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Layers of The Earth
and Plate Tectonics
Learn it, know it, love it.
Inside the Earth
The inside of the
Earth contains four
layers: The crust,
mantle, inner core
and outer core.
These layers occur
due to physical and
chemical differences
Crust
The crust is
approximately 32
KM thick. (20 miles)
Made up of
aluminum, silicon,
and oxygen.
The crust is solid.
Mantle
2900 Km thick
(about 1700 miles)
Made up of
magnesium and iron
Plastic-like- has the
ability to act like a
solid or liquid.
Based on pressure.
Outer Core
2270 Km thick
(about 1400 miles)
Made up of iron and
nickel
Liquid due to the
temperature.
Inner Core
1300 Km thick (780
miles)
Iron and Nickel
Solid due to the high
pressure
Journey to the Center of
the Earth
People used to believe the earth was solid rock with many caverns.
Believed there were giant animals and large treasures awaiting explorers.
Earth does not have these hollow spaces, but it is not solid rock either.
Earth’s Interior
Physical and chemical
makeup of the layers
changes with depth.
Materials increase in
density. (That is why the
crust floats)
Temperature and
pressure increase as
you go through the
earth.
Mantle’s 3 layers
Based on physical properties
Lithosphere- crust and the uppermost part of the mantle. Floats on the next layer
Asthenosphere-Convection occurs here. This layer is plastic-like
Mesosphere- Mostly solid layer. Heats the asthenosphere.
Convection Currents
When a substance is heated, it becomes less dense. This causes the substance to rise.
It then cools down, since it is away from the heat source, becomes more dense, and sinks.
Heated objects expand, cooled object contract.
Think hot air balloon or lava lamp.
Plasticity
The mantle has the
ability to act like a
solid or a liquid.
This is based on the
amount of pressure
applied to the
mantle
Example: Oobleck.
How do we know about
the inside of the earth?
We can make some direct observations: crust and magma
The interior of the earth cannot be directly observed.
We have never drilled through the crust.
Scientists gain most of their information through indirect observations or inferences.
Seismic waves
These waves travel through the earth when an earthquake happens.
Called P and S
S waves bounce off the outer core. Since S waves cannot go through liquids, we say the outer core is liquid
When an energy wave bounces off an object, we call this reflection.
More on P and S waves
The P waves go through the entire earth, but they bend as they go through the different layers.
This means the layers must be made of different material.
When an energy wave goes through a substance and bends, we call this refraction.
Shadow zone
P and S waves can be detected all over the earth.
There are zones that cannot detect some earthquakes.
These are called Shadow zones.
Shadow- when an energy wave is blocked.
Shadows show the waves are bending.
Meteorites
We say the core is made of iron and nickel, but how do we know that?
Most meteorites, rocks from space, are made up of iron and nickel.
Scientists think meteorites are the pieces of broken planet cores.
So we hypothesize that our core is like other planets.
Plate tectonics
Developed in the
1960’s.
This theory says
that the earth is
broken into plates
and those plates are
moving in different
directions and at
different speeds.
Plates
Plates- the sections that the crust is broken into. (think puzzle pieces)
They are made up of the crust and the upper part of the mantle.
Called Lithospheric plates.
Plasticity
The lithospheric
plates float on the
asthenosphere and
move around.
The plates can
move together,
apart, or side by
side.
Continental Drift
Idea that the
continents were
once together in a
large landmass
called Pangaea and
have moved over
time.
Developed by Alfred
Wegener.
Big Al !!!!!!
Wegener said that Pangaea, which means “all land or all earth”, broke apart 200 million years ago.
Wegener stated that the continents were moving by plowing through the crust.
What would happen to the continents if they did plow through the crust?
His idea was initially rejected and he was laughed at for proposing it.
Wegener’s Clues
Shape- The continents seem to fit together.
Fossils- Mesosaurus fossils were
found in S. America and Africa. How could a fresh-water lizard be found in both places?
Glossopteris- tropical fern found in Antarctica? Climate had to be warmer at one time.
More Evidence
Several landmasses show
evidence of an ice age. They
had to be together to
experience this climate change.
If the continents were together
at one time, then wouldn’t the
rocks that make up the
continents be the same?
They are. Mountain ranges
in N. America line up with
mountain ranges in Europe
and Greenland.
Mountains in S. America
line up with those in Africa.
Life After Wegener
Alfred Wegener died on an expedition in Greenland in 1930.
Year after his death, scientists found evidence that supported his theory.
Ships began mapping the ocean floor using sonar and as they did this, they found many features they did not expect to find.
Sea-Floor Spreading
They found the Mid-Ocean Ridge in the Atlantic Ocean.
As they tested the rock, they found the rock at the center of ridge was younger than the rock closer to the continents.
If the sea-floor all formed at the same time, what should the age of the rocks be?
Sea-Floor Spreading
• When rocks form at the bottom of the ocean, the magnetic minerals line up with magnetic North (like on a compass)
• The ocean floor has some rocks pointing to magnetic north and some pointing to magnetic South
Why is that happening?
Sea-Floor Still Spreading
• If the rocks had formed at the
same time, all the iron would point
in the same direction.
• Since it is pointing in opposite
directions, the rocks formed at
different times.
• Different times means that the
sea-floor is spreading.
The magnetic field of the Earth
will at times switch north to
south. This would explain the
iron pointing in different
directions.
Plate movement
The mantle rises because as it is heated, it becomes less densethan the mantle around it. Less dense objects rise
The mantle then strikes the crust and it is like rock hitting rock. (oobleck)
This constant force of hitting gradually moves the plates 3-4 inches / year.
Types of Plate
Boundaries
Convergent- When two
plates are moving
toward each other.
Two Possibilities
Subduction- When one
plate that is weaker
buckles under another.
Forms trenches in the
ocean and volcanic
mountains on land.
Convergent #1
Convergent (continued)
Collision- Where two
continental plates
come together.
Usually forms high
mountain ranges
Ex. Himalayas,
Appalachians, and
the Alps.
Convergent #2
Divergent Plates
Occurs between
plates that are
separating.
Usually indicates
sea-floor spreading.
Ex. Mid-Atlantic
Ridge
Divergent Boundary
Transform Boundary
Occurs where plates
slide past each
other.
Localized
deformation, low
mountains and
valleys.
Ex. San Andreas
Fault
Features of plate
tectonics
Faults
Earthquake and
volcanoes
Mid-ocean ridges
Mountains and
valleys
Ocean trenches
How do we measure
plate movement?
Scientists use lasers and satellites to test for plate movement
Laser are shot from ground locations to orbiting satellites and they are used to mark the exact ground location of that laser.
They are tested each year and measurements are made.
Earthquakes and Volcanoes
.
Causes of Earthquakes
• Elastic Limit- amount of stress an object
can absorb and bend before it breaks.
• When a rock breaks you have a fault
• Fault- A break in the rock in which both
sides of the rock are moving.
• The break releases energy which causes
earthquakes.
Faults
• Hanging wall is the
wall above the fault
line. Top is larger than
the bottom
• Footwall is the wall
below the fault line.
Bottom is larger than
the top.
Types of Faults
Normal Fault
• When a fault moves
apart.
• Caused by tension
forces
• The hanging wall
moves down in
relation to the
footwall.
• Can form mountains
Reverse Fault
• When a fault moves
together.
• Caused by
compression forces.
• Hanging wall moves
up in relation to the
footwall.
• Also causes mountains
Strike-Slip Faults(Transform)
• When a fault moves
side by side.
• Caused by shear
forces.
• Does not always have
a hanging and footwall
• Most earthquakes are
caused by this fault.
Seismic Waves
P, S, and L
Seismic Waves - P and S
• P waves are faster.
• S waves are slower.
• P waves move like a
slinky dog. The front
shoots out and the
back catches up.
• S waves look like a
snake with an up and
down motion.
Love Waves
• When P and S waves
combine at the surface
of the Earth, you get
Love waves.
• These waves are the
destructive waves.
• Move up and down
and side to side.
Parts of a Fault
• Focus- Where the rock
breaks and an
earthquake begins
• Epicenter- The point
on the Earth’s surface
directly above the
focus. The epicenter
is the most effected
area by the earthquake
Locating Epicenters
• Scientists use seismographs to record P and S
waves from Earthquakes.
• By measuring the difference in P and S wave
arrival times, a seismologist can determine the
distance to the epicenter.
• They take three cities and draw circles around
those cities. The radius of the circle is equal to the
distance they are away from the earthquake.
• Where the three circles meet is the epicenter.
• Triangulation
Triangulation
Richter and Mercalli Scales
• Richter measures magnitude or size and is
based on a power of 10 scale. Each
earthquake is 10 times greater than the one
before. Can be measured during the quake.
• Mercalli measures intensity or what it felt
like. This 12 step scale is based on eye-
witness accounts and is used after the
earthquake has happened.
Tsunami
• Large wave caused by
an earthquake
underwater.
• The energy wave
compresses as it
reaches shore. The
compressed energy
pushes back and
causes large waves.
Volcanoes
Def- Any opening in the Earth’s crust
which erupts ash, cinders, lava or
bombs. Often forms mountains.
Volcano States
• Active- has erupted in the past 100 years.
• Dormant- has not erupted in 100- 1000
years
• Extinct- has not erupted in over 1000 years.
How do volcanoes form?
• A pocket of magma
called a magma
chamber forms under
the crust.
• If the pressure and heat
are great enough, the
magma will force itself
up through the crust.
• Magma that reaches the
surface is called lava
Parts of a volcano
• Magma Chamber- Large
pockets of magma that form
underground.
• Pipe- Long, vertical crack in
the crust that connects the
magma chamber to the vent
• Crater- Hollowed-out area at
the top of a volcano
• Vent-opening in the crater that
tephra emerges from. These are
common on top of a volcano,
but can also occur on the sides.
Where do volcanoes occur?
• Volcanoes occur in
places directly related
to plate boundaries.
• Volcanoes occur
where plates are
moving together,
moving apart, or at hot
spot volcanoes.
Hot Spot Volcano
• Some areas of the mantle
are hotter than others.
• This “hot spot” burns
through the crust at
specific places.
• The magma hits the ocean
and cools. More magma
comes out on top of the
new rock and eventually
may rise up out of the
ocean.
Violent or Non-Violent Eruption
• There are two factors which determine if an eruption is
violent: amount of silica in the magma and the amount of
water vapor and other gases present in the magma.
• If gases get trapped in a volcano, they will build up
pressure just like a pop can that is shaken. The more
pressure, the more violent the eruption.
• Magma with lots of silica is thick and traps gas and
produces violent eruptions. Magma that is silica-poor
flows smoothly, traps very little gas, and has quiet
eruptions.
Shield Volcano
• Quiet eruptions
• Silica-poor magma
• Broad volcano with
gently sloping sides.
• Looks like shield
laying on the ground
• Hawaiian volcanoes
are examples.
• Lava only.
Cinder Cone Volcano
• Explosive eruptions
• Tephra- rock or
solidified lava thrown
into the air.
• Cinders, ash, bombs
• No lava flow, only
hardened lava.
• Steep, loosely packed,
tall
• Paracutin (Farmer)
Composite Volcano
• Can have quiet or
strong eruptions
• Can release lava only,
tephra only, or both.
• Alternating layers of
lava and tephra.
• Found where
subduction occurs.
• Mt. Saint Helens
Volcanic Features
• Batholith- form when
magma cools
underground before
reaching the surface.
• Dike- Magma that is
squeezed into a
vertical crack and
hardens.
Volcanic Features Cont.
• Sill- Magma that is
squeezed into into a
horizontal crack and
hardens.
• Volcanic neck- a volcano
stops erupting and the
magma hardens in the
vent. This hardens
igneous rock is exposed
by weathering and
erosion.
Volcanic features
• Caldera- The top of a
volcano collapses after
an eruption.
• Lakes can form if
water collects into the
caldera
• Crater Lake in Oregon
is an example of a
Caldera
Finally…… the end
• Pyroclastic flow- large cloud of ash rushes
down the side of a volcano. Usually comes
from the ash cloud collapsing. Travel 100
mph and the temperature is 1300 degrees F.
• Ring if Fire- area around the Pacific plate
that contains a large amount of earthquakes
and volcanoes.
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