How Salt Gets Into the Ocean
Rainwater is slightly acidic and dissolves minerals from rocks, soil, and mountains as it flows across the land. Rivers carry these dissolved minerals, including salt, into the ocean. Volcanic activity also releases minerals and gases into the water. Over hundreds of millions of years, these processes added enormous amounts of salt to the oceans.
Why Salt Stays in the Ocean
The ocean loses water through evaporation, but salt cannot evaporate. When seawater evaporates and turns into water vapor, only the water molecules escape into the air. The salt crystals are left behind in the ocean, making the remaining water even saltier. This process has continued for billions of years, constantly concentrating the salt.
Ocean Salt Composition
Sodium chloride, the same salt people use in cooking, makes up about 85 percent of ocean salt. Other dissolved minerals include magnesium, calcium, potassium, and various other elements. All these minerals together create the salty taste of ocean water and affect ocean properties like density and temperature.
Salt Balance in the Ocean
While salt keeps accumulating, the ocean's salinity remains relatively stable because the amount of salt entering equals the amount being removed through various geological processes. Some salt gets trapped in sediments on the ocean floor, and some is used by sea creatures to build shells and skeletons. This balance has kept ocean salinity fairly constant for millions of years. 
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