4.4. Forces for the Plate Movement

At the time of Wegener, it was believed that the earth was a solid, motionless body. However, sea floor spreading and tectonic plate theories emphasized that both the surface of the earth and the interior are dynamic. Generally, it is accepted that tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere. The convection currents (proposed by Arthur Holmes) get diverted or converged on approaching the crust layer. Heat within the earth comes from two main sources: radioactive decay and residual heat.