The amount of water on the earth, an estimated 326 million cubic miles, is impossible to comprehend. An enormous proportion of this total, approximately 97.2%, fills the oceans of the world. Scientists pay a great deal of attention to the exchanges of water between the oceans, the atmosphere and the continents. This unending circulation of the earth's water supply has been named "The Hydraulic Cycle," which is constant and repeated endlessly.
The water cycle has persisted since oceans and lands became the dominant features of the evolving Earth. The cycle is somewhat complex in its extent and process, but stated simply, water is constantly evaporated from the oceans and into the atmosphere. Prevailing winds blow this moisture-laden air over the land where the water is precipitated out as rain or snow. In fact, hurricanes, considered nature's most destructive handiwork, are the most efficient means of changing water into salt-free rain. This water is then carried back to the sea by rivers and underground flow.On its trip back to the sea, flowing water comes in contact with almost all of the elements present in the upper part of the earth's crust, which includes over half of the 103 known elements. Some of the material is dissolved and carried to the sea in solution. As a result, the mineral richness of the sea is immense; most of the elements and minerals that occur on the land are also present in the oceans, including gold!
The oceans of the world carry in suspension about 25 tons of gold in each cubic mile of sea water. Although this is an impressive figure, so is a cubic mile of ocean. If mining it to its fullest were at all possible, there would be enough to give each person on earth about nine pounds of solid gold. Since gold is dispersed throughout the water, it is present in such minute concentrations that no method has yet been devised to extract marine gold profitably.
Imagine, for example, a modest-size room 10 feet wide, 12 1/2 feet long, and 8 feet high. These dimensions represent a volume of one thousand cubic feet. Filled to capacity with sea water, the room would contain only about five thousandths (0.005) of an ounce of gold. That is certainly not enough to get excited about, and of course not enough to try to extract. Although there are 27 million tons of gold in the world's oceans, only about 5 ounces of gold can be found in a billion ounces of sea water (one part per 200 million)! So don't bother packing your gold pan for the next ocean voyage. There have been many scientific attempts to recover the minute flecks of gold strewn throughout the sea, and all have failed.
At present the only metal that has been successfully extracted from the sea in commercial quantities is manganese. It occurs as nodules carpeting the ocean floor in an almost continuous layer, so in many places it is easy and economical to recover. The manganese appears to be precipitated over other mineral deposits, for within the nodules are about 40 different minerals, and an occasional shark's tooth, whale bone or piece of pumice. The nodules are valued more for the other minerals, such as cobalt, zinc, nickel, or copper than for the manganese.
Of all substances dissolved in the oceans, 85 percent is sodium chloride, the mineral halite, best known as common table salt. Each cubic mile of sea water contains over 166 tons of dissolved salt, enough to supply the world's demand for several years. Scientists have calculated that if all the salt were extracted and spread over the land it would form a layer more than 500 feet thick!
In some places salt is still recovered from sea water by simple evaporation, the same method used by the Chinese as early as 100 B.C. At present most salt is mined from brine wells and salt domes, which are evidence that the continental area in which they are found was once covered by oceans. Being cut off from the sea, the water was subject to evaporation, and the mineral matter carried in solution eventually would precipitate out. In many cases the result is enormous concentrations of salt ready for the dinner table. Of course this is an oversimplification of the complex mining methods that are applied, but salt is salt.
Phosphate, the commercial product from phosphorite, is used extensively as a fertilizer and, because it is much in demand, is a valuable economic commodity. Scientists know that a rich deposit of phosphorite lies on the sea floor off the coast of San Diego, and economic recovery is quite feasible. However marketable the deposit may appear, it will never be mined because the area was once a naval firing range. As a result, thousands of live shells and mines are spread out over the phosphorite waiting to explode when even slightly disturbed. The deposit has been thoroughly studied by scientists of many specialties, and all have concluded the risk is so great that this will remain forever a lost treasure in the sea. Several people were heard to say, as they walked away from all these riches, that such are "the fortunes of war."
Phil and Nancy Seff are the authors of several science books, including "Our Fascinating Earth." Their column runs regularly in the Deseret News Science/Technology section.