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GEOG 2110L (50)


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University of Georgia
GEOG 2110L
David Stanley

PLATE TECTONICS ** The theory of global dynamics in which the lithosphere is believed to broken into individual pieces or plates that move in response to convection in the upper mantle. History of the theory: *** Alfred Wegener, a German meteorologist, gave it serious consideration in 1915, and was the first to suggest that continents were moving, and to supply some evidence for it. His Theory of Continental Drift took awhile to be fully accepted by the established scientific community * evidence: similarities of fossils, climate records, & geologic record between distant countries, esp. South America &Africa EX: * the land dwelling, mammal-like reptile Lystrosaurus, whose fossils have been found in SouthAmerica, Africa, Antarctica andAsia * mountain belts of similar age, rock sequence, fossils & structural style appear on both sides of the NorthernAtlantic (Appalachians & those of Ireland, Scotland & Norway) * Wegener proposed that one landmass existed about 200-225 MYBP (Triassic-Jurassic Periods) and called it Pangea. This began to split over the next 10-20 million years. * by about 135 MYBP (early Cretaceous) it had broken into 2 large pieces, Laurasia (basically present-day North America, Europe, &Asia) & Gondwana (the southern continents) * 1940-1960's,Atlantic Ocean floor mapping enhanced our knowledgeof tectonic processes * 1960's,Harry H. Hess & Robert S. Dietz proposed a theory of Sea-Floor Spreading * Sea-floor spreading: the movement of crustal material by the upwelling of magma along a system of mid-oceanic ridges KNOW THATTHE OLDEST ROCK IS 4 BILLION YEARS OLD * the upwelling pushes the crust away from the ridge * oldest crust is furthest from the ridge, newer crust closest * oldest sea floor dated so far formed ~200 MYBP * idea of magnetic reversals or paleomagnetism enhanced this theory * discovery of magnetic reversals, or paleomagnetism, tested and proved the theory of sea-floor spreading. Paleomagnetism refers to the magnetic alignment of charged particles (esp. Iron material) in the rock which exhibit a symmetrical pattern as you move away from the mid-oceanic ridge. The polarity, the orientation of positive(+) & negative(-) to the Poles of the Earth, changes as you move away from the mid-oceanic ridge because the rock cools/forms at different times. * By 1980's the theory ofPlate Tectonics had been developed, which combined the ideas of sea-floor spreading, continental drift, paleomagnetism and other ideas. Plate Tectonics: is the theory covering crustal movements and the foundation of crustal tectonic processes * Tectonic processes: upwelling of magma, plate movement, subduction of crust, folding, faulting, warping, fracturing, earthquakes, volcanic activity Distribution of Plates: * currently at least 20 - 22 plates are recognized, with 8 - 10 major plates * major plates: Pacific, N.American, S.American, Eurasian, African, Australian, Indian, Antarctic, Nazca * Several smaller plates: Cocos, Caribbean, Arabian,
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