Wegener · Continental drift
If continents move, what is pushing them?
That time, that place
Wegener was a meteorologist who once set a record by staying aloft in a balloon for fifty-two hours. That he was not a geologist would matter later.
That the coastlines on either side of the Atlantic fit like puzzle pieces had been noticed long before, and was generally put down to coincidence.
Why this question
He was not only looking at the shapes of coasts.
Rock formations in Brazil and Africa continue across in type and in age. The same fossils appear on both sides of the Atlantic, including freshwater reptiles that could not have swum it. Mountain ranges break off on one continent and resume on the other.
Any one of these might be coincidence. All of them cannot be.
What was found
The conclusion was that the continents had once been one and had drifted apart.
Evidence was ample. The problem lay elsewhere: what pushed them?
He proposed the centrifugal effect of the Earth's rotation and lunar tidal forces. Calculated out, those forces fall hopelessly short. Geologists went straight at that point, and at an American meeting the criticism came close to ridicule.
A theory with evidence and no mechanism.
The continents were fixed where they are
Matching strata, fossils of creatures that could not cross an ocean, and mountain ranges that resume across the sea
He died on the ice during a Greenland expedition, just after his fiftieth birthday. In the 1950s and 60s, seafloor mapping and rock magnetism confirmed he had been right. What moved the continents was convection in the mantle