- noun a geological theory that the present continents were once part of a single landmass and have gradually drifted away from each other over a period of millions of years
- The relative motion of large areas of the Earth’s surface. Similar effects have been hypothesised for other terrestrial planets, notably Venus. On the Earth, continental drift is driven by convection movements deep within the Earth and involves volcanic and earthquake activity along the lines where matter is pushed to the surface or sucked beneath it. This way of looking at the Earth has in recent years established itself as a powerful scientific technique but its application to other planets remains uncertain.