CONTINENTAL DRIFT... Continental drift is the movement of the Earths continents relative to each other by appearing to drift across the ocean bed.[1] The speculation that continents might have drifted was first put forward by Abraham Ortelius in 1596. The concept was independently and more fully developed by Alfred Wegener in 1912, but his theory was rejected by some for lack of a mechanism (though this was supplied later by Holmes) and others because of prior theoretical commitments. The idea of continental drift has been subsumed by the theory of plate tectonics, which explains how the continents move Evidence of continental drift: Evidence for the movement of continents on tectonic plates is now extensive. Similar plant and animal fossils are found around different continent shores, suggesting that they were once joined. The fossils of Mesosaurus, a freshwater reptile rather like a small crocodile, found both in Brazil and South Africa, are one example; another is the discovery of fossils of the land reptile Lystrosaurus from rocks of the same age from locations in South America, Africa, and Antarctica.[22] There is also living evidence—the same animals being found on two continents. Some earthworm families (e.g.: Ocnerodrilidae, Acanthodrilidae, Octochaetidae) are found in South America and Africa, for instance. The complementary arrangement of the facing sides of South America and Africa is obvious, but is a temporary coincidence. In millions of years, slab pull and ridge-push, and other forces of tectonophysics will further separate and rotate those two continents. It was this temporary feature which inspired Wegener to study what he defined as continental drift, although he did not live to see his hypothesis become generally accepted. Widespread distribution of Permo-Carboniferous glacial sediments in South America, Africa, Madagascar, Arabia, India, Antarctica and Australia was one of the major pieces of evidence for the theory of continental drift. The continuity of glaciers, inferred from oriented glacial striations and deposits called tillites, suggested the existence of the supercontinent of Gondwana, which became a central element of the concept of continental drift. Striations indicated glacial flow away from the equator and toward the poles, in modern coordinates, and supported the idea that the southern continents had previously been in dramatically different locations, as well as contiguous with each other Wegener and his predecessors: Alfred Wegener The hypothesis that the continents had once formed a single landmass before breaking apart and drifting to their present locations was first presented by Alfred Wegener to the German Geological Society on 6 January 1912.[12] Although Wegeners theory was formed independently and was more complete than those of his predecessors, Wegener later credited a number of past authors with similar ideas:[13][14] Franklin Coxworthy (between 1848 and 1890),[15] Roberto Mantovani (between 1889 and 1909), William Henry Pickering (1907)[16] and Frank Bursley Taylor (1908). Eduard Suess had proposed a supercontinent Gondwana in 1858 and the Tethys Ocean in 1893, from a sunken land-bridge/ geosyncline theory point-of-view, though. John Perry had written an 1895 paper proposing that the earths interior was fluid, and disagreeing with Lord Kelvin on the age of the earth.
Posted on: Wed, 29 Jan 2014 07:59:04 +0000
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