Continental Drift Hypothesis
This hypothesis postulates that all of the present continents formed a unified Pangea (pan-continent) that began to split in the Middle Mesozoic (or Permian) Era and drifted long distances to their present locations. This hypothesis is supported by evidence from the morphology of continental margins, lithologies and rock facies, geological structure, fauna and flora, glaciers, palaeoclimate and geophysical characteristics. These data have revealed that continental drift has occurred in two main directions: towards the equator and westward. The hypothesis postulates that the mechanism of continental drift is the movement of the silica-aluminium-rich layer (sial) on top of the silica-magnesium-rich layer (sima). It is widely accepted that the lithosphere is drifting above the asthenosphere, as supported by the seafloor spreading and plate tectonics hypothesis.