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Tuesday, April 18, 2023
The Earth’s Crust
The Theory ofContinental Drift
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Alfred Wegener – a German scientist who proposed (in 1915) that the continents were slowly drifting apart (the theory of continental drift)
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Wegener said that all of the continents were once joined together in a supercontinent (which he called Pangaea) which existed about 200 million years ago.The continents then broke apart and drifted to where they are today.
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Evidence:1. Fit of the Continents The coastlines of Africa and South America looked like they fit together.
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Wegener then noticed that the other continentslooked like they could have fit together too.
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2. Fossil Evidence - fossils of the same plants and animals are found today on widely separated continents (including Africa, South America, Antarctica, Australia, and Asia – India)
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Mesosaurus - fossils have only been found in South America and Africa.
Mesosaurus was a fresh water reptile so it’s difficult to imagine him migrating across the ocean.
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Lystrosaurus - fossils of this little land reptile were found in Africa, India and Antarctica!
It would have been even harder to imagine Lystrosaurus swimming across an ocean.
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Cynognathus – fossils of this creature are found in Africa and South America
It’s unlikely Cynognathus could have made it across the ocean either.
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Glossopteris – fossils of this tropical tree are found in South America, Africa, India, Australia and Antarctica!
That’s one mobile tree!
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Of course, none of these living things had to move anywhere if Wegener were right.
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If the continents had been together as Wegener claimed, then the animals that became fossils would have been living close together…
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…and then been split apart as the continents moved.
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This animation shows the pre-driftlocations of Glossopteris and
Lystrosaurus.
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3. Mountain chains - match up on each side of the Atlantic Ocean The Appalachian Mountains seem to end in North America… …but mountains in Europe are the same age.
Appalachian Mountains
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And if the continents are put back to their pre-drift locations the mountains form a continuous chain.
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4. Climate Evidence- evidence of glaciers on the equator and tropical forests in the arctic.
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We find evidence of glaciers along the equator (the warmest area of the planet)….
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…and fossils of tropical rain forests in New Brunswick, northern Canada and northern Europe.
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Again, it doesn’t make much sense unless the continents are moved back to their pre-drift location.
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Now the glaciers are near the pole and the palm trees are on the equator.
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In spite of this evidence, the scientific community rejected Wegener’s ideas and he was forgotten for almost fifty years. (He couldn’t explain how the continents moved)
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http://kids.earth.nasa.gov/archive/pangaea/Pangaea_game.html
http://www.scotese.com/pangeanim.htm
World Geography Quiz
http://www.pbs.org/wgbh/aso/tryit/tectonics/intro.html
If you finish early check these sites: