Lesson 13:

Plate Tectonics I

Geological Oceanography

We’ve learned a lot about physical motions in the ocean

Waves, tides and currents are all physical processes

There are other types of movement on Earth that are important to marine science, too, like the movement of Earth’s plates

To understand what we mean by the movement of plates, we need to learn some basic geology

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Some geology fundamentals

1. The Earth is composed of three layers: core, mantle and crust

2. The Earth’s lithosphere is a rigid layer composed of part of the upper mantle and crust

3. The Earth’s lithosphere is not continuous, but made up of large pieces fit together like a puzzle

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Visualizing Earth’s layers

What would you see if you could cut Earth down the middleand look inside?

A thin outer crust

A thick,fluid-like mantlesurrounding the core

A core

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There are two types of crust: oceanic crust and continental crust

The thick continental crust and thin oceanic crust both lie on the more dense mantle

Oceanic crust is younger, thinner and more dense than continental crust

Continental crust tends to lie higher than oceanic crust and forms continents

The very uppermost part of the mantle and the crust form rigid plates, called the lithosphere

These plates cover the Earth and move with respect to one another

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The lithosphere and asthenophere

The lithosphere is made up of rigid plates composed of the top of the upper mantle and the crust

Beneath the uppermost layer of the mantle is an area of weakness called the asthenosphere, on which the rigid plates move with respect to one another

Lithosphere

Asthenosphere

Ocean

LandOceaniccrust

Continental crust

uppermost portion of mantle6

Now you know about the composition of the lithosphere, but did you know it is not one continuous layer?

The lithosphere is actually composed of many large pieces that fit together like a puzzle

These large pieces are called plates

You may have heard of Earth’s plates or plate tectonics – what exactly is a plate?

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Earth’s crustal plates

This picture shows the boundaries of Earth’s crustal plates. Some plate names are given for examples. Plates contain oceanic crust, continental crust or both types.

Ph

oto

: NO

AA

/NG

DC

PacificPlate

AfricanPlate

North AmericanPlate

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Earth’s plates are constantly moving

Remember that the asthenosphere beneath the plates is relatively soft and plastic

The asthenosphere is slowly, but constantly, moving The plates “floating” on top of this layer are thus

always in motion. Do know some of the ways that plates move in relation to one another?

They can move past one another, crash into one another, even rise and sink

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Plates move with respect to one another

For example, the North American plate and Eurasian plate are moving away from one another, forming a ridge. Relative plate motions are discussed in detail in the next lesson (Lesson 14).

Ph

oto

: N

OA

A/N

GD

C

North American Plate

Eurasian Plate

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How fast do plates move?

In today’s activity, you will figure out how fast the Pacific Plate is moving

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