Pangaea
Alfred Wegener thought that the fit of the continents wasn’t just a coincidence. He suggested that all the continents were joined together at some point in the past. In a 1912 lecture, he proposed the idea of continental drift. According to the hypothesis of continental drift, continents have moved slowly to their current locations. Wegener suggested that all continents were once connected as one large landmass that broke apart about 200 million years ago. He called this large landmass Pangaea, which means “all land.”
Long after Wegener’s death in 1930, his basic hypothesis, that the continents have moved, was accepted. The evidence Wegener had to support his idea hadn’t been enough to convince many people during his lifetime. However, Wegener’s early evidence has since been joined by other important observations. Let’s explore both Wegener’s clues and some newer ones.
Fossil Clues
Besides the puzzle like fit of the continents, other clues were found from fossils. Fossils of the reptile Mesosaurus have been found in South America and Africa. This swimming reptile lived in
eroded material along and deposit it somewhere else. Glacial erosion and deposition change large areas of Earth.
Rock Clues
If the continents were connected at one time, then rocks that make up the continents should be the same. Similar rock structures are found on different continents. Parts of the Appalachian Mountains of the eastern United States are similar to those found in Greenland and western Europe. If you were to travel to eastern South America and western Africa, you would find rock structures that are similar. Rock clues like these support the idea that the continents were once connected.
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freshwater and on land. How could fossils of Mesosaurus be found so far apart? It’s unlikely that it could have swum between the continents. Wegener thought this reptile lived on both continents when they were joined as one giant landmass.
Another fossil that helps support the hypothesis of continental drift is Glossopteris. This fossil fern has been found in Africa, Australia, India, South America, and most recently in Antarctica.
The presence of this fern in so many areas led Wegener to suggest that all of these regions were once connected and had a similar climate.
Climate Clues
Glacial deposits and grooved bedrock found in South America, Africa, India, and Australia show that these continents were once covered with glaciers. How could you explain why glacial deposits were found in areas where no glaciers exist today? Wegener thought that these continents were all connected and covered with ice near Earth’s south pole at one time.
Glaciers
Glaciers are agents of erosion. As glaciers pass over land, they erode it, changing its features. Glaciers then carry
How could continents drift?
Although Wegener provided evidence to support his hypothesis of continental drift, he couldn’t explain how, when, or why these changes had taken place. Because other scientists at that time could not provide explanations either, Wegener’s idea of continental drift was rejected. The idea was so different that most people closed their minds to it.
Rock, fossil, and climate clues were the main lines of evidence for continental drift. After Wegener’s death, more clues were found and new ideas that supported continental drift were discovered. One of these new ideas, seafloor spreading, helped provide an explanation of how the continents could move.
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