Oceans and seas cover about 7/10 of the Earth’s surface. Large areas of water are called oceans. There are four oceans: the Pacific, the Atlantic, the Indian and the Arctic Oceans. Smaller areas of water are called seas and most of them are part of the oceans or are joined on to them. The largest ocean is the Pacific, the smallest is the Arctic.

No one is certain how the oceans formed. Some scientists think that when the Earth was formed thick clouds surrounded it. As the Earth cooled down, rain fell and formed the first oceans. Large amounts of water may also have come from comets that crashed into the Earth during its early history. When the continents moved, water filled the gaps they left and formed the oceans as we know them today.

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