Continental Drift and Plate Tectonics

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Geol/continent_drift_pubs_usgs_201x251.jpg”/> Millions of years ago the present-day continents comprised one huge land mass. Over time they drifted apart and regrouped several times in different ways. But understanding why and how the continents became separate entities took centuries.

In Europe, as early as the 1500s a notion of drifting continents circulated, but until the beginning of a geological science it was difficult to develop the concept. In the nineteenth century, serious investigations of geology, natural history, and evolution all suggested that present continents must have been a single mass in the remote past. James Lyell and James Hutton in England gathered geological evidence that would prove the Earth was much older than the accepted view (which was still based on the Biblical view).

A German scientist, Alfred Wegener developed the theory of continental drift to account for distinct geological and biological relationships between the continents. He carefully assembled geological evidence to demonstrate, for example, how South America and Africa had to have once been joined, and described flora and fauna fossils that indicated that many species on the two continents were related. In addition, many living species on the two continents appeared to be related, and the huge distance between South America and Africa ruled out accidental drifting of so many varieties of organisms. Wegener introduced the radical idea that the continents were gradually split off from an original single landmass by forces in the sea floor that caused ruptures in the crust of the Earth. Of course, he had no way to prove his conjecture. When he presented his theory to a prestigious scientific meeting he was ridiculed and ordered to stop.

The continental drift theory was not accepted until the 1960s when the technology necessary for deep-sea scientific investigation became available. The data revealed unquestionable evidence that the Earth’s crust was made up of tectonic plates. The movement of these plates caused deep fissures (rifts) in the ocean floor, regular shifts of the planet’s magnetic polarity, volcanoes and earthquakes. With the established evidence for tectonic plates, scientists at last could explain the distribution –and continued drift– of the continents.