If something defines the earth, it is a "blue planet". Water occupies 71% of its surface. The ocean was formed around 4,000 million years ago. Then, when the tectonic plates separated, they divided the five big oceans that we currently know: The Pacific, the Atlantic, the Indian, the glacial Arctic and the glacial Antarctic.Before developing the navigation and mapping techniques, human beings saw the ocean as distinct units. In each ocean, there are delimited areas, close to the continents or even interiors, which form the regional seas. The peninsulas, islands and archipelagos are geographical accidents that mark the presence of terrestrial areas in the oceanic immensity. The oceans along with rivers and lakes form thehydrosphere; that is to say, theglobal set of waters of the planet earth. The oceans contain 96% of liquid water in the Earth. It means that just 4% is fresh water.The salinityof water comes from three sources: salt and potassium thatrain washes from terrestrial rocks, the sea water filtration through the cracks of hydrothermal vents in the seabed that comes back loaded with salt and the eruptions of submarine volcanoes. The temperature is not the same in all oceans. The superficial layer of variable depth (between 30 and 500 m, according to the zones), it is tempered (12 to 30 ° C). Below that layer is the cold-water layer, with temperatures between 10 and 1 ° C. Of course, the water is warmer in the equatorial and tropical zones; colder in the temperate zones and icier near the poles. In countries with four seasons it is warmer in summer and colder in winter.The oceans’ function determines the climate and is the cause of the divergence of life that exists on our planet. They are the largest lungs on the planet, since they provide more than half of all the oxygen in the atmosphere
