Continental Drift

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Continental Drift
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Evidence Fossils
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Evidence Rock Sequences
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Evidence Glaciation
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Evidence Glaciation (contd)
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Evidence Rock Types/Climates

• glacial till striations (scratches on rock)
  polar climate
• sand dunes desert climate
• coral reefs tropical climate

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Evidence Rock Types/Climates
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Evidence Polar Wander??
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Uh-Oh! Problems with Continental Drift.
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an alternate explanation?
1928 Arthur Holmes suggested fluids rise toward
the crust, spread, and sink again. 1930 Wegner
dies, unable to adapt Holmes idea to his theory.
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Mantle/Crust Structure
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Earths Structure
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A New Hope Sea-floor Spreading
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Testing the model.
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Paleomagnetic reversals.
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The seafloor spreading model is confirmed!
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Todays model
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Boundaries Converging
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Boundaries Diverging
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Boundaries Transform
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So, what causes plates to move?

• Convection currents drag and move the
  lithospheric plates above the asthenosphere
• (three sources of heat produce the convection
  curents)
• cooling of Earths core
• radioactivity within the mantle/crust
• cooling of mantle

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Convection Cells
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Convection Cells
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SUMMARY OF P.T.

• The plate tectonic model suggests
• (1) continents can move across the surface of the
  globe
• (2) patterns of volcanism can change and shift
  across the globe as plates and their boundaries
  evolve and move
• (3) new oceans may grow
• (4) oceans basins close and are deformed to
  produce mountains