Substance Circulation

SUBSTANCE CIRCULATION. The substance of the earth's crust is in continuous movement, caused by various reasons related to the physico-chemical properties of the substance, planetary, geological, geographical, and biological conditions of the earth. This movement invariably and continuously occurs throughout geological time - at least one and a half and apparently not more than three billion years. - In recent years, a new science of the geological cycle has grown - geochemistry, which has the task of studying the chemical elements that make up our planet. The main subject of its study is the movements of chemical elements of the earth's substance, whatever causes these movements. These movements of elements are called migrations of chemical elements. Among migrations there are such that during a greater or lesser period of time a chemical element inevitably returns to its initial original state; the history of such chemical elements in the earth's crust can thus be reduced to a reversible process and represented in the form of a circular process, a cycle. This type of migration is characteristic not of all elements, but of a significant number of them, including the vast majority of chemical elements that build plant or animal organisms and our surrounding environment - oceans and waters, rocks and air. For such elements, the entire or overwhelming majority of their atoms are involved in substance circulation (S.C.), while for others only a negligible part is covered by cycles. Undoubtedly, most of the substance of the earth's crust to a depth of 20-25 km is covered by cycles. The following chemical elements have circular processes as characteristic and dominant among their migrations (the number indicates the ordinal number). H, Be₄, B₅, C₆, N₇, O₈, P₉, Na₁₁, Mg₁₂, Al₁₃, Si₁₄, P₁₅, S₁₆, Cl₁₇, K₁₉, Ca₂₀, Ti₂₂, V₂₃, Cr₂₄, Mn₂₅, Fe₂₆, Co₂₇, Ni₂₈, Cu₂₉, Zn₃₀, Ge₃₂, As₃₃, Se₃₄, Sr₃₈, Mo₄₂, Ag₄₇, Cd₄₈, Sn₅₀, Sb₅₁, Te₅₂, Ba₅₆, W₇₄, Au₇₉, Hg₈₀, Tl₈₁, Pb₈₂, Bi₈₃. On this basis, these elements can be separated from other elements as cyclic or organogenic elements. Thus, cycles characterize 42 elements out of 92 in the Mendeleev system of elements, and this number includes the most common dominant terrestrial elements. Practically - by weight - these elements make up about 99.7% of the upper part of the earth's crust, which is accessible to precise scientific study (16-20 km). Of the 2-2.2 × 10¹⁹ tons of substance of this crust, less than 10¹⁷ tons falls to the share of other elements. - Cyclic elements acquire special importance for studying the phenomena of life, firstly because they in the vast majority enter into the composition of organisms, and secondly because the migrations caused by life (biogenic migrations) are an integral part of the geochemical cycles characteristic of these elements. Biogenic migrations, including the metabolism of elements in organisms during their life, are regularly connected with geochemical cycles. All cyclic elements except cadmium (and possibly Hg) are constantly part of living organisms. (Probably cadmium will also be found in organisms. Its geochemistry has not been studied.) For living organisms, many more elements are known; currently 55 elements are established, but probably there are more than 70. But all these elements - besides cyclic ones - occur in negligible amounts, hardly exceeding 10^-3-10^-4% of the weight of a living organism. Cyclic elements make up 99.995-99.985% of the weight of living beings in nature. They can rightly be called organogenic elements. - Entering into geochemical cycles, organogenic elements introduce into these cycles the substance that builds living organisms. Without this substance, geochemical S.C. cannot exist. Since these cycles are regular and life phenomena constitute their integral part, it can be considered that living organisms constitute a part of the mechanism of the earth's crust, expressed in geochemical S.C. Until the appearance of civilized humanity (in the last 20-30 thousand years), there were no changes in geochemical cycles during geological time. We live at the beginning of their change introduced by culture. It is necessary to pay attention here to biogenic migrations of chemical elements due to the interest of these phenomena for physicians; biogenic migrations are called those movements of chemical elements that are introduced: 1) by the metabolism of organisms, i.e., their life processes - respiration, nutrition, internal metabolism; 2) by the growth of organisms; 3) by the reproduction of organisms; 4) by the biology of organisms, i.e., the conditions of their life (e.g., migration), and 5) by the technique of their life, so vividly manifested in modern humanity. The phenomena of reproduction and the technique of life are the most powerful forms of biogenic migrations. - Biogenic migrations and the biogenic parts of cycles connected with them occur in the biosphere (see), but in their effect they go beyond its limits. The cycles of chemical elements in the vast majority of cases involve several earth shells. Observing them in the biosphere, we see directly only parts of the cycle. About their inaccessible parts, one can judge indirectly, studying the accessible deep parts of the cycle in the biosphere - rocks, minerals, waters, etc. They distinguish cycles that involve several earth shells (geochemical cycles of the first kind), and cycles that involve one shell (geochemical cycles of the second kind). All cycles connected with life phenomena belong to the latter, or those that begin and end in the oceans. Let us dwell on cycles of the first kind, involving biogenic migrations. These cycles involve the biosphere (i.e., the atmosphere, hydrosphere, weathering crust). Under the hydrosphere they involve the basaltic shell approaching the ocean floor. Under the land they in sequence of depth embrace the thickness of sedimentary rocks (stratosphere), metamorphic and granitic shells and enter the basaltic shell. From the earth's depths lying beyond the basaltic shell, the substance of the earth does not enter the observable cycles. It also does not enter them from above beyond the upper parts of the stratosphere. Thus, the cycles of chemical elements are surface phenomena occurring in the atmosphere up to heights of 15-20 km (not higher), and in the lithosphere - not deeper than 15-20 km. Any cycle, in order to be constantly renewed, requires an influx of external energy. Two main and certain sources of such energy are known: 1) cosmic energy - solar radiation (biogenic migration depends almost entirely on it) and 2) atomic energy associated with the radioactive decay of elements of the uranium, thorium, potassium, rubidium series. With less accuracy, one can distinguish mechanical energy associated with the movement (due to gravity) of earth masses, and probably cosmic energy penetrating from above (Hess rays). The existence of primordial terrestrial cosmic energy - a remainder of the primary stages of the planet - has not been proven, which for a long time explained the high temperature of deep layers of the earth's crust. These original sources of energy are expressed in the migrations of elements - biogenic (living beings), chemical (e.g., volcanic eruptions), thermal (e.g., internal heat of the earth's crust), magmatic (solidification of massive rocks), etc. Cycles involving several earth shells proceed slowly, with stops and can be noticed only in geological time. Often they cover several geological periods. They are caused by geological displacements of land and ocean. Parts of the cycle can proceed rapidly (e.g., biogenic migration). Let us dwell on several basic cycles for life of elements. Nitrogen by weight constitutes approx. 0.04% of the earth's crust (about 8×10¹⁵ tons). Its geochemical significance is enormous, as in gaseous form it constitutes the atmosphere (75.7% by weight, about 4×10¹⁵ tons) and is the main element of living matter, entering into the composition of proteins (in a living plant, tenths of a percent of nitrogen by weight, in living animals more than one percent - up to 5% and more). In living organisms, amounts of N of the order of 10¹⁰-10¹¹ tons must be present. Due to its presence in the atmosphere, N dissolves in waters; in the ocean it is present in amounts up to 0.02% by weight (i.e., 4 × 10¹⁴ tons). The primary deep forms of N are native nitrogen N₂, possibly nitrogenous metals and ammonia. Ammonia is released in some volcanic eruptions and in deep waters associated with them. The possibility of finding primary ammonium in aluminosilicates of massive rocks is not excluded. The main feature of the cycle is the formation in the biosphere of native nitrogen 'bound' nitrogen. This process proceeds partially in the atmosphere under the influence of short solar radiations and radioactive bodies, partially in soils and vegetation (mainly bacteria). Nitrates and oxides of N are obtained (in the atmosphere), NH₃, combining with nitrogen oxides (NH₄NO₃) or oxidizing; in organisms N gives numerous compounds (in proteins 14-19% N).

When organisms are destroyed, a significant portion of N returns to its native state, and then the original circulation begins. A negligible portion of N accumulates in the biosphere in minerals (nitrates), which temporarily leave the circulation. Ultimately, in geological time, they return to the circulation. Native nitrogen ^ nitrogen oxides and ammonia 'living substance'? Aluminum is the third most abundant element in the earth's crust; there is more than 7.5% of it (1.5 × 10¹⁸ tons). It is one of the main elements of igneous rocks (averaging 8.1% Al by weight). Its quantity decreases with depth in basic rocks (in some dunites - a few tenths of a percent). In igneous rocks, it is mainly found in aluminosilicates (kaolin) of potassium, sodium, calcium (e.g., orthoclase K₂Al₂Si₆O₁₆), to a lesser extent in spinels (e.g., MgAl₂O₄), and even more rarely in oxides. The aluminosilicates of igneous rocks are unstable in the biosphere, lose metals, absorb water and transform into free acids (clays, for example, kaolin - H₂Al₂Si₂O₈·H₂O). The process proceeds under the influence of CO₂ and water and often (perhaps always) is associated with life. Clays-kaolin in some soils and marine sediments (perhaps always under the influence of biochemical processes) decompose, giving hydrates of aluminum oxide [the limit is hydro-arillite-Al₂(OH)₆]. Part of the aluminum is found in waters; in aqueous solutions, besides the Al ion, micelles of aluminum oxide hydrates or clays (kaolins) may be present; for fresh waters of the biosphere, Al is present in thousandths and hundred-thousandths of a percent (for the ocean this value is not determined). From aqueous solutions, aluminum passes into organisms, where it concentrates (in plants - hundredths of a percent, in animals - more) and enters into water-rich, difficultly soluble magnesium silicates. These forms of aluminum occurrence are unstable in the deep parts of the earth's crust, in the metamorphism zone, where they enter during geological time due to displacements of the earth's crust during mountain formation. In the upper parts of the metamorphism zone, new compounds are formed - kaolin aluminosilicates - from clays (e.g., orthoclase), chlorites (aluminosilicates of H and Mg, sometimes Fe, of special structure) from aluminum oxide hydrates, dark micas and surface Al-Mg(?) silicates, Al₂SiO₅ oxides (from clays). All these bodies, with further increase in temperature and pressure, return to the original bodies of igneous rocks (in gneisses and magmas). The circulation continuously proceeds in different parts of the earth's crust throughout all geological time: Oxides, kaolin, aluminosilicates of Ca, K, Na, spinels Chlorites, kaolin, aluminosilicates, oxides Aqueous solutions, organisms, clays, aluminosilicates of K, etc. The circulation of aluminum also determines the circulation of Si, with which it is connected in primary compounds. Silicon is the second most abundant element. More than a quarter of the substance in the earth's crust consists of silicon (25.7%, i.e., about 5×10¹⁸ tons). Negligible amounts of silicon are in the atmosphere; there is more in the ocean (0.0003%, i.e., about 4 × 10¹² tons). Organisms receive it from water and concentrate it (there are tens to hundreds of times more silicon in them than in water). Like Al, Si decreases in the deep parts of the crust. For Si, besides primary aluminosilicates of K, Ca, and Na, characteristic in igneous rocks are silicates of Mg and Fe and ferrisilicates of Mg, Na, K, H (for example, black micas). Part of SiO₂ is separated SiO₂ (primary quartz), Aluminosilicates of K, Na, Ca, kaolin silicates of Mg micas (Mg, Fe ^Ц> I -) in the free state (quartz). In the biosphere, these primary compounds decompose, giving aqueous silicates and ferrisilicates, ultimately opals (SiO₂+nH₂O - colloids) and quartz (SiO₂). In the destruction of silicates and aluminosilicates, the activity of organisms is sharply manifested. There are a number of very common silicon-containing organisms, containing several percent of Si per living organism. Their residues, modified by later processes, give the largest accumulations of SiO in the earth's crust. The constantly recurring circulation of Si under the influence of geological displacements can be expressed by the following scheme, where the limiting members are indicated: {SiO₂ secondary, Aqueous solutions of Si, Organisms. Clays, kaolin, etc. Aqueous magnesium silicates. The fourth most abundant element is iron. In the earth's crust, iron makes up 4.7% by weight, and in igneous rocks on average 5.0%. Its quantity thus decreases toward the earth's surface. In deep rocks, for example basalts, it averages 8.7%, in many varieties more - up to 40% and even 65%. In the biosphere, very few compounds of Fe are completely stable; all others transform into them over time. These are hydrates of iron oxide, mainly limonite (brown iron ore) 2Fe₂O₃·3H₂O; apparently these are colloids of the type 2Fe₂O₃(H₂O)₂·H₂O. Part of the 'brown iron ores' consists of chlorites (aqueous ferrisilicates of ferrous iron). Part of the iron is in solutions: in oceans up to 0.00015%, in fresh water less (hundred-thousandths). From water, iron is eagerly absorbed by organisms. In organisms, concentration occurs (tenths to hundredths of a percent, sometimes percent). The largest accumulations of iron ores are created by organisms (e.g., ores of Lorraine, Kerch). The primary compounds are ferrisilicates, silicates, spinels (magnetic iron ore); in smaller quantities - sulfur compounds of Fe: pyrite (FeS₂), pyrrhotite (r.4.o6p.FeS), etc. Pyrite also forms in the biosphere under special conditions. The circulation is continuous, its extreme members being as follows: / Hydrates of iron oxide and aqueous ferrisilicates, Aqueous solutions, Organisms. Silicates (augites, olivines, etc.), Ferrisilicates (micas, etc.),

Magnetic iron ore (magnetite), Native iron (Fe,Ni), Sulfides (pyrite, etc.). Similar to nitrogen, it is not the quantity of mass, but the speed of transformations that characterizes the circulation of carbon. The amount of C in the earth's crust reaches tenths of a percent, of the order of 0.5%. [In new calculations, Clarke and Washington give 0.087%. This number is probably underestimated.] Its quantity rapidly increases toward the surface of the planet and in the biosphere is calculated in percentages (close to 1%), in some places, e.g., in places of accumulation of living organisms, in soils-even of the order of tens of percent. Carbon constitutes 0.008% of the atmosphere by weight. In the ocean C is more than 0.0035% by weight, of a larger order of numbers for fresh waters of the land (up to many hundredths of a percent). Carbon in waters is found mainly in the form of CO₂, in ions CO₃^2- and in complex organic complexes, associated with phenomena of life. Carbon concentrates in living organisms (sometimes over 20%, but in some marine organisms-few hundredths of a percent). Extremely characteristic in the circulation of C is the abundance of its gaseous compounds and the enormous, primary importance of biogenic migration. Living organisms continuously release and absorb CO₂. A negligible part of the substance passing through them is released in the form of minerals-coals, bitumens, metal carbonates. But these, barely noticeable in the annual solar cycle bodies, accumulate in geological time in huge accumulations of limestones, petroleum, coals, graphite, humus. In its primary forms C is found mainly in the form of gases [CO₂, CO, hydrocarbons (methane-CH₄)]. Native carbon (graphite) is stable. Other compounds, e.g., calcite (CaCO₃), are rarer and in the general scheme can be omitted. Taking into account the end products, we have the following circulation: /CaCO₃ (limestones, partly MgCO₃, etc.), CO₂, CO₂ with CH₄- Living substance, / Aqueous solutions, biogenic carbon minerals, / Organic CO₂. The role of hydrogen in the earth's crust is enormous, mainly bound with O (water). The total amount of H is about 1% by weight, and by the number of atoms-more than 17%. Water covers by weight in the earth's crust (up to 20 km thickness) the main mass of hydrogen, and more than half of it is concentrated in the ocean. In the atmosphere there is on average about 1% H₂O, i.e., about 0.1% of hydrogen; it is possible that beyond the stratosphere in the rare, negligible by weight upper part hydrogen predominates. In organisms H is one of the dominant elements; its amount exceeds 10% in aquatic organisms and fluctuates around this number in terrestrial ones. On the earth's surface in the biosphere hydrates are characteristic, for example oxides of iron, aluminum, and products of decomposition of living substance. (On the role of H₂S see below.) The primary compounds for it are H₂O, hydrocarbons (mainly CH₄) and native hydrogen. In deeper parts of the earth's crust in magmas the latter should predominate due to the decomposition of water. When magmas solidify into massive rocks, part of H (tenths of a percent by weight of the rock) enters aluminosilicates. Characteristic in the circulation is the predominance of gaseous forms and biogenic migration. The extreme members determine the following circulation: H₂O, H₂O -> / Living bodies and their products, CH₄ / -> H₂S, CH₄; hydrates. H₂S

Phosphorus is a characteristic biogenic element. By weight it constitutes more than 0.1% of the earth's crust. In waters it is quickly captured by living organisms. In sea water it is about 0.00005%. Of the same order (less) in fresh water. It is an important / Aqueous solutions, HPO₄^2-, { Living substance, / Sulfates (mainly Ca- VCaSO₄. part of living substance (it is part of proteins, etc.). Its amount by weight (in a living organism)-tenths of a percent (often more than 0.5%). The circulation is determined by life. Of the huge number of phosphorus atoms participating in the metabolism of a living organism, a negligible part leaves the life cycle and is deposited in the form of phosphorites (marine process), passing into apatites. The primary basic compound of P in massive rocks are complex calcium phosphates-apatites. The circulation is determined by the extreme members: \

Living substance, Apatites \ 7_~* { Aqueous solutions, J "* I Phosphorites and apatites. With life is also connected sulfur. Its amount exceeds 0.1%. (Clarke and Washington give 0.048%. This number appears to be underestimated.) Sulfur is found in the ocean (about 0.09%) and in most fresh and salt waters of the land; in fresh water-on average thousandths of a percent. It is one of the basic elements of living substances (in all proteins). The main initial body is H₂S (in the atmosphere oxidizing to SO₃); in massive rocks sulfur accumulates in the form of metal sulfides (mainly with Fe). The gaseous nature of H₂S, its oxidation and biogenic migration characterize the circulation: H₂S S Metal sulfides FeS₂ .2H₂O). Calcium is the most important of the metals in the composition of living substance. The total amount in the earth's crust is 3.4%, in the water of the ocean on average 0.05%, in fresh waters it reaches several thousandths of a percent, perhaps up to 0.01%. Greedily absorbed by living organisms. In organisms on average it may reach up to 1%, fluctuates within the limits of hundredths and thousandths of a percent to tens of percent (it accumulates in plasma, in skeletal parts, etc.). A huge amount is released from the life cycle in the form of CaCO₃ (calcite, limestones) and (Ca, Mg)CO₃ (dolomites)-mainly in seas and oceans. Almost all the calcium brought into the oceans by rivers is deposited this way annually. The primary compounds of calcium are aluminosilicates (feldspars), silicates. The circulation in extreme forms: )

( CaCO₃, (Ca, Mg)CO₃, Aluminosilicates ->) CaSO₄.2H₂O, Silicates

Natural waters. Similar to the preceding one is the circulation of magnesium, which has enormous importance in organisms due to its inclusion in chlorophyll and connection with proteins. Its amount in the earth's crust is about 2%, in the oceans-0.14%, in terrestrial fresh waters-up to several thousandths of a percent, in living organisms-tenths of a percent. In the biosphere it gives stable water silicates. The main compounds are silicates, aluminosilicates (micas). Perhaps its amount increases in deep rocks (in basalts more than 3.7% Mg). The circulation in extreme members: Aluminosilicates (micas),

| «- | ⁽mi|'_y) ^a)C°^{3 (Д0Л}° Potassium, emitting ?- and thermal rays plays an enormous role in the phenomena of life, apparently not entering into carbon compounds. Its amount in the earth's crust is 2.4%; in oceanic water-0.04%; in fresh waters of the land-up to hundredths and thousandths of a percent. It is always present in living substance usually tenths of a percent-up to 1% (large algae). In the biosphere-mainly in solution and in living substance; a significant part-is in unstable secondary aluminosilicates. The primary forms are aluminosilicates of the mica group, feldspars. In the extreme members the circulation is determined: \

C Aqueous solutions, Aluminosilicates

[-y) Living substance, (feldspars, micas) t <- \ Unstable aqueous J

^aluminosilicates. The same picture is given by all other cyclic elements. For all, life is an important and necessary member of the circulation. This is especially clearly manifested in the dominant element of the earth's crust:-in oxygen. Its amount in the earth's crust is more than 49.5%; in deep rocks it decreases (to 40%); it is thought that it disappears in the earth's core. In the ocean it is about 89%, less-in living substance (more than 70%). Part of the O₂ of natural waters is in an active, bound state in ions and in complexes of salts (up to 0.1% of water). The main function of green plants (chlorophyll) is the release of free O₂, formed in the biosphere only by life. Its role is enormous; it causes countless chemical reactions in the biosphere. Its mass is 1.2 - 2x10¹⁵ t. Part of it is dissolved in the waters of the biosphere (a characteristic feature of them). It is found in all circulations of organogenic elements. In the main extreme members the circulation is the following: \

( Free O₂, Aluminosilicates, I -► I natural waters, Silicates, spinels j ч- ^ Living substance. In the circulation of oxygen it is clearly seen that from a geochemical point of view life is an inseparable part of the mechanism of the earth's crust; with its exhaustion all migration of substances of the PLANET should stop.

V. Vernadsky. Through the organism, particles of matter are constantly moving, entering it from the external world (e.g. in the form of food) and again being removed as final products of metabolism. In this way, the substances which are excreted by some organisms as waste are assimilated by others, serving as a source of nutrition for them. Thus, the individual elements that make up substances forming living organisms, passing from one compound to another, move as if in a circle, constantly returning to their original state. The aforementioned C. v. can be divided into two branches: one descending and the other ascending. In the descending branch, chemically energy-rich complex organic substances, while in one organism or successively passing from one living being to another, gradually decompose, break down. In this process, the reserve of latent energy in them gradually diminishes; it is used by organisms for carrying out diverse life phenomena—movement, increase in body temperature, growth, etc. In the final outcome of this process, the organic substances are completely "mineralized", transformed into CO₂, water, elementary nitrogen, nitric and sulfuric acids, etc. These substances can no longer be used by organisms as sources of energy, but they can serve as material for building new organic substances. This process constitutes the second ascending branch of C. v.—If in the first part of the circle there was expenditure of chemical energy of organic compounds, then here, on the contrary, its accumulation occurs. For this, organisms must receive energy from somewhere outside. In the vast majority of cases, the source of this energy is sunlight, which is captured by green plants (see Assimilation). The further synthesis of more complex organic substances then occurs at the expense of the chemical energy of the formed organic compounds. It can take place not only in the cells of green plants but also in the bodies of animals and microorganisms. Each of the above-mentioned branches of C. v. is a very complex phenomenon, consisting of a series of individual links, individual chemical processes. These processes can occur together in one cell, but in a number of cases they are separated in such a way that only part of the transformations can take place in one organism, while the further course of decomposition or synthesis occurs in a number of other living beings. Thus, for example, carbohydrates, which are the main source of energy for organisms, are decomposed, so to speak, in two stages: first, the decomposition of their molecule into smaller pieces (fermentation) takes place, with only part of the latent energy being released, used by the organism for its own purposes. The substances obtained in the described decomposition still contain a significant reserve of this energy. It is released only in the second stage of the process during the oxidation of these substances (respiration). The cells of higher plants and animals are capable of carrying out both the first and second stages of the process. Therefore, they decompose carbohydrates to CO₂ and water, completely using the latent energy in them. On the contrary, lower organisms in most cases can carry out only one or another separate part of the decomposition process, using only part of the energy of organic substances and releasing into the external environment products that can be further decomposed or oxidized by other microorganisms. Thus, for example, yeast, fermenting sugar, decompose it to CO₂ and alcohol; the latter is used by acetic acid fermentation bacteria, which oxidize ethyl alcohol to acetic acid. But this acid still contains a certain reserve of energy, and therefore it can serve as a source of nutrition for a number of molds, which burn it to CO₂ and water. Similarly, in the case when the bodies of dead animals or plants undergo decomposition by microorganisms, this process has a number of individual links that are successively carried out by different kinds of microbes. In particular, the decomposition of cellulose of decaying plants begins with butyric acid fermentation, leading to the formation of CO₂, butyric acid, hydrogen, and methane. The last three compounds are still very rich in energy, and therefore they serve as "food" for a number of other microorganisms, which oxidize them to water and CO₂ and thus return the carbon of cellulose to C. v., transforming it into a compound that can be assimilated by green plants.—In some cases, however, such a complete closing of the circle does not occur, and part of the carbon at least temporarily exits from C. v. This happens when the second (oxidative) stage of the decomposition process cannot be carried out due to lack of oxygen, for example in the case when plant residues undergo fermentation underwater without access to air. In this case, their carbonization occurs, a process in which the oxygen of carbohydrates is released in the form of CO₂, H in the form of methane or other hydrocarbons, and a residue rich in carbon is obtained. Carbonization lies at the basis of peat-forming processes, the formation of coal deposits. By burning coal and transforming it into CO₂, man returns carbon to C. v. A. Oparin