Alfred Wegener brought together several lines of evidence to support his theory of continental drift. One is quite simple -- that the continents look like they could "fit" together, much like puzzle pieces that have drifted apart. Then, he noticed that when you put the continental puzzle pieces back together, other things started to fit. For example, the rock layers that form the Appalachian mountains of the eastern U.S. matched quite well with those in Scotland. Fossils found on the east coast of Brazil match quite nicely with fossils found in western South Africa. Also, he noticed that a lot of the fossilized life found in the rock record didn't fit in the climates they were found in. For example, rocks in Alaska contain fossil palm tree leaves, though there have not been palm trees at that latitude for a very long time! Thus, he concluded that the continents must 'drift' around the Earth, occasionally colliding with one another. Though his ideas were not popular at the time, they were the foundation of one of the greatest scientific revolutions in history!