What is the reason of the continental drift?

Answer 1

First, the continents do not drift! The theory of continental drift was based on observations of how the outlines of different continents appear to fit like pieces of a jigsaw puzzle and that when so fitted various ancient mountain ranges, etc. align from one continent to another. But for them to 'drift' they would have to 'plow' through the solid rock of the ocean floor, which is clearly not happening. The theory of continental drift was long ago discarded and replaced as new evidence was uncovered.

The speculation that continents might have 'drifted' was first put forward by Abraham Ortelius in 1596. The concept was independently and more fully developed by Alfred Wegener in 1912, but his theory was rejected for lack of a mechanism.

Following WW2 the US Navy made a series of observations showing symmetrical bands of magnetic field reversals on opposite sides of the midocean ridges. Because this information had value for military navigation, it was kept classified into the 1960s. When this information was made available to geophysicists, it confirmed key parts of the theory of plate tectonics (originally proposed in 1953).

The idea of continental drift has been subsumed by the theory of plate tectonics, which explains how the continents appear to move. Convection currents in the semisolid mantle rock drag both continental and oceanic plates that float above the mantle around. The light granitic continental plate material tends to float higher, while the denser basaltic oceanic plate material tends to float lower so if they collide the continental plate will override the oceanic plate, causing it to subduct under the continental plate down into the mantle. If identical type plates collide the plates crumple and fold causing mountain ranges to form.

The important thing to realize is the continents are not drifting, the tectonic plates (both continental and oceanic) of the crust are floating on the moving top surface of the mantle.