The document discusses how continental drift occurs through plate tectonics. It explains that convection currents in the asthenosphere, the liquid layer between the lithosphere and inner core, cause the movement of tectonic plates. Hot magma in the mantle rises due to convection currents, cools and sinks, moving the rigid tectonic plates comprising the lithosphere over geologic time. This cyclical movement of magma drives the drifting of continents via plate tectonics.