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Chapter 4
Layers of the Earth
Continental Drift
Plate Tectonics
Deformation of Earth’s Crust
Layers of the Earth

Crust
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
Mantle


Thin, outermost layer of Earth
uppermost part of lithosphere
Layer of Earth between crust and core
Core

Central, spherical part of Earth below the mantle
Crust

5 to 100 km thick
thinnest layer of Earth

continental crust



similar to granite
oceanic crust

similar to basalt
Mantle




between crust and core
contains most of Earth’s mass
similar to olivine
large amounts of iron and magnesium
Layers of the Mantle

Lithosphere

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Asthenosphere


Outermost, rigid layer of Earth
consists of crust and rigid upper part of mantle
Soft layer of mantle on which pieces of the lithosphere move
Mesosphere


“middle sphere”
strong, lower part of mantle between asthenosphere and
outer core
Core

extends from bottom of mantle to
center of Earth
slightly larger than Mars

mostly iron



small amounts of nickel
possibly some sulfur and oxygen
Outer Core

liquid layer of
Earth’s core

lies beneath mantle

surrounds inner core
Inner Core

solid, dense center
of Earth
Tectonic Plate



a piece of
lithosphere
moves around on top
of the
asthenosphere
How do Scientists know about
the structure of the inside of
the Earth?
Earthquakes


When an earthquake occurs, seismographs
measure the difference in arrival times of
seismic waves and record them
Seismologists use these measurements to
calculate the density and thickness of each
layer
Continental Drift

The theory that continents can drift
apart from one another and have done
so in the past
Pangea


“all earth”
land mass that existed 245 million years ago
made up of all of the continents put together

Laurasia


northern half of Pangea; formed 180 million years ago
when Pangea broke in half
Gondwana

southern half of Pangea; formed 180 million years ago
when Pangea broke in half
Pangea
On the Sea Floor…

Sea Floor Spreading


The process by which new
oceanic lithosphere is
created at mid-ocean
ridges
older materials are pulled
away from the ridge

Mid-Ocean Ridge


a long mountain chain
that forms on the
ocean floor where
tectonic plates pull
apart
usually extends along
the center of ocean
basins
Magnetic Reversals

the process by which
the Earth’s north
and south magnetic
poles periodically
change places
Wegener’s Theory

What was Wegener’s theory of continental
drift?


The theory that continents can drift apart from
one another and have done so in the past
Why was Wegener’s theory not accepted at
first?

Scientists at that time did not understand what
force of nature could move continents
Sea Floor Spreading
Mid-Ocean Ridges

How does sea floor spreading provide a way
for continents to move?

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It forms new crust in between the places where
the spreading takes place
How does new oceanic crust form at midocean ridges?


As tectonic plates move away from each other, the
sea floor spreads apart and magma rises to fill in
the gap
This magma cools to form new crust
How do magnetic reversals
provide evidence for sea-floor
spreading?

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The molten rock contains tiny grains of magnetic
materials which align themselves with Earth’s current
magnetic field
They are “set in stone” as the molten rock cools and
solidifies
As the sea-floor continues to spread, these rocks are
carried away from the spreading center
The magnetic fields are found in bands along the
oceanic crust
Plate Tectonics

The theory that states that Earth’s
lithosphere is divided into tectonic
plates that move around on top of the
asthenosphere
Convergent Boundaries

Convergent Boundary
 The boundary
between two colliding
tectonic plates

Subduction Zone


The region where an
oceanic plate sinks
down into the
asthenosphere at a
convergent boundary
usually between
continental and
oceanic plates
Three Types of
Convergent Boundaries

Continental/Continental Collisions

Continental/Oceanic Collisions
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Oceanic/Oceanic Collisions
Divergent Boundaries

The boundary between two tectonic
plates that are moving away from each
other
Transform Boundaries

The boundary between two tectonic
plates that are sliding past each other
horizontally
What are the 3 forces thought
to move tectonic plates?

Convection

Slab Pull

Ridge Push
Convection

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
Hot material from deep with in Earth
rises while cooler material near the
surface sinks
As warmer material cools, it becomes
more dense and sinks
The motion drags tectonic plates
sideways
Convection
Slab Pull



oceanic lithosphere is denser than the
asthenosphere
the edge of the oceanic plate sinks
pulls the rest of the tectonic plate with
it
Ridge Push


An oceanic plate sides down the
lithosphere-asthenosphere boundary
occurs where oceanic lithosphere is
higher than continental lithosphere
Measuring Plate Movement

using a network of satellites called the
Global Positioning System


allows scientists to record the time it
takes for radio signals from a position on
Earth to reach the satellite
by monitoring changes in this, scientists can
tell how much the plates have moved
Stress

The amount of force per unit area that
is put on a given material

Deformation

the change in the shape of rock in response to
stress applied
Compression

The type of stress
that occurs when an
object is squeezed
Tension

The type of stress
that occurs when
forces act to
stretch an object
Fault

A break in the Earth’s crust along which
blocks of the crust slide relative to one
another due to tectonic forces
Types of Faults

Normal Fault

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Reverse Fault

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a fault in which the hanging wall moves up relative to the
footwall
Strike-slip Fault

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a fault in which the hanging wall moves down relative to the
footwall
a fault in which the two fault blocks move past each other
horizontally
Fault Block

The blocks of crust on each side of the fault
Folding

The bending of rock layers due to
stress in the Earth’s crust
Types of Mountains

Folded

Fault-Block

Volcanic Mountains
Folded Mountains
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form when rock layers are squeezed
together and pushed upward
example:

Appalachian Mountains
Fault Block Mountains
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where tectonic forces put enough tension on
the Earth’s crust, a large number of normal
faults can result
this faulting causes large blocks of Earth’s
crust to drop down relative to other block
example:

The Tetons (in western Wyoming)
Volcanic Mountains

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when molten rock erupts onto the
Earth’s surface
examples:

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Ring of Fire
Mount St. Helen’s