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chemical elements in the earth’s crust; their forms of existence and classification

1 geochemistry classification of chemical elements

The first question that appeared in geochemistry was that of the number of bodies subject to its study: i.e., the number of different chemical elements and atoms that exist or possibly exist in the Earth’s crust. At present we can only investigate this problem as far as it concerns the surface layer of the Earth. As for this area, the question can be answered definitely enough. In general, taking into account only the isotopes we know, and not the possibly existing ones, we can state more than 200 different compositions of atoms, corresponding to the 92 atomic numbers – N. Moselli’s numbers – in the Periodic Table of D. I. Mendeleyev (table 1).

Within the limits of Mendeleyev’s table, all the representatives of its 92 atomic numbers are apparently known; they are either isolated, or their existence on our planet is confirmed by exact data. But it is possible that in the world – on our planet – there are several elements that are not covered by this table elements lighter than hydrogen, for which Moselli’s number is one, or heavier than uranium, which has atomic number 92. We do not understand as yet why the periodic system includes the number 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 without any hypothesis in view. “A natural classification” is always strictly an empirical generalization, based without exception on scientifically proven facts. When the Periodic Table of chemical elements was being created, geochemical facts were not taken into consideration. That is why geochemical classification cannot be replaced by chemical classification. Geochemical classification should be based on the most general phenomena of the history of chemical elements in the Earth’s crust – all particularities should be ignored.

The most general phenomena can be reduced to the following three characteristic features:

1 Presence or absence of chemical or radiochemical processes in the history of the given chemical element in the Earth’s crust.

2 The character of these processes; their reversibility or irreversibility.

3 Presence or absence in the history of the chemical elements in the Earth’s crust of their chemical compounds, or molecules consisting of several atoms.

As in all natural classifications, the limits between the groups may happen to be indistinct. Sometimes, for instance, one and the same chemical element can be placed into different groups. In this case, the history of the main part of the mass of the atoms or the most striking feature of their geochemical history will be crucial.

So, in the history of very radioactive elements (for example in the history of radium) we notice reversible chemical processes for its compounds, and irreversible radiochemical processes for its atoms. Radium will find its place in a group of elements for which the reversibility of the processes will be the most striking feature. I think that the general difficulties we shall come across here do not exceed those inherent in any natural classification, for classification inevitably leads to simplifying parts of nature that are indivisible and inseparable in essence.

At present it is impossible to classify only three elements from the viewpoint described above: the newly-discovered #43, and also the more familiar #85 and #87, whose masses have not been determined as yet. From this point of view, chemical elements can be subdivided into the following six geochemical groups (table 4). The percentages are related to the 92 elements of the Periodic System. The figures in subscript correspond to the atomic masses.

In all these groups, the difference between even and uneven numbers is evident. For groups 1, 4, and 5 it can be expressed quantitatively with sufficient precision (table 5), and for groups 1 and 5 this correctness is without doubt. For group 3, embracing the majority of the elements, it becomes noticeable only concerning widespread elements; that is, elements that make up a large portion of the total mass of matter.

table 4 chemical elements in geochemical groups

table 5

For the other three groups the data are less precise. But F. Clarke’s table, which was presented long before the appearance of our ideas about atomic numbers and the positive charges of nuclei (and quite independently from them) shows that the elements of these groups, which are comparatively widespread, correspond to the even atomic numbers (table 6). So the prevalence of the mass of chemical elements with even atomic numbers is quite evident in five groups of natural classification; only group 4 does not include elements with even numbers.

table 6

The first group – that of rare gases – includes elements that take no part in the main terrestrial chemical processes, and that make up compounds with other elements only in exceptional cases. These atoms are preserved practically unchanged throughout geological time. A closer study of their history makes us discard the early ideas of C. Moureux, who suggested that they are absolutely inert in geological history, and that in them we observe the remains of the cosmic history of our planet. The quantitative intensity of their chemical manifestations in the thermodynamic field of our planet is so different from other compounds, so relatively small, that their actual difference from other terrestrial elements cannot arouse any doubt. However, their geochemical significance is enormous, and their role in the worlds beyond the Solar System must be great, too.

One of them – helium – is very widespread in the substance of celestial bodies, and apparently it plays a significant role there that has not yet been discovered. Its quantity in the Earth’s crust is changeable and seems to be increasing, as it is continuously appearing there due to decomposition of the nuclei of uranium, ionium, radium, radon, RaA, RaC, RaCl, polonium, thorium, radiothorium ThX, thorone, ThA, ThC, protactinium, radioactinium, AcX, actinone, AcA, AcC, AcCl, samarium, and possibly beryllium. It is expected that the process does not stop here, and that there are other elements that secrete alpha particles (just as helium atoms carrying two charges while decomposing, eventually lose their charges and transform to ordinary helium gas).

But there are cases in which the rare gases, called this way by chemists because of the difficulty of creating their chemical compounds under the conditions of our laboratories, do give compounds. These compounds, in the form of water solutions and hydrates as was recently shown by V. G. Chlopin, must play an important role in the structure of the biosphere. Finally, they may include also radon, a rare gas from group five, which is a carrier of great active energy in its different isotopes. In general, the role of the rare gases in the structure of our planet is much greater than their relatively small quantity; and this role is just beginning to reveal itself to us.

The second group – that of inert elements of noble metals in the Earth’s crust – includes the two last columns of D. I. Mendeleyev’s Periodic Table of elements; gold can be included here too. These elements give an almost infinite number of compounds in our laboratories and this is their difference from the rare gases. But their compounds are almost absent in the Earth’s crust. The minerals corresponding to them, mainly alloys, existing because of a complicated pneumolythic and magmatic process, or (for gold) because of abyssal hydrothermal processes in thermodynamic conditions that are distinctly different from those of the biosphere, change very little or not at all in the course of geological time. This stability, as well as that of the rare gases, is not complete. For some small part of their terrestrial mass, very slow chemical reactions must exist that change them, and these reactions are not well studied.

For instance, in the biosphere, oxygen compounds of palladium emerge. For palladium and for the nuggets of platinum and gold, there are numerous phenomena of weathering connected with the re-crystallization and change of the chemical composition of the alloy. For gold, their phenomena are connected with decomposition of telluride compounds. But these slow and local chemical reactions do not change the general character of the group – its terrestrial chemical inertness. It is furthermore characteristic of the whole group that these elements are only slightly affected by the aquatic structure of the Earth. They find themselves in a dispersed state in water solutions or connected with phenomena of sorption.

The third group of cyclical or organogenic elements is the largest in mass. It includes the greatest number of chemical elements and makes up almost the entire Earth’s crust. It is characterized by numerous reversible chemical processes. The geochemical history of these elements may be expressed by cycles. Each element gives compounds characteristic of a certain geosphere; these compounds are constantly being renewed. After more or less long and complicated changes, an element returns to its initial compound and begins a new cycle. This character of terrestrial chemical reactions was noticed for oxygen in the second half of the eighteenth century; the great scientists of that time, who had discovered the terrestrial gases and their properties, foresaw these characteristic chemical cycles.

I think that Dr. J. Pringle, the President of the Royal Society in London, was the first to express these notions in 1773, in his speech about J. Priestley. He defined the general features of the great equilibrium of vegetative green chlorophyll matter, together with animal matter, in relation to free oxygen and carbon dioxide. In 1842, two French scientists – J. B. Dumas and J. Boussingault – gave a clear picture of these cycles, and in the 1850s C. G. H. Bischof, J. Liebich and K. Moor transferred these notions to the rest of the matter of the Earth’s crust. Since then, science has collected a great quantity of empirical facts confirming these generalizations. These facts were not coordinated though, and are in a state of almost complete chaos. The importance of living matter for these cycles is being confirmed. This importance is observed not only for organogenic elements, such as C, O, H, N, P, and S, but also for metals such as Fe, Cu, Si, V, Mn, etc., and for all the chemical elements of this group, as we shall see.

The elements of this group are part of cycles that are characterized by chemical compounds, molecules, or crystals. These cycles are reversible only for the main part of the atoms involved, some of the elements inevitably and continually leave the cycle. This is natural; that is, the cyclical process is not completely reversible. Among such ways of leaving the cycle, the most significant dispersal of an element is its exit in the form of free atoms. In this way the element may leave the cycle forever. Still, it is clear that even if future discoveries more or less alter our present-day ideas, they will not deny the main empirical generalization regarding the prevalent significance of chemical compounds and reversible cycles in the history of the main mass of the Earth’s crust. The cyclic elements are included and play an important role in the aquatic apparatus of the Earth’s crust: they are included in water solutions (ions), and make up minerals formed by water. Only zirconium and hafnium seem to stand aside in this respect. Zr and Hf do not enter living matter, and germanium has not yet been found in it either, but judged by its aquatic history, it surely will be.

In the next group, that of dispersed elements, free atoms prevail. They cover a small part of matter, and they also have their cycles, which renew constantly. Not always though are they expressed by chemical compounds, by molecules; their compounds decompose more or less completely in one area of these cycles and renew under different thermodynamic conditions in another area. All the dispersed elements are characterized by the absence or rareness of chemical compounds, not only in certain areas of the Earth’s crust, but in the Earth’s crust as a whole.

There are two cases that are distinctly different from each other. Some of the elements, such as Li, Sc, Rb, Y, Cs, Nb, Ta and maybe In, form chemical compounds only in deep zones of the Earth’s crust. Their minerals are located in the surface area in the biosphere, but the new compounds of these elements – new minerals – are not formed here; the elements do not form vadose¹⁹ minerals. Instead, the elements are dispersed throughout the surrounding substance as “traces,” as analysts say, and have seemingly nothing to do with the mountain rocks they are found in.

The second case is that of iodine and bromine. They enter compounds with other elements only in the biosphere, which means that all their minerals are of vadose nature. If we try to reconstruct their history and find out their origin, we shall make sure that the sources of iodine and bromine are water solutions, and that living matter has extracted and concentrated them from those very solutions. In the depths of the crust we find iodine and bromine only dispersed as traces in minerals or in rocks – both metamorphic and plutonic – without any apparent relation to their chemical composition. Our knowledge is not sufficient to fully discover the history of gallium, but apparently it belongs to the second group as well. At the present time, its compounds are not known. The maximum content of gallium in a mineral – germanite – does not exceed 7 × 10^-10 % of metal, and in micas its content reaches the same order.

All these are minerals of the deep regions of the Earth’s crust. Hence, the cyclic processes corresponding to these elements are specific; the elements give chemical compounds and free atoms in turn. But the majority of them do not enter compounds at all. They are constantly dispersed everywhere in the matter of our surroundings, apparently in the state of free atoms. They appear to be in a state close to that of rare gases, outside chemical reactions in the parts of the planet accessible to our investigation. The fact that all these elements belong to one and the same group, to that of atoms with uneven atomic numbers, evidently shows that the structure of these atoms has peculiar characteristics connected with this way of spreading.

This phenomenon deserves much more attention than is usually paid to it. Such a state of chemical elements can bring about processes of great cosmic importance. If it is the common property of elements with uneven atomic numbers, it can explain the prevalence of their antipodes – even elements – in the Earth’s crust and meteorites. All the uneven elements, except for Sc, Nb, and Ta, take part in the aquatic regime of the planet by being there in a dispersed state. Some of them, such as Li, Br, and I, are concentrated by living matter; Sc, Ga, Y, Nb, In, and Ta are concentrated by organisms that have not yet been studied.

The fifth group of elements includes very radioactive elements: the families of uranium, actinouranium and thorium. Here the incomplete reversibility of processes is quite evident. In general, uranium and thorium make up compounds included in reversible cycles, the closed cycles, which are analogous to the cyclic processes of the cyclic elements. But part of their atoms is lost in the course of the cyclic processes and does not return; it gets decomposed, changes and gives birth to other elements, two of which, helium and lead isotopes, belong to the groups of rare gases and cyclic elements, which are quite different chemical groups.

Now it is becoming clear that radioactive decomposition is characteristic not only of heavy atoms, but of light atoms as well. In 1907, Campbell discovered two radioactive elements with beta-radiation: potassium (from the group of cyclic elements) and rubidium (from the group of dispersed elements). In the case of rubidium, atoms of strontium must appear (belonging to a different geochemical group), and in the case of potassium, atoms of calcium (belonging to the same group) and of argon. Twenty-five years later, another period of discoveries began, in which von Hevesy and Pahl discovered the radioactivity of samarium, belonging to the group of rare Earths; it transforms to neodim through alpha-radiation. We seem to be on the verge of great 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 not realized from this point of view, I would like to make it clear by dwelling upon the history of two chemical elements that belong to the group of dispersed elements: iodine and bromine.

3 geochemistry of iodine and bromine

From the everyday experience of our laboratories, we know that iodine and bromine can make up thousands of compounds with other simple bodies. Many of these compounds are very stable in the thermodynamic conditions of the Earth’s crust, but they do not appear there. We can find only 13 minerals containing iodine, and 3 to 4 minerals containing bromine. The quantity of bromine in the Earth’s crust is no less than 10¹⁶ t, and the quantity of iodine is about 10¹⁵ t. Iodine and bromine are much more widely spread, by thousands of times more, than antimony, selenium or silver, but the number of minerals of which the latter are part exceeds 100 for each of them, while for bromine and iodine it is not larger than 17. There are five dubious minerals with iodine, and not a single mineral containing either bromine or iodine was found in large quantities.

Hundreds of thousands of tons of iodine are contained in iodic-acid calcium, perhaps also in iodic-acid sodium, and in very little investigated minerals of which lautarite is the most well studied. These iodic-acid minerals are dispersed in the saltpeter and gypsum deposits of South America. Iodide and bromic compounds of silver exist in smaller quantities and seem to be more stable in the lower areas of the biosphere below the oxygen surface. All other minerals of bromine and iodine are mineralogical rarities; sometimes they are found in kilograms or even smaller quantities. The quantity of iodine and bromine in minerals probably does not exceed a maximum of several million tons. The quantity of iodine in isomorphic admixtures seems to be even less. On the whole, the quantity of iodine in minerals is small compared to its mass existing in the Earth’s crust. All minerals of iodine and bromine are vadose (i.e., they appear and exist only in the upper layer of the crust, in the biosphere). Their volcanic forms should also be considered vadose, since they cannot exist in deeper layers of the Earth’s crust in a solid state. There is not a single mineral of iodine or bromine that has appeared in deeper metamorphic or magmatic parts of the crust.

Large quantities of iodine and bromine are contained in all organisms of living matter, as was discovered by W. Courtois. Many organisms seize it rapaciously. For instance, in the opinion of A. Gautier, all the iodine of the biosphere – of the surface layers of the ocean to a depth of 800 m, the soil and the atmosphere – exists only in that state; that is, gathered in living matter. A considerable quantity of iodine (and of bromine) is concentrated in aquatic terrestrial solutions, where it exists as ions I^- and IO^-3, and as free iodine. Organisms draw and concentrate their iodine (and bromine) from solutions, such as the deeper layers of the sea, lakes and saline swamps, salty springs, surface waters, and all fresh waters. Iodine and bromine penetrate into all the waters of the Earth’s crust, not only into those of the biosphere. From time to time they concentrate in mineral springs or in stratum waters. The source of the iodine in water solutions is to a considerable extent its biogenic migration, which apparently is a general phenomenon. Iodine may reach the order of 10^-2 % when it exists in these waters in the forms of ions (I^-), and free iodine.

Millions and millions of tons of free iodine do not enter either organisms, metals or natural waters; they are dispersed in rocks. According to A. Gautier, all the erupted and metamorphic rocks and the minerals contained in them, to say nothing of sedimentary rocks, contain iodine in the form of traces (in quantities of 1.7 × 10^-5–1.25 × 10^-4 %). According to the new analyses of G. Fellenberg and his colleagues, these quantities are smaller (1.9 × 10^-5–8.1 × 10^-5 %). The dispersal of iodine is extensive, and in this respect it resembles the existence of radioactive elements to which we are already acquainted. We may think of iodine as a model of radium; it can be found in all minerals without exception, and it is present in different, sometimes relatively large quantities. The numerous measurements of Fellenberg indicate a range from 3.8 × 10^-3 (bornite) to 5 × 10^-6 % (calcite).

The dispersal in the form of such “traces” is the most typical and usual form of existence of iodine in the Earth’s crust. We cannot state any correlation between its quantity and that of other elements of the rocks and minerals in which it is found, as if the atoms, or maybe the ions of iodine, are dispersed throughout the terrestrial substance under the influence of physical instead of chemical forces, and maybe of interatomic ones. Nevertheless, it is quite probable that iodine and bromine exist in capillary water permeating terrestrial solid matter as a weak solution. The existence of iodine in organisms, waters, and solid bodies is closely related to its content in the terrestrial atmosphere, from which it can penetrate back into water and organisms through atmospheric fall out. Our knowledge of bromine’s spreading is less complete, but it is clearly generally similar to the history of iodine.

Here we see a closed cycle of a new type. Iodine and bromine in a dispersed state become part of the substance of the Earth’s surface. Their atoms or free ions are captured by living organisms and concentrated in the compounds they make up, which contain up to 8.5% of iodine and sometimes more, as for example the bodies of sea sponges.²⁰ Apparently, part of the dispersed atoms of iodine is also seized by chemical reactions of the surface, and makes up vadose minerals. It is quite possible though, that these chemical reactions can take place only in direct or indirect relation to living matter, or that they are observed only under conditions that are favorable for accumulating organic matter, the product of life. In the course of time, iodide and bromic products of organisms, as well as vadose organic minerals, which are always related to life, decompose. Iodine and bromine thereby return to the state of atoms and ions in order to begin the same cyclic process again.

Two phenomena are typical in this cyclic process: the influence of life and the weak concentration of iodine. It takes a long time for the cyclical process to be completed. Lately a new factor has appeared, which is humans. Throughout geological time, the iodine collected by life remained intact in coal with a weak concentration of about 6 × 10^-4 %. Now, humans burn coal and, in such a way, introduce many thousands of tons of iodine into the atmosphere, which, after a million years returns to living matter. Another process of this kind concerns the iron ores that are always rich in iodine; they appear in the biosphere through an organogenic method or with the participation of life.

Such a cyclic process, covering a geologically long period, involves a small number of iodine atoms at a time. The main mass of iodine atoms is in a state of complete dispersal. This example shows that studying only minerals and rocks is far from giving us a complete picture of the existence of chemical elements in the Earth’s crust. It should also include the most widespread elements constituting the Earth’s crust – the cyclic elements. Here, not dispersal, but living matter, living organisms, plays a conspicuous part. The history of chemical elements cannot be understood without it.

4 living organisms in the earth’s crust

From the geochemical point of view, living organisms are not an accidental phenomenon in the chemical organization of the Earth’s crust; they make up its most essential and integrated part. They are inseparably connected with the inert matter of the Earth’s crust such as rocks and minerals. In the majority of their papers, biologists who study living organisms ignore the inseparable and functional connection existing between a living organism and its surroundings. Although realizing clearly the organization of the organism, they fail to realize the organization of the surroundings in which the organism lives (i.e., the biosphere.) They see these surroundings as inert and independent of the organism, “cosmic,” as Claude Bernard has well put it.

So by studying an organism they do not study a natural body, but an ideal product of their thought. Often it is a convenient, even necessary method of scientific work that is very widely adopted in the natural sciences. According to this method, complex natural phenomena are replaced by simplified models, and empirical conclusions and facts are idealized and deviated from. A material triangle is not the triangle of geometry, the “atmosphere” of physics is not the troposphere surrounding us, and an animal or plant of a biologist is not a real living body, not a natural organism. This must always be understood, and sooner or later the moment comes when it is necessary to crucially change the principal ideas. This moment is about to arrive for the biological sciences.

The great biologists of the past realized the inseparable connection of an organism with its surroundings. In the late eighteenth century, F. Vique d’Azir brilliantly expressed these ideas in the lectures he delivered in Paris, in which he tried to introduce a scientific and logical definition of life. This was one of the numerous definitions of life, one of the attempts to solve the problem (more a logical than a scientific one), which had drawn the attention of scientists and philosophers for many generations. In his influential report on the state of sciences in post-revolution France, presented to Napoleon in 1808, Cuvier expressed the same thoughts as Vique d’Azir with a peerless clarity and precision. He deepened these thoughts in his other papers. He wrote, “So life is a more or less fast, more or less complicated whirlpool, which always captures molecules possessing certain qualities, and which has a constant direction. But it is always penetrated by, and always deserted by individual molecules, so the form of a living body is more significant for it than its substance. As long as this motion exists, the body within which it occurs is alive, it lives. As soon as the motion comes to a complete standstill, the body dies.” One of the main thoughts expressed here, that of the greater importance of the form of a living body than of its substance, was the principal idea of biology throughout the whole nineteenth century. It was accepted, but everything else significant for Cuvier was discarded. In fact, in the nineteenth century, not only the substance, the molecules, were put aside, but also the influence of an organism on the environment, i.e., the motions of the molecules of the environment that, according to Cuvier, were essential for life.

In the late nineteenth and the early twentieth centuries, the notions of the relations between life and environment, or the understanding of Cuvier’s formula, became more profound. The roots of these changes are to be found in geological and biological research. Geologically, they brought forth the discovery of the organized character of the biosphere adjusted to life and regenerated by life. Its particular manifestations are the biogeochemical processes studied in this book. The whirlpool of atoms entering and leaving a living organism is determined by a definite organization of life’s environment, by a geologically definite mechanism of the planet – the biosphere.

Biologists come to the same conclusion proceeding from the living organism. The form becomes clear only when both parts of Cuvier’s whirlpool are taken into consideration: that in the environment and that in the morph [form] the organism. The outstanding and original French zoologist, F. Houssait, was quite right to point out “schema-tization”; the complete discrepancy between the biologists’ “living organism” and a real living organism. The real organism is inseparably connected with the environment and can be separated from it only theoretically.

One cannot study and understand an organism, comprehend its form and vital activities, without studying and knowing its environment. A younger contemporary of Houssait, the English physiologist D. Haldan, insisted on an even closer connection between the environment and the organism’s functions. Another physiologist, the American L. Henderson, put these concepts into a distinct and more profound form; he connected them into a single unity with geological processes. But all these scientific studies of biologists could not channel scientific biological work into a different direction.

The grand manifestations of living organisms that are evidently connected with the environment – their respiration and nutrition – continued to be studied and have been studied while disregarding their influence on the environment from which the organisms receive chemical elements, and to which they return them by means of these processes. A living organism of a biologist in the “cosmic” environment is, in the greatest majority of cases, different in its scientific scope from the real body of empirical knowledge – a living organism of the biosphere.

Whole fields of biological problems have remained outside the realm of biology. But separate thinkers among the biologists have long been trying to go deeper, to approach the general substratum of inert and living matter while handling biological problems. In the archives of science we find profound ideas of this kind, which should draw the attention of our time as well. These ideas are revivified now. The old scientists of the late eighteenth century were less limited by patterns and habits of mind than their descendants. Before the new chemistry was finally formed, the idea of a universal cosmos had dominated, and consequently a search for a universal power ruling the world. In all the phenomena of our life, such as an apple falling from a tree, and in the greatest cosmic manifestations, such as the movement of celestial bodies, hence in the whole system of nature, one and the same universal power was seen: gravity. I. Newton, who had discovered the law of gravity, and who ruled supreme in scientific understanding of the cosmos in the late eighteenth and in the nineteenth century, had not been the author of the idea of “universal gravity,” but he also tried to transfer his laws to new fields such as chemistry, where it is not they that dominate as we will see.

In the eighteenth and nineteenth centuries, the manifestations of “universal gravity” were looked for everywhere. This led to the discovery of new laws and to the clarification of complicated and tangled phenomena, but at the same time the scientists always came to the conclusion that the newly discovered forces were different from “universal gravity.” In the eighteenth century, Coulomb proved that the laws of attraction and repulsion of electrified bodies were similar to those of gravity, but that these laws are similar only in their outward appearance. Proceeding from gravity, Laplace came to the theory of special capillary forces. Attempts to find manifestations of “universal gravity” in the phenomena of chemistry and in chemical affinity brought forth the discovery of new laws and fruitful generalizations that had nothing to do with Newton’s attraction of gravity.

In 1782, the St. Petersburg Academy of Sciences put forward a problem for a competition in the realm of biology, generated by the same trend of thought. The question was whether there were any relations between Newton’s gravity and the force acting in the processes of nutrition and respiration of living matter. Which force makes it possible for living organisms to extract from their environment all the substance necessary for them to live and grow? Caspar Wolff, one of the most outstanding members of our Academy, a great investigator of life and one of the creators of embryology, initiated this question and published a memoir after the competition, in which he proved what seems obvious to us – that the forces of nutrition and respiration are quite different from Newton’s attraction of gravity. But the thing that can intrigue us in this forgotten episode of the past is the question itself. In fact, this question is an attempt to scientifically embrace the reflection in the environment, in the biosphere, of the countless minute phenomena of respiration and nutrition of living beings. Respiration and nutrition are considered not only as phenomena of the organism but also as planetary phenomena.

In the late eighteenth and early nineteenth century, another scientist, the well-known Polish medical man J. Sniadecky, returned to the same ideas. He compared Newton’s attraction of gravity with the “attraction” of matter – the respiration and nutrition of living beings. He expressed the idea that the intensity of the force inducing these processes in an organism grew in inverse proportion to the mass of the organism, while Newton’s gravity acts in direct proportion to the mass. Small living beings unseen by the eye produce the most significant effects. This trend in biological research soon died out completely, but the complex of ideas that had induced it has lately reappeared in geochemistry because the influence of living beings in the history of chemical elements of the Earth’s crust is exerted mainly by their nutrition and respiration.

In geochemistry, organisms manifest themselves and can be studied only from the point of view of the general effect created by these physiological phenomena, the complex of which makes up a planetary phenomenon. But these ideas are even more profoundly connected with our thought. They are most closely related to a biogeochemical study of life, as in the research of Wolff, Sniadecky, and earlier in that of Buffon. The universal gravity by Wolff, and the atoms in life’s biogeochemical embrace by Sniadecky, are attempts to connect the phenomena of life with the main elements that manifest themselves in the cosmos.

5 the history of free oxygen

The planetary significance of the phenomena of life, namely of respiration, can be well understood if we consider the history of free oxygen in the Earth’s crust – one of the innumerable chemical bodies introduced into the biosphere by living matter.

Free oxygen as molecular O₂ in gaseous form, and especially in water solutions, plays quite an exceptional role in all the chemical reactions of the Earth’s surface. We can even say that its presence changes the course of these reactions. The quantity of perpetually existing O₂ molecules in the Earth’s crust is enormous. It can be determined with sufficient precision. In the atmosphere (the troposphere and the lower stratosphere), the weight of free oxygen or O₂ molecules amounts (according to S. Arrhenius) to a minimum of 1.2 × 10¹⁵ t and a maximum of 2.1 × 10¹⁵ t. This mass exceeds that of many chemical elements in the Earth’s crust by hundreds of thousands of times.

The atmosphere does not contain all the free oxygen; a considerable part is dissolved in waters and mainly in salty water, which makes up the world’s ocean. This amount hardly exceeds 1.5 × 10¹³ t. Free oxygen is also dissolved in the fresh water on land and dissolved or occluded in snow and ice. But this quantity is much smaller than that of the marine part of the hydrosphere, because according to W. Halbfass, the volume of fresh water makes up only 3.6 × 10^-10 % of the volume of ocean water, even when it includes snow and ice, which present the dominating part of the weight of terrestrial water. So, according to W. Halbfass, the volume of ice corresponds to 3.5–4 × 10⁶ km³, the volume of ocean water to 1.3 × 10⁹ km³ (O. Kruemmel), and the volume of the lake, swamp, river, and surface waters maximumly to 7.5 × 10⁵ km³. Furthermore, the whole amount of free oxygen included into sedimentary rocks slightly exceeds 1.5 × 10⁵ t and comprises approximately 1/10⁵ of all the oxygen of the Earth’s surface.

We know that free oxygen exists only on the Earth’s surface. The water of deep springs does not contain it, as was proven in the late eighteenth century by the English physician D. Pearson (1751–1828). The gases of volcanic and metamorphic rocks are almost devoid of it too. The quantity of free oxygen in the biosphere is undoubtedly one of the most precisely estimated physical constants of our planet. It determines the geochemical work of living organisms and allows us to understand the significance of free oxygen in the history of chemical elements. Free oxygen is the most powerful agent among all known chemical bodies of the Earth’s crust; it changes, or oxidizes, a great quantity of chemical compounds, it is in constant motion, and it constantly forms compounds. We know thousands of chemical reactions by which it is captured, and during which it enters the compounds. The most significant ones among these compounds are the oxidized forms of metalloids such as sulfur and carbon (including the compounds of organisms) and the compounds of metals such as iron or manganese.

The history of all cyclic elements of the Earth’s crust is determined by their relation to free oxygen. Recent investigations have even pointed out its major influence in volcanic phenomena. The atmospheric oxygen captured by burning lava yields oxidized products (such as waters, sulfur oxides, etc), and the heat liberated by these reactions plays a most significant role in the thermal effects of lavas. The temperature of lava rising from the entrails of the crust, which has not yet contacted the oxygen of the air, is often hundreds of degrees lower.

In spite of the significance of these reactions for numerous terrestrial processes of this kind, the overall amount of free oxygen on the planet seems constant or almost constant. Evidently, some reverse processes must exist, which liberate free oxygen into the surroundings. We know only one reaction of this kind in the biosphere, if we consider large-scale reactions. This reaction is biochemical; it is the release of oxygen by chlorophyll plastids of terrestrial organisms. This reaction was discovered in the late eighteenth century by J. Priestley, subsequently deepened by the works of outstanding scientists of that time, and presented in all its significance, its general character and its main features, by the scientist T. de Saussure of Geneva at the beginning of the last century.

This reaction of forming free oxygen in the Earth’s crust is undoubtedly not the only one, but as far as we can judge, it is the only one releasing considerable masses of free oxygen to the structure of the atmosphere that envelopes our planet. The excretion of free oxygen outside the influence of life is proved to be, or most probably, due to the processes of radioactive dissociation, decomposition of gases by ultraviolet radiations, and metamorphism. Oxygen must be isolated in the depths of the Earth’s crust, since the compounds rich in oxygen appearing on the surface, such as sulfates and bodies containing ferric oxides, turn into compounds that are poorer in oxygen, or which do not contain it at all, upon reaching the deep layers of the crust. But this free oxygen must immediately enter compounds, for we fail to see its manifestations anywhere.

Even if from time to time and at some places free oxygen rises from the depths of the Earth’s crust, its mass in the biosphere is insignificant in comparison to the amount of oxygen produced in a biogenic way. The isolation of free oxygen in the stratosphere under the influence of ultraviolet radiation and in connection with decomposition of water vapor and perhaps carbon dioxide, might prove to be much more important. This field of phenomena is still less studied and recorded than the isolation of oxygen in the metamorphic envelope. But two circumstances that greatly diminish the geological significance of this phenomenon should be taken into consideration:

1 The small mass of the rarefied gases in the stratosphere and higher.

2 Their slow exchange with the troposphere.

Finally, there is a third factor to be considered: the dissociation of water molecules under the influence of alpha- and partly beta-radiation of the ubiquitous atoms of radioactive elements. The existence of these phenomena is certain, but nowhere do the concentrations of such atoms seem large enough to be taken into account within the limits of the biosphere. Unfortunately, this phenomenon is not sufficiently studied either through experiment or natural observation.

In view of all this, we can assert now that the free oxygen of the troposphere and the surface waters (gases dissolved in natural waters; i.e., more than one-fifth of the troposphere) is created by life. Furthermore, a quite similar phenomenon is observed for the free nitrogen of the troposphere, and it will be correct to conclude, and to take into account from now on, that the terrestrial gaseous envelope – our air – is created by life. Thus, the history of free oxygen turns out to be a clear measure of the geological and geochemical significance of life.

6 living matter

Life manifests itself in the Earth’s crust in a way that is different from the phenomena studied by biologists. Here we notice two new features of its structure. We see that life acts only by means of the energy, quantity, and composition of the matter inherent to it. Secondly, we see that individual organisms move to the background in regard to the greatness of the observed phenomena; we notice only the general, total effects of their activity.

The geochemical manifestations of life present a picture quite opposite to that imagined by biologists and clearly expressed in Cuvier’s definition of life more than 100 years ago. The effect of organisms on the migrations of elements of the Earth’s crust has almost completely moved to the background, but the matter of the organisms, the motion of its molecules and its energy, manifest themselves in all the observed phenomena. Such a manifestation of life is as real as the richness and complexity of morphological and physiological processes that are studied by biologists as the only reality. Suggesting a new standard of studying life that is completely different from the usual one, we approach unprecedented phenomena and prospects. The complex effects of minute phenomena, which have not attracted the biologists’ attention up till now, reveal an unexpected scope.

In geochemistry, life manifests itself through the joint activities of myriads of living organisms. In this totality the statistical laws and generalizations connected with life are studied. Only some separate properties of life attract the mind. In order to be able to study life in geochemistry, it is necessary to present it in the same terms, with the same logical parameters, as other forms of existence of chemical elements to which we are comparing it here; that is, minerals, rocks, magmas, water solutions, and dispersions. In other words, the totality of organisms must be expressed only from the standpoint of their mass, their chemical composition, their energy, their volume, and the character of the space corresponding to them.

Expressing the totality of organisms in these parameters, we should introduce new concepts, new terms for denoting life. I will refer to the totality of living matter expressed in mass, chemical composition, units of energy, and in the character of space related to it. With such an expression of life, all the aggregates of various organisms are fully preserved and have a precise definition: the species, subspecies, genera, etc., that are identified by biologists on the basis of the study of their morphology or physiological functions. The average mass, the chemical composition, the geochemical energy, and the character of space (for instance left or right-handedness) turn out to be as distinguishing for organisms as the characteristics underlying biological classification. In this respect, a geochemist should distinguish between homogeneous living matter comprised of aggregates of one and the same species, genus, race, etc., and aggregates of heterogeneous matter that consist of organisms belonging to different species, genera, races, etc.