Geochemistry and the Biosphere. Vladimir I. Vernadsky
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discoveries.
It is quite probable that frailty is a property of all elements. Even if these probabilities become scientifically proven facts, it will not affect the specific position of the group of radioactive elements in the system of classification. Decomposition of elements in this group is quantitatively incomparable with its possible manifestation in all other elements. Weak radioactive elements, in their geochemical manifestation, can be united into one group with strong radioactive ones as little as ferromagnetic elements can be united with the usual paramagnetic ones in case of magnetic properties.
The last group – that of rare Earths – must here and in the Periodic Table of chemical elements be presented as a special group. I think it consists of 15 elements that correspond to atomic numbers 57 to 71 without a break. Scandium and yttrium are sometimes included into this group although they do not really belong there. As we have seen, they belong to the group of dispersed elements. Concerning scandium, this seems certain to me from the chemical point of view. As for yttrium, some chemists, for instance R. Vogel, have come to the conclusion that it should be separated from the rare Earths for purely chemical reasons.
From the geochemical point of view, the main characteristic feature of these elements is the complete absence of their vadose compounds (compounds that have appeared in the biosphere). But their history in the biosphere is not quite clear as yet. It is evident that some of them get dispersed in it: for instance, gadolinium, samarium, europium, and neodymium. They, as well as cerium and lanthanum, enter living matter where their history is unknown. But at the same time, their principal minerals such as monacytes, xenotymes, and orthites, which appeared in magmas or pegmatite veins under conditions of high temperature and high pressure, are very stable in the thermodynamic field of the biosphere, which is quite different from those original conditions. It is possible that the majority of their atoms stay inert there and do not migrate.
There are indications of genetic correlations between the elements of these groups, but these indications are, until now, beyond the realm of facts. But one essential fact arouses no doubt: All the elements of this group, “the chemical nebula” as it was called by Crookes, usually remain together in one body under diverse terrestrial conditions since they do not react with the majority of terrestrial chemical elements. The question is being solved now. The observations of von Hevesy seem to indicate the genetic radioactive connection between samarium and neodymium, and further investigations will reveal more. But even if radioactivity – the weak type – is proven, it will not interfere with the isolation of this geochemical group. The elements of this group do furthermore not comprise any noticeable part of the aquatic structure of the Earth’s crust. Minerals coming from water solutions are not known.
The quantities of matter concentrated in each of the six geochemical groups of elements are very different (table 7).
table 7 the masses of geochemical groups of elements in the Earth’s crust.
| Geochemical groups | Weight in tons |
| Rare Gases | 1014 t |
| Noble Metals | 1012 t |
| Cyclic Elements | 1018–1019 t, close to 2 × 1019 t |
| Dispersed Elements | 1016 t |
| Elements of High Radioactivity | 1015 t |
| Elements of Rare Earths | 1016 t |
Of course this table can be regarded as a first approximation to reality, but the order of the phenomena is expressed rather exactly. The cyclic elements comprise more than 99.7%, almost the whole mass of the Earth’s crust. But the remainder of 0.3% is not an insignificant quantity. It makes up quadrillions of metric tons. It includes, for example, the radioactive elements, whose great significance in the mechanism of the biosphere will become clear further on. It refers to matter in a chemically active state that possesses free (atomic) energy, and it therefore performs an enormous amount of chemical work in the Earth’s crust. The quantity of this matter is measured by a number of the order of 1015 t. This number is close to the mass of another kind of “active” matter of the Earth; that is, living matter (living organisms), which is as deeply implanted into the mechanism of geochemical processes. In fact, the small fractions of the Earth’s crust that correspond to them bring about all the grand geochemical (and apparently a lot of geological) processes of our planet.
2 forms of existence of chemical elements
The history of chemical elements in the Earth’s crust can always be reduced to their various movements, or shifts, that in geochemistry we shall call migrations. The movements of atoms making up compounds, their transmissions in liquids, gases and solid bodies, and in the processes of breathing, nutrition, the metabolism of organisms, etc., are all migrations. These migrations within the Earth’s crust create large systems of various chemical equilibria.
In geochemistry, the principal task is the study of equilibrium systems resulting from the elements’ migrations. These systems can always be expressed in terms of mechanics, and in the form of dynamic and static systems, those of atomic equilibria. The laws of equilibrium, of homogeneous and non-homogeneous systems of any kind of bodies, embrace the whole of geochemistry. The profound synthesis of these laws was made at the end of the last century by the American scientist J. W. Gibbs, and was deepened by the investigations of G. Duham, H. le Chatelier, G. V. Backius-Rosenbum, K. Brown, G. H. Tammann, and others.
In the history of chemical elements of the Earth’s crust, we can separate several different groups of equilibrium systems, which can contain the elements for an indefinite amount of time – “eternally” on the scale of geological time. These groups of equilibrium systems are more or less independent and a chemical element is subject to different physical and chemical regularities in each group. The study of geochemical problems can be reduced to the study of the history of every chemical element in the conditions of each of these groups, and to the mutual correlation between the histories traced in such a way, because a characteristic feature of the terrestrial history of the chemical elements is the incessant migration of elements from one equilibrium group to another throughout geological time.
I will refer to these different groups of equilibrium systems as different forms of existence of chemical elements. I cannot give a detailed account of the forms of existence of chemical elements here. The only thing I will say is that these forms must be quite numerous, but that not many of them can be observed on the Earth, to say nothing of the Earth’s crust. If we go beyond the limits of the Earth’s crust, and moreover, beyond the limits of our planet, we will come across alien forms of existence of chemical elements that are unknown to us here. Among them are the “gases” of solar corona electrons, the states of a comet or nebula substance, and heavy gases of stars such as star B of Sirius. The forms of existence have been determined in a purely empirical way, and each of them has turned out to contain atoms in specific states. In fact, they are fields of different states of atomic systems.
In the Earth’s crust, we distinguish four different forms of existence for chemical elements. First, the following three:
1 Molecules and their compounds in minerals, rocks, liquids and gaseous terrestrial masses.
2 The existence of chemical elements in living beings; the autonomous manifestations of living matter.
3 The existence of elements in silicoaluminum magmas; complex, ever-changing systems, more or less viscous, which have a high temperature and a high pressure and which are supersaturated with gases.
We can clearly imagine neither chemical processes nor states of atoms in these media, which exist in a thermodynamic field of phenomena that is alien to us. But there is one more, the fourth form of existence, which is usually not distinguished and not taken into consideration – that of the dispersal of chemical elements. In migrations of elements this form plays a very important role. As we have seen, it is typical of a certain geochemical group of elements. While studying the geochemical history of elements, none of these forms of existence can be ignored. We must consistently study the fate of each element in all of them and pay special attention to the migrations of elements from one form to another, which are not at all accidental. As the significance of the elements’ dispersal is usually