What is the theory of plate tectonics?

The theory of plate tectonics states that the Earth's crust is divided into several large areas known as plates. These plates float on the mantle (the layer of the earth under the crust that consists mostly of magma). They move (probably because of earth's gravitational force, but I'm not 100% sure) and scrape against one another. That is why there are earthquakes. One plate is colliding with another. Volcanos are also most common along the lines where two plates intersect because there is more ready access to the mantle's magma. These intersecting lines are called fault lines. The theory of plate tectonics explains how Pangaea (the great supercontinent of the primitive world) became the various continents of today: the moving plates broken the land apart.