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Physics - Restless Continents

Most land lies in seven mighty chunks: the continents. These are scattered round the world. But scientists think that long ago all the continents were stuck together.

Several clues show that this is likely. For instance, the east coasts of North and South Amercia could have fitted into the west coasts of Europe and Africa. Then, too, rocks on each side of the Atlantic Ocean match one another. Even some of the plants and animals in continents now far apart share the same close ancestors.

A shifting Jigsaw Puzzle

At first it seemed impossible that continents could drift about, but scientists have now discovered how it could happen.

They believe that the continents are moved by currents of molten rock flowing through the Earth’s core. Where a rising current reaches the Earth’s crust the current spreads out in opposite directions and pulls the crust apart. Then the current plugs the gap with molten rock. Where spreading currents cool they grow heavier and sink, dragging crust down into the mantle.

It seems that the Earth’s crust is made up of a dozen interlocking plates or slabs. Some of these carry ocean floor. Some carry continents. All fit like pieces of a jigsaw puzzle- but a puzzle where the pieces keep on moving.

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