Tuesday, October 20, 2009

Earth crust

The continents of the old world (The Europe, Asia and Africa) and the new world (The Americas) have been slowly drifting on the surface of the Earth since our planet became solid. In the last 150 million years, the Atlantic has gradually opened up, separating the Americas from Africa and Europe. Alaska and Siberia were once joined, but at present Alaska and Siberia are separated by the Bering Strait. The crust of the earth is a relatively thin layer. Scientists believe it is divided into huge sections called ‘plates’. These are moved very slowly by convection currents inside the Earth. The scientist Alfred Wegener suggested in 1915 that the continents might have moved. He had noticed that their shapes fit together like a jigsaw. His theory was called ‘continental drift’. The oldest rocks found so far are thought to be about 3850 million years old, so the earth had a solid crust by then. Some meteorites and pieces of moon rock are probably 4600 million years ago, so scientists think that the earth formed about 4600 million years ago. Scientists measure the earth’s age by studying the rate of decay of radioactive elements with special equipment. This technique is called carbon-dating.

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