If you look at a map, the coasts of South America and Africa seem to fit together like puzzle pieces. That's because about 200 million years ago, all the continents on Earth were joined together into one huge supercontinent called Pangaea. Over time, the processes of plate tectonics slowly broke this massive landmass into smaller pieces that spread out to form the continents we know today.

Definition: a supercontinent made of all of the Earth's landmasses
When it existed: about 200 million years ago
Proposed by: Alfred Wegner in 1915
Cool fact: Scientists have found tropical plant fossils in polar regions and signs of glaciers in arid regions of Africa. These different climate zones are evidence that the continents are moving.

Image credits: Eric Hamilton; Rondi Davies, AMNH.