Plate Tectonics
Inside the Earth
The composition of the Earth

The Earth is divided
into three layers –
the crust, the
mantle and the
core – based on the
compounds that
make up each layer.

A compound is a substance composed of
two or more elements.

The less dense compounds make up the
crust and mantle, and the densest
compounds make up the core.

The layers form because heavier elements
are pulled toward the center of the Earth by
gravity, and elements of lesser mass are
found farther from the center
The Crust

The outermost layer of Earth is the crust

Is 5 to 100 km thick

The thinnest layer of Earth

Two types: continental crust and oceanic crust
The Mantle

The layer of the Earth between the crust
and the core is the mantle

Is much thicker than the crust and
contains most of the Earth’s mass

No one has ever visited the mantle; crust is
too thick to drill to the mantle.

Sometimes the mantle pushes through
the Earth’s surface, which allows scientist
to study the rock directly

Also study the ocean
floor for clues about
the mantle.

Underwater
volcanoes give many
clues about the
composition of the
mantle

Is denser than the
crust
http://www.youtube.com/watch?v=hmMlspNoZMs
Volcanic vents on the ocean
floor, such as this vent off the
coast of Hawaii, allow magma to
rise up through the crust from
the mantle.
The Core

The layer of Earth that
extends from below the
mantle to the center of
the Earth is the core.

Think it is mostly made
of iron and contains
smaller amounts of
nickel but almost no
oxygen, silicon,
aluminum, or
magnesium

Make up roughly 1/3 of
the Earth’s mass
The Physical Structure of the
Earth

The Earth is divided into 5 physical
layers – the lithosphere, asthenosphere,
mesosphere, outer core, and inner core.
http://www.youtube.com/watch?v=aoV4d
mXIt_8
1. Lithosphere – the outermost,
rigid layer of the Earth

Made of two
parts: the crust
and the rigid
upper part of the
mantle

Is divided into
pieces called
tectonic plates
2. Asthenosphere – a plastic layer of the mantle
which pieces of the lithosphere move

Is made of solid rock
that flows very slowly
3. Mesosphere – strong lower part of the mantle,
found under the asthenosphere

Extends from the bottom of the asthenosphere to
the Earth’s core
4. Outer Core – the liquid layer of the Earth’s
core that lies beneath the mantle and surrounds
the inner core
5. Inner Core – the solid, dense center of our
planet that extends from the bottom of the outer
core to the center of the Earth, which is about
6,380 km beneath the surface. (almost
4 thousand miles)
Tectonic Plates

Tectonic Plates are
blocks of lithosphere
that consist of the
crust and the rigid,
outermost part of the
mantle.

All the tectonic plates
have names.

Each plate fits
together like a puzzle.

Can include just oceanic crust, or just
continental crust, or a combination of the
two.

The plates cover the surface of the
asthenosphere, and they touch one
another and move around. The lithosphere
displaces the asthenosphere. Thick
tectonic plates displace more
asthenosphere than do thin plates.
http://www.youtube.com/watch?v=nfziy_860GU
Mapping the Earth’s Interior

When an earthquake happens, seismic waves are
produced. Seismic waves travel at different speeds
through the Earth. Their speed depends on the
density and composition of material that they pass
through.

Seismographs are machines that measure the
times at which seismic waves arrive at different
distances from an earthquake.

Scientists can then use these distances and travel
times to calculate the density and thickness of
each physical layer of the Earth.
By measuring changes
in the speed of seismic
waves that travel
through Earth’s interior,
seismologists have
learned that the Earth
is made of different
layers
Wegener’s Continental Drift
Hypothesis

In the 1900’s Alfred
Wegener wrote about
his hypothesis of
continental drift.

Continental drift is the
hypothesis that states
that the continents
once formed a single
landmass, broke up,
and drifted to their
present locations.

Continental drift explains how well the
continents fit together, and why fossils of the
same plant and animal species are found on
continents that are on different sides of the
Atlantic Ocean.

In addition to fossils, similar types of rock and
evidence of the same ancient climatic
conditions were found on several continents.
Fossils of Mesosaurus, a
small, aquatic reptile, and
Glossopteris, an ancient plant
species, have been found on
several continents
The Break-up of Pangea

Pangaea existed 245 million years ago – when all
the continents were joined in a single huge continent.

This is where the earliest dinosaurs roamed the
earth.

Pangaea split into two huge continents – Laurasia
and Gondwana – about 180 million years ago.

These two continents split again and formed the
continents we know today.
http://www.youtube.com/watch?v=cQVoSyVu9rk&feature=related
Sea-Floor Spreading

Mid-ocean ridges are underwater
mountain chains that run through Earth’s
ocean basins.

Mid-ocean ridges are places where seafloor spreading takes place.

Sea-floor spreading is the process by
which new oceanic lithosphere forms as
magma rises toward the surface and
solidifies.

As tectonic plates move away from each
other, the sea floor spreads out and
magma fills the gap.

As new crust forms, the older crust gets
pushed away from the mid-ocean ridge
http://www.youtube.com/watch
?v=GyMLlLxbfa4&feature=rela
ted

Evidence for sea floor
spreading is the
magnetic reversals
recorded in the ocean
floor.
 Throughout history, the
north and south magnetic
poles have changed
places many times.
 When the Earth’s magnetic
poles change places, this
change is called a
magnetic reversal.
http://www.youtube.com/watch
?v=x-p49IBuR1Y

That magma contains
iron in it which acts like
a compass by aligning
with the magnetic poles
as it hardens, thus
recording the direction
of the poles over time.

As the sea floor spreads
away from a mid-ocean
ridge, it carries with it a
record of magnetic
reversals and this
record was the final
proof that se-floor
spreading does in fact
occur.
Magnetic reversals in oceanic
crust are shown as bands of
light blue and dark blue oceanic
crust. Light blue bands indicate
normal polarity, and dark blue
bands indicate reverse polarity

Plate tectonics is the theory that the
Earth’s lithosphere is divided into
tectonic plates that move around on top
of the asthenosphere.
Tectonic Plate Boundaries

A boundary is a place
where the plates touch.

All tectonic plates share
boundaries with other
plates.
There are 3 types of boundaries:
1. Convergent – when two tectonic plates
collide

What happens
depends on the type
of crust at the
leading edge

Three types are
continentalcontinental,
continental-oceanic,
and oceanic-oceanic
boundaries
2. Divergent – when two tectonic plates
separate

New sea floor
forms at divergent
boundaries

Mid-ocean ridges
are the most
common type of
divergent
boundary
3. Transform – when two tectonic plates slide
past each other horizontally

Example is the San
Andreas Fault in CA;
the place where the
Pacific and North
American plates are
sliding past each
other.
Possible Causes of Tectonic Plate
Motion
1.
Ridge Push – At mid-ocean ridges, the oceanic
lithosphere is higher than it is where it sinks into the
asthenosphere. Because of ridge push, the oceanic
lithosphere slides downhill under the force of gravity.
2.
Convection – Hot rock from deep within the Earth rises,
but cooler rock near the surface sinks. Convection
causes the oceanic lithosphere to move sideways and
away from the mid-ocean ridge.
3.
Slab Pull – Because oceanic lithosphere is denser than
the asthenosphere, the edge of the tectonic plate that
contains oceanic lithosphere sinks and pulls the rest of
the tectonic plate with it in a process called slab pull.
Tracking Tectonic Plate Motion

Tectonic plate movement is so slow and
gradual that you can’t see or feel them
move – is measured in cm per year!

Scientists use GPS (global
positioning system) to measure the
rate of tectonic plate movement

Radio signals are
continuously beamed from
satellites to GPS ground
stations, which record the
exact distance between the
satellites and the ground
station. Over time, these
distances change slightly.

By recording the time it takes
for the GPS ground stations
to move a given distance,
scientists can measure the
speed at which each tectonic
plate moves.

Stress is the amount of force per unit
area on a given material.
Deformation

The process by which the shape of
rock changes because of stress is
called deformation.

Compression: the type of stress that
occurs when an object is squeezed
 When compression occurs at a convergent
boundary, large mountain ranges can form

Tension: is stress that occurs when
forces act to stretch an object
 Occurs at divergent plate boundaries, such
as mid-ocean ridges, when two tectonic
plates pull away from each other
Folding

The bending of rock layers because of
stress in the Earth’s crust is called
folding.
3 Types of Fold:
1.
Anticlines – upward-arching folds; the
most common
2.
Synclines – downward trough like folds
3.
Monocline – rock layers are folded so that
both ends of the fold are horizontal
The large photo shows mountain-sized
folds in the Rocky Mountains. The small
photo shows a rock that has folds smaller
than a penknife.
Faulting

The surface along rocks break and slide past each
other is called a fault.

The blocks of crust on each side of the fault are called
fault blocks

2 Walls of a Fault are the footwall and the hanging
wall.
Types of Faults:
1.
Normal Faults – when it moves it causes the hanging
wall to move down relative to the footwall;
 usually occur when tectonic forces cause tension that pulls
rocks apart
2.
Reverse Faults – when it moves, it causes the
hanging wall to move up relative to the footwall;
 is the reverse of a normal fault.
 Usually happen when tectonic forces cause
compression that pushes rocks together
Telling the Difference???
Normal Fault
Reverse Fault
3.
Strike-slip fault –
form when
opposing forces
cause rock to
break and move
horizontally
 Example is the San
Andreas Fault in
CA
Plate Tectonics and Mountain
Building

When tectonic plates collide, land
features that start as folds or faults can
eventually become large mountain
ranges.

Mountains exist because tectonic plates
are continually moving around and
bumping into one another. (Example is
the Andes Mountains)
The Andes Mountains
The Andes
Mountains formed
on the edge of the
South American
plate where it
converges with the
Nazca plate
3 Common Types of Mountains:
1.
Folded Mountains
 The highest mountain ranges in the world
 Form at convergent boundaries where continents have
collided
 Folded mountains form when rock layers are squeezed
together and pushed upward.
 About 390 million years ago, the Appalachian Mountains
formed when the landmasses that are now North America
and Africa collided.
 Other examples are the Alps in central Europe, the rural
Mountains in Russia, and the Himalayas in Asia.
The Appalachian Mountains were once as tall as the Himalaya
Mountains but have been worn down by hundreds of millions
of years of weathering and erosion
2. Fault-Block Mountains

Form when this tension causes large
blocks of the Earth’s crust to drop down
relative to other blocks.

When sedimentary rock layers are tilted
up by faulting, they can produce
mountains that have sharp, jagged
peaks.

Example: the Tetons in western
Wyoming
When the crust is subjected to tension, the
rock can break along a series of normal faults,
which creates fault-block mountains
The Tetons formed as a result of tectonic forces
that stretched the Earth’s crust and caused it
to break in a series of normal faults
3. Volcanic Mountains

Most of the world’s major volcanic mountains are
located at convergent boundaries where oceanic crust
sinks into the asthenosphere at subduction zones.

The rock that is melted in subduction zones forms
magma, which rises to the Earth’s surface and erupts
to form volcanic mountains.

Can also form under the sea, sometimes rising out of
the sea to form islands

The majority of tectonically active volcanic mountains
on the Earth have formed around the tectonically active
rim of the Pacific Ocean, known as the Ring of Fire
Uplift and Subsidence

The rising of regions of Earth’s crust to
higher elevations is called uplift (can go
through deformation)
 Can form mountains
 Rebound – a process where areas rise without
deforming; when the crust rebounds is slowly
springs back to its previous elevation
 Uplift often happens when a weight is removed
from the crust

The sinking of regions of Earth’s crust to
lower elevations is known as subsidence (do
not undergo much deformation)
 Occurs because rocks that are hot take up more
space than cooler rocks
 Cooler rocks are more dense
 Can also occur when the lithosphere becomes
stretched in rift zones
 Rift zones are sets of deep cracks that form
between two tectonic plates that are pulling away
from each other. As tectonic plates pull apart, stress
between the plates causes a series of faults to form
along the rift zone.
The East African Rift, from Ethiopia to Kenya, is part of a
divergent boundary, but you can see how the crust has
subsided relative to the blocks at the edge of the rift
.
zone