plate tectonics

Movement of the Continents

According to plate tectonics, the ocean basins are viewed as transient features that have periodically opened and closed, first rending and then suturing the continental masses, which are permanent features on the earth's surface. Geologists now believe that the continents were sutured together 200 million years ago at the beginning of the Mesozoic era to form a supercontinent named Pangaea. Initial rifting along the Tethys Sea formed a northern continental mass, Laurasia, and a southern continental mass, Gondwanaland. Then plate movements caused North American and Eurasian separation coincidentally with the separation of South America, Africa, and India. Australia and Antarctica were the last to separate. The major plates are named after the dominant geographic feature on them such as the North American and South American plates.

Plate motions are believed to have transported large crustal blocks several thousand miles, suturing very different terrains together after collision with a larger mass. These "exotic" terrains may include segments of island arcs quite unrelated to the history of the continent onto which they are sutured. Some geologists believe that continents grow in size primarily by the addition of exotic terrains.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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