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Structure of the earth
– Core
• Inner: solid, high temp and pressure, made of: nickel and iron
• Outer: liquid, cooler than the inner core, Made of: nickel and iron
– Mantle
• Made of iron, oxygen and silicon (Rock called peridotite)
• Solid at the bottom becomes more Pliable and plastic near the
surface.
• Upper layers: asthenosphere and the lithosphere
– Crust
• Thinnest zone (6 miles deep to 35 miles deep)
• Mostly made of silicon and oxygen in the Form of quartz (SiO2)
• Two types of crust:
- oceanic-which is dense and made of basalt
- continental crust Which is less dense and made of: granite
Geologic Processes
35 km (21 mi.) avg., 1,200˚C
Crust
100 km (60 mi.)
200 km (120 mi.)
Crust
Low-velocity zone
 Structure of
the Earth
Mantle
Lithosphere
Solid
10 to 65km
2,900km
(1,800 mi.)
3,700˚C
Outer core
(liquid)
Core
Inner
core
(solid)
100 km
Asthenosphere
(depth unknown)
200 km
5,200 km (3,100 mi.), 4,300˚C
Fig. 10.2, p. 212
Internal Earth Processes
Plate tectonics: theory developed in the
1960’s about the crust of the earth. The
theory says that the crust is not one large
piece, but is broken into large segments
called plates. When these plates move and
collide they form:
Divergent Plate Boundary
Divergent plate boundary: where plates
move apart in opposite directions
•
Landforms: under water mountain chains
called mid-ocean ridges, on land forms rift
valleys
• Examples: Mid-Atlantic Ridge, African Rift
Valley, Iceland, Baja California
Convergent Plate Boundaries
Convergent plate boundary: Where plates collide
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•
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Forms subduction zones where one plate rides up
and over the other plate, this causes deep-sea
trenches, and steep sided composite cone volcanoes.
This only occurs where continental crust collides with
oceanic crust or where oceanic crust collides with
continental crust.
Continental crust can collide with continental crust
and form folded mountains.
Examples: Mt. Everest, Mt. St. Helens, Mt. Fuji,
Mt. Vesuvius
Continental VS Continental
Continental VS Oceanic
Oceanic Vs. Oceanic
Transform Boundaries
Transform Boundary: plates slide past one another
in opposite, but parallel directions.
•
Examples: San Andreas Fault
Transform
California Geology
External Earth Processes
–
Weathering: Breaking down rock into smaller pieces
•
•
–
Mechanical weathering: roots, animals, freeze-thaw:
Chemical: lichens, organic acids, acid rain and:
Erosion: Picking up small rocks and carrying them
away
•
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•
•
Wind: desert pavement, san dunes, abrasion
Water: beaches, levees, oxbow lakes, meanders
Ice: glaciers – Kettle lakes, moraine, till, u-shaped valleys,
horns
Gravity: Mudslides, landslides
Erosion by Wind
Erosion by Water
Erosion by Glaciers
Erosion by Gravity
Mineral Resources and The Rock Cycle
Mineral: naturally occurring,
solid, inorganic
Material with a
crystalline structure and
a Definite chemical
composition
Rock: Mixture of minerals
Mineral Resource: a minerals
that can extracted and
converted into a
resource at affordable
prices
Natural Hazards
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•
•
•
Earthquakes
Volcanoes
Floods
Mass Movements
Earthquake: stress in earth’s crust can cause solid rock to
deform until it suddenly fractures and shifts along the fault
producing a fault.
– Two types of Earthquakes:
• Deep-focus: caused when one plate slides under another plate
(subduction), the plate gets jammed and pressure builds up, then
with a sudden movement the plate slips under the other causing a
very big earthquake.
• Shallow focus: caused by plates sliding past one another. When
the plates get locked up and then suddenly move the earthquake
is created.
• Epicenter: point on earth’s surface directly above the:
• Focus: point where initial movement takes place.
• Magnitude: size of quake measured on a logarithmic scale called
the Richter scale.
• Tsunami: earthquake generated water wave.
• Control of quakes: geologic mapping, examine history records,
building codes, ideally learn to predict
•
Volcanoes: when magma reaches earth’s
surface through cracks or fissures
3 Types:
– Composite Cone:
large, steep sided,
explosive, thick
granitic magma,
associated with
convergent plate
boundaries, lots of
gas and ash.
•
Examples:
Shield Volcano
Shield: flat, nonexplosive, lots of
liquid basaltic lava,
associated with
divergent plate
boundaries and
hot spots
Example:
Mass Wasting: movement of rock by
gravity
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slump, creep, rockfalls, landslides,
mudflows
factors that affect mass wasting:
steepness of slope, amount of
moisture, roads, building, fire
subsidence: land sinks and forms
sinkholes. Caused when underground
caves collapse. Can also be from
removal of excess oil or groundwater
Example:
Soil composition
Soil Horizons: series of layers or zones with a distinct
texture and composition
Soil profile: a cross-sectional view of horizons in soil
O-horizon: top layer, surface litter which is leaves and debris
A-horizon: topsoil layer: some inorganic materials and humus
which is partially decomposed organic material.
• these two top layers have fungi, bacteria, and protists
that break down complex organic solids
• A thick topsoil layer is good for crop.
B-horizon: (subsoil) broken down inorganic rock
C-horizon: parent rock
Leaching:
•
water infiltration
occurs when
precipitation occurs,
this rain washes
minerals out of the
top layers of soil
Soil Texture: The relative amounts of clay, silt an sand, soil with equal
amounts of each are called loams which are the best types for
growing crops
– Soil Porosity: a
measure of the volume
of pore spaces in the
soil
– Soil Permeability: the
rate that water moves
through the soil, which
is determined by soil
porosity
– Soil porosity, texture
and permeability
determine a soils water
holding capacity,
aeration and
workability
•
Soil Acidity: (pH), influences the uptake of
soil nutrients by plants, also acid soil causes
the leaching out of nutrients. PH of 5.5 to
8.5 is an acceptable range for most plants
Soil Erosion
• Soil erosion is the movement of soil
components from one place to another,
usually from wind or water. Plant anchor the
soil so that it is not washed away faster than it
forms
• Farming, logging, construction, overgrazing,
off road vehicles, burning of vegetation all
increase soil erosion
• Losing topsoil makes soil less fertile and
decreases its water holding capacity. The
sediments also chokes lakes and streams
How serious is global erosion:
• Topsoil is eroding faster than it forms on
about on third of the earths cropland
• Each year we must feed 90 million more
people with 26 million tons less topsoil
• The cost of erosion is about $400 billion
worldwide in direct damage to agricultural
lands, waterways, infrastructure and human
health
• In the U.S. soil is eroding 16 times faster than
it can be replaced.
Desertification: process whereby the productive potential of
arid or semi-arid land drops by 10% or more
– Overgrazing, deforestation, surface mining,
irrigation techniques that lead to increased
erosion, salt buildup and water logging of soils,
farming on land with unsuitable terrain or soil,
soil compaction due to farm machinery and
cattle hooves.
– Every year an area the size of Kansas undergoes
severe enough erosion to make farming not
feasible in the area.
– The only way to stop this is to reduce all the
causes and to reforest land.
Irrigation
– Most irrigation water has very dilute salts that
build up over time in the soil, this is called
salinization.
– It takes thousands of years for precipitation to
wash the salt out of the soil
– Water logging occurs when too much water is
applied to crops and this water sinks down into
the groundwater causing the water table to rise
and then salty water can envelope the roots of
plants, killing them.
Soil Conservation
• 1. Soil conservation: reducing the soil erosion
and preventing and restoring
soil fertility
• Conventional tillage farming: the land is
plowed and the soil is broken up and
smoothed to make a planting surface
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Conservation tillage: the idea is to disturb the soil
as little as possible while planting crops. Special
tillers break up and loosen only subsurface soil
without overturning topsoil, previous crop
residues, or any cover vegetation. This saves fuel,
cuts costs, hold in more water, keeps soil from
getting packed down and allows more of a crop
growing season
Terracing: reduces erosion on slopes by creating a
series of broad level terraces.
Contour farming: on gently sloping land, you plant
rows across rather than down the sloped contour
of the land.
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Strip cropping: rows crops like corn are
planted in strips with another crop like
grasses or legumes that completely cover
the soil
Agroforestry: intercropping with trees
Windbreaks and shelter breaks
Land classification: classifying land that is
not suited to agriculture
PAM (polyacrylamide): Gel that hold soil
together
Conserving soil fertility
•
1.organic fertilizers
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Animal manure: the best for crops but expensive to haul
Green manure: plowing under green vegetables
Compost
Crop rotation
2. Inorganic fertilizers
» Phosphorus, potassium and nitrogen
» Easily transported, stored and applied, without them we
would starve
» Problems: wash into lakes and streams, they do not add
humus to the soil, only supplies 2 or 3 out of some 20
needed materials
Nitrogen fixing
by lightning
Commercial
inorganic
fertilizer
Crop
plant
Organic fertilizers,
Animal manure,
Green manure, compost
10-6-4
N-P-K
Dead
organic matter
Application
to land
Nitrogen fixing
Decomposition
Nutrient removal
with harvest
Absorption of nutrients
by roots
Supply of
available plant
nutrients in soil
Nutrient loss
by bacterial
processes
such as
conversion
of nitrates to
nitrogen gas
Weathering
of rock
Fig. 10.14, p. 222
Nitrogen fixing
by bacteria
Nutrient loss
from soil erosion