Plate Tectonics - Plate Tectonics USGS Plate Tectonics...

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Plate Tectonics USGS
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Plate Tectonics Plate Tectonics - Earth’s surface is composed of a few large, thick plates that move slowly and change in size Intense geologic activity is concentrated at plate boundaries , where plates move away, toward, or past each other Combination of continental drift and seafloor spreading hypotheses
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Continental Drift Hypothesis Alfred Wegener ~1915 Continents fit together and drifted apart through time Hypothesis initially rejected
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Early Case for Continental Drift 1. Puzzle-piece fit of continents 2. Rock & Fossil evidence 3. Glaciation Patterns 4. Paleoclimate / Polar Wandering
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Early Case for Continental Drift 1. Puzzle-piece fit of coastlines of Africa and South America Supercontinent Pangea 225 mya Split into Laurasia & Gondwanaland 135 mya
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Early Case for Continental Drift 2. Fossil Evidence: South America, Africa, India, Antarctica, and Australia have almost identical late Paleozoic rocks and fossils Glossopteris (plant), Lystrosaurus and Cynognathus (animals)
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Early Case for Continental Drift 3.Late Paleozoic Glaciation patterns on southern continents best explained by their reconstruction into Gondwanaland
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Early Case for Continental Drift 4.Reconstructed paleoclimate belts suggested polar wandering, potential evidence for Continental Drift
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Early Case for Continental Drift Continental Drift hypothesis initially rejected No viable driving force continents should not be able to “plow through” sea floor rocks while crumpling themselves but not the sea floor
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Seafloor Spreading In 1962, Harry Hess proposed seafloor spreading Seafloor moves away from the mid-oceanic ridge due to mantle convection Convection is circulation driven by rising hot material and/or sinking cooler material
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Convection Convection is circulation driven by rising hot material and/or sinking cooler material Hot mantle rock rises under mid- oceanic ridge and sinks at the trenches after cooling
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Plate Tectonics - Plate Tectonics USGS Plate Tectonics...

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