When All Land Was One
Hundreds of millions of years ago, the Earth looked nothing like it does today. Instead of seven separate continents scattered across the globe, almost all of the planet's land was joined together into one enormous supercontinent. That supercontinent was called Pangaea. Its name comes from Greek words meaning "all the Earth," a fitting description for a single landmass that held nearly every part of today's continents.
One Giant Land, One Giant Ocean
Pangaea existed roughly 300 million years ago. Because all the land was packed into one place, the rest of the planet was covered by a single, vast world-ocean. This enormous ocean, surrounding the supercontinent on all sides, is known as Panthalassa. A creature living back then could, in theory, have walked across land from what is now North America all the way to Africa or Antarctica.
Why the Continents Drifted Apart
Pangaea did not last forever. The Earth's outer shell is broken into giant slabs called tectonic plates, and these plates are always slowly moving. Over millions of years, the forces beneath the surface pulled Pangaea apart. The supercontinent slowly cracked and split into the pieces that drifted away to become the continents we know today. They are still moving, a few centimeters every year.
How We Know Pangaea Existed
It might seem impossible to know about a world so ancient, but the evidence is surprisingly strong. The coastlines of continents like South America and Africa look as though they could fit together like puzzle pieces. Identical fossils of the same ancient plants and animals have been found on continents now separated by entire oceans. Matching rock formations appear on different continents. Together, these clues convinced scientists that the continents were once joined as Pangaea.
Source
This article was written using information from Wikipedia.