Why salt is in seawater

The cause of salt in seawater is a complex issue related to the origin of the Earth, the formation of the oceans and the process of evolution. It is generally believed that salts mainly originate from weathering products of crustal rocks and soluble compounds ejected from submarine volcanoes. In addition, rivers around the globe deliver 5.5×1015g of dissolved salt to the oceans each year, which is also a source of seawater salts.

The salt content of seawater in the world's major oceans varies from place to place, averaging about 3.5 percent, and these inorganic salts dissolved in seawater are most commonly sodium chloride, or table salt for daily use. Some of the salt comes from volcanoes on the ocean floor, but most of it comes from rocks in the Earth's crust. The rocks are weathered and disintegrated, releasing the salts, which are then carried to the sea by rivers.

In the cycle of vaporizing seawater and then condensing it back into water, the salt stays behind as the seawater evaporates and gradually builds up to its current concentration. The oceans contain so much salt that they can lay down a salt layer about 500 feet thick on land around the globe.

Expanded Information

Sea water is salty because it has about 3.5 percent salt. Most of this is sodium chloride, with small amounts of magnesium chloride, potassium sulfate, calcium carbonate, and so on; it is these salts that make seawater bitter and astringent, making it hard to swallow. So where do these salts come from? Some scientists believe that the Earth in the long geological period, just beginning to form the surface water (including seawater) are fresh water.

Later, as the water flow eroded the surface rocks, the salts in the rocks constantly dissolved in the water. These currents in turn continued to merge into large rivers rushing into the sea, making the sea the final destination for salts. With the evaporation of water, salts gradually deposited, over time, the more salts accumulated, so the sea became salty. This is a kind of "acquired theory". According to this theory, with the passage of time, seawater will become more and more salty.

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