To date, scientists have put forward two hypotheses to explain this fact from a scientific point of view.Despite the fact that the river is considered freshwater, the salt in them is still contained, however, ten times less than in the seas and oceans. The inland sea and its composition can be significantly saltier ocean. These facts have guided the scientists on the idea that salt is entering the oceans is washed out by rivers from soils and hard rocks all along the riverbed, and eventually comes in the seas and oceans. And the difference in the composition of ocean and river water, namely the absence in the rivers of salts of carbonic acid (carbonates) due to the fact that they are used by living organisms for the structure of the bone skeletons and shells.Another version explains the salinity of the oceans volcanic activity, which was very active during the formation of the earth's crust. Eruptions during that period were very active and volcanic vapors were spilled on the ground acid rain. The oceans at that time was acid. Acid, in turn, entered into a chemical reaction with basalt and granite, the result of which was formed by alkaline elements, mainly magnesium, sodium, calcium and potassium. This helped to neutralize acidic water, which eventually became salty.However, especially disputes the two theories are not caused, scientists eventually agreed on the opinion that they are both quite compelling and each has a right to exist, moreover one theory complements the other.