Continental driftnotes


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Continental driftnotes

  1. 1. In 1910, Alfred Wegener developed the hypothesis that all the continents had been joined together in a single land mass and have drifted apart.
  2. 2. This single land mass was called Pangaea (latin for “all lands”)
  3. 3. The idea that the continents are slowly drifting apart is known as continental drift. He published his evidence in a book called Origin of Continents and Oceans in 1915.
  4. 4. Evidence From Landforms • Wegener pieced together maps that showed mountain ranges that matched up in South Africa and South America.
  5. 5. European coal mines matched up with coal mines in North America. Original Pangaean Coal Deposits in the "Gray Band"
  6. 6. Evidence From Fossils •A fossil is a trace of an organism that has been preserved in rock. • Fossils for Mesosaurus and Lystrosaurus were found in places now separated by oceans.
  7. 7. Neither reptile could have swum long distances across salt water.
  8. 8. Evidence From Fossils • Another example was Glossopteris which is a fernlike plant that lived 250 million years ago. It was found in rocks in Africa, Australia, India and Antarctica. • The seeds of this plant could not have been carried by the wind and are too fragile to survive an ocean trip.
  9. 9. Evidence From Fossils • Wegener concluded that fossils of the reptiles separated by an ocean that they could not have swum and the widespread occurrence of the fern’s fossils supported his hypothesis of continental drift.
  10. 10. Evidence From Climate • Spitsbergen is an island in the Artic Ocean north of Norway. • The island is ice-covered with harsh polar climates. • Fossils of tropical plants were found on this island. When these plants lived 300 million years ago, the island must have had a warm and mild climate. •Wegener concluded that the island must have been located near the equator.
  11. 11. Evidence From Climate • Geologists also found evidence that at the same time it was warmer in Spitsbergen, it was much colder in South Africa. • There is evidence that continental glaciers once covered South Africa. •Continental Glaciers are thick layers of ice that covered hundreds of thousands of square kilometers. •The climate of South Africa today is too mild to have sustained continental glaciers.
  12. 12. Explanations • Wegener also attempted to explain how the drift took place and offer a new explanation for how mountains form. • He thought that when the drifting continents collide, their edges fold or crumble. •The folding continents slowly push up huge chunks of rock to form mountains.
  13. 13. Scientists Reject Wegener’s Hypothesis What forced or pulled the continents apart? Wegener thought there were centrifugal and tidal forces moving the continents, but had no mechanism to prove it. Other scientists calculated that these forces could never be strong enough to move land masses.
  14. 14. Scientists Reject Wegener’s Hypothesis Geologists would have to reject their own theories of how mountains form. The fact that his work crossed disciplines exposed him to the territoriality of those disciplines. The authorities in the various areas attacked him as an interloper that did not fully grasp their own subject. More importantly however, was that even the possibility of Continental Drift was a huge threat to the established authorities in each of the disciplines. One of Alfred Wegener's critics, the geologist R. Thomas Chamberlain, could not have summarized this threat any better : "If we are to believe in Wegener's hypothesis we must forget everything which has been learned in the past 70 years and start all over again."
  15. 15. Scientists Reject Wegener’s Hypothesis Geologists in the early 1900 thought that the Earth was cooling and shrinking. It suggested that the Earth had been in a molten state, and features such as mountains formed as it cooled and shrank. As the interior of the Earth cooled and shrank, the rigid crust would have to shrink and crumple. The crumpling could produce features such as mountain ranges. True geologists were unwilling to believe that the evidence already collected about mountain formation could be explained away by an unqualified scientist (Wegener was a trained astronomer and meteorologist, not geologist).
  16. 16. Scientists Reject Wegener’s Hypothesis • According to this idea, Wegener said the crust would wrinkle all over the Earth. • Wegener noted that mountains are formed in narrow bands along the edges of the continents. • Wegener’s theory was rejected until the 1950s when new evidence about the Earth’s structure caused scientists to reconsider the hypothesis.