Alfred Wegener's Theory of Continental Drift
- Track Progress
- 0:05 Background on the Ground
- 0:54 Alfred Wegener
- 1:21 Fossil Evidence
- 2:37 Other Clues
- 3:28 Trouble with the Theory
- 4:26 Lesson Summary
People used to think that the Earth was static, and that it never changed. Gradually, a body of evidence was gathered that made no sense in this model. Alfred Wegener, Geologic Supersleuth, laid the groundwork for a whole new theory for the large-scale changing nature of the earth.
Background on the Ground
Have you ever had the experience where you see a younger relative or friend after not seeing them for a few years, and you're taken aback at how much they have grown? We have an image in our minds as to what they looked like the last time we saw them, and they are much different. If the continents of the earth move and grow, why don't we notice that? Well, for two reasons. One, we really don't see what whole continents look like in real time, and two, they move so slowly that people die before any noticeable changes can take place.
As far back as 1620, people often noticed that the coastlines of North and South America looked like they fit together with Europe and Africa. These observers noticed these coastlines but had no easy explanation for how that could have occurred since everyone believed the continents were stationary. Solving this mystery would take the work of a geologic supersleuth.
Alfred Wegener, the Geologic Supersleuth
Alfred Wegener, a German meteorologist, was the first to begin to work out details to explain this interesting observation. To begin with, the current geologic theory was that the crust was all stationary, and continents were relatively unchanging - they didn't move around.
Alfred Wegener knew that other people had made observations of the fit of the coastlines. He accidentally became drawn in to that topic by discovering evidence that might explain that phenomenon.
In the fall of 1911, though, he came across a scientific paper that described the locations of identical plant and animal fossils on very different continents.
These fossils included mesosaurus, which was a freshwater reptile, lystrosaurus, a land reptile, cynognathus, a land reptile, and glossopteris, which was a tropical fern.
These were on very different continents, and he wondered how could these same plants and animals be on such different land masses? How could they have migrated over such vast distances or survived in such harsh conditions? The current theories were that the continents were connected by land bridges that have since eroded away or by stepping-stone islands. (Stepping-stone islands would be a series of islands that traversed the ocean.)
Wegener developed a much simpler hypothesis that stated perhaps the continents were all together at one point, thereby also explaining the fit of the coastline.
He then theorized a supercontinent he named Pangea, which meant 'one earth'. He realized, though, that if this idea were to be accepted, he would need much more supporting data than he had (just fossils and fits of coastlines).
Other clues came from more research. He discovered that in his Pangea model, large geologic features such as mountain ranges on separate continents often lined up closely. Rock strata from Africa and South America also matched when placed together with South America and Africa lining up.
Puzzling data of fossils of plants and animals found in climates where they could never have survived was also explained, similar to the glossopteris tropical ferns growing in Antarctica. Coal was found in Antarctica and Britain, areas that could never support coal formation today.
Putting all this data together, Wegener concluded that the continents were at one time all together in a giant supercontinent and that somehow they broke apart and migrated to their present location.
Trouble with the Theory
There was some trouble with this theory, though. He called this theory continental drift and talked to many other scientists and geologists about it. His theory overall was soundly rejected, and often in harsh and scathing language. The big problem was that Wegener had no convincing evidence for how the continents might actually move from place to place.
He thought the continents broke through the ocean floor much like an icebreaker plows its way through an ice sheet. There was some scattered support for his theory, but he passed away before the discoveries that would provide the mechanism for his theory and ultimate acceptance. As countries began to map the ocean floor after World War II, additional surprising clues from the geography of the ocean floor were brought to the surface, which would ultimately provide a mechanism for his theory and lead to ultimate vindication. These included underwater mountain ranges and the separation of the ocean floor at giant cracks.
Many people had observed clues about the earth's past and could not put them together to solve the puzzle about how the earth operated or how continents moved. Based on the fit of the coastlines, fossil evidence, rock types, and mountain ranges found on separate continents, Alfred Wegener developed a new theory he called 'continental drift'. Unfortunately, he failed at convincing the jury of public opinion that he was on the right track, but ultimately, this geologic supersleuth would be proven correct by future discoveries from the ocean floor.
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- 2. Properties of Matter (10 lessons)
- 3. Fundamentals of Thermodynamics (13 lessons)
- 4. Mechanics (7 lessons)
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- 21. Ecology (11 lessons)
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