It is apparent from a glance at the map: the earth's continents can be made to fit together like parts of a giant jigsaw puzzle. Yet for years most scientists stoutly resisted the conclusion that some time in the remote past, the earth's land masses began splitting up and drifting apart—a theory known as "continental drift." Sheer nonsense, they insisted. No known forces could possibly have propelled huge continents across the earth's dense, basaltic crust.
Discoveries of the past few years have now turned skeptics into believers. Scientists have not only uncovered the basic mechanism that moves continents, but are becoming increasingly convinced that it provides explanations of many fundamental mysteries about the earth. What causes earthquakes? How are mountain ranges formed? The answers have thoroughly jolted the once staid earth sciences. "It's a revolution," says Oceanographer Melvin Peterson of the Scripps Institution of Oceanography. "We are riding the crest of a breaking wave."
In making their case for continental drift, scientists used some obvious evidence: geological strata in South America that matched those of West Africa in areas where the continents might have been joined; fossils of plants and animals from one continent that were identical to those on another, even though they are separated by thousands of miles of ocean. Just off Antarctica's Ross Ice Shelf, for example, an Ohio State University expedition recently discovered the fossilized bones of a hippopotamus-like reptile called Lystro-saurus that had been thought to live only in prehistoric South Africa and Asia.
Missing Deposit. More subtle clues came out of the ocean depths, although few scientists at first recognized their importance. By 1959, Columbia University's marine geologists had completed charting a mysterious 47,000-mile-long chain of undersea mountains and ridges that twist through the middle of the major oceans like the seams of a giant basketball. Strangely enough, the water temperatures near these ridges are considerably higher than those elsewhere in the ocean. In addition, there are ocean-floor fault lines or cracks that were apparently caused by movement of the seabed itself. Although the oceans are billions of years old, sonar measurement of the depth of accumulated sediment indicated that the sea floor is no more than a few hundred million years old; the deposit of sediment should be much thicker.