Plate Tectonics I Geological Oceanography

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

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

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

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

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

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

Earth’s crustal plates Photo: NOAA/NGDC North American Plate Pacific Plate African Plate Photo: http://www.ngdc.noaa.gov/mgg/ocean_age/data/2008/ngdc-generated_images/whole_world/2008_age_of_oceans_plates.jpg; 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.

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

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).

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