Describe the evidence that supported the hypothesis of Continental Drift.
http://www4.uwsp.edu/geo/faculty/ozsvath/lectures/continental_drift.htm
http://www.scientus.org/Wegener-Continental-Drift.html
http://www.enchantedlearning.com/subjects/dinosaurs/glossary/Contdrift.shtml
The theory of Continental Drift, proposed by Alfred Wegener in the early 20th century, suggests that the Earth's continents were once joined together in a single landmass called Pangaea, which later broke apart and drifted to their current positions. This hypothesis revolutionized the field of geology and laid the foundation for the modern theory of plate tectonics. The evidence supporting the hypothesis of Continental Drift can be categorized into four main types:
1. Fit of the Continents: Wegener noticed that the shape of the continents on both sides of the Atlantic Ocean appeared to fit together like puzzle pieces, especially the east coast of South America and the west coast of Africa. This observation hinted at the possibility of them being connected in the past.
2. Fossil Evidence: Wegener found several matching fossils of plants and animals on widely separated continents. For example, the fossils of the reptile Mesosaurus were discovered in both South America and Africa. These organisms were not capable of crossing vast oceans, suggesting that the continents were once connected and then drifted apart.
3. Rock Types and Geologic Formations: Similar rock types, geological features, and mountain ranges were found to span across continents that are currently separated by oceans. For instance, the Appalachian Mountains in eastern North America matched the Caledonian Mountains in Europe. The presence of these similar structures provided evidence that the continents were once joined together.
4. Paleoclimate Evidence: Further support for Continental Drift came from the examination of ancient climate indicators preserved in ancient rocks and fossils. Ancient glacial deposits, such as striations and tillites (rocks formed from glacial debris), were found in regions that presently have tropical or temperate climates, like India and Australia. This evidence suggested that these continents were once located closer to the South Pole and moved to their present positions.
It is crucial to note that while the evidence supported the theory of Continental Drift, the mechanism behind the movement of the continents was not understood until the development of plate tectonics in the mid-20th century. Plate tectonics provided a comprehensive explanation of how and why the continents drift, with their movements driven by the motion of Earth's rigid lithospheric plates.