Media Credit: Katrina Perry Plate tectonic researcher Lisa Gahagan discusses adding plates to the global plate model as part of the Plates Project at the University of Texas Institute for Geophysics at the Pickle Research Center Wednesday afternoon.

The theory of plate tectonics illustrates how rock plates from five to 25 miles thick move at fractions of inches per year over Earth. Plates sink into the earth, and new crust is created by molten rock solidifying at ocean ridges. This motion brings continents together and breaks them apart. Now, scientists using the Global Positioning System are able to directly measure the movements of the plates. The theory, however, took decades to be accepted.

Alfred Wegner first published the theory of continental drift in a 1912 paper. He matched coastlines together like a jigsaw puzzle and saw that they fit remarkably well.

"[Continental drift] started from asking 'How can we explain the distribution of things? How can we explain the origin of mountains and ocean basins?'" said Mark Cloos, a UT geology professor.

Many thought the theory was ridiculous.

"In North America, it died out as even a concept. If you go look at the textbooks from the 1930s, 1940s and 1950s, to even have a paragraph on the subject of continental drift was being generous," Cloos said. Early on, prominent physicist Harold Jeffreys discounted the theory. By studying seismic waves, he established the earth's crust was rigid. He extrapolated the rigidity of the earth to geological timescales, and he believed there was no way for the continents to move through such a hard shell.

"The theory said it was impossible, and the people who made the observations simply said, 'Wegner's seeing things.' The big breakthrough that happened in the 1950s is that we started studying the oceans, using a large array of technologies that had been put together in World War II," Cloos said.

After WWII, much of the instrumentation used to look for submarines was available to study the ocean bottom. New observations forced scientists to re-evaluate their ideas.

"We started to discover that the oceans, which everyone had pretty much assumed were like the continents except under water, are completely different," Cloos said. "The hills are all volcanoes, the oldest rocks are cretaceous and 150 million years old, and the biggest mountain belt on Earth runs right down the middle of the Atlantic - the ocean ridge system."

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