Every child knows that the water in the seas and oceans, which cover most of the planet's surface, is salty. At the same time, in most rivers and lakes, which are somehow connected with the world's oceans, the water remains fresh. What's the matter? If water flows from one place to another, then why does it remain fresh in the rivers?
The salt content in water is measured by scientists in ppm. For example, the saltiest water on the planet is found in the Dead Sea. Here salinity ranges from 300 to 350 ppm. Translated into understandable Russian, this means that the salt content per liter of water is approximately 300 to 350 grams. For comparison, the salinity in the Pacific Ocean is 34.5 ppm, in the Mediterranean Sea - 39, in the Black Sea - 18, in the Azov Sea - 11, in the Atlantic Ocean - 35.4. At the same time, the salinity of water in the Bay of Biscay (north of Spain and west of France) is considered the reference indicator of sea salinity (all instruments are calibrated against it). There, the salinity is exactly 35 ppm. Water is considered fresh if it contains less than 1% of salts.
So why are the sea and ocean salty, while lakes and rivers are often fresh? In fact, everything is extremely simple. There are exactly two culprits for the current state of affairs on the planet. First of all, there is, in principle, a lot of salt in the sea. It has been contained in water in a dissolved form since time immemorial prehistoric times, when there was still no life on earth, and the planet and its atmosphere were just passing through a period of formation. Gases of bromine, fluorine, chlorine escaping from the earth's crust reacted with water (primarily in the form of steam) and formed acids. Acids entered with solid elements on the future seabed, resulting in the formation of salts. These salts lie at the bottom, dissolve in water and precipitate again to this day.
Secondly, the water cycle is to blame for everyone. The salt is too heavy to take to the sky. Therefore, when salt water evaporates and travels to the heavens as gas, all the salt remains in the seas and oceans. Having formed clouds, sea water, having lost its salt and becoming fresh, falls out in the form of precipitation (snow and rain) all over the planet, feeding river networks and saturating groundwater. That is why the rivers turn out to be fresh. Of course, the soil contains a certain amount of minerals, including salts, but there are too few of them to make the river water salty like in the sea. In addition, rivers flow and gradually wash out minerals into the world's oceans.
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