1. Plate Tectonics I Geological Oceanography

2. The Theory of Plate Tectonics
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

3. Some geology fundamentals
The Earth is composed of three layers: core, mantle and crust
The Earth’s lithosphere is a rigid layer composed of part of the upper mantle and crust
The Earth’s lithosphere is not continuous, but made up of large pieces fit together like a puzzle

4. Visualizing Earth’s layers
What would you see if you
could cut Earth down the middle
and look inside?
A thick,
fluid-like mantle
surrounding the core
A thin outer crust
A core

5. 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

6. The lithosphere and asthenophere
Ocean
Land
Oceanic
crust
Continental
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
uppermost portion of mantle

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

8. Earth’s crustal plates
Photo: NOAA/NGDC
North American
Plate
Pacific
Plate
African
Plate
Photo:
Accessed: November 2010
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.

9. 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

10. Plates move with respect to one another
Photo: NOAA/NGDC
Eurasian Plate
North American Plate
Teacher’s Note: When geologists classify plate motion, it is always discussed in terms of the frame of reference of one plate to another. In the above slide, the blue arrows indicate that the North American and Eurasian plates are diverging from 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).

11. How fast do plates move?
In today’s activity, you will figure out how fast the Pacific Plate is moving