Continental drift is the theory that explains how the continents have moved over geological time. It suggests that the Earth's continents were once joined together in a single landmass called Pangaea, which began to break apart around 200 million years ago. This movement is driven by the tectonic plates that float on the semi-fluid layer of the Earth's mantle. As these tectonic plates shift, they cause the continents to slowly drift apart or collide, leading to the formation of mountains, earthquakes, and other geological features. The concept of continental drift was first proposed by Alfred Wegener in the early 20th century, and it laid the groundwork for the modern theory of plate tectonics.