Oceans cover about 71% of the Earth's surface and are immeasurably important to all life on the planet. Oceans play an important role in regulating the climate.
One example of how the oceans affect our world can be found in the Gulf Stream, an Atlantic Ocean current that brings warm water from south of the equator through tropical waters to areas of Europe, including the United Kingdom. The warm water in the current warms the air. Without the Gulf Stream, temperatures in the UK would be significantly colder.
Oceans are also an important part of the carbon cycle, which helps to regulate the amount of carbon bearing greenhouse gases, such as carbon dioxide, that enter the atmosphere. Scientists investigating climate change want to better understand the oceans' ability to absorb carbon dioxide.
Image: Waves crash against the cliffs at Land's End, Cornwall, England
Volcanoes and comets bring water to the Earth.
Dr Iain Stewart explains the theory that steam from volcanoes and water from comets filled the Earth's oceans.
A continent is breaking apart at Ethiopia's Afar Depression.
Dr Iain Stewart explains how new oceans are created when continents are broken apart by the Earth's moving plates.
Shifting continents caused the Mediterranean to dry out.
Dr Iain Stewart explains how, six million years ago, the continents of Europe and Africa moved together and cut off the Mediterranean Sea. He also explains how rivers erode the land and bring salt to the oceans.
Tiny organisms in the oceans produce about half the planet's oxygen.
Dr Iain Stewart explains how phytoplankton produce about half of the Earth's oxygen.
An accident reveals the complexity of ocean currents.
Dr Iain Stewart shows how containers of rubber duck toys lost at sea graphically reveal the complexity of the ocean currents that distribute oxygen, nutrients and heat around the planet.
An ocean (from Ancient Greek Ὠκεανός, transc. Okeanós, the sea of classical antiquity) is a body of saline water that composes much of a planet's hydrosphere. On Earth, an ocean is one of the major conventional divisions of the World Ocean, which occupies two-thirds of the planet's surface. These are, in descending order by area, the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. The word sea is often used interchangeably with "ocean" in American English but, strictly speaking, a sea is a body of saline water (generally a division of the world ocean) partly or fully enclosed by land.
Saline water covers approximately 72% of the planet's surface (~3.6×108 km2) and is customarily divided into several principal oceans and smaller seas, with the ocean covering approximately 71% of the Earth's surface. The ocean contains 97% of the Earth's water, and oceanographers have stated that only 5% of the World Ocean has been explored. The total volume is approximately 1.3 billion cubic kilometers (310 million cu mi) with an average depth of 3,682 meters (12,080 ft).
Because it is the principal component of Earth's hydrosphere, the world ocean is integral to all known life, forms part of the carbon cycle, and influences climate and weather patterns. It is the habitat of 230,000 known species, although much of the oceans depths remain unexplored, and over two million marine species are estimated to exist. The origin of Earth's oceans remains unknown; oceans are believed to have formed in the Hadean period and may have been the impetus for the emergence of life.
Extraterrestrial oceans may be composed of water or other elements and compounds. The only confirmed large stable bodies of extraterrestrial surface liquids are the lakes of Titan, although there is evidence for the existence of oceans elsewhere in the Solar System. Early in their geologic histories, Mars and Venus are theorized to have had large water oceans. The Mars ocean hypothesis suggests that nearly a third of the surface of Mars was once covered by water, and a runaway greenhouse effect may have boiled away the global ocean of Venus. Compounds such as salts and ammonia dissolved in water lower its freezing point, so that water might exist in large quantities in extraterrestrial environments as brine or convecting ice. Unconfirmed oceans are speculated beneath the surface of many dwarf planets and natural satellites; notably, the ocean of Europa is believed to have over twice the water volume of Earth. The Solar System's gas giant planets are also believed to possess liquid atmospheric layers of yet to be confirmed compositions. Oceans may also exist on exoplanets and exomoons, including surface oceans of liquid water within a circumstellar habitable zone. Ocean planets are a hypothetical type of planet with a surface completely covered with liquid.