Objectives- describe continental drift and the evidence for it; explain why continental drift was rejected
In 1910, a German scientist named Alfred Wegener proposed a theory called continental drift. The theory says that all the landmasses were once together forming a giant continent called Pangaea and have slowly drifted to their current locations.
Wegener had lots of indirect evidence for the theory. But that is where the problem was. The evidence was indirect. Indirect evidence uses logic to prove something. The evidence needs interpretation.
One piece of evidence was from landforms. Included in landforms clues is the puzzle like fit of the landmasses. Africa would fit into South and North America. North America and Europe would fit together. Another piece of evidence was the mountain ranges on the continents and rock types more or less match up when the landmasses are together. In addition to the mountain chains matching up, so do rock types and rock layers.
Fossils also provide clues to support Wegener’s theory. If you think about the types of plants and animals on each continent, they are different than those on other continents. So finding the same types of fossils on different continents is unlikely. But that is what was found. This was true for both plants and animals. Wegener suggested that the only this could have happened was if the landmasses were together.
A third type of evidence presented by Wegener was climate clues. Would you expect to find signs of glaciers in Africa, India or Australia? Maybe not but they exist. What about coal in the Artic regions? Coal forms when large swampy forests die. Such forest can only live in warm humid climates, certainly not what is found there today. One of two things had to happen so both of these could occur. Either worldwide climates have changed or as Wegener suggested, the continents have moved.
If just one or two pieces of the evidence were looked at, it would be easy to say the relationship between it and continental drift was purely coincidental. But when all the evidence is looked it, it is much harder to dismiss. However Wegener lacked one thing that prevented the scientific community from accepting the theory. What was lacking was how the landmasses could move across the surface of the earth.
1. In your own words, what did the Theory of Continental Drift state.
2. Wegener named his supercontinent ______________.
3. What did Wegener think had happened to this supercontinent?
4. What were the three categories of evidence Wegener used to support his theory?
5. Give an example of evidence from landforms that supported Wegener’s idea of continental drift.
6. Why was Wegener’s theory rejected?
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