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Earth
The Dynamic Planet
Earth’s Interior
Courtesy of the USGS
Core
The core is differentiated into an inner
solid region and an outer liquid region.
Both regions are composed mostly of
iron and nickel
Inner core is not solidly tied to rest of
Earth, and is free to rotate
Diagram from USGS
Earth’s magnetic field created by electrically conductive fluid
flowing past magnetic field, which creates an electric current;
current strengthens the magnetic field
Mantle
Mantle is composed mostly of
silicon
Thought to exhibit a plastic
behavior; solid on short time
scales, liquid over long time
scales
Diagram from the USGS
Differences in temperature between core and crust cause mantle
to convect; this convection drives movement at the surface
Crust
Crust is mostly SiO2
Two types of crust: oceanic
and continental crust
Diagram from USGS
Oceanic crust is thinner and denser; darker in color;
basaltic (only about 50% silicate)
Continental crust is thicker and less dense; lighter in color;
granitic (about 70-80% silicate)
Seismology
Surface waves - Travel along the Earth’s surface,
do not penetrate the crust, slowest wave speed
Compressional body waves - particles move in direction of
wave velocity, fastest wave speed;
called P-waves
Transverse body waves - particles move perpendicular to
the direction of wave velocity, slower than compressional,
but faster than surface; also called
shear waves since the particles will
experience a shearing action;
called S-waves
Seismology, cont.
Use earthquakes to probe the
interior of the Earth
Waves travelling through the
Earth are refracted (bent) and
reflected depending upon their
properties and those of the
different layers of the Earth
S-Wave shadow zone
Plate Tectonics
Originally conceived of as continental
drift by Wegener; he noticed similarities
in coastlines, fossil record, rock layers,
and glacial scarring
Modern satellite technology
allows us to measure the
relative movement of the plates
Plate Boundaries
Divergent - Plates move apart from each
other
Convergent - Plates move toward each
other
Transform - Plates move parallel to the
boundary in opposite directions
Divergent Plate Boundaries
•Start as rift valleys
•Basaltic, high density magma
wells up from the mantle-crust
interface to replace rock
•New crust that forms is thinner
and denser; as it cools, it sinks
lower than the surrounding
continental crust
•Ocean water eventually fills in
between the two continents
Convergent Plate Boundaries
If oceanic crust collides with
continental crust, oceanic crust goes
under (subduction zone), melts, and
resurfaces as an island arc
Ex. New Zealand, Aleutian Islands
If two continental plates collide,
crustal material “piles up” and
a mountain chain is developed
Ex. Himalayan Mountains
Transform Plate Boundary
As plates move past one another,
friction causes sides to stick together
While sides are stuck, stress builds
between the plates
When stress gets high enough, sides
violently slide past one another

Photograph by Robert E. Wallace, USGS
Loma Prieta Earthquake, 1989, Courtesy of the USGS
Rock Types
Constant plate movement drives the rock cycle
Three different types of rock are igneous, metamorphic, and
sedimentary
Igneous
Rock formed
from a molten
state
Type of igneous rock determined by 1) type of magma from
which rock cools and 2) location where rock cools
Volcanic - extrusive; magma cooled at the surface; smaller crystals
Plutonic - intrusive; magma cooled below the surface; larger crystals
Sedimentary
Formed from sediment that
is cemented together
Type of rock depends upon
1) size of sediment and
2) origin of sediment
Photo of Canyonlands National Monument by Pratte
Two Types
Clastic - broken rock and mineral that are cemented together
Ex.: sandstone, shale, conglomerate
Chemical - minerals that precipitate out of solution
Ex.: limestone, chalk
Metamorphic
Formed from other rocks by
changing mineralogy or texture
without passing through a molten
state
Change occurs because of one or more of the following
parameters:
1. pressure - causes rock crystals to change orientation and
structure (Ex. gneiss)
2. temperature - induces different chemical bonds without melting
(Ex. hornfels)
3. chemically reactive fluid - minerals in the fluid replace minerals
in the rock (Ex. petrified wood) or form new bonds
Rock Cycle
Processes like weathering,
erosion, and plate tectonics
change the rock from one
form to another
Rock can be transmuted from
any form to any other form’
by these processes
Example: An igneous rock that is brought to the Earth’s surface is
weathered and eroded. Sediment pile is buried, causing cementation
into a sedimentary rock. Further burial creates pressures strong
enough to change chemical bonds, creating a metamorphic rock.
Soil Types
Soil - a mixture of organic and
inorganic sediments found on the
Earth’s surface; comprised of
different layers
O horizon - consists of decomposing organic matter; might be missing
A horizon - comprised of a mixture of organic and inorganic matter
E horizon - light colored, acidic layer found in evergreen forests
B horizon - brown or red layer enriched in clay, iron, and/or aluminum
K horizon - enriched with calcium carbonate; found in arid regions
C horizon - lowest layer comprised almost entirely of inorganic rock
sediment
Soil Forming Factors
Different horizons
occur at different
locations for many
reasons
Some factors:
1. Climate - temperature, precipitation, and wind affect weathering,
erosion, vegetation, and decomposition of organic matter
2. Local rock - provides the inorganic material for soil
3. Topography - steeper slopes mean more erosion
4. Vegetation - holds soil in place; provides the organic material for soil
5. Time - more mature soils have had elements working on it longer
6. Mankind - our activities affect erosion and soil nutrients
Weathering and Erosion
Weathering - the breaking apart of rocks either physically or
chemically
Erosion - the removal of sediment from a location; can occur by
water, wind, landslide, etc.; enhanced by mankind’s disturbances