Alfred Wegener originally proposed the theory of continental drift in the early 20th century, hypothesizing that the continents are slowly drifting around the Earth. He suggested that hundreds of millions of years ago, all the continents were joined together in a single landmass called Pangea. Pangea has since broken apart, with evidence found in matching fossil and rock formations between separated continents and the way the continents appear to fit together like puzzle pieces. While initially criticized, Wegener's theory of continental drift has since been supported by further evidence of plate tectonics showing how the movement of tectonic plates can cause the continents to drift apart over millions of years.