chapter3 - Chapter 3 Earth Definitions Development of the...

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Chapter 3 Earth Definitions Development of the theory - Earth is the only planet whose surface is defined by the processes called plate techonics. Continents, ocean basins, and mountain ranges are all produced by place techonics · Continental drift o Role of Wegener; evidence, lack of obvious mechanism - first steps toward formulation of a theory were made by Alfred Wgener, he grouped his ideas under the heading “continental drift.” He was struck by the jigsaw fit of continents scorss the atlantic ocean. He figured that the fit was so good that conindicen was inpossible. Add to that the wonderful fit of glacial terrain of continents in the southern hemisphere when those land masses were fitted together (Fig.5), the continuity of old geological structures and fossil stratigraphy from continent to continent (Fig.6), and Wegener had some pretty strong ideas to sell. By the way, the „supercontinent that Wegener was picturing in his jigsaw fit, he called “Pangaea”; Figures 4, 5 and 6 show parts of it. We ll refer to it many times later in the course, and will see better illustrations then and there. - in the second world war magnetics were used to find ships and subs that sank. They founf that they could detect curious, repetitive magnetic records in ocean floor rocks Following the war, two lines of research (one to hunt for natural resources, and the second simply to map the geographic features) began to produce the first comprehensive maps of the ocean floors. In the Atlantic Ocean, the most amazing discovery was definition of a huge volcanic ridge that extended right from the far north and connected with other similar ridges in the far south. Not only that, it was discovered that the volcanoes defining the ridge were active for almost its whole length – the largest volcanic system anyone had ever seen - Harry Hess, conjectured, in 1960, that these ridges represented spreading centers where Earth’s crust was moving in opposite directions like conveyor belts, allowing new ocean floor to be built from volcanic rock at the ridges. He calculated that, because of this activity, the Atlantic Ocean was widening by about 2.5 cm/year; if you took that rate and worked backward, North/South America and Europe/Africa were in contact some 180 million years earlier. Alfred Wegener was already dead, but his skeleton was probably happy because his idea of continental drift was finally finding support! · Sea floor mapping o Discovery of paleomagnetism (study of earths magnetic field through earths history) § Understand Earth’s magnetism model - points to north and south - protects us from space radiation and solar storms but we don’t know much about it, we are left to study effects closer to the surface and interpret activity inside earth - magnetic poles. [The positions of geographic poles are the poles of planet rotation; positions of the magnetic poles are not the same - electric currents are generated by enormous „dynamos driven by circulating hot currents
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This note was uploaded on 11/01/2010 for the course EARTH SCIE 2010 taught by Professor Neil during the Fall '10 term at UWO.

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chapter3 - Chapter 3 Earth Definitions Development of the...

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