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Ch. 6 Plate Tectonics
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6-1 Continental Drift Continental Drift theory that the continents were once a single land mass that broke apart Pangaea supercontinent
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Evidence of Continental Drift
South America & Africa look like they fit together Fossils of mesosaurus found in S. America & Africa
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Evidence of Continental Drift cont.
Mountains on different continents match U.S. & Canada match w/ Greenland & Europe Sizes of diamonds in Brazil & W. Africa match
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2 types of crust Continental Oceanic 6-2 Seafloor Spreading Less dense
More dense
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Mid-ocean ridge underwater mt. chain in the oceans
6-2 cont. Mid-ocean ridge underwater mt. chain in the oceans Rift crack Rift valley flat area btw. ridges
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New seafloor magma rises up through a rift
6-2 cont. New seafloor magma rises up through a rift Magma cools making new crust New crust pushes floor apart at ridges
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6-3 Evidence of Seafloor Spreading
Trench deep canyons in the ocean floor Most in the Pacific Ocean Old crust ends up in trenches Melts & becomes magma again
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Subduction zone area where crust is forced down in trenches
6-3 cont. Subduction zone area where crust is forced down in trenches Youngest fossils = closest to rift valleys, ridges, & trenches
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Tectonic plates the lithosphere broken into pieces
6-4 Plate Tectonics Tectonic plates the lithosphere broken into pieces 7 major plates & 8 minor plates Asthenosphere liquid part of the mantle
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Theory of Plate Tectonics explains how & why plates (continents) move
Lithosphere floats on asthenosphere
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Convection current less dense warm rises & denser cool sinks
6-5 Plate Tectonics Convection current less dense warm rises & denser cool sinks 3 types of plate boundaries Convergent Divergent Transform
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Transform 2 plates sliding past each other
6-5 cont. Transform 2 plates sliding past each other Cause earthquakes
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Convergent 2 plates move toward each other
6-5 cont. Convergent 2 plates move toward each other Oceanic + continental = oceanic subducts under the continental Continental + continental = mountain
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Divergent 2 plates move away from each other
6-5 cont. Divergent 2 plates move away from each other Cause rift valleys Cause seafloor spreading
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6-6 Effects of Plate Tectonics
Earthquakes plates slide past each other at a fault Mountains plates collide & buckle upward
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Volcanoes oceanic plate dips down & magma collects
6-6 cont. Volcanoes oceanic plate dips down & magma collects Hot spots place where magma reaches the surface Islands plates move over hot spots & volcanoes build
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