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Unformatted text preview: Physical Geology 101 1 3. Plate Tectonics I (p. 37-46) Plates in Motion The tectonic plates are constantly in motion. Where they collide, the compression can result in the production of high ______________________. Where they rip apart, __________________ may form. Despite our observation of such features for a very long time, the theory of plate tectonics is nonetheless a fairly recent idea. The beginnings of plate tectonic theory were introduced by Alfred Wegener in the year __________. He called his new hypothesis ________________________. This concept implied that the continents have not always been in their present positions, but have drifted and changed positions over long periods of geologic time. What observation about the continents led to Wegener s hypothesis? ______________________________________________________________________ It was hypothesized that all the continents had once been joined together as one large supercontinent called _________________. At some point in time, this supercontinent broke apart, and the continents drifted off to their present locations. Initially, these ideas were highly criticized by geologists, who could think of no mechanism by which the granitic continents could possibly force their way through solid basaltic ocean crust. It took many decades for geologists to finally realize what the mechanism is that allows continental drift to actually occur. In fact, plate tectonics is responsible for the mountain ranges; ocean basins; ocean current circulation patterns; climatic variations; distributions, evolution and extinctions of plants and animals; volcanoes and earthquakes; and economic mineral locations. It is a unifying theory for all topics of geology. Evidence for Plate Tectonics Continental Fit One of the most convincing lines of evidence for continental drift and plate tectonics is the way that the continents seem to fit so well together despite being separated by oceans today. Example: _____________________________ and __________________________. It must be more than sheer chance that these coastlines match so well. But, if we look only at the present day coastlines of these continents, there seem to be large gaps between them when we bring them back together....
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- Fall '08