Plate tectonic theory states that Earth's lithosphere is divided into 7 major and several minor tectonic plates, composed of both continental and oceanic crust. These plates move horizontally over the asthenosphere, which is the upper layer of the earth's mantle made up mostly of molten rock, as rigid units. These plates have been constantly moving over the globe throughout the history of the earth and will move in the future as well.

Continental Drift Theory proposed by Wegener postulates that initially all the continents formed a single continental mass named Pangea, which was surrounded by a mega ocean Panthalassa. Around 200 million years ago, Pangea broke into two large continental masses - Laurasia and Gondwanaland and subsequently, they broke into smaller continents that exist today. The movement responsible for the drifting of the continents was caused by buoyancy and tidal force. Zig-saw fit of coastlines, similarity of age of rocks and similar fossil in different continents were the evidences of the theory.

However, contrary to Wegener, it is now evident from Plate-tectonic theory that it is the lithospheric plates and not the continent that move. Rather continents are a part of these plates. Tectonic plates are able to move because the Earth's lithosphere has greater mechanical strength than the underlying asthenosphere. This is explained by the Seafloor spreading theory of Harry Hass which states that at mid-ocean ridges, new oceanic crust is formed through volcanic activity, which then gradually moves away from the ridge. These ridges in the middle of the oceans are the result of magma breaking through, creating a divergent boundary where the seafloor spread apart.

Heat generated from the radioactive decay of elements deep in the interior of the Earth creates magma (molten rock) in the aesthenosphere.Large convection currents in the aesthenosphere transfer heat to the surface, where plumes of less dense magma break apart the plates at the spreading
centers, creating divergent plate boundaries.

When oceanic plates diverge or converge, stress causes fractures to occur in the lithosphere. This tectonic activity is manifested as earthquakes. Majority of seismicity on the planet occurs at plate boundaries, although intra-plate seismicity can occur as well when stresses build up in the plate. Seismic data provides us valuable information about whether the plates’ movement is convergent i.e. moving towards, divergent i.e. moving away or transform i.e., slide along each other.

Thus, the theory of plate tectonics is a convergence of Wegener’s Continental Drift theory, Hass’ Sea floor spreading thesis and synthesis of seismic data. It has comprehensively explained the past geography of continents and oceans and the process controlling creation and destruction of landforms.