About 97 percent of the all the water on Earth is found in the ocean. According to NOAA’s National Geophysical Data Center, there is an estimated 321,003,271 cubic miles of water in the ocean. In one cubic mile of seawater, the weight of the salt in that seawater is estimated to be about 120 million tons since approximately 3.5 percent of the weight of seawater is salt. This means there is roughly 38.5 quadrillion tons of salt in the oceans.
The heaviest object ever physically weighed on Earth is NASA’s Revolving Service Station at Kennedy Space Center. It weighs 2,423 tons. It would take 15.9 trillion Revolving Service Stations to equal the weight of the salt in the oceans.
This is so much salt that if it was somehow removed from the ocean and spread across the entire surface of the earth evenly, it would make a layer more than 500 feet thick. That is the equivalent to about the height of the Washington Monument in Washington D.C. or about the height of a forty-story building.
Why Are the Oceans Salty?
There’s a simple answer why the oceans are salty. They’re salty because of rocks from the land. Rain that falls over land contains carbon dioxide making it slightly acidic due to the formation of carbonic acid. The rain then erodes rock physically and chemically, and the dissolved minerals are broken down into ions. These ions eventually find their way to the oceans. Those ions not used by organisms remain in the ocean and increase in their concentration. The two ions that are in the highest concentration in the ocean are sodium and chloride. They make up 90 percent of the ions in seawater. Sodium chloride is the compound that is formed which is salt.
Two other processes occur that contribute to the salinity of the ocean; hydrothermal vents and underwater volcanoes. Minerals are dissolved from the crust and flow into the ocean when seawater reacts with hot rock.