLEAR POWER Energy from Breaking Apart Atoms. Neutrons strike nuclei of
fuel molecules to cause fission. Fission produces neutrons to split other nuclei. Fission
produces other elements. Fission produces heat. Most reactors use fuel rods of
uranium oxide pellets.
*Nuclear power can be used to generate electricity. Nuclear power emits no green
house gases. Nuclear power plant “self-sustains” by balancing neutron generation and
absorption by uranium fuel.
*Control rods absorb neutrons slowing fission. Fission produces enormous amounts
of energy. High pressure steam is created in a closed reactor loop. Heat transferred to
external water loop. Steam in external loops spins turbines to create electricity. Can
be safe is well designed and constructed and placed in safe locations
Fukushma (2011) cast doubts on safe sighting and operation of reactors in
geologically active areas.
*Nuclear Power Problems -Many nuclear power plants store used reactor cores in
spent fuel pools. Circulation of water prevents rod-jacket melting and release of
radiation. This occurred at Fukushima, Japan (2011) In addition, the problem of long
term geologically safe storage has not been solved. Thus a huge poison is building up
in our environment.
*OTHER ENERGY SOURCES
Not all energy options require digging, pumping or processing nuclear fuel. They also
produce little CO2:Geothermal Energy. Hydroelectric power. Wind energy. Solar
Power. Hydrogen fuel cells. Biofuels - but they produce CO2 when burned.
*Geothermal Energy -Energy from Earth’s internal heat. Geothermal gradient hotter
with depth. Gradients vary form 15 to 50oC/km. Higher gradients:hotter at shallower
depths. Geothermal may produce waste brines. Geothermal produces no CO2.
*Hydroelectric Power -Running water represents kinetic energy (KE). Dams halt
flow, converting KE into potential energy (PE) by storing water above sea level.
Water is released, converting PE back to KE. Flows through turbines to create
electricity.
*Other Sources of Energy - Wind farms turn turbines produce energy. Solar Power
most abundant source of energy at Earth’s surface. Creates electricity or heat.
Hydrogen fuel cell – hydrogen and oxygen are reacted to yield electricity and water in
“fuel cells”.
*ENERGY PROBLEMS Use reflects industrialization and population growth. Oil the dominant energy source - is dwindling. Many countries import oil to meet
demand. Burning oil produces CO2
*The Oil Crunch Oil extinction will occur between 2050 and 2150 Future historians
will see “oil Age” as 200 year era. We are near the peak of global oil.
*Environmental Issues: Ground Fossil fuel production, use damages environment. Oil
spills – Deepwater Horizon spill, Gulf of Mexico.
Coal – Strip mining and acid damage. Shale gas – groundwater contamination from
“fracking.” Nuclear power – radiation releases, destruction of Fukushima &
Chernobyl stations and storage of waste.
*Environmental Issues: Air quality -Using fossil fuels causes air pollution affects
climate. Unburned hydrocarbons add to photochemical smog. Sulfur dioxide (SO2)
contributes acid rain. Burning coal lofts toxic metals and soot into air. CO2stimulates
global warming and climate change.
Mineral Resources
*Two major categories. Metallic: Gold.Silver .Copper .Lead
Zinc .Iron . Aluminum - Nonmetallic : Sand and Gravel
Gypsum . Halite .Dimension stone Fluorite cleavage octahedra
*METALS AND THEIR DISCOVERY -Opaque, shiny, smooth, conductive solid.
Metal properties from metallic chemical bonds. Delocalized electrons move from
atom to atom easily. Electron fluidity renders metals electrically conductive.
*Metal Properties -Not all metals behave the same way. Metal properties due to bond
type and structure. Metals may be extremely hard (titanium) or soft (copper) . Ductile
– able to be drawn into thin wires. Malleable – able to be hammered into thin sheets
*Discovery of Metals -Native metals occur naturally in pure form.
Gold . Silver . Copper . Iron .People used native metals for thousands of years Tools
– easily shaped by cold working. Money – rare and durable
* Three principal metals – copper, iron, aluminum
*Copper used first (4000 BCE) > Smelting Cu sulfides easiest. Copper too soft for
tolls or weapons. Sumerians discovered bronze (~ 2800 BCE) > Copper alloyed with
tin. > Bronze is stronger than either metal.
* Iron is superior to copper or bronze. Stronger Harder. .More abundant.
Iron much harder to smelt. Requires Much higher temperatures.
Chemical reactions with (Carbon Monoxide) CO.
*Smelting -Discovered by unknown prehistoric genius. Smelting releases metals
from ore minerals. - Nonmetallic waste called slag. *Steel – iron smelted with
Carbon.Blending metals creates alloys
Alloys are unlike pure metals Bronze – alloy of copper and tin. Brass copper
alloyed with zinc
*Metals in Use -Over 60 metals used in modern world. Precious metals – gold, silver
and platinum. Base metals – copper. lead, zinc, tin.
Before 1700 only nine metals in use. Au, Cu, Hg, Pb, Sn, Sb, Fe and As
*ORES, ORE MINERALS/DEPOSITS Ore-Rock with metal-rich
minerals. Concentrated enough to be economic to mine.
Metal must be readily extracted form mineral. Many are sulfides or oxides.
*Distribution of Ores. Ores not uniformly distributed through the crust. Geologic
processes concentrate metals deposits. Concentrations must be high enough to yield a
profit. Amount of useful metals present is the ore grade.
* Ores form by geologic processes. Magmatic activity. Hydrothermal alteration.
Secondary enrichment. Groundwater transport (MVT). Sedimentary processes.
Residual weathering. Hydraulic sorting. Magmatic Deposits
*Magmatic deposits – from cooling pluton. Sulfide minerals crystallize early and
sink in magma. Form massive sulfides at the bottom of chamber. Sulfides include:
Pyrite. Galena
*Hydrothermal deposits – chemically active water. Hot fluid leaches metal ions out
of rock near plutons. Minerals precipitate in lower P and T locations. Occur
disseminated through intrusion or in veins.
*Secondary Enrichment deposits These add O2, OH, and CO2
Groundwater leaches and oxidizes primary sulfide ores. The secondary deposit often
has beautiful minerals. > Turquoise *Secondary Deposits: Special Conditions .
Banded iron formations (BIFs). Layered gray iron oxides and red chert (jasper) Formed 2-5 – 1.8 Ga from O2 build up in Atmosphere. * Manganese (MnO2rich)
nodules. - Rich in trace elements, these grow slowly on sea floor.
*Residual Mineral Deposits -Occur in rainy tropical settings.
Formed via extreme chemical weathering in wet tropics. Intense weathering strips
almost everything out of soil. The residual soil is enriched in Fe and Al oxides. >
Bauxite – primary ore of aluminum
*Hydraulic sorting -Placer deposits from flowing water. In high velocity water. >
Low density minerals suspended in water washed away
> High-density grains are concentrated by settling out. - Important for Gold tin and
iron. Best preserved in fossil stream sediments.. Ore source can be traced upstream.
* Where are Ore Deposits found? Tectonic Processes are a dominant control.
Igneous and hydrothermal activity occur > At plate boundaries. > Along rifts. > At
hot spots. - Tectonic events are overprinted by the hydrologic cycle.
*ORE EXPLORATION PRODUCTION-Ore Location. Ores are located by evidence
of metal enrichment. Color – enrichment may brighten rock and soil. Systematic
geologic investigation – technology based. > Geophysical surveys – magnetism,
gravity, radioactivity. > Geochemical surveys – water, sediment and soil.
*Finding, Developing an Ore. Geologists map jungles, deserts etc for ores. When
identified ore deposit is assessed by; Geophysical response.
Core drilling. Geochemical analysis. If economic, a deposit is developed for mining.
Environmental concerns accommodated.
Ore can be extracted for a profit.
*Types of Mined Deposit -Depends on proximity to surface. *- Shallow ore body open-pit mining. *Deeper ore body - underground mining.
*Open-pit Mining -For Shallow ore bodies. Less expensive and dangerous than
tunnel mines. . Usually require ore within 100 m of surface. Open pit mines create
large excavations. Rock is broken by explosives removed for processing.
*Underground Mines- Ore is obtained by tunneling. Tunnels or vertical shafts are
excavated. Ore is loosened by blasting and haled to surface. - Underground mines are
expensive and dangerous.
*NON METALLIC MINERAL RESOURCES -Industrial Materials
Society use many materials that do not contain metals. Called industrial minerals.
:Dimension stone. Crushed stone/concrete
*Dimension Stone -Rock slabs used as building material. Rock is chosen for visual
appeal and durability. Requires rock with special properties be carefully cut..
*Crushed Stone -An aggregate used for many purposes. Forms the foundation for all
roads and railways. Raw material for cement, concrete and asphalt. Used extensively
in modern world
*Nonmetallic Minerals and Homes. Calcite – base material for cement and concrete.
Clay – bricks, pottery, porcelain and ceramics. Gypsum – wall board and plaster.
Quartz – window glass.
*GLOBAL MINERAL NEEDS How Long Resources Last. World demand for energy
resources is enormous. Industrial countries consume vast quantities. In Us we use 4
billion tons of Geologic materials /year.
*Continued use of scarce resources will require:
Discovery of New Resources. increase prices to make hard to get reserves profitable.
Increased efficiency and conservation.
Substitution. Recycling. Doing without.
* Mineral extraction and processing leaves big scar.
Open pit mines are large scars on the landscape. Mining creates huge volumes of
waste tailings Sulfides react with O2 from sulfuric acid.
This reacts with water, forming acid mine drainage (AMD).
Water from spoil poles is acidified. .Acidity dissolves iron, which coats stream in rust.
AMD mobilizes heavy metals and kills stream biota. Ore processing releases toxic
chemicals. These dispersed to nearby areas by air and rain.
CHAP 19*Earth’s Surface.
Not terra firma, mostly unstable. Mass movement/wasting is: downslope motion of
rock, soils sediment, snow, ice. Driven by gravity operating on any sloping surface.
Characterized by a wide range of rates (fast to slow).
*Mass movements. Costly type of natural hazard: crucial component of weathering.
Often create damage to living things, buildings. *Types of Mass Movement.
Classification based on: type of material (rock, regolith, snow, or ice), rate of
movement (fast, intermediate, or slow), nature of mass (cloud, slurry, or distinct
blocks), immediate surroundings (sub aerial or submarine). *Creep: slow downhill
movement of regolith. Due to seasonal soil expansion and contraction (wetting &
drying/freezing & thawing). Grains are moved: perpendicular to slope upon
expansion, vertically downward by gravity upon contractions.
*Rock Glaciers: mixture of rock fragments and ice. Rocks are added faster than ice
accumulates. Behave like glacial ice, flowing downhill slowly. Slumping: regolith
sides as coherent block. Slippage occurs along spoon-shaped “failure surface.”
Display a variety of sizes and rates of motion. Distinctive features: head scarp,
bulging toe, discrete fault slices.
*Mudflows, Debris flows, lahars: h2o rich movement. Mudflow: a slurry of water and
fine sediment. Common in tropical settings with abundant rainfall. *Lahar: special
volcanic mud and debris low. Volcanic ash (recent or ongoing eruptions) mixes with
water from heavy rains or melted glacial ice. *1963 Valont Dam Disaster. Heavy
limestone shale in deep synclinal gorge. Sides gave way on old faults after heavy
rains. 600 million tons limestone into resevoir, 2600 dead, dam still stands.
*Avalanches: turbulent clouds of debris and air. Wet avalanches behave like a viscous
slurry (hug the slope entraining little air, move slow- 30 km/hr) Dry avalanches move
cold, powdery snow (move above ground, on layer of pressurized air, move fast- up to
250 km/hr) *Rock Falls and Debris Slides. Bedrock and regolith falls rapidly
downward. On impact, they fragment and continue moving. Talus builds up as bas of
slope. *Submarine Mass Movements. Three types based on degree of disintegration.
Submarine slumps: semi-coherent blocks break and slip. Submarine debris flows:
broken material moves as slurry. Turbidity currents: sediments move as a turbulent
cloud. *Gigantic submarine Mass Movements. Much larger than land based mass
movements. Important process for shaping marine settings. Mass movements tied to
catastrophic tsunami.
*Requirements for a Mass Movement Occur. Earth materials need to be subjected to
topographic (slope) forces. Be weakened or loosened by fragmentation, weathering.
Fragmentation and weathering: upper crust is broken by jointing and faulting.
Chemical and physical weathering produces regolith: surface material is much weaker
than solid rock.
*Slope Stability. Slope stability dynamic= balance between two forces. Downslope
force-gravitational pull. Resisting force- material properties that repel motion.
Movement occurs when downslope forces prevail. Steeper slopes have larger forces.
*Angle of Repose. Loose granular material assumes slope angle. Angle of reposes
material property due: particle size and surface roughness. Fine sand: 35˚, coarse
sand: 40˚,angular pebbles: 45˚. * Failure surfaces. Weak subsurface can initiate
motion. Types of failure surfaces: saturated sand/clay layers, joints parallel to the land
surface, weak sedimentary bedding (shale, evaporates, bentonite), metamorphic
foliation. *Destabilizing Event. Usually triggers slope failure. Triggers are both
natural and manmade: shocks, vibrations & liquification, changes in slope loads,
steepness and support. Changes in slope strength. *Liquification. Vibrations cause
sediments to liquefy. Quick clay: pore water slurries clay flakes when shaken.
Saturated sand: fluidized by increased pore pressure. *Changing Slope
Characteristics. Can destabilize slope. Loading: adding weight to top of slope: water
(as rain or via humans (lawns, septic systems), materials (buildings, waste materials,
fill etc). Angle: steepening slope beyond angle of repose (river incision, excavation
for buildings and roads). Remove support: undercutting a slope leads to failure:
natural (waves eroding the bottom of a cliff), human (excavating the base of a slope).
*Slope Strength. Weathering: creates weaker regolith. Vegetation: stabilizes
slopes/removing vegetation (greatly slows removal of excess water, destroys the roots
a stabilizing mechanism, slope failures common after fires that destroy vegetation).
*Where Mass Movements Occur. Factors significant: relief (steeper slopes have more
movement), Climate (more rainfall creates more water problems). *Tectonic
Processes: influence mass movements. Create uplift- topography directly linked to
gravity. Fragments crust- joints and faults ease disintegration. Generates seismicityearthquakes trigger motion.
*Identify Slope Hazards. Geologic mapping can identify regions at risk: highlight past
failures, reveal unstable slopes. GPS can detect slow movements. *Hazard Maps:
computer model that maps landslide potential. Based on: slope steepness, strength of
substrate, degree of water saturation, vegetations cover, and earthquake probability.
*Revegetation/Terracing/ Roots anchor regolith. Water removed by
evapotranspiration. Removes excessive mass loading on slope. *Undercutting.
Slowing/eliminating undercutting- increases stability. Removing agent of erosion a
base of slope. Reducing the effect of agent of erosion. *Engineered Structures: built to
improve slope stability and reduce movement hazards. Retaining walls: barriers that
pin base and trap rock. Covers: fencing/coating that drapes over outcrop. Rock
Staples- rods drilled into rock, holds loose faces. Avalanche shed- shunt avalanches
snow. Controlled blasting- removal of dangerous rock.
*CHAP 20 STREAMS AND RIVERS
Streams & rivers: concentrate flow water channels.
Runoff: sheet like flow over land surface
*Stream runoff= important geologic agent. Flowing water: erodes, transports, and
deposits sediments. Sculpts landscapes, transfers mass from continents to oceans.
*Forming streams: stream flow begins as scattered runoff. *sheetwash. Runoff
coalesces into sheetwash (this surface layer of water, pulled down steepest slope,
erodes substrates, creates rills [small channels]. Rills deepen, coalesce into tiny
tributaries). *tributaries and trunks. Over time, channels (tributaries) enlarge and
merge. Tributaries eventually flow into a single trunk stream. The array of linked
drainage channels and the adjacent slopes form a drainage network.
*Drainage Basins. Land areas draining into trunk stream or body of water. Also
known as watershed or catchments. Ridges and peaks separate drainage basins.
*Drainage Divides. Watersheds exist at multiple scales. Large watersheds contain
many smaller ones. Continental divides separate drainages that flow to different water
bodies. *Permanent streams: water flows all year, at or below water table,
humid/temperate climates.
*Ephemeral streams: dry up for part of year, above water table, dry climates.
*Discharge: amount of water flowing in channel (volume passing point per unit timemultiple area by velocity). Varies due to season and other factors. Affected by friction
due to banks. Many times have turbulent chaotic flow.
*Erosional Processes. River Erosion: energy of flowing water form mass and gravity,
streams convert potential energy to kinetic energy, fast water flow lifts and moves
solids. Erosion is greatest during a flood because kinetic energy is higher, transports
more. Streams break, abrade, and dissolve material. Scouring: water picks up and
moves sediment. Breaking and lifting with rapidly moving water can: break chunks or
rock from channel, lift rocks and sediments off the bottom.
*Sediment transport. Sediment load, material moved by running water load. Types of
load: dissolved load (ions form chemical weathering), suspended load (fine particles,
silt and clay, in water), bed load (larger particles roll, slide, and skip along bottom).
Competence: the maximum clast size transported. Capacity: the maximum load
transported. Capacity and competence change with discharge. High discharge- large
cobbles and boulders may move. Low discharge- large clasts are not moved.
*Sediment Deposition. Decrease water velocity affects sediment transport:
competence reduced, sediment drops out. Boulders then gravels then sand fill channel
bottoms. Sands form inside banks. Silts and clays drape flood plains. Deposition in
streams and river systems: Sands build up the point bars inside meander beds, muds
deposited away from the channel during floods, mid-channel bars may be present, a
stream builds a delta upon entering a lake. *Streams change along length: longitudinal
changes. Character of stream changes along length. In profile grdient describes a
concave up curve. Gradient= drop in elevation, per distance flowed.
*Valleys and Canyons. Valley- gently sloping sidewalls and wider bottom. Canyonsteep sidewalls and narrower bottom. In mountains, river eroded valleys V shaped.
*Terraces. If base level rises, flow slows, valley fills with sediment. If base level falls
flow quickens, channels are incised. Leaves fluvial terraces. Terraces mark former
floodplains. *Rapids. Caused by turbulent flow of water. Reflect steep gradient and/or
high friction. Flow over bedrock steps (edges of resistant layers), flow over large
clasts, narrowing of a channel. Increase in gradient. *Waterfalls. Gradient is so steep
water cascades or free falls. Water falls (high kinetic energy) scours deep (plunge)
pool. Basal erosion leads to collapse of overlying rocks. Waterfalls are temporary
base levels. *Alluvial Fans. Build at Canyon mouths. Sediment drops out as water
spreads from mouth. Coarsest material dropped first, close to mouth. Finer material
carried further, to distal edge fan. Sediment creates a conical, fan shaped feature.
*Meandering Streams. Have sinuous, looping curves (meanders). They form where:
stream gradient is low, substrate is soft and easily eroded, stream exists within a broad
flood plain. Meanders evolve during times of flood. Curves migrate down stream
during floods: sinuosity increases, floodwater overtop or cut outside bank (create
shorter pathway downstream), water slows down in the cutoff loop, sediment settles
in the upstream and downstream end.
*Delta. Forms when stream enters standing water: stream divides into fan of
distributaries. Velocity slows, sediment drops out. Delta morphology is a dynamic
balance: sediment load, waves, storms, tides, and slumping. Mississippi is a sediment
dominated delta. In flood river may break through a levee: flow jumps to more direct
path to Gulf of Mexico.
*Landscapes. Evolve with time. Stream flow= cause of most change. Examples:
uplift resets the base level, stream cuts downward, valleys widen and hills erode, new
& lower floodplain is formed, landscape denuded to base level. *Drainage Reversal.
Due to tectonic events: tectonic uplift can alter the course of major river. In early
Mesozoic, South America drained westward. Western uplift raised the Andes,
diverting flow to East.
*Floodwaters. Flow exceeds channel capacity. Water over flows channel onto land:
fast moving water from channel flows onto flood plain, slows down and drops
sediment, forms natural levees. *Floods. Triggered by various conditions: torrential
rains dump large volumes of water, rapid snowmelt across a large drainage basin (risk
is increased if soil pores already saturated), failure of dam or levee. *Monsoons.
Climate driven flooding that occurs annually. In India & Himalayas. Typically several
months of rain severe flooding. 1990 monsoon season killed 100,000 in Bangladesh.
*Flash Floods: water rises rapidly with little warning. Caused by intense rainfall or
dam failures. Very destructive.
Which of the following lists contains only fossil fuels? Coal, oil, natural gas
Nearly all of the commercially exploited minerals are either native metals or
ore minerals. FALSE
The stereotypical gold rush prospector panning for gold in a stream bed is an
example of exploiting a. placer deposits
Which mineral resources are renewable? No mineral resources are renewable.
What longitudinal profile? cross-sectional image of a stream along its length
In a region with prominent orthogonal sets of joints, a __45.6 %__ drainage
network is expected.? Rectangular
Moving away from its headwaters, the flow of a stream becomes more?
laminar
U-235, the isotope of uranium commonly utilized in nuclear power plants, is?
rare even in uranium oxide deposits, and thus able reactor fuel must be
enriched with respect to this isotope
Coal is the altered remains of ancient? terrestrial plants
Which of the following is a renewable resource?. wind
The competence of a stream is? Max particle size the stream can carry
Ultimately, the base level of a stream valley can be no lower than Sea level
At a delta, stream gradient decreases and a single channel breaks into multiple,
radiating distributaries channels
Most prominent force inducing tides on Earth is the? Moon’s gravitational pull
The ability of a metal to be bent, molded and stretched is called malleability.
Copper sometimes occurs as a native metal.
3.Which ore minerals are commonly found in ancient sedimentary deposits
that are 2 billion years old? Iron oxides
Mineral-rich veins within plutons, deposited by hot groundwater into fractures
within the rock, characterize hydrothermal deposits.
The US has active mines within its boundaries that are sufficient to maintain a
steady supply of all strategically important metals. TRUE
Compared to coal mining, there is no adverse environmental impact of mineral
mining. FALSE.
Which is the slowest mass movement in the Earth’s crust? creep
Which of the mass movements is least coherent (most like a liquid? mudflow
In which of submarine mass movements are the events ordered in terms of the
proportion of water included in the moving mass (least water to most water)?
Submarine slump, submarine debris flow, turbidity current.
“flooding the sediment with water to the point of saturation” increases the risk
of mass movement.
capacity of a stream= the total quantity of sediments it can carry.
small mountain stream has greater competence than the Mississippi River
The Mississippi River has greater capacity than a small mountain stream
The distinction between a valley and a canyon is the sides of a canyon are
more steep than those of a valley.
The inner edge of a meander, when sediment is deposited, is a point bar.
The shape of a delta is primarily determined by whether river current, wavedriven currents, or tidal currents are locally predominant
The discharge of a river traveling through a humid region will typically
increase; the discharge of a river traveling through an arid region will typically
decrease downstream.
All else equal, water flows faster in a stream that has a steep stream gradient
(vs gentle stream gradient)
All else equal, water flows faster in a straight channel (vs well-developed
meanders)
Which of the following types of mass movement is likely to move most
rapidly? Rock slide (not slump, creek, debris slide)
draw pic from #5
Contact #1 is: fault
The surfaces named contacts #2 and #3: unconformitites
The oldest geologic unit in the cross section is the: limestone
The youngest geologic unit is: conglomerate
The marble rind surrounding the granite pluton must be younger than the
limestone according to the principle of: baked contacts
Radiometric dates applied to sedimentary rocks produce areas that are: too old
(pre-date sedimentary deposition)
The age of Earth cannot be reliably estimated from sediment thicknesses
because: sedimentation rates are not likely to remain constant at any one
locality over all of Earth’s history; sedimentary rocks can be metamorphosed
or melted; locally, much of Earth history is represented by unconformities
between strata rather than the strata themselves.
Eon represented by abundant deposits of strata w/ shelly fossils: Phanerozoic
The K-T boundary event took place: 65 million years ago
An iridium rich layer of clay, glass spherules, and shocked quartz grains
strongly suggest that the K-T boundary extinction were at least in part caused
by: the impact of a bolide (meteoroid or comet)
The generally accepted scientific theory for the origin of our moon involves:
impact between Earth and a Mars-sized body during the Hadean
Oxygen in Earth’s atmosphere is derived from: photosynthesis
Banded-iron formations were abundantly produced during: Proteorozoic Eon
Most commonly used sources of industrial energy in US: coal, oil, natural gas
A permeable & porous rock, regardless of lithology, is a good candidate to
serve as a in a resevoir rock in an oil producing scenario.
An impermeable rock, regardless of lithology, is a good candidate to serve as
a seal rock in an oil producing scenario.
Most of the worlds coal was deposited in coal swamps during the Jurassic
The worlds supply of oil is likely to be depleted in about 100 years
An episode of mountain building is termed orogeny
Deformation brought on by orogeny can metamorphose, produce folds, &
produce faulting in rock