Continental Drift

Continental Drift - Continental Drift - Wegener The Origin...

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Continental Drift - Wegener “The Origin of Continents and Ocean” - Wegener proposed supercontinent of Pangea o Breakup about 20,000 yrs ago o Spead about 30m. year o Continents “float” on top of oceanic crust o Jigsaw puzzle fit of continents o Similar rock assemblages across ocean - When Wegener hypothesized continental drift, he thought which of the following about continents? o They “float” on top of oceanic crust o They used to be closer together than they are today Why Continental drift didn’t work o No sufficient force to move continents o Additional evidence drives new ideas: Convection in the mantle Seafloor spreading Plate Tectonics o Identifying seafloor spreading Seafloor is made of young basalt Mapping of long “crack” running through the Atlantic Later became known as the Mid-Atlantic Ridge Marie Tharp thinks the long crack is a rift valley o The crust is separating and pulling apart o She is initially dismissed o Almost all earthquakes in Atlantic Ocean are along the “crack”
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o b/c earthquakes are produced during active faulting, the “crack” must be active o Marie Tharp is vindicated Hess and Dietz, early 1960s o Crust seperates at mid-ocean ridges o New crust is formed by upwelling magma o New seafloor spreads away from rift o If crust is always being formed at mid ocean ridges, is the earth expanding? Or is the seafloor being recycled somewhere? o Ocean crust is being recycled o Related to intense volcanism and earthquakes o C oncentrated on margins of the Pacific Ocean- “The Ring of Fire” The Theory of Plate Tectonics o The
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This note was uploaded on 09/14/2011 for the course GEO 1010 taught by Professor Rogers during the Spring '11 term at Missouri (Mizzou).

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Continental Drift - Continental Drift - Wegener The Origin...

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