If you consider that about 70 percent of the Earth’s surface is covered with water, and 97 percent of that water is saline, you quickly realize that our planet has a lot of salt water. Where does all that salt come from? Over time, dissolved carbon dioxide from rain, in the form of carbonic acid, erodes rock and ultimately carries salts and minerals into the sea. The National Oceanic and Atmospheric Administration estimates that if all of the salt from the oceans could be spread evenly across the Earth's surface, it would form a 500-foot (166-m) layer. That’s the height of a 40-story office building.
Keeping an "ion" the ocean:
- Chloride and sodium make up more than 90 percent of all dissolved ions in the ocean. Some are used by organisms, but most just build up over time, increasing the overall saline concentration.
- In a cubic mile of seawater, the weight of the salt comes to about 120 million tons.
- To a lesser extent, salt also finds its way into oceans from hydrothermal vents and from the eruption of underwater volcanoes.