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| Natural sea salt |
Common table salt is a compound. A compound is a chemical substance in which two or more elements are joined together. An element is a substance that cannot be broken down into a simpler substance. Elements, either alone or joined together as compounds, make up every object. The elements sodium and chlorine join together to make table salt.
Sodium is represented by the symbol "Na," and chlorine is represented by the symbol "Cl." Because one atom (smallest unit that has all the chemical and physical characteristics of an element) of sodium joins with one atom of chlorine, table salt is represented by the symbol "NaCl."
The need for salt
All animals, including humans, require salt. Salt is needed to regulate many bodily functions including maintaining a regular heart rhythm, blood pressure, and fluid balance in the body. Additionally, salt is required for nerve cells to communicate efficiently, and for regulating the electrical charges moving into and out of cells during processes such as muscle contraction.
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An adult human has about 9 ounces (about 250 grams) of salt in the body. As the body cannot produce salt, animals must get salt from food and water. If too much salt is consumed, the kidneys remove the salt and flush it out of the body.
Salt is also economically important. In ancient societies, salt was often traded for other valuable goods. Early cultures used salt for food preservation and Roman soldiers were paid partially in salt, probably giving rise to the word soldier from the Latin sal dare for "giving salt."
Today salt is used in food, on food, to de-ice highways, and in the production of industrial chemicals. Nearly 250 million tons (220 metric tons) of salt are produced worldwide every year.
Getting salt
Salt comes from a variety of sources. Salt is known as rock salt, or halite, when it is found in the ground. Rock salt can be mined from beneath the surface through drilling, blasting, and hauling it to the surface. Most mined rock salt is used to de-ice roads in the winter. Salt may also be extracted by solution mining, which involves pumping water underground.
The water dissolves the salt, creating brine, which is then pumped back to the surface. The water is evaporated out of the brine, leaving behind salt deposits. Solution mining produces purer salt than rock salt mining. Solution mining is often used to produce edible (able to be eaten) salt.
The oceans hold more salt than humans could ever use. Salt accounts for about 3.5% of the weight of the oceans. The oceans contain an estimated 39 quadrillion tons (39 million, billion tons, or 35 million, billion metric tons) of salt! The oceans are getting even saltier. Flowing rivers pick up dissolved salts and minerals such as chloride, sodium, sulfate, and magnesium from the rocks and soils.
Once rivers flow into the ocean, these salts and minerals are deposited in the ocean. Salts and minerals do not evaporate out of the ocean. Once salts are deposited, they will remain there forever, unless humans remove them. Gradually, the ocean gets saltier as more dissolved salts are carried into it.
