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The Red Sea

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(center) is becoming wider because moving plates are forcing Africa (left) and Arabia (right) apart.

The evidence Most geologists did not accept the idea of continental drift until the 1960s. They have now found plenty of evidence to support it. South America, Africa, Antarctica, and Australia all have rocks and fossils of similar species (kinds) of reptiles and plants. This proves that they were once joined together in a supercontinent.

Theory of plates A theory called plate tectonics explains how continental drift happens. It says that the Earth’s crust is not solid, but is made up of a number of sections, or plates , which are moving. Some of these plates carry the continents. The plates are made of solid rock. But the rocks beneath them, in the upper part of the mantle, are hot and semi–molten (partly liquid), like thick pudding. The rocks in the mantle flow slowly. They rise as they heat up, spread beneath the crust, then sink again as they cool. This is similar to the way warm air rises, cools, and sinks in a heated room. As the squishy rock flows beneath the crust, it carries the plates with it. In

∆ The Earth today. The lines show the boundaries between the plates that make up the crust.

some places the plates are moving apart, and in others they are being pushed together. There are seven large plates and many smaller ones.

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