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Having a shaker full of salt in every house on Earth today is aΒ privilege that would have made our ancestors cry.

That’s because salt is one of the most important substances to life on Earth.

To find out why, we need to look at what salt actually is. Salt is a molecule made of a sodium and a chlorine atom joined together with an ionic bond, losing the properties of each and becoming something new. That is fortunate, as sodium is a highly reactive metal and chlorine will kill you.

An ionic bond happens when an atom donates an electron to another atom. This gives the first atom a positive charge, and the second atom a negative charge, and they are both now called ‘ions’. The ions are not physically stuck to each other, but the different charge makes them attracted to each other, and the ions all stick together in a big crystal-shaped lattice.

A salt rock is one big crystal lattice. Green is chlorine ions, purple is sodium ions.

The attraction between ions holds salt crystals tightly together. You can heat, Heat it, smash it, burn it, nothing will pull the ions apart from each other.

That is, unless you give the ions something even more attractive to them than each other.

Salt is a junkie for water. Water has a special property (called ‘polarity‘) that makes its molecules irresistable to lots of ionic molecules. As soon as water touches salt, it falls apart. The ions split off and float around in the water instead. That is what’s happening when we see salt dissolving in water.

All animals need sodium ions about as much as they need food and water. It’s crucial in how our muscles move, it’s used to generate nerve impulses so we can feel, and to regulate blood pressure so we don’t die.

Because of how it dissolves, salty water is a perfect way to transport those crucial sodium ions through our bodies.

If you don’t have enough sodium ions in your body at all times, your brain swells, you fall into a coma, and die.

If you have too many, they will pull water out of your cells like air in a vacuum-sealed bag, which unwinds all of your important proteins. This kills the cell. If this happens in the brain, you’ll have a stroke.

Living things that don’t have skin like snails, slugs, leeches, and bacteria, are vulnerable to salt. If you dump a pile of on them, it will dissolve into their bodies and kill them. This is why we salt our meats and other food as a form of preservation; it kills the vulnerable bacteria. Our ability to preserve food in this way has been called a “founder contributor to the development of civilisation.”[1]

To make things difficult for life, our body is constantly losing salt through bodily functions, and it must constantly be replaced. But it’s not easy to get, particularly if you live inland or far from a salt flat.

Salt flats are usually the remnants of saltwater lakes, now evaporated. This is Salinas Grandes, Argentina. Image source: Kevin Jones

Carnivores are usually fine as they get salt from meat. But herbivores and omnivores need to supplement it. This is why we need to give our rabbits, horses, and cattle salt licks to stay healthy, but not our cats and dogs.

But if you’re a large inland herbivore like an elephant and you don’t want your brain to swell and die, you often have to travel vast distances to salt rich clays or rocks, or venture deep into underground caves.

Throughout human history, hunter-gatherer tribes generally did not require salt supplementation as their diets were rich in meat.

Settled societies on the other hand, more reliant on vegetables and grains, went absolutely f*cking crazy over salt.

Empires have been shaped by our need for salt:

Taxes

  • Salt was the subject of the first tax in history (in Ancient China), and sustained the Empire for thousands of years. At times tax on salt brought in half of the Empire’s tax revenue.

Revolutions

  • The French revolution was in part motivated by an extremely high and unpopular tax on salt, called the gabelle, which disproportionally affected the poor.
  • The Indian independence movement was in part motivated by high salt taxes imposed by the British Raj.

Trade and infrastructure

  • Salt production was one of the original human industries.
  • It was one of the first international commodities, with merchants creating salt routes across the Sahara and Mediterranean Sea.
  • The first great Roman road to be built was the Via Salaria, or ‘Salt Road’, built for the purpose of transporting salt across the Italian Penninsula. It was eventually extended to run 242 kilometers.
  • ‘Salt Roads’ traversed Europe throughout much of the Middle Ages, and many modern highways were built on top of them.

Cities

  • The oldest settlement in Europe, Solnitsta in Bulgaria, was built around a salt production facility and supplied salt to people living in the Balkans.
  • Rome was founded where it was because it was next to a saltwork site, and a river.
  • Munich, Germany was built along one of Europe’s salt roads, and flourished as a result of a salt tax.
  • In the 19th Century, salt mined in Cheshire, UK was brought to the nearest port, called Liverpool, before being exported globally. It transformed Liverpool from a small port to a prime city.
  • Timbuktu, Mali was a market city for salt, gold, ivory, and slaves for centuries.
  • Salzburg, Austria. Salzburg means ‘Salt Castle’ and it sits on is the Salzach River, or ‘Salt River’, both references to the nearby salt mines and the river on which salt barges have travelled since the 8th Century.
  • Tuzla, the third largest city of Bosnia, was built on a salt mine (Tuzla meant ‘salt mine’ in Ottoman Turkish). Because of past excavations, parts of the city are now sinking into the ground.
  • Every city in Britain that ends in -wich, like Norwich, was the site of a salt water spring once used for salt production.

Empires

  • Poland’s salt mines in part contributed to its 16th Century golden age, until disrupted by German sea salt production.
  • Venice, Italy. Venice rose to prominence in part because it secured a salt monolopy over the Mediterranean, which it traded in Constantinople for exotic spices until disrupted by salt production in the newly discovered Americas.

Wars

  • War of Ferrara, Italy (1482-4)
  • The Salt War, Italy (1540)
  • During the American Revolutionary War, Loyalist forces attacked Revolutionaries’ salt shipments in order to interfere with their ability to preserve food.
  • San Elizario Salt War, Texas (1877-8)

The ‘Salt Castle’ has greeted salt barges travelling on this river for centuries. Photo by Reinhard Kraasch

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Ben McCarthy

Ben McCarthy

Ben is the Founder of Discover Earth and the author of the Big Ideas Network.