The theory that the existing continents moved to their present position following the break up of an ancient landmass. The idea was first proposed by A. Wegener in 1912 but was discarded by the geophysicists of the time. However evidence from bioge-ographic and oceanographic studies and the emergence of plate tectonics theory has established its validity. It is thought that the original landmass, Pangaea, broke up in the Mesozoic into Gondwana (or Gondwanaland) and Laurasia. The subsequent break-up of Gondwana resulted in the formation of the landmasses of the southern hemisphere, i.e. Africa, India, South America, Australia, Antarctica, and New Zealand, while the break-up of Laurasia gave rise to North America and Eurasia. The theory helps to explain the present disjunct distributions of certain plant and animal groups. See also vicariance. |
