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The determined age of the Earth as 2 billion years opened doors for theories of continental movement during this vast amount of time.[25] In 1912 Alfred Wegener proposed the theory of Continental Drift.[26] This theory suggests that the continents were joined together at a certain time in the past and formed a single landmass known as Pangaea; thereafter they drifted like rafts over the ocean floor, finally reaching their present position. The shapes of continents and matching coastline geology between some continents indicated they were once attached together as Pangea. Additionally, the theory of continental drift offered a possible explanation as to the formation of mountains. From this, different theories developed as to how mountains were built. Unfortunately, Wegener’s ideas were not accepted during his lifetime and his theory of Continental Drift was not accepted until the 1960s.[27] In the 1960s new found evidence supported the theory of Continental Drift. The term Continental Drift was no longer used but was replaced by the concept of Plate Tectonics that was well supported and accepted by almost all geologists by the end of the decade. Geophysical evidence suggested lateral motion of continents and that oceanic crust is younger than continental crust. This geophysical evidence also spurred the hypotheses of seafloor spreading and paleomagnetism. The hypothesis of seafloor spreading, proposed by Robert S. Dietz and Harry H. Hess, holds that the oceanic crust forms as the seafloor spreads apart along mid-ocean ridges. Paleomagnetism is the record of the orientation of the Earth’s magnetic field recorded in magnetic minerals. British geophysicist S. K. Runcorn suggested the concept of paleomagnetism from his finding that the continents had moved relative to the Earth’s magnetic poles |
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