Initially rejected as unlikely, only in the 1960s with the arrival of evidence from geological research was the theory was incorporated into a now accepted concept of plate tectonics. Continental drift resulted in the separation of Earth's continents from a single continental block called Pangea. It is thought that the Earth has had several supercontinents similar to Pangea in its past, and that they have repeatedly broken apart and recoalesced over hundreds of millions of years.
Evidence for continental drift
Nowadays there exists lots of evidence for plate tectonics. The most obvious is the way in which the continents seem to fit jigsaw-like (for example Africa and South Asia) together when looked at on a map. More scientific evidence comes in the form of plant and animal fossils of the same age found around different continent shores, suggesting that they were once joined. For example the fossils of the freshwater crocodile found in Brazil and South Africa. There is also living evidence - the same animals being found on two continents. An example of this is a particular earthworm found in South America and South Africa.
There exist two main forms of more geological evidence evident: rock sequences and magnetic stripes. When the rock strata of the tips of separate continents is very similar it suggests that these rocks were formed in the same way implying that they were joined initially. The second piece of evidence arises when the rocks were formed from magma erupting out of a volcanoe. When this happens the iron particles align with the earth's magnetic field and set in this position. As the earth's magnetic field flips every half-million years, strips of land of alternating magnetic orientation are formed - symetrical from the volcanoe. This showed how some plates are moving away from each other.