German geologist Alfred Wegener proposed the theory of continental drift in 1912, which hypothesized that the continents were once joined together in a single landmass called Pangaea before drifting apart to their current locations. Wegener provided three key pieces of evidence to support this: the continental margins fit together like puzzle pieces, matching fossil and rock formations were found on separated continents, and the same fossils of non-marine animals were discovered on continents far apart. Later, scientists developed the theory of plate tectonics to explain the forces causing the continental drift, proposing that movements in underground plates pushed the continents apart or together.