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Salt of the season.

What would your summer be like without this edible rock?

Take a look at the seashore scene above. How would the picture change if the world's salt supply disappeared? For starters, forget about that splashy beach attire. Salt in the dyes keeps the colors from bleeding all over your skin. Next, erase any radios, coolers, sunglasses, or bottles of lotion. That's right, you need salt to make plastic.

Now get ready for the biggest change of all: Take away salt, and you might as well get rid of all the kids in the photo. We humans need salt. Our hearts wouldn't beat without it, and our nerves wouldn't send signals. Salt also helps keep the right amount of water in our cells. Without it, we'd shrivel like jellyfish stranded on hot sand.

Where and how do we get this seasoning for summer and all other seasons? Read on for answers to these and other salty questions.

Why do salty foods taste so good?

Salt makes all flavors taste stronger. Clumps of salt-sensitive taste cells dot our tongues, explains food chemist Manfred Kroger. These taste cells can't be stimulated by plain french fries, for example. But add a dash of salt, and you activate loads of them. Result: an extra flavor burst.

Why do we have these salt-loving taste cells?

They're a product of evolution. They ensure that we eat some salt every day. That's a good thing since the human body cannot store salt the way it can store, say, fat. Salt-sensitive taste cells make us crave the mineral so we constantly replenish our supply.

So where do we get our salt?

From the oceans. They contain enough salt to cover Earth's surface with a layer 14 inches deep--if the water ever dried up, that is.

How did the seas get so salty?

Billions of years ago, the oceans were filled with fresh water, says marine geologist Phil Meyers. But ancient rivers dumped loads of eroded rock into them. This sediment was rich in the element sodium (Na). At the same time, undersea volcanoes spewed a mixture of gases into the water, including large quantities of chlorine (Cl). In the ocean's chemical soup, these disolved elements--both highly reactive--found each other and bonded to make NaCl--salt.

So how do we get the salt we need out of the water?

"It depends on where you live," says salt chemist Susan Gelb. In hot, dry regions, people harvest salt by evaporating sea water (left). When the water goes, it leaves behind a sediment of salt crystals.

The rest of us get our salt by mining massive underground deposits (below). These deposits are the salty remains of seas that evaporated in hot, dry regions millions of years ago. Because pieces of Earth's crust have moved around a lot since then (see SW 2/7/92, p. 10), you'll find these deposits all over the world.

Will we ever use up Earth's salt supply?

Not likely. All the salt we use gets recycled--naturally. Take the salt we spread on icy highways. Rainwater eventually washes it into rivers and streams, which flow back to the ocean. Salt deposits on land can erode and return to the ocean in the same way.

Even the salt you sprinkle on your french fries will eventually move through this land/sea cycle. You excrete it in urine and sweat, then flush it or wash it away.

Where will that salt turn up next? Think about it the next time you're sitting on the beach scarfing down some fries.
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Title Annotation:the many uses of salt
Author:Plaut, Josh
Publication:Science World
Date:May 7, 1993
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