Alfred Wegener proposed continental drift in his 1915 book The Origin of Continents and Oceans. He argued that today's continents were once joined in a supercontinent, which he called Pangaea, and later moved apart.
Wegener supported the idea with several lines of evidence. The coastlines of Africa and South America appeared to fit, similar fossils occurred on continents now separated by oceans, and matching rock formations crossed modern continental boundaries. Ancient climate clues, such as glacial deposits in now-tropical regions, also challenged the idea that continents had always occupied their current positions.
Many geologists initially rejected the proposal because Wegener could not provide a convincing mechanism capable of moving continents. Later discoveries about seafloor spreading, oceanic crust and plate tectonics supplied that mechanism. Modern plate tectonics therefore confirmed the central insight of continental movement, while replacing Wegener's original explanation of how it happened.