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Name seven different layers of Earth in DECREASING order of DENSITY. Then name the primary component(s) that make up each layer. Drifting Continents Notes Continental ... – PowerPoint PPT presentation

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Title: Bellringer

  • Name seven different layers of Earth in
    DECREASING order of DENSITY. Then name the
    primary component(s) that make up each layer.

Drifting Continents
  • Notes

Continental Drift
  • Some continents appear to be shaped like puzzle
    pieces. For example the west side of Africa and
    the east side of South America look like matching
    puzzle pieces.

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Continental Drift
  • Scientists Alfred Wegener tried to explain why
    continents are shaped the way that they are.
  • Until the 1900s scientists thought that the
    continents had always remained in the same place.
  • Even then it wouldnt be until the 1970s until
    the idea was firmly planted into mainstream

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Continental Drift
  • Wegener thought that Earth had one big continent
    about 300 million years ago. The big continent
    broke into smaller pieces and formed smaller
    continents. The continents slowly drifted apart.
    Wegener called this continental drift.
  • According to Wegener, the continents has drifted
    together to form the supercontinent Pangea and a
    single superocean called Panthalassa.

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Continental Drift
  • Evidence shows that continental drift really
    happened. Mountain ranges in Africa and South
    America as well as North America and Africa line
    up as if they were once part of the same mountain
  • At the time, most scientists believed that
    mountains formed because Earth was still cooling
    and shrinking, causing the surface to wrinkle
    like that of a dried-up apple.
  • Wegener claimed that if this were the case, then
    mountains would be everywhere. He proposed that
    because mountain ranges usually occur near
    continental edges, then they formed when
    continents collided with each other.

Formation of the Appalachian Mountains
Matching Mountain Ranges across S. America and
Continental Drift
  • Wegener also used the existence of specific
    fossils spanning multiple continents that are now
    separated by vast oceans as evidence that the
    continents were once connected.
  • His primary fossil was Glossopteris, a fern-like
    plant that lived 250 million years ago, and can
    be found on Africa, S. America, Australia, India
    and Antarctica.
  • The existence of Mesosaurus and Lystrosaurs
    across many continents also supported Wegeners

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Continental Drift
  • Wegener also used evidence from climate change to
    support his hypothesis. As a continent moves away
    from the equator, its temperature will drop. As a
    continent moves towards the continent, its
    temperature will increase.
  • Tropical plant fossils have been found in islands
    above the Arctic Circle, meaning that at one time
    that landmass was in a much warmer climate.

Continental Drift
  • Large scratches in the bedrock of South America
    prove that at one point in its history, S.
    America was once much close to the south pole.
    These scratches only appear where continental
    glaciers once existed on top of the land.
  • Currently both Greenland and Antarctica are
    covered by continental glaciers. As the glaciers
    melt in the summer months, they leave behind
    large scratches or grooves in the rocks over
    which they once covered.

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Wegeners Hypothesis Rejected
  • Despite all of his evidence, Wegener could not
    explain what causes continental drift. He saw
    that it did indeed happen, but he couldnt
    explain how or why.
  • His original idea had the continents plowing
    through the ocean floor. (oops)
  • Because he did not have a fully developed idea,
    most other scientists of his time thought that he
    was wrong.
  • More evidence would be required before Wegeners
    ideas would be accepted.
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