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Written in stone
Natural History, Sept, 2006 by Nick W. Atkinson
A dogma of the Earth sciences may be on shaky ground. Geologic hotspots--long thought to be relatively fixed points beneath Earth's shifting tectonic surface--are themselves moving around.
Hotspots are areas of long-term volcanic activity that have served as handy reference points for tracing the movements of tectonic plates. The Hawaiian Islands, for instance, are thought to have formed from the lava spewed by a hotspot up onto the Pacific plate as the plate moved northwestward over the hotspot. The islands, known as a hotspot "trace," thus record the track of the plate over the hotspot (which is now centered under the Big Island of Hawai'i). From the ages of the islands, the direction and speed of the plate's movement can be inferred.
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To model the movements of the planet's plates, earth scientists have assumed for more than three decades that the hotspots remain fixed relative to one another, and that the plates themselves have not undergone any recent reorganization in the ways they butt up against one another. Now a statistical analysis by Shimin Wang and Mian Liu, geophysicists at the University of Missouri in Columbia, have confirmed mounting evidence that at least one of those assumptions must be wrong. The hotspot traces, they discovered, aren't where they should be if both assumptions are correct.
The geologists' analysis indicates that though there has been no major reorganization of the plates in the past 40 million years, the hotspots have been moving. The good news is that they seem to be moving in the direction opposite to that of the plates that overlie them. Thus geologists need not abandon hotspot traces to make inferences about the movements of the Earth's crust. (Geology 34:465-8, 2006)
COPYRIGHT 2006 Natural History Magazine, Inc.
COPYRIGHT 2008 Gale, Cengage Learning
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