Continental Drift: The Beginning of Plate Tectonics

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Continental DriftThe Beginning of Plate
Tectonics
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Theory of Continental Drift
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Continental Drift

• Theory that the continents are drifting apart and
  towards each other
• Alfred Wegener
• Idea that all continents were all pieced together
  245 million years ago
• Pangaea All Earth

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Continental Drift
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Argument for and against Continental Drift

• Same fossils on different Continents
• Rock formations
• Climate conditions evidence
• Glacial grooves on separated continents

• Species could travel over bridges
• Rock cycle occurs
• Climate has cycles
• Glaciers covered majority of Earth

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Ultimate Question

• How could gigantic continents move?
• What natural force could move entire continents?

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An Answer Sea Floor Spreading

• Process in which new oceanic lithosphere is
  created as older material is pulled away
• Process forces tectonic plates away from each
  other
• Creates mid-ocean ridges which are underwater
  mountain chains

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Sea-Floor Spreading
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Evidence for Sea-Floor Spreading

• Eruptions of molten material
• Magnetic strips in the rock of the ocean floor
• Ages of rock from drill samples

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Magnetic Reversals

• Earths magnetic poles change place
• Mineral grains of molten rock align to the poles
  of Earth
• Rocks freeze trapping history of magnetic
  reversals

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Question ????

• If new crust is being made at mid ocean ridges
  and the sea floor is spreading, then why isnt
  the Earths surface getting larger?

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Subduction at Plate Boundaries

• Subduction is a process in which the dense ocean
  floor sinks back into the mantle
• Occurs at deep-ocean trenches
• Convergent boundaries

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Quiz

• What are the three layers of the Earth Based on
  Composition?
• What are the 5 layers based on Structure?
• What is Pangaea?
• What process showed Continental Drift is correct?