There is really only one ocean, because all oceans are connected and make up one large body of water. This covers over 70 per cent of the surface of the earth.
Scientists called geographers have divided this vast area of water into five oceans and named them the Atlantic, Pacific, Indian, Arctic and Antarctic Oceans. All the bays and seas connected to each ocean are considered to be part of it.
The Pacific is the largest ocean. In area it is about 180,000,000 square kilometres. All the land areas in the world put together are smaller than the Pacific Ocean.
For many years most Europeans knew nothing of the world's oceans although some scholars now believe the Norseman, Lief Ericsson, crossed the Atlantic from Scandinavia to America around 1000 AD. Modern exploration really began in the late 14th century when Henry the Navigator, a Prince of Portugal, sent voyagers down the west coast of Africa. The first captain who eventually rounded the Cape of Good Hope into the Indian Ocean was Vasco da Gama in 1498.
In 1492 Christopher Columbus, financed by Ferdinand and Isabella of Spain, crossed the Atlantic and discovered America, although he thought he had reached the East Indies.
An expedition led by Ferdinand Magellan which passed north of Cape Horn, via the Strait which bears his name, in 1520 reached the Pacific for the first time. Magellan was killed in the Philippines but one of his vessels completed the first circumnavigation of the world in 1522.