of elements we observe now (92), but it is inevitable for scientific thought to try to expand these limits, both by theoretical speculations and by experiment.17
Up till now these efforts were unsuccessful. The attempt of V. Harkins to regard the neutron as a chemical element is sure to be proven unsuccessful too. But as long as it is possible to approach the solution of these problems experimentally, they should not be dropped. This concerns the possible existence of transuranic elements (93 and higher). We should assume that the number of elements (92) and the number of the known isotopes (219) is not final but only temporary, as has been stated empirically.
Geochemistry can study elements only in the thin surface layer of the Earth, which does not exceed 16 to 20 km and which comprises the upper part of the Earth’s crust. I shall dwell upon this crust later, and we shall see that its total thickness reaches 60 to 100 km. The atmosphere is situated above it, but only its lower part, the troposphere, is chemically related to the Earth’s crust: its thickness is 10–15 km. The height of the whole atmosphere (i.e., of the gases following the movement of our planet’s body) is much more considerable, and it undoubtedly exceeds 700 km. The chemical elements of the Earth’s crust and the troposphere are distributed in quite different ways. The difference in the quantity of the various elements contained in it is enormous. The quantity of oxygen – the most widespread element – exceeds the quantity of radium by hundreds of billions of atoms, but radium is not the rarest elementary substance of the Earth’s crust.
Here I give a table (table 2) of the quantities or masses of the chemical elements contained in the Earth’s crust (including the atmosphere), expressed both in weight percentage of the Earth’s crust and in tons. The distribution of chemical elements in the Earth’s crust is given in weight percentage and is categorized by orders of ten: The mass of the Earth’s crust at a maximum thickness of 20 km is 3.25 × 1019 tons.
table 2 the abundance of chemical elements in the earth’s crust as a percentage by weight
(the weight of the earth’s crust at a maximum thickness of 20 km is 3.25 × 1019 t)
Comment: less than 10-11 % are Kr, Xe, Ne, Po, Pa, Ac and Rn.
This table was presented in its general features by the American scientist F. Clarke, who had studied these problems for more than forty years. I have introduced some corrections and changes and given it a different form. It is created on the basis of a huge number of exactly stated facts and many thousands of chemical analyses. The latest calculations of F. Clarke and W. Washington are based on 5508 complete chemical analyses of rocks that were done during the last 30 years. More than 100 years ago, in 1815, the English mineralogist W. Phillips was the first to make such calculations for 10 chemical elements. He returned to this task several times but his calculations, supported by D. Phillips and H. de La Beche, did not become part of science. Still, a small number of scientists, including Elie de Beaumont and A. Daubret, did not drop the task. Much later, in 1889, F. Clarke returned to this problem by systematically studying the principal chemical elements, and at the end of the nineteenth century, I. Focht tried to cover all the chemical elements in this way. Forty years is a sufficient amount of time to judge the correctness of this empirical generalization, and we must say that no significant changes have been made in F. Clarke’s table since then.
Studying the table, we see that there is a correlation between the abundance of chemical elements in the Earth’s crust and the composition of corresponding atoms. This correlation is very complicated and is not quite known to us. Prof. G. Oddo from Pavia had noticed long ago that chemical elements possessing even atomic numbers and containing nuclei of helium; that is, elements whose atomic mass is divisible by four, strongly prevail in the Earth’s crust; they comprise 86.5% of its total mass. Later, similar investigations were made and deepened by Prof. W. Harkins in Chicago. Harkins proved that the same fact could be observed in meteorites, where the prevalence of elements with even atomic numbers is still more considerable. It reaches 92.22% for metallic meteorites, and 97.69 % for stony meteorites.
Meteorites are celestial bodies independent of the Earth, and maybe of the Solar System as well. Their chemical processes have a very indefinite and distant analogy with the processes of the Earth’s crust. But the same regularity is observed in them – the same prevalence (even more pronounced) of elements with even atomic numbers, of atoms with even electric charges of nuclei.18 Nevertheless, this very simple observation raises very important problems. It proves that the chemical composition of the thin surface film of our planet, which as far as we know does not at all correspond to the composition of the whole planet, is not accidental.
The chemical composition of the Earth’s crust is connected with the definite structure of its atoms. Long ago, before Oddo’s time, D. I. Mendeleyev had pointed out that the entire principal mass of the substance of the Earth’s crust consists of light elements (not heavier than iron, #28). Apparently, if the even ordinal elements prevail, the even columns of the Mendeleyev table prevail too. The importance of these observations is evident, for they show that the chemical composition of the Earth’s crust cannot be explained by geological reasons. But no important further conclusions have been drawn yet, and the main point is that the field of empirical observation was not expanded after all, in spite of numerous attempts. Hypotheses and extrapolations dominate here. Very often scientists point to the lesser stability of the nuclei of uneven atoms, but this too is a hypothesis.
This phenomenon may be connected with another one, for observations show that the surface parts of not only our planet, but also those of other celestial bodies – the Sun and stars – have a similar composition. This gives the impression that some regularities exist, which may be connected to the exchange of matter between all the outer envelopes of all the cosmic bodies. The existence of such incessant matter exchange is almost completely ignored now, although one can hardly doubt it.
The connection between atomic composition and the abundance of elements in the Earth’s crust manifests itself distinctly in another phenomenon discovered not long ago by V. M. Goldschmidt. For the lithosphere – the Earth’s solid crust – it is possible to calculate the volume occupied by different atoms. Proceeding from the numbers of Clarke and Washington for massive rock formations, and taking into account the fact that in crystalline silicates and alumsilicates the atoms are ionized so that an isotropic (spherical) field of application of their forces could be assumed for them, Goldschmidt calculated the volume occupied by atoms in the solid lithosphere (table 3).
table 3 percent by volume of atoms in the lithosphere
Although the fields of atoms cannot have an ideal spherical form, the amendment will not change the principal conclusion about the distinct prevalence of oxygen and the rarity of silicon within the lithosphere’s volume. The lithosphere consists mainly of oxygen atoms, and they are almost contiguous within it. A similar phenomenon is observed for the hydrosphere, which consists almost completely of oxygen by mass (88.89%).
The influence of the structure of atoms must manifest itself also in other properties of the Earth’s crust, and must first of all be expressed in the scientific classification of natural bodies, in the “natural classification” as it was called in the eighteenth and nineteenth centuries. Any observational science is always based on such a classification, and geochemistry is one of these sciences. That is why we must begin an account of it with the classification of its objects – chemical elements – on the basis of studying the phenomena they create in the Earth’s crust.
There is a premise necessary for such a classification: it should be constructed
