Continental Drift

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Continental Drift

• Chapter 9.1

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The Continental Puzzle

• For 300 years, people noticed that the continents
  looked like pieces of puzzle
• In 1915, Alfred Wegener proposed that all the
  continents had been joined together to form one
  continent called, Pangaea.
• This hypothesis was called Continental Drift.

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Evidence for Continental Drift

• Matching Fossils
• Rock Types
• Ancient Climates

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Evidence 1 Matching Fossils

• Several fossil organisms found on different
  landmasses that could not have crossed the ocean
• Ex Mesosaurus, a fresh water reptile has fossil
  remains in South America and Africa
• Ex Glossopteris, a plant fossil found in South
  America, Africa, and India
• Ex Lystrosaurus, a land reptile. S.A. Africa

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How did they get there?

• Some thought that maybe the animals had crossed
  on land bridges that are now underwater.
• However, there are no signs of any land bridges
  in the Atlantic Ocean
• Wegener concluded that the landmasses had been
  joined in the past.

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Evidence 2 Rock Types

• If the continents were once part of Pangaea, the
  rocks found in a particular region on one
  continent should closely match in age and type
  the adjoining region
• Matching types of rocks in several mountain belts
  that are separated today be oceans are evidence
  of continental drift.

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Rock Type Example

• The Appalachians in North America and the
  Mountains in the British Isles and Scandinavia
• Rocks in those mountains are the same age and
  type
• Form a continuous belt if you put North America
  next to Europe.

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Evidence 3 Ancient Climates- Glaciers

• Between 220 mya and 300 mya ice sheets covered
  large areas of the Southern Hemisphere- South
  Africa, South America, India, Australia.
• If the continents had not moved, then the ice
  would have had to move from the sea to land (very
  unusual)
• The ice movement makes more sense if Pangaea had
  been connected with Antarctica

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Ancient Climates- Tropical Swamps

• Between 220 mya 300 mya there were tropical
  swamps in North America, Europe, and Siberia.
• Because it was warm in these areas at this time,
  Wegener decided that there was not an ice age
  causing the glaciers.