1. What are some of the evidence that led Wegener to propose his theory, why it met with hostility and why the theory was revived in the 1950’s?
Wegener's theory has to with tectonic plate motion being a primary cause of earthquakes. The location of most strong earthquakes and volcanic activity along so-called "rings of fire" is strong evidence that he was correct. His theory was rejected because Wegener was not a geologist. He was trained in another field, which I believe was fluid mechanics, Check his biography.
Alfred Wegener proposed the theory of continental drift in the early 20th century, suggesting that the continents were once connected and had been slowly drifting apart over millions of years. The theory faced hostility initially but was eventually revived in the 1950s due to several reasons.
1. Evidence for Continental Drift:
a. Fit of the Continents: Wegener noticed that the coastlines of South America and Africa fit together like pieces of a puzzle. He argued that such correspondence was unlikely unless the continents were once joined.
b. Fossil Distribution: Similar fossils of plants and animals were found on different continents that were now separated by vast oceans. For example, fossils of the freshwater reptile Mesosaurus were discovered in both South America and South Africa, suggesting that these continents were once connected.
c. Rock Strata and Mountain Chains: Wegener observed that certain geological formations and mountain ranges, such as the Appalachian Mountains in the eastern United States and the Caledonian Mountains in Europe, matched across continents. He argued that these formations were connected before the continents separated.
d. Paleoclimate Evidence: The presence of ancient glacial deposits in tropical regions, such as India, and coal deposits in Arctic regions, such as Antarctica, indicated that these areas had different past climates. This evidence supported the idea that the continents had moved.
2. Hostility towards the Theory:
a. Lack of Mechanism: Wegener proposed that the continents plowed through the oceanic crust to move, but he couldn't provide a convincing mechanism to explain how this occurred. Without a plausible explanation, many scientists dismissed the idea.
b. Rejection of New Ideas: In the early 20th century, the scientific community was skeptical of new theories that challenged well-established beliefs. Wegener's ideas contradicted the prevailing belief in the fixity of continents, leading to resistance and hostility from many geologists.
3. Revival in the 1950s:
a. Paleomagnetism: The discovery of paleomagnetism provided evidence that supported Wegener's theory. Scientists found that Earth's magnetic field has reversed over time, leaving magnetic imprints in rocks. By studying the distribution of these magnetic imprints on different continents, researchers found that the rocks matched up when the continents were rearranged to form a supercontinent called Pangaea.
b. Seafloor Spreading: In the 1950s, evidence emerged for seafloor spreading, a process where new crust forms at mid-ocean ridges and spreads outward. This provided the missing mechanism in Wegener's theory. As new crust was created, it pushed the continents apart, explaining how they moved.
c. Plate Tectonics: The combination of paleomagnetism, seafloor spreading, and other geological observations led to the development of the theory of plate tectonics. This comprehensive model explained the movement of continents, the formation of earthquakes and mountains, and other Earth processes. Plate tectonics gained broad acceptance in the 1950s and is now a fundamental concept in geology.
In summary, Wegener's theory of continental drift faced hostility due to a lack of a plausible mechanism and resistance to new ideas. However, the theory was revived in the 1950s when new evidence, such as paleomagnetism and seafloor spreading, provided the missing pieces of the puzzle and led to the development of the theory of plate tectonics.