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Continental Drift was a theory revived by Alfred Wegener (1890
- 1930) in 1912.. He assumed that all continents were once part of
a single giant continent which he called Pangaea (all lands).
This super continent broke apart about 200 million years ago.
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The figures above show how the continents broke
apart and drifted to their present positions. Wegener depicted the
continents as giant rafts moving through the oceanic crust because of the
Earth's rotation. But there was insufficient force to overcome the
rocks' strength. Rocks would disintegrate. Seafloor spreading
was a theory suggested by H. H Hess, an American geologist in
1960. Seafloor spreads slowly and moves sideways away from the mid-oceanic
ridges. Mid-oceanic ridge systems stretch though out the oceans,
the most prominent being the Mid-Atlantic Ridge. They are caused
by convection currents of . subterranean
molten materials. This theory is supported by studies of remnant
magnetism which indicates the direction of Earth's magnetic field at
different times in its history.
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