Lesson 13: Plate Tectonics I Geological Oceanography

1. Lesson 13: Plate Tectonics I Geological Oceanography

2. 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

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

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 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 Continental crust Land Oceanic crust Lithosphere Ocean Asthenosphere The lithosphere and asthenophere 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 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 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