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Evidence of techtonic Plates

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Introduction

The evidence in the Theory of Plate Tectonics In the 1900's many scientists believed that the earth has and always had been cooling down since the "big bang" and that the earth's surface contracted and wrinkled like the skin of a raisen. This "raisen" theory implied that mountain ranges and hills were once leveled to the ground but had been forced up by the 'wrinkling process'. This theory was later challenged by Alfred Wegener, a German geophysicist and meteorologist who was not satisfied by this explanation. His ideas drew on the widely recognized fact that the continent, Africa and South America appeared to fit together like jigsaw puzzle pieces. He soon collected data from the continents on both sides of the Atlantic, finding that many fossils and rock types along the eastern coast of South America matched those on the western coast of Africa! This evidence caused Wegener to join the continents using a map and find an explanation. When he added the northern continents to the puzzle, Wegener realized that the chain of Appalachian Mountains in North America continued as the Caledonian Mountains in northern Europe. ...read more.

Middle

Wegener tentatively suggested two candidates: centrifugal force caused by the rotation of the Earth, and tidal-type waves in the Earth itself generated by the gravitational pull of the sun and moon. He realized these forces were inadequate, however, he noted that one thing was certain: The forces that displace continents are the same as those that produce great fold-mountain ranges. Continental drift, faults and compressions, earthquakes, volcanicity, ocean transgression cycles and polar wandering are undoubtedly connected on a grand scale. Wegener's final revision came to the supporting evidence from many fields, including testimonials from scientists who found his hypothesis resolved difficulties in their problems much better than the old theories. Wegener considered such paleoclimatic validation one of the strongest proofs of his theory. Conversely, continental drift has since become the organizing principle of paleoclimatology and other paleosciences. Despite general rejection, Alfred's compelling concept continued to attract a few advocates over the next several decades. Then, beginning in the mid-1950s, a series of confirming discoveries in paleomagnetism and oceanography finally convinced most scientists that continents do indeed move and, just as Wegener had predicted, the movement is part of a grand scale process that causes mountain-building, earthquakes, volcanic eruptions, sea-level fluctuations, and apparent polar wandering as it rearranges Earth's geography. ...read more.

Conclusion

Problem explaining how convection involved both the asthenosphere and lower mantle and how heat is transferred from the outer core to the mantle. * Mantle Plumes - Hot spots, or plumes, of hot rising mantle material are known to exist around the world. Hot spots occur primarily at spreading centers (black smokers), although a few occur in the centers of oceanic plates and result in the formation of volcanic island chains. Hot plume upwarps overlying lithosphere which cracks and moves laterally away from the plume. Downward flow of the mantle must occur somewhere to balance the upward flow in the plumes. * Push-Pull Model - Lithospheric plates are pushed apart at hot spreading centers. Cold lithospheric plates are dense and tend to sink into the mantle, pulling the rest of the plate with it. Each part of the model can operate independently and are gravity driven. * Expanding Earth - Model holds that the Earth has expanded through its history, so that overall new crust is being created at spreading centers. Has few supporters. Would require a 50% increase in the volume of the Earth over the last 200 million years. ...read more.

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