Alfred Wegener first proposed the theory of continental drift in 1915, hypothesizing that 200 million years ago the continents were joined together in a supercontinent called Pangaea. Pangaea began breaking apart in the late Triassic period, forming the continents of Gondwanaland and Laurasia separated by the Tethys Sea. By the end of the Cretaceous period the continents had separated into their modern positions. Wegener published his theory of continental drift and the existence of Pangaea in his 1915 book.