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The Drifting History
Plate tectonic theory had its beginnings in 1915 when Alfred Wegener proposed his theory of "continental drift." Wegener
proposed that the continents plowed through crust of ocean basins, which would explain why the outlines of many coastlines
look like they fit together like a puzzle. Wegener was not the first to notice this puzzle-like fit of the continents, but
he was one of the first to realize that the Earth's surface has changed through time, and that continents that are separated
now may have been joined together at one point in the past.
Paleomagnetic studies, which examine the Earth's past magnetic field, showed that the magnetic
north pole seemingly wandered all over the globe. This meant that either the plates were moving, or else the north pole was.
Since the north pole is essentially fixed, except during periods of magnetic reversals, this piece of evidence strongly supports
the idea of plate tectonics.
Following World War II, even more evidence was uncovered which supports
the theory of plate tectonics. In the 1960's a world-wide array of seismometers were installed to monitor nuclear testing,
and these instruments revealed a startling geological phenomenon. It showed that earthquakes, volcanoes, and other active
geologic features for the most part aligned along distinct belts around the world, and those belts defined the edges of tectonic
plates.
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