Salt is, of course, the most common substance found in sea water, but it is far from being the only one. In fact, sea water is actually quite rich in mineral solids.

The solids dissolved in sea water vary from about 1 per cent where rivers enter the sea to about 4 per cent where the circulation of water is partly restricted, but they average about 3.5 per cent (one hundred pounds of sea water, if boiled away, will leave behind close to 3.5 pounds of solids). Most of this is ordinary salt -- sodium choloride.

Considering the dissolved material as elements and simple groups of elements, the solids in sea water are:

*Traces of gold, iron, copper, and many other elements and compounds.

In themselves, the figures above may not mean much. But what follows should make them clearer. There is very, very little iron dissolved in sea water (less than one-thousandth of 1 per cent), but the total amount of iron comes to about 11.5 trillion tons. If it was possible to extract that iron, it would be enough to supply the world for more than 100,000 years at our present rate of use.

The fresh water that flows into the seas from rivers carries small amounts of dissolved minerals as well as undissolved solids. These dissolved minerals add about 3 billion tons of elements and compounds to the seas every year, which amounts to about 87 tons from every square mile of land on earth.

An interesting by-product of all this figuring is an estimate of the age of the seas. By assuming that all water was fresh in the beginning and that the elements and compounds have all been added by rivers at rates similar to the present, and then making allowances for a number of other factors, one can safely estimate the seas to be at least 100 million years old.

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Our Wonderful World. New York: Grolier Incorporated, 1965.

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This page was last updated on 06/25/2017.