You may be aware that the oceans cover over 70% of the Earth’s surface and that 97 percent of all water on and in the Earth is saline, implying that our planet has a lot of salty water. According to some calculations, removing the salt from the ocean and spreading it equally across the Earth’s land surface would result in a coating more than 500 feet (166 meters) deep, equivalent to the height of a 40-story office skyscraper. Where did all this salt come from, though? If you go into mythology and folklore, you’ll see that practically every civilization has a narrative about how the waters became salty. The solution is actually rather straightforward. The salt in the water derives from land-based rocks. Here’s how it works!
From precipitation to the land to the rivers to the sea
You may be aware that the oceans cover over 70% of the Earth’s surface and that 97 percent of all water on and in the Earth is saline, implying that our planet has a lot of salty water. According to some calculations, removing the salt from the ocean and spreading it equally across the Earth’s land surface would result in a coating more than 500 feet (166 meters) deep, equivalent to the height of a 40-story office skyscraper. Where did all this salt come from, though? If you go into mythology and folklore, you’ll see that practically every civilization has a narrative about how the waters became salty. The solution is actually rather straightforward. The salt in the water derives from land-based rocks.
Chloride and sodium are the two most common ions found in saltwater. Over 90% of all dissolved ions in saltwater are made up of these two. By the way, the salinity (salt content) of seawater is around 35 parts per thousand. In other words, dissolved salts account for around 35 of 1,000 (3.5%) of the weight of saltwater; the weight of sodium chloride in a cubic mile of seawater is about 120 million tons. To prove that saltwater isn’t worthless, a cubic mile of it may hold up to 25 pounds of gold (at a concentration of 0.000005 parts per million). Think about how much a cubic mile is (1 cubic mile contains 1,101,117,147,000 gallons!) before you go out and try alchemy on saltwater.
Salt comes up from below, too
Dissolved salts are not just found in rivers and surface runoff. Hydrothermal vents are newly found phenomena on the crests of oceanic ridges that provide the seas with dissolved minerals. These vents are the points on the ocean floor where sea water that has seeped through the oceanic crust’s rocks has heated up, dissolved some of the crust’s minerals, and then flowed back into the ocean. Large levels of dissolved minerals are present in the hot water. According to current estimates of the amount of hydrothermal fluids pouring from these vents, the whole volume of the seas might seep through the oceanic crust in around 10 million years. As a result, this mechanism has a significant impact on salinity. However, the interactions between saltwater and oceanic basalt, the rock that makes up the ocean crust, are not one-way; some of the dissolved salts react with the rock and are subsequently eliminated from the seawater.
Submarine volcanism, or the eruption of volcanoes beneath water, is a last process that feeds salts to the seas. Seawater reacts with heated rock, dissolving part of the mineral elements, in a similar way to the preceding process.
