Oceans

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.  More than half of this area is over 3,000 meters (9,800 ft) deep. Scientists estimate that 230,000 marine life forms of all types are currently known, but the total could be up to 10 times that number.

World Ocean

Though generally described as several 'separate' oceans, these waters comprise one global, interconnected body of salt water sometimes referred to as the World Ocean or global ocean. This is divided into five principal oceans namely Pacific, Atlantic, Indian, Arctic and Antarctic. Smaller regions of the oceans are called seas, gulfs, bays, straits and other names. Despite their names, smaller landlocked bodies of saltwater that are not connected with the World Ocean, such as the Aral Sea, are actually salt lakes.

Pacific

This is the largest ocean covering 1/3 of the earth’s surface and spanning for 169.2 square kilometers. It separates Asia and Australia from the Americas and its name was given by Portuguese explorer Ferdinand Magellan.

Atlantic

This is the second largest ocean covering 22% of the earth’s surface and spanning for 106.4 million square kilometers. It separates the Americas from Eurasia and Africa. The first part of its name refers to Atlas from Greek mythology, making the Atlantic the "Sea of Atlas" and first referred to by Herodotus, the historian.

Indian

It is the third largest ocean covering about 20% of the earth’s surface. It is 77.5 million square kilometers in size and the only ocean to be named after a country. It separates South Asia from Africa and Australia.

Antarctic

It is the fourth largest and comprises the southern most waters of the World Ocean. It lies immediately south of Australia surrounding the continent of Antarctica.  

Arctic

The smallest of the earth’s oceans is also the shallowest and is situated in the Northern Hemisphere. Almost completely surrounded by Eurasia and North America, the Arctic Ocean is partly covered by sea ice throughout the year.

Importance

Oceanic evaporation, as a phase of the water cycle, is the source of most rainfall. Ocean temperatures determine climate and wind patterns that affect life on land. Life within the ocean evolved 3 billion years prior to life on land. Ocean currents greatly affect the earth's climate by transferring heat from the tropics to the Polar Regions, and transferring warm or cold air and rain to coastal regions, where winds may carry them inland. The ocean is the biggest natural habitat and more than half of the earth’s life forms live in it. The oceans are essential to transportation as most of the world's goods move by ship between the world's seaports. The ocean is also the biggest source of the fishing industry.