Alfred Lothar Wegener geophysics |
Continental drift
Eduard Suess had lined up the mountains on different continents by linking their fossils, but he claimed that land-bridges connecting the continents must have sunken below the ocean, which Alfred Wegener realized would not work because it contradicted the geological buoyancy of the continental masses. Wegener further realized that the continents had been slowly drifting about the globe, and that the mid-ocean ridges were being filled with new seafloor as each side spread apart. Nevertheless, Wegener did not understand the cause of continental drift. That waited for the theory of plate tectonics.
Pangaea
Pangaea, which Wegener called Urkontinent, existed from three hundred million years ago when all the continents and subcontinents were jammed together. Two hundred million years ago, Panaea began to split into Gondwana to the south and Laurasia to the north. Gondwana included Antarctica, Africa, Madagascar, Australia, Arabia, India, and South America and began to break up in the early Jurassic, about one hundred eighty-four million years ago. Laurasia included Europe without the Balkans, Siberia, Asia without India, Greenland, and North America and began to break up at the end of the Paleocene, about fifty-five million years ago. Today, India is ramming into Asia lifting up the Himalayas and the Great Rift is separating Africa from its horn.
My drift
If you get my drift, my slowly imperceptible displacement, then you might begin to correlate other facts in reconstructing my past. Not everything has been lost, I could say, none of the important things, but even trivial fossils have become important enough to cherish.
Alfred Wegener thought that continents drifted because of centrifugal forces; today the picture is more complicated, involving convection in the upper mantle, the motions of the seafloors spreading from the mid-ocean ridges and their densities varying with age, gravitational forces, tidal forces, and centrifugal forces. Scientists have differing theories.
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