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Scientists Shake Up Theory of Plate Tectonics

Earth
Image: ALESSANDRO FORTE, JERRY MITROVICA

Ideas about continental movement, earthquakes, volcanism and even climate change need to be rethought, according to two Canadian earth scientists. In a study published today in Nature, they claim that huge plumes of hot rock are floating upward from the earth's liquid core, profoundly influencing what happens on the surface.

"In effect we have found that the solid earth is being churned by a four-piston heat engine with two immense sinking cold slabs and two equally large rising hot plumes," Alessandro Forte of the University of Western Ontario says. Measuring earthquake waves that travel deep inside the planet, the scientists were able to retrieve images of what goes on inside the earth's mantle at a depth of about 3,000 kilometers. They noticed that the waves traveled faster in two vast arc-shaped regions under the margins of the Pacific Ocean (blue in the illustration), while they slowed down in two equally large plume-shaped regions below the central pacific and Africa (red).

Whereas current scientific belief holds that the "slow" regions have been stagnant since the earth was formed, Forte and his colleague Jerry Mitrovica of the University of Toronto believe that they are actually rising to the surface, while the "faster" portions, containing heavy material, are sinking toward the core. As proof, the researchers cite tiny variations in the earth's rotation and gravity field, as well as deflections of continental regions like southern Africa¿now one kilometer higher than northern Africa.

Plate tectonics theory does not draw a link between movements of the continental plates and processes taking place deep inside the earth, a view that Forte and Mitrovica hope will be overturned by their findings. "It's a road map for resolving a contentious debate that has hampered global earth science since the plate tectonics revolution," Mitrovica says.

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