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This unit will explore the layers of theearth, the driving force behind themovement of Earths plates, and thevarious type of plate movements.

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Earth consists of three mainlayers, the crust, the mantle,

and the core.

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CrustEarths outer layer, which is firm and seems

solid but is broken up into plates that areable to move.

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Mantlethickest layer of the earth, located beneath the cr

and above the core.

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Core

nter part of the earth which consists of two lThe outer core is liquid.

The inner core is thought to be solid.

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The lithosphere plays a significant role in the changing of Earthssurface due to convection currents.

The lithosphere consists of the crust and theupper layer of the mantle.

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The Role of Alfred

Wegener

What was histheory?What was his evidence?

What was missing?

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Alfred Wegners Theory is referred to

as Continental Drift

Wegener proposed the idea of asupercontinent, he called Pangaea. He

went on further to say Pangaea broke apart.The continents slowly moved to their

present positions and continue to move.

His evidence consists of the following:

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The Shapes of the Continents

Match

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The Rocks Match

Wegener found similar rocks ondifferent continents.

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The Ice Matches

Wegener also found that glaciers

existed long ago in what are nowAfrica and South America. He thought

the only explanation was that thecontinents were once connected.

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Wegeners ProblemDespite his evidence, Wegener could not

explain how the continents moved.

In the late 1900s scientists had a betterunderstanding of the upper layers ofEarth.

They now think the crust and the upper

mantle are made up of large sectionscalled plates which move because theyrest on a plasticlike layer within the

mantle.

Technological advances provided a clearer

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Seafloor SpreadingScientists discover the plates move!

After exploring the ocean floor scientists discover areaswhere magma oozes out. These areas, called mid-oceanridges, have a gap in the center. In this area, new oceancrust is being formed as the magma cools. As the new

magma moves up onto the surface, the two sides of theridge are pushed apart.

This process that forms new ocean crust is calledseafloor spreading.

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Convection Currents play arole in the changing of

Earths surface.

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The cycle in which hot magma isforced upward towards Earths

surface, becoming cooler and moredense , then sinking back into themantle, where it is heated again.

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Convection currents are the result of theheating and cooling of magma.

Hot magma is forced upward to the surface,

becoming cooler and more dense. The cooler, moredense magma sinks back into the mantle. Deep inthe mantle, the magma is heated again, and the

cycle repeats over and over again.

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Plate movementsPlates move away from, toward, or slide past

each other. Geologists call these divergent,

convergent, and transform plate boundaries.

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Divergent Plate

BoundaryAt a divergent plate boundary plates move

away from each other. The mid-Atlantic Ridgeis an example of a divergent plate boundary.

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Convergent Plate BoundaryAt a convergent plate boundary, plates move

toward each other.

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Transform Plate

BoundaryAt a transform plate boundary, plates slide

past each other. The San Andreas fault inCalifornia is an example of a transform plateboundary, where the Pacific Plate slides pastthe North American Plate.

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At the completion of this unit

you should have a betterunderstandingof the following:

The layers of the earth and the role they playin the changes that occur to the earthssurface.

The person behind the explanation for the

changes that occur to earths surface, histheory, and the theories that followed.

The driving forces behind these changes.

And the types of changes that can occur.

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Work C