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The sea, the world ocean, or simply the ocean is a body connected with seawater that covers more than 70% of the Earth’s surface (361,132,000 square kilometers (139,434,000 square miles), with a total volume of about 1322 million cubic kilometers (320,000,000 cubic miles)). It moderates the Earth’s climate and plays an important role in the water cycle, carbon cycle and nitrogen cycle.
It has been traveled and explored since ancient times, while ocean exploration – oceanography – dates back to Captain James Cook’s travels in exploring the Pacific between 1768 and 1779. The word sea is also used to refer to small, partially land areas from the ocean and some large, completely enclosed salt waters such as the Caspian Sea and the Dead Sea.
The most common solid dissolved in seawater is sodium chloride. Water also contains salts of magnesium, calcium and potassium, among many other elements, some in minimal concentrations. Salinity varies widely, being lower at the surface and in the mouths of large rivers and higher in the depths of the ocean; However, the relative proportions of dissolved salts vary little in the oceans.
Wind blowing above the surface of the sea generates waves that break when entering shallow water. Winds also create surface currents through friction, creating a slow but steady circulation of water in the oceans. The directions of circulation are determined by such factors as the shape of the continents and the rotation of the Earth (Coriolis effect). Deep-sea currents, known as the global conveyor belt, carry cold water from the poles to each ocean.
The tides, usually rising and falling twice a day at sea level, are caused by the rotation of the Earth and the gravitational effects of the sun rotating around the moon and, to a lesser extent. Tides can have a very wide range in bays or estuaries. Submarine earthquakes resulting from the movement of tectonic plates beneath the oceans can lead to devastating tsunamis, as well as volcanoes, huge landslides or the effects of large meteorites.
A wide variety of organisms live in the sea, including bacteria, protesters, algae, plants, fungi and animals, offering a wide range of marine habitats and ecosystems, from the sun and the coastline to great depths and cold pressures, the area and latitude of cold waters under polar ice caps to a variety of coral reefs in tropical areas. Many major groups of organisms evolved into the sea, and life may have begun there.
The sea provides significant food supplies for people, mainly fish, as well as for mussels, mammals and algae, whether caught or caught. Other human uses of the sea include trade, travel, mineral extraction, power generation, warfare and recreational activities such as swimming, sailing and diving. Many of these activities create marine pollution.
The sea plays an important role in human culture, and mainly appears in literature, at least from the Odyssey of Homer, in marine art, in cinema, theater and classical music. It is symbolic that in mythology the sea looks like a monster, like Scylla, and represents the unconscious mind when interpreting a dream.