Plate tectonics — driven primarily by mantle convection currents (heat-driven flow in the viscous mantle), ridge push (elevated mid-ocean ridges push plates apart), and slab pull (dense subducting slabs drag plates toward trenches) — is the mechanism responsible for continental drift. Wegener proposed continental drift in 1912; the mechanism was later explained by seafloor spreading (Hess, 1960) and plate tectonic theory.