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.