The land on Earth has not always been separated into the seven continents, at one time a
massive supercontinent, known as Pangaea, covered one-third of Earth’s surface. Additionally,
the supercontinent was surrounded by ocean waters called Panthalassa, much of which were in
Earth’s Southern Hemisphere. Geologists believe that the supercontinent split apart over
millions of years because of the movement of the tectonic plates that form Earth’s crust. In fact,
experts predict that over the next 250 million years the movement of the plates will cause the
seven continents to merge into a supercontinent again.

The question refers to the Continental Drift Theory.

Explanation:

Continental drift is a theory proposed in 1912 by the German meteorologist and geophysicist Alfred Wegener explaining the origin of continents by the disintegration of the original Pangea supercontinent.

The original idea that the continents fit together was supported by Wegener by comparing geological and paleontological findings mainly from the coasts of Africa and South America. Today, the theory of continental drift is part of the theory of plate tectonics, which explains not only the motion of continents but also the dynamics of the Earth's mantle.