Scrupulous "accounting" of the reserves of chemical elements started with a scientific feat accomplished by the American scientist Clark. He performed more than 5500 chemical analyses of a great variety of minerals from the tropics and from the tundra, of all kinds of water from lakes in the depths of the wilderness and from the Pacific Ocean. He studied samples of various soils from all parts of the world. This titanic work took him twenty years. Thanks to Clark and other scientists mankind got a quite distinct idea of the abundance of different elements on Earth.

   So was born the science of geochemistry. It told wonderful stories such as had never before been known to man. It appeared that the first 26 representatives of the Mendeleyev Table, from hydrogen to iron, form practically the entire crust of the Earth. They constitute 99.7 per cent of its weight, leaving only a "miserly" three tenths of per cent for all the other 67 elements occurring in nature.

   Now what is there the most of on Earth? Neither iron, nor copper, nor tin, though man has been using them for thousands of years and the supply of these metals seemed immense, even inexhaustible.

   The most abundant element is oxygen. If we place all the Earth's resources of oxygen on one pan of an imaginary pair of scales and all the rest of the elements on the other, the scales will strike an almost perfect balance. Almost half of the Earth's crust is oxygen. It is everywhere: in water, in the atmosphere, in an enormous number of rocks, in any animal and plant, and everywhere it plays a very important part.

   One quarter of the Earth's "firmament" is silicon. It is the ultimate foundation of inorganic nature. Further, the elements of the Earth arrange themselves in the following order of abundance: aluminium, 7.4 per cent; iron, 4.2 per cent; calcium, 3.3 per cent; sodium, 2.4 per cent; potassium and magnesium, 2.35 per cent each; hydrogen, 1.0 per cent; and titanium, 0.6 per cent. Such are the ten most abundant chemical elements on our planet.

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