What Is the Ocean?

Oceans cover 70% of the Earth’s surface and are one of the major components of the world’s hydrosphere. They absorb a great deal of the sun’s energy, distribute heat around the globe and regulate temperature.

An ocean is a large body of salt water. It’s also a vital part of the Earth’s ecosystem, providing food and shelter for numerous species.

The name “ocean” is derived from the Greek sea god Oceanus (, Okeanos). In ancient mythology, Oceanus was a giant river that encircled the world. Scientists think that the first oceans formed in the Hadean eon, when sizable amounts of water were included in the primordial material from which the Earth was formed. These early oceans may have had some of the characteristics of modern oceans, including large areas of ice and variable temperatures.

Oceanographers divide the ocean into different zones based on physical and biological conditions. The photic zone is the layer of the open ocean where sunlight penetrates. Here, free floating phytoplankton and algae are able to perform photosynthesis. The twilight zone is the layer of the ocean above the photic zone, where light intensity decreases significantly. This is where deep-sea fish, shrimp and lobsters live.

Other ocean zones are divided by the temperature of the water, by its salinity or by the chemistry of its waters. The boundaries of these zones are called thermoclines, haloclines, chemoclines and pycnoclines. Temperature and salinity control the density of ocean water, which in turn controls global ocean circulation.

Most of the water in the ocean comes from rivers and precipitation. However, some is carried into the ocean by winds and waves. Marine pollution, which includes chemicals, pollutants, waste and invasive species, is another important source of water in the ocean.

Although the vast, open space of the open ocean may seem empty, it is teeming with life. The open ocean provides habitats for many species of plants and animals, from whales and dolphins to crabs and anemones. It also allows animals to travel long distances. Closer to shore, tide pools are small ocean habitats that provide a haven for creatures when the tide is out.

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