Geophysics

A Saltatory Itinerary

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Science  20 Dec 2002:
Vol. 298, Issue 5602, pp. 2285-2287
DOI: 10.1126/science.298.5602.2285d

Plate tectonics drives the major plates (including the continents) over Earth at rates of several centimeters per year (or hundreds of kilometers per tens of millions of years). Reconstructions of these paths are based on inferring spreading across ocean basins and using paleomagnetic data to estimate the paleolatitudes of continents (because the inclination of Earth's predominantly polar magnetic field varies with latitude). Extensive and precisely dated magnetic records in continents allow for the compilation of an apparent polar wander path, which describes the motion of a plate or continent over time (essentially, the drift of the continent) over Earth. Such paths help in reconstructing continental geometry and in evaluating the assembly of continents; biologic evolution in response to geologic events; climate change; and, if many paths change abruptly, major changes in mantle dynamics.

Besse and Courtillot provide an update on the polar wander paths of many plates over the past 200 million years. Their analysis describes periods when mantle dynamics were relatively stable, and some episodes, such as during the Cretaceous, when mantle flow became reorganized with respect to Earth's spin. However, they do not see evidence of episodes of rapid reorganization that have been proposed in some previous studies. — BH J. Geophys. Res. 107, 2300 (2002).

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