If we could extract all of the salt in Earth's oceans, it would cover the planet in a layer 500 feet deep. There are about 4-and-a-half ounces (almost 8.5 tablespoons) of salt in every gallon of ocean water averaged over all of the Earth’s oceans. That’s a lot of salt, but how did it get there?

 

Rain water dissolves a small amount of the carbon dioxide in the atmosphere as it falls. This produces an acid (carbonic acid) that breaks down things like rocks and dirt into their constituent molecules and pieces of molecules. As rain water finds its way into streams and rivers, it carries all of those bits and pieces along with it. A lot of the bits and pieces eventually end up in the oceans. 

 

Two of the most common bits that find their way to the oceans are sodium and chlorine ions. The electric charges of these atoms make them clump together. Sodium and chlorine bonded together makes salt.

 

Sodium and chlorine ions can also get deposited in the ocean through volcanic fissures along some parts of the ocean floor. Minerals in the Earth's crust are dissolved by the extremely hot gas and liquid that seeps from these hydrothermal vents. This provides another source of the building blocks of salt. 

 

The salinity of the oceans—the amount of salt compared to the amount of water—is not constant from one place to another or from time to time. Close to land, where rivers dump large amounts of relatively fresh water into the ocean, salinity can vary by as much as 25 percent from spring to fall. Rain dropping directly into the ocean tends to make the surface a bit less salty than deeper down, decreasing the salinity of the ocean’s surface. 

 

The salinity near the surface can increase when air temperature rises. Evaporation increases, but because salt is heavy it doesn’t evaporate along with the water. Less water, same amount of salt— increased salinity. The heavier, saltier water sinks, changing ocean currents and, in turn, weather patterns. 

 

Drinking salty water increases the salinity of your blood and other fluids in your body. It’s hard for salt to get inside your cells, so drinking salty water creates an imbalance in the levels of salt inside and outside of your cells. In response to this imbalance, water moves, or diffuses, outward across the membranes that enclose your cells. Your cells shrivel, and you can probably imagine that isn’t a good thing. 

 

Your body also tries to rid itself of excess salt by flushing it out through the elimination of fluid, i.e., urination. Your kidneys can produce liquid only slightly less salty than ocean water, so drinking ocean water causes you to urinate large quantities of fluid. The result is severe dehydration—also not good.

 

If you live near a coast, enjoy the beach on a nice, warm day this summer. Just be sure not to drink the water.

 

 

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Parts of the world experience droughts and some are just historically dry. People have been experimenting with “desalination”—removing the salt from ocean water—to generate drinkable, fresh water. What do you think are the advantages and disadvantages of desalination as a means to solve our water shortage problems?