Wegener knew most people would find it hard to believe that the continents were drifting, so he worked hard to collect evidence to support his claim. He looked at the shape of the continents, rock types, distribution of fossils, and ancient climates.
Wegener pointed out that some of the continents look like they could be fitted together, like the pieces of a jigsaw puzzle. For instance, the eastern coast of South America and the western coast of Africa look like two matching pieces of a puzzle.
But Wegener went beyond looking at shapes. He also looked at geological features. He found that the geological features along the western coast of Africa corresponded quite closely with those along the eastern coast of South America. Wegener said the geological features of the two continents fit together like the two halves of a torn newspaper: "It is just as if we were to refit the torn pieces of newspaper by matching their edges and then check whether the lines of the print run smoothly across. If they do, there is nothing left but to conclude that the pieces were in fact joined in this way."
Wegener applied the same logic to other continents. He reasoned that, if North and South America were once joined with Africa, Europe, and Asia, then there should be similar rock formations on these now separate continents. Wegener did some research and found that some rock formations were in fact similar. The Appalachian Mountains in North America were about the same age and contained the same kinds of rocks as the mountains in Scotland and those in Scandinavia. Looking at the current configuration of the continents, you would not guess that these mountains have anything in common. They look like three completely distinct mountain ranges. But Wegener argues that the geological similarities showed that these mountains once mad up a single, continuous mountain range. You can see this ancient chain of mountains on Wegener's map of the "pre-drift" locations.
Wegener also presented fossil evidence to support his theory. He pointed out that identical fossils can be found on continents that are now separated by vast expanses of ocean. For example, fossil remains of the Mesosaurus, a small crocodile-like reptile, are found on the coast of South America and also along the coast of Africa. The Mesosaurus is not thought to have been a good swimmer - certainly not good enough to have crossed the huge expanse of ocean that currently separates the two continents. The more likely explanation was that, during the age of the Mesosaurus, the two continents were connected.
Fossils of the fern Glossopteris provided Wegener with additional evidence for Pangaea. Glossopteris thrived in cool climates 200 million years ago. Fossil imprints of Glossopteris have been discovered in Antarctica, but also in South America, Africa, India, and Australia. Glossopteris fossils are found in climates that are now too warm for the fern to grow. Wegener argued that all these land masses were once joined together in a cool climate that allowed Glossopteris to flourish.
Wegener also pointed to data about ancient climates. Rocks in South America, Africa, India, and Australia showed signs of having once been covered with glaciers. But scientists found it hard to explain how warm areas far from the poles - places like Africa and India - could have been covered with glaciers. Wegener explained this by suggesting that millions of years ago these landmasses were part of Pangaea and were closer to the South Pole.
Despite all the evidence Wegener gathered, he was not able to convince many scientists that continents drift. When he died in 1930, most scientists still scoffed at his hypothesis. One of the main objections to Wegener's hypothesis was his inability to explain how continents move across the ocean floor. Wegener suggested that continents plow through the oceanic crust, much as an ice breaking ship cuts through ice. However, there was no evidence that the ocean floor was weak enough to allow the continents to plow through without breaking up the ocean floor in the process; nor could Wegener point to a force strong enough to do this.
Key Notes:
- Wegener worked hard to collect evidence to support his theory - looked at continental shape, rock types, location of fossils, ancient climates, and geological similarities
- North and South America once connected to Africa, Europe, and Asia - research showed all have some rock formations
- Appalachian Mountains in North America is about same age and contains same type of rock as Scotland and Scandinavia - once was a single mountain range
- Wegener found identical fossils on different continents that are now separated
- Mesosaurus: small crocodile-like reptile found in South America and Africa - not a good swimmer
- Glossopteris: fern thrived in cool climate 200 million years ago - found in Antarctica and South America, Africa, India, and Australia
- South America, Africa, India, and Australia was once covered by glaciers
- Wegener died in 1930 - other scientists still did not believe him because he couldn't explain how the continents moved across the ocean floor.
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