The ocean is constituted by 96,5% of water and 3.5% of other 75 elements, of which 6 (chlorine, sodium, sulphur, magnesium, calcium and potassium) are responsible for 99% of the ocean's salinity, mainly in the compound sodium chloride. These elements come in part from the erosion of land rocks, brought to the sea by rivers. Rain water (which by itself when crossing the atmosphere drags many particles, what shows that fresh water also has dissolved substances) that falls on land is infiltrated consequently in it dissolving and carrying to rivers and ocean mineral substances that contribute to the salinization (substance concentration dissolved in parts for a thousand of weight of these substances) of the water of the ocean. This allied to high evaporation and occurring during hundreds of millions of years (it is thought that the current ocean has about 500 million years) had contributed to become the water of the ocean salty (220 times saltier than the water candy). The existence of rocks with 3800 million years in Greenland and 3500 million years in the South of Africa designates the beginning of great rains that had disintegrated the rocks and had dragged to the ocean floor many layers of sediments as well as many substances that had been in solution or suspension. This process occurs not only in the ocean but also in salty lakes: the water that enters in the lake is drained by no effluent one; then it can only evaporate, leaving what it brought dissolved in the lake. The Caspian Sea, the Dead Sea and the Great Salty Lake are examples of salty lakes (the two last ones are 10 times saltier than the ocean).