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The Sea's Bounty
| Article
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13749 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
8 / 1988 |
2,642 Words |
| Author
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Harold Goldwhite
Harold Goldwhite is professor of chemistry at California
State University, Los Angeles. |
The saltiness of our tears reminds us of the central part that salt--sodium chloride--has played in the human drama. The modern evolutionary view is that tears are salty because our remote biological ancestors developed in the salty oceans and their internal fluids contained the oceanic salts. Later life forms have retained in their vital fluids the salty characteristics of their ancestors. There is still a remarkable similarity between the composition of salts in sea water and of human blood plasma. Life, originating in salt water, depends critically on salt.
Early History
Since prehistoric times the pleasant taste of salted foods, as well as salt's role in the preservation of meat and fish, led to its being a prized commodity. There is evidence that the production of salt is one of the earliest organized human activities and that salt trade was one of the driving forces for some of the earliest voyages of exploration. Some historians have argued that the first cities were set up to deal with trade in salt and that early road networks were created to make that trade easier. Salt certainly seems to have been a civilizing force in those early times.
Most of this early salt was obtained directly from the sea. In areas with warm climates, like the shores of the Mediterranean, simple solar evaporation from ponds at the seashore provided ample supplies of salt. Although seawater contains many other compounds besides sodium chloride, the material first deposited when seawater is partially evaporated is almost pure sodium chloride. In cooler climates, like those of cloudy northern Europe or northern China, salt is extracted by seawater evaporation in pots over wood fires. Brine springs or lakes, like the Dead Sea, are also common in many parts of the world. These may be considerably saltier than seawater and were exploited early for their salt. In a few areas, deposits of mineral rock salt occur close to the surface, and some of these were mined in early times.
The major problem of the salt trade in prehistoric times seems to have been not supply--for there were many sources of salt--but distribution. There were consequently areas, well into historic times, where salt was a luxury. Indeed, salt has been used as a medium of exchange, a kind of currency. In Roman times, salt was valuable and highly prized, and a special guard protected salt caravans from being pillaged by robbers. The guards were paid in part with salt: They earned their salary--the familiar word is based on a Latin term that means salt money.
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