Wegener proposes idea of continental drift
Ever since the continents were all mapped, people had noticed that many coastlines, like those of South America and Africa, looked as though they would fit together if they could be moved like puzzle pieces.
Alfred Wegener was one of those people. Though trained as an astronomer, he was a specialist on Greenland. He noticed that, based on nineteenth-century longitude determinations, it appeared that Greenland had moved a mile away from Europe in a hundred years. And Paris and Washington, D.C., seemed to be moving apart by about 15 feet each year while San Diego and Shanghai got about six feet closer. On top of that, Wegener learned that related species, too small to swim the oceans, were found on different continents, as were similar fossils.
In 1912 he proposed that the continents we know today were once all attached in a single landmass he called Pangaea (Greek for "all earth"). They were surrounded by one global ocean, but then broke apart and somehow "drifted" to their separate places on the globe. Although the calculations of Greenland's movement were found to be due to faulty determinations of longitude, the other evidence seemed to match up: the shape of the continents, fossil evidence, matching rock types and geologic structures, and evidence of ancient climate patterns. But Wegener could not come up with an acceptable way to explain how the continents moved.
Few people accepted Wegener's views in his day, but they became the center of heated debate. The year after Wegener died, Arthur Holmes published his idea that thermal convection in the earth's mantle could cause continents to move. Holmes also suggested that the continents didn't move but were "carried" by larger pieces of the earth's crust. The controversy quieted down and fell from prominence until the 1960s, when new evidence was brought to the fore. Discoveries of the Mid-Ocean Ridge and the work of Harry Hess and others led to the development of plate tectonics. Though not without problems, this theory has gained wide acceptance. It is the most complete theory of global dynamics yet, and its roots lie in the work of Alfred Wegener.