Evidence for Continental Drift
Continental drift refers to the idea that the present continents once formed a single. giant continent called Pangaea, and since that time have been slowly drifting apart. In 1915 the originator of this idea, the German meteorologist Alfred Wegener, was impressed by the close resemblance of coastlines of continents on opposite sides of the Atlantic Ocean, particularly South America and Africa. However,the configuration of the coastlines results from erosional and depositional processes and therefore is constantly being modified, so even if Wegener was right and the continents had separated in the distant past, it is not likely that the coastlines would fit exactly. But decades later it was shown that the continents fit together well along the continental slope (the broad underwater shelf on the edges of continents), where crosion is minimal, and recent studies have confirmed the close fit between continents when they are reassembled to form Pangaea.
If the continents were at one time joined, then the rocks and mountain ranges of the same age in adjoining locations on the opposite continents should closely match. Such is the case for the continents thought to have together formed the southern supercontinent Gondwana when Pangaca broke up into a northern and a southern supercontinent, mostly during the Jurassic period (200-146 million years ago) Antarctica, South America, Africa,Australia-New Guinea, and India comprised Gondwana. Marine, nonmarine, and glacial rock sequences of the Pennsylvanian epoch(325-299 million years ago)to the Jurassic period are almost identical for all five Gondwana continents, strongly indicating that they were joined at one time. The trends of several major mountain ranges also support the hypothesis of continental drift. The folded Appalachian Mountains of North America, for example, trend northeastward through the eastern United States and Canada and terminate abruptly at the Newfoundland coastline. Mountain ranges of the same age and deformational style occur in eastern Greenland, Ireland Great Britain, and Norway. Even though these mountain ranges are currently separated by the Atlantic Ocean, they form an essentially continuous mountain range when the continents are positioned next to each other.
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