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Home > Earth > Plate Tectonics > A Lesson in Plate Tectonics

How Plate Tectonics Works

Way back in 1912 a scientist by the name of Alfred Wegener came up with a crazy idea. He noticed that all of the continents seemed to fit together like the pieces of a giant puzzle. He thought, "Maybe they were once all joined together in a single, giant landmass that broke up and drifted apart over time?". He decided to give this supercontinent a name and called it Pangea, meaning, "all lands". At the time he presented his idea to the scientific community it came to be known as continental drift theory. Wegener was unable to find solid evidence to support his theory, so the other scientists laughed him off as a crackpot. One of his suggestions for the cause of continental drift was that centrifugal force from the rotation of the earth caused the continents to slide into each other and move around on the surface. They all calculated that there wasn't enough force generated by the earth's rotation to cause shifting of the crust and nobody took him seriously. They were all convinced the earth was rock-solid and immovable.

USGS plate tectonics mapBut then in 1929, along came a scientist named Arthur Holmes who didn't think that Wegener's theory of continental drift was too farfetched. "Now wait just a minute. Maybe he's got something here", he told them. He mentioned one of Wegener's other theories about the source of continental drift; the idea that the molten mantle beneath the earth's crust experiences thermal convection and that the movement of these convection currents in the mantle could cause an upwelling beneath the crust, forcing it to break apart and move. Now, that sounded like a semi-reasonable explanation for the movement of the earth's crust. As a matter of fact, if you looked closely at this idea it explained a lot of things, not just the continental puzzle idea. It also explained how mountain ranges were formed - by continents crashing into each other and 'rumpling up rock'. Still, the other scientists just nodded and said, 'Yeah. Fine. Whatever'. And the theory was neatly tucked away and ignored.

Scientists are trained to be skeptical. They were all waiting for a preponderance of evidence that backed up this harebrained theory.

Over the next thirty years a lot of new and surprise discoveries were made as new technologies were developed for exploring the ocean floor . The discovery of volcanic activity on the ocean floor in the middle of the Antlantic that turned out to be part of a long, unbroken mountain chain of undersea volcanoes was the most ground-breaking discovery that supported the theory of continental drift. Scientists developed instruments for measuring earthquake activity around the world and began plotting the locations of earthquakes. They all got together and started drawing a new map of the world that showed volcanic and seismic (earthquake) activity was concentrated along certain areas that looked like the margins of huge crustal plates. During the 1960s several scientists published papers that reviewed the preponderance of evidence that had been gathered for the theory of continental drift and it soon came to be known as the theory of plate tectonics. The evidence that supports the geomagnetic anomalies ->

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