The Dynamic Earth @ National Museum of Natural History

Main Menu > Plate Tectonics and Volcanoes > Geological Revolution > Continents Adrift?

What Did Earth Look Like 200 Million Years Ago?
Most of the land was concentrated in a single supercontinent. Plate tectonics explains how it broke up into today's continents. About 200 million years ago, it broke into pieces that drifted apart and eventually became today’s continents. This idea became known as the theory of continental drift.
Throughout history, people assumed that the continents were fixed in place. In 1912, German meteorologist Alfred Wegener challenged this prevailing notion. He argued that today's continents were once part of a supercontinent called Pangaea, from the Greek words meaning "all Earth."

Wegener’s Evidence

Studying global maps, Wegener noticed (like others before him) that Africa and South America look like pieces of a jigsaw puzzle. The widespread distribution of certain rock formations and fossils often in unlikely places further convinced him that all the continents had once been joined.

"It is just as if we were to refit the torn pieces of a newspaper by matching their edges, and then check whether the lines of print run smoothly across. If they do, there is nothing left but to conclude that the pieces were in fact once joined in this way."
– Alfred Wegener

Ludicrous or Prophetic?

"Can geology still call itself a science, when it is possible for such a theory as this to run wild?"
– Rollin T. Chamberlain, University of Chicago, 1928

Wegener's theory was widely ridiculed particularly in the U.S. The chief criticism was that he failed to adequately explain what forces caused continents to drift.

"I believe that the final resolution of the problem can come only from geophysics, since only that branch of science provides sufficiently precise methods."
– Alfred Wegener, 1927

When geophysicists began probing the ocean floor several decades later, Wegener’s ideas were shown to be basically correct.