If you look at a map of the Atlantic Ocean, you will see that the coastal shapes of the Americas resemble those of Europe and Africa. Might these continents have once been joined together like pieces in a giant jigsaw? A German meteorologist, Alfred Wegener (1880-1930), thought so. He wrote a book saying that, about 200 million years ago, all the continents were joined together. But this supercontinent later split apart and the pieces ‘drifted’ to their present position.
The problem with Wegener’s theory of ‘continental drift’ was that no one could explain how continents move. In the 1960s, scientists came up with an answer based on studies of the ocean floor. They suggested that the solid crust and part of the upper mantle are divided into large blocks, or plates. Beneath these plates is semi-fluid rock which moves around in slow currents. It is these currents which move the plates and the continents which rest upon them-very slowly.