Alfred Wegener and the Theory of Continental Drift

In the late 1800s, a German scientist named Alfred Wegener proposed a theory that all the continents had once been joined together in a single landmass he called Pangea.

Wegener based his hypothesis on several lines of evidence.

• First, he noted that the east coast of South America seems to fit snugly against the west coast of Africa, as if they were once connected.
• Second, he found ancient fossilized plants and animals in rocks from different continents that were very similar to each other—too similar to be explained by chance. For example, fossils of Mesosaurus, a reptile that lived in fresh water, have been found on both South America and Africa.
• Third, Wegener found evidence that Earth's climate had been more uniform in the past than it is today. For example, glaciers once covered areas near the equator—something that would be impossible under today's climate conditions.

Based on this evidence, Wegener concluded that all the continents had once been joined together in a supercontinent he called Pangea (pronounced pan-jee-uh). The name comes from two Greek words: pan meaning all and gaia meaning Earth. According to Wegener's theory, over time Pangea broke apart and the continents slowly drifted to their present locations.

Wegener presented his idea in 1912 at a meeting of the Geological Society of America. At first, most geologists didn't take him seriously because they couldn't think of a mechanism—a force—that could make continents move around Earth's surface. Then in 1929, another scientist discovered something that would provide part of an answer: radioactivity!