Bellringer

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Bellringer

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

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Drifting Continents

• Notes

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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
  society.

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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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http//www.suu.edu/faculty/colberg/hazards/platete
ctonics/18_Pangaea.html
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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
  range.
• 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.

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Formation of the Appalachian Mountains
Matching Mountain Ranges across S. America and
Africa
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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
  hyposthesis.

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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.

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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.