Continental drift is caused by movement of the tectonic plates that continents sit on top of. Continental drift has continuously occurred throughout time, and continues to do so today. Rough estimates say that Europe and North America are drifting away from each other 2.5 centimeters per year.
The concept of continental drift was presented by Alfred Wegener in the early 1900s. By noting the similarities of the shape of coasts along South America and Africa, Wegener theorized that at one point, the two continents had been attached. Finding fossils of the same lifeforms on both coasts confirmed this suspicion. Further work has indicated that a super-continent, called Pangaea, existed 200 to 240 million years ago.