Theory of Continental Drift
The world was made up of a single continent through most of geologic time. That continent eventually separated and drifted apart, forming into the seven continents we have today. The hypothesis asserts that the continents consist of lighter rocks that rest on heavier crustal material—similar to the manner in which icebergs float on water. It is said that the relative positions of the continents are not rigidly fixed but are slowly moving—at a rate of about one yard per century.