Why is the ocean salty?

As rain is formed in the atmosphere, it absorbs carbon dioxide, making it slightly acidic when it falls on the land. This rain physically and chemically erodes the rock and carries various minerals and salts as it runs off into the ocean.

As the water re-evaporates into the atmosphere, the salt is left behind in the ocean. Over a long time period, the salt accumulates and becomes more concentrated. According to the U.S.G.S., about 3.5 percent of the weight of seawater comes from the dissolved salts. In addition to surface runoff, hydrothermal vents on the ocean ridge also contribute a large amount of salt and minerals to the ocean, adding to the overall salinity.