Geochemistry and the Biosphere. Vladimir I. Vernadsky

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.

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