Earth has seven main pieces of land, called continents. The seven continents are Asia, Africa, North America, South America, Antarctica, Europe, and Australia/Oceania.
Usually, nearby islands are also part of a continent. For example, Japan is part of Asia. Greenland and all the islands in the Caribbean Sea are usually considered part of North America. Only a very few islands are not part of any continent.
Europe and Asia are not really separate pieces of land. They are both part of a single, huge piece of land called Eurasia. Still, they are usually thought of as two separate continents because their societies developed separately.
For hundreds of millions of years, the tectonic plates underneath Earth’s surface have been slowly sliding around. They are still sliding today. Scientists believe their constant sliding formed the continents.
The continents first began to form nearly four billion years ago. At that time, a huge ocean covered Earth. Then pieces of land began to appear. They built up along the edges of tectonic plates. They were made of rock that rose up when plates crashed into each other.
Some of this rock formed into small islands. When plates carrying these islands crashed into each other, the separate islands sometimes joined together. Over time, these islands grew larger and larger. They became the first continents.
The early continents were scattered chunks of land. These chunks slowly moved toward each other. In time, they formed into a single, huge continent. Scientists call this supercontinent Pangaea.
About 200 million years ago, Pangaea began to break apart. The separate pieces then slowly moved away from each other. They were the beginnings of the continents we know today.
The positions of the continents are always changing. North America and Europe are moving away from each other. They drift apart by about 2.5 cm (one inch) a year. The continents are also continuing to break apart. In time, part of California will likely separate from North America. It will become an island.
The surface of the continents has changed many times. Great mountains have risen. Then, they have been worn away. Ocean waters have flooded huge areas and then slowly dried up. Huge ice sheets have come and gone. They shaped the land as they advanced and then melted away.