The salt in the sea has been transported there by rivers during most of the millions of years. When the sea water is vaporized, then it gets up in the air and becomes cloudy. The same cloud rises in the ground and rains in the form of rain. During the rainy season, his contact is in the air with carbon dioxide, sulfur dioxide, nitrogen oxides etc. These gases dissolve in water, causing rain water to become slightly acidic. When this acidic water falls on the rocks and ground, it turns the salts present in them. When this water reaches the rivers after reaching the water, it also comes in the water of the river, but the salt water is very sweet because of the low salt content. This saline water of the rivers reaches into the sea. In this way gradually the salt brought by the rivers for millions of years has been gathering in the oceans.
There are rocks at the bottom of the ocean, whose salt also dissolves in sea water. Similarly, there are volcanoes below the oceans, which also occasionally breaks the gases such as lava and chlorine, sulfur dioxide etc. There are also sodium substances in the sea. With these the reaction of chlorine etc. becomes salts. The salt of the food is the compound of sodium and chlorine (NaCl). So in this way the salt continues to grow in the sea.
The salt that exists in the sea water remains in it, but the water of the ocean by the heat of the ocean becomes vaporized and comes out of the ocean, and becomes dense in the sky and becomes cloudy. This vapor is pure water, i.e. there is no salt in it. In this way the water of the sea continues to be re-cycled, but only the salt deposits in the sea.
Due to these procedures, sea water has become saline in millions of years.
You may be thinking that due to continuous movements of the above mentioned processes, the seepage of the sea will continue to grow progressively. But this is not so. Many such processes occur under the sea, due to which the salt water is deposited in the sea level. There are also some chalk-styled animals and animals in it. These organisms take salts from the sea water to make their shells. When it dies, its shell starts gathering at the bottom of the ocean, and after a lot of time it turns into limestone. During the movement of the ground surface, the limestone layers reach somewhere, i.e. exit from the sea. By mining these, we get the lime in the walls of the house. Once turned into rocks, sea salts can not make sea water saline again. So the salination of the sea remains one and the same for millions of years.
Sea water has an average of 3.5 percent salt. This means that every 100 grams of sea water will give you 3.5 grams of salts. This salts are mainly chlorine salts, such as eater salt (NaCl). This concentration of salts is not uniform everywhere in the ocean. For example, the salinity of sea water near the river faces decreases because there is heavy inflow of sweet water due to the rivers there.
Similarly, salinity in some small oceans can be much more. For example, in the Dead Sea, whose salinity is ten times more than the normal sea, i.e. about 33.7 percent. The reason for this is that it is isolated from other seas, so that they can not exchange water. The second reason is that vaporization is very high in this ocean. Therefore, the concentration of salts is also very fast.
Due to so much saltwater the buoyancy of the Dead Sea is unusually high, so that the man can not drown in this ocean, it will float in the water like a wood.
Due to this high salinity, micro-organisms do not grow in the Dead Sea, and hence there are fewer fish and other living organisms that survive by eating micro-organisms. Perhaps for this reason this ocean is called the Dead Sea. But the ocean is very popular in the tourists, probably because they can rest from the fear of drowning and play water sports. People also believe that water in this ocean has the ability to cure many diseases.