What is Plate Tectonics? - Definition, Theory & Components

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  • 0:02 What is Plate Tectonics
  • 1:22 A Giant Soccer Ball
  • 2:02 How Do the Plates Move?
  • 3:03 Types of Movement
  • 3:59 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

Imagine ice floating in a glass. Would you believe that we are all living on giant pieces of floating rock, just like the ice in that glass? This lesson explains that theory, an idea known as plate tectonics.

What Is Plate Tectonics?

Imagine a nice, hot summer day. You've just poured yourself a tall glass of lemonade and are watching how the chunks of ice are clinking against each other. As you take that first refreshing sip, you feel a little rumble in the ground beneath your feet. The earthquake only lasts for a second, but it's enough for a bit of your lemonade to spill out on the table. The ice clamors against the other cubes for the few seconds of the tremor.

Your lemonade and that earthquake have more in common than you might think. Just as you were watching the ice cubes collide in your glass, the whole surface of the Earth floats on a molten layer of melted rock known as the mantle. The mantle is about the consistency of a milkshake, which is ironic, as it's so hot that putting it in a cup would be painful, much less drinking it! The world's crust, the part we live on, floats on top of this in a number of large chunks known as plates. We call this idea that the world's surface is indeed a collection of plates the theory of plate tectonics. It is still a theory because we have no way of proving it with absolute certainty. However, gravity is also a theory, and we're just as sure of its existing as we are of plate tectonics existing. Both of these theories, like all theories, have been subject to the process of the scientific method and are more than just a wild guess.

A Giant Soccer Ball

As a result of these plates, the world's surface actually is more like a soccer ball, with each panel rubbing against the others. The places where these plates rub against each other are called faults. Now before you get scared, these faults are not cliffs to the center of the earth. However, when there is an earthquake, chances are you would not want to be near one. This is because places near faults often experience the most damage because earthquakes are the result of tectonic plate movement. Also, note that the plates are not all of equal size. Some are rather large, like the Pacific Plate or the North American Plate. Others are very small, like the Juan de Fuca Plate off the West coast of the United States.

How Do the Plates Move?

When you pick up your glass of lemonade, you shake around the ice cubes and make them move. For the Earth, it's a bit different, but really much the same. Imagine that if you had ice cubes that wouldn't melt. Now imagine that you put your lemonade over a heat source and boiled it! Better yet, probably best to use someone else's lemonade. In any event, the bubbling of the heat would cause the ice cubes to move even before the lemonade boiled. The same is happening under the Earth's surface. Here there is a process known as thermal convection. Thermal convection happens when hot mantle from close to the core rises to the crust. In some places with plenty of volcanoes, like Iceland and Yellowstone National Park, this heat source is close enough that it warms up hot springs and geysers. Just like the ice cubes in your drink, this heat causes the plates to move. Also, the movement of other plates can create underground vacuums that suck a plate into a new position.

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