1. The Fit of the Continents:
* Geographic Fit: Wegener observed that the coastlines of South America and Africa seemed to fit together like puzzle pieces, especially along the continental shelf. He pointed out that the coastline fit better when considering the submerged shelf rather than just the visible coastline.
2. Fossil Evidence:
* Matching Fossil Distributions: Wegener found identical fossils of plants and animals on continents that are now separated by vast oceans. For example, fossils of the reptile *Mesosaurus* were found in both South America and Africa. This suggested that these continents were once connected, as it was unlikely these creatures could have crossed vast bodies of water.
* Glacial Evidence: Wegener noticed that glacial deposits from the late Paleozoic era (about 300 million years ago) were found in South America, Africa, India, Australia, and Antarctica. The pattern of these deposits indicated a single, large ice sheet that covered the southern continents. This was only possible if these continents were clustered together near the South Pole.
3. Rock Formations:
* Matching Rock Formations: Geological formations, like mountain ranges and rock types, were found to match across continents separated by oceans. For example, the Appalachian Mountains in North America have similar rock types and structures as mountains found in Scotland and Greenland. This suggested a common origin for these landmasses.
4. Paleoclimate Evidence:
* Climate Indicators: Wegener observed evidence of tropical climates in regions currently located in temperate or even polar zones. For example, coal deposits (formed in warm, swampy environments) were found in Antarctica, indicating a different climate in the past. This provided further evidence that the continents had shifted their positions over time.
Wegener's challenges:
While Wegener presented a compelling argument, his theory faced initial resistance from the scientific community. The primary criticism was that he couldn't provide a plausible mechanism for how the continents could move through solid rock. This mechanism wouldn't be discovered until the development of the theory of plate tectonics decades later.
Plate Tectonics:
The theory of plate tectonics, developed in the 1960s, provided the missing mechanism. It explained that the Earth's outer layer is composed of large plates that move on a semi-molten layer called the asthenosphere. This movement, driven by convection currents within the mantle, is what causes continents to drift. Wegener's observations provided the foundation for plate tectonics, which has since become the widely accepted explanation for the movement of continents and the formation of mountains, earthquakes, and volcanic activity.
