PLATE TECTONICS

PLATE TECTONICSChapter 5

How do we study the Earth’s interior?

Geologist use 2 main types of evidence to learn about the Earth’s interior

1) Direct evidence from rock samples2) Indirect evidence from seismic

waves

Direct evidence from rock samples

Drilling holes deep intothe earth give

geologistsclues about the interior.Volcanoes also blast rocks from within the Earth that may be studied.

Indirect evidence from seismic activity.

When earthquakes occurgeologists look at recorded seismic waves and can determine the type of material thatmakes up the earth’s Interior by looking at the speed of the traveling waves and the paths they take.

The Earth is made up of three main layers. The three

main layers:1) Crust2) Mantle3) Core

Two factors change regularly as you go towards the center of the Earth.1) Temperature:In general, temp goesUp steadily2) Pressure:Pressure increases the deeper into the earth Y ou go.

THE CRUST The thinnest layer of

the Earth. (5 – 40 km thick)Includes the soil &

waterthat covers the earth.Two types of crust:1) Oceanic crust –

mainly basalt (thinner)

2) Continental crust – mainly granite (thicker)

The MantleNearly 3,000 km thickMade of the Upper Mantleand the Lower Mantle.

Upper Mantle has 2 layers:

1) Lithosphere – like the crust; solid, rigid layer

2) Asthenosphere - less rigid; can bend like plastic; hotter

Lower Mantle is solid all the way to the core.

The CoreThe core is made up mostly of Fe and Ni.There are two layers:1) Outer core – liquid

metal2) Inner core – dense,

solid metalScientists believe the liquid outer core movesand creates the Earth’s magnetic field.

Convection & The Mantle(Section 2)

Before you can understand some of the processes on and in the earth, you must understand heat transfer.

There are 3 types of heat transfer:1) Radiation2) Conduction3) Convection

RadiationRadiation is the transfer of heat energy

through space. Sunlight is radiation.

ConductionConduction is heat transfer through the

actual contact of two objects. The hotter object transfers heat energy to the cooler object.

Convection

Heat energy that is transferred through the movements through liquid or air. It is caused by the differences in temperature which cause differences in density. The hotter something is the LESS dense it is. The colder it is the MORE dense it is.

Hot air rises. Think about hot air balloons!

Convection currents in the EarthThe extremely hot outer core heats

up the lower mantle which heats up the more mobile/tar-like asthenosphere. This hot rock rises then cools and sinks back down. This heating then cooling cycle creates a current within the Earth’s mantle.

The same thing happens when you heat water ina pot!

Drifting ContinentsIn 1910, a scientist named Wegener,

proposed that all the continents were once joined together in a single land mass and drifted apart over millions of years.

PANGAEA – the supercontinent His theory became known as continental

drift. He based his theory on several sources of evidence.

The theory of

Continental Drift

Wegener’s EvidenceWegener studied 3 main areas that

supported his continental drift theory.1) Land Features2) Fossils3) Climate change

The EvidenceLand features: Mtn ranges on South

Amer. and Africa line up when they are pieced together and coal fields in Europe & North Amer line up.

Fossils: Ancient fern fossils have been found in all continents including Antarctica!

More evidence….Climate: In warmer climates certain

foliage flourishes that could not grow in much colder environments. Wegener found fossils of tropical plants on an island in the Arctic Ocean. There was also evidence of glaciers once covering South Africa!

South Africa was once close to a much colderclimate according toWegener’s theory.

Seafloor Spreading (sect 4)

In all oceans on Earth there is a series of Mid-Ocean Ridges. They are like a mountain system underwater.

Seafloor Spreading (cont) Seafloor spreading is a process by

which the sea floor spreads apart along both sides of a mid ocean ridge adding new crust to the ocean floor.

Evidence of Seafloor Spreading Molten material found at the ridges

from lava erupting. Magnetic stripes – iron pieces in molten

rock align themselves according to earth’s poles and harden as the lava cools. It is a permanent record of earth’s magnetic history.

More evidence Drilling – rock samples were taken

from each side of the ridges and ages were determined. Youngest rocks found near center of ridge and oldest rocks found farther away from the ridges on either side.

New crust is being made but the Earth is not getting bigger!

If the Earth is staying the same size, and new crust is being made, that means somewhere, crust is being removed or recycled!

This happens by a process called:

SUBDUCTION

SUBDUCTION Subduction – happens at deep ocean

trenches. This is where the ocean floor sinks back into the mantle.

Seafloor spreading and subduction work together!

Some facts: The ocean floor is renewed every 200

million years! The Pacific Ocean is shrinking and the

Atlantic Ocean is expanding. In Pacific Ocean crust is being

swallowed up faster (subducting) than it is being made at the ridges.

PLATE BOUNDARIES 3 TYPES OF BOUNDARIES:1) Divergent – two plates moving apart Like what happens at mid ocean ridges!

Crust is created!2) Convergent – two plates come together

or converge! Some crust is destroyed!3) Transform – when two plates slip past

each other moving in opposite directions. Crust is not created or destroyed!

Divergent Boundary

Convergent Boundary

Transform Boundary

Click the flag to see animations!

Plate Tectonics This theory explains the formation,

movement and subduction of the Earth’s plates.

Convergent Boundary Here is a

convergent boundary between two plates at the Himalayan Mountain Range. The mountains are getting taller! One plate is going under the other making the top plate higher!

Divergent Boundary

In Iceland, there is a divergent plate boundary right throughthe middle of the country!

What will happen to Iceland?

Transform Boundary Where the Pacific

plate and the North American plate meet is a transform boundary.

Many earthquakes happen at transform boundaries!

San Andreas Fault

The end!