As a system of interconnected bodies of salt water, oceans cover 70 percent of the earth's surface and hold 97 percent of the planet's water supply. The five major oceans of the world are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the Southern Ocean and the Arctic Ocean.
As the world's largest ocean, the Pacific covers an area of the planet larger than all of the continents combined, about one-third of the earth's surface. It is also home to the world's tallest mountain, Mauna Kea. The second largest ocean, the Atlantic, covers about 20 percent of the world's surface.
Scientists believe that life on earth began in the oceans. The oceans also play a crucial role in the planet's water cycle, acting as an important source of water vapor in the atmosphere, which is important in the transportation and distribution of heat across the planet. Oceans also help in removing carbon dioxide from the atmosphere and storing it in carbon reservoirs. In this way, oceans have a key role in maintaining the world's atmosphere, climate and temperature. For example, the Gulf Stream, an ocean current, distributes heat from lower latitudes to higher latitudes, creating a milder climate in the British Isles and Northwest Europe.