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The sea common Earth's weather and has an important role in the sea water cycle, carbon cycle, and the nitrogen cycle. Humans are utilizing and studying the sea have been noted since ancient times, and proved well into prehistory, while its modern scientific study is known as oceanography. The most abundant solid dissolved in the seawater is sodium chloride means salt water. The water also contains salts of magnesium, calcium, potassium, and mercury, amongst many other elemental individuals, some in minute concentrations level. Salinity varies widely, being lower virtual by the surface area and the mouths of wide variety of rivers and the higher in the depths of the marine source; however, the relative proportions of dissolved salts vary little across the seas. Winds blowing over the exterior of the oceans produce waves, which are breakable when they are enter into the shallow liquid portions. Winds also generate external currents through the frictional forces, setting up slow but stable movements of water throughout the marine areas. The directions of the circulation are governed by components, including the shapes of the continents and Earth's revolving called the Coriolis effect. Deep-sea currents called as the global conveyor belt, carry cold water from the near poles to every ocean area. The generally two times in a day rise and fall of sea quantities, are caused by Earth's rotation and the gravitational effects of the orbiting Moon and to a smaller extent of the Sun. Tides may have a high range in bays or estuaries. Submarine area earthquakes emerge from the tectonic plate movements under the marines can lead to noxious tsunamis, as can volcanoes, huge landslides, or the clash of large meteorites.

Numerous of the major classifications of organisms evolved in the marine and life may have started there. The sea supplies substantial providing of food for humans, mainly fish, but also shellfish, mammals, and seaweed, whether caught by fishermen or farmed below the sea water. Other human benefits of the sea include trade, travel, mineral extraction, power generation, warfare, and leisure occupations such as swimming, sailing, and scuba diving. Many of these activities generate marine pollution. The sea has therefore been for humans an integral individual throughout history and culture.