The theory of plate tectonics

Theories about the movement of the continents have evolved ever time as the ability to conduct scientific study of the continents has improved. Thus, Today's theory of plate tectonics, rather than contradicting its predecessor,had its roots in the older theory of continental drift.
According to the theory of continental drift, the continents are not fixed in position but instead move slowly across the surface of the earth, constantly changing in position relative to one another. This theory was first proposed in the eighteenth century when mapmakers noticed hos closely the continents of the earth fit together when they were matched up. It was suggested then that the present-day continents had once been one large continent that had broken up into pieces which drifted apart.
Today the modern theory of plate tectonics has developed from the theory of continental drift. The theory of plate tectonics suggests that the crust of the earth it divided into six large, and many small, tectonic plates that drift on the lava that composes the inner core of the earth. These plates consist of ocean floor and continents that quite probably began breaking up and moving relative to one another more than 200 million years ago.