What evidence did Wegener use to support his theory of continental drift?
Alfred Wegener used several lines of evidence to support his theory of continental drift:
1. Fit of the Continents: Wegener noticed that the coastlines of Africa and South America appeared to fit together like puzzle pieces. He argued that the matching shapes of these continents suggested they were once connected as part of a larger landmass.
2. Fossil Evidence: Wegener found similar fossilized plants and animals on different continents that are now far apart, such as the Glossopteris fern. These fossils suggested that the continents were once joined because the organisms couldn't have traversed vast oceans.
3. Rock and Mountain Chains: Wegener observed that certain mountain ranges and rock formations had corresponding geologic features on both sides of the Atlantic. He noted the similar structure and age of the Appalachian Mountains in eastern North America and the Caledonian Mountains in Europe. Such similarities implied a common geological history.
4. Paleoclimatic Evidence: Wegener proposed that past climate data could support continental drift. For example, glacial deposits, striations, and ancient coal beds were found in areas that are currently located in tropical or subtropical zones, indicating that these regions were once near the poles within ice sheets.
By combining these pieces of evidence, Wegener formulated the theory of continental drift, suggesting that the continents were once joined together in a supercontinent called Pangaea and gradually drifted to their present-day positions.
Alfred Wegener proposed the theory of continental drift in the early 20th century. He gathered several lines of evidence to support his theory, which revolutionized our understanding of Earth's geology. Here are the main pieces of evidence Wegener used:
1. Continents Fit: Wegener observed the remarkable fit between the coastlines of the eastern coast of South America and the western coast of Africa. The jigsaw-like fit suggested that the continents could once have been connected.
2. Similar Fossil Distributions: Wegener noticed similarities in the fossil assemblages found on the east coast of South America and the west coast of Africa. For example, fossils of the ancient reptile Mesosaurus were found in both regions, indicating that these areas were once joined.
3. Matching Rock Formations: Wegener compared rock formations on opposite sides of the Atlantic Ocean, which showed remarkable similarities. For instance, the Appalachian Mountains in Eastern North America aligned well with the Scottish Highlands.
4. Glacial Striations: The presence of glacial striations, scratches left behind by glaciers, on different continents, indicated that large ice sheets had once covered areas that are now widely separated, such as Africa, India, and Australia.
5. Paleoclimatic Evidence: Wegener utilized evidence from ancient climate indicators like coal deposits and the distribution of certain land-dwelling reptiles, which were incompatible with their current locations but made more sense if the continents were once closer to the poles.
To support his theory of continental drift, Wegener compiled these various lines of evidence from different scientific disciplines such as geology, paleontology, and climatology. It was through the accumulation and synthesis of this evidence that Wegener proposed his groundbreaking theory.