MODERN SCIENCE ABOUT THE ORIGIN OF LIFE

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Опубликовано в библиотеке: 2021-09-23
Источник: Science in Russia, №6, 2011, C.17-25

by Acad. Mikhail FEDONKIN, Director of the Geological Institute of the Russian Academy of Sciences

 

The origin of life is one of the most intriguing mysteries, and at all times scientists were keen to outline, at least, avenues to unravel it; but is it possible to find the point of reference in complete uncertainty? A French naturalist of the 18th-19th centuries, Georges Cuvier, who is the author of the theory of catastrophes causing global regeneration of the flora and fauna, compared a living organism to a whirlwind, when an atmospheric vortex takes the form of a cloud arm which, growing quickly, sucks in and then scatters dust and debris, moves on and breaks apart (multiplies). However, this monster exists as long as the wind blows. Permanent energy is the guiding star for a researcher pondering over the mechanism of the origin of the first beings. Director of the RAS Geological Institute Academician Mikhail Fedonkin, interviewed by our correspondent Yevgeniya Sidorova, had to say about his research in this field the following.

 
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-- It is common knowledge that the scientific community is not unanimous as to the origination of life on our planet. But what facts are adduced about the time of its origin?

 

-- Merely 150 years ago, at the time of the great British scientist Charles Darwin, the earliest vital signs (shells and other remains of invertebrates) were found only in the Cambrian rocks whose age, as is now known, is less than 542 mln years. The deposits formed earlier seemed empty--no petrified remains! True, this worked against the theory of evolution created by Darwin. But years went by, and the situation has changed. Geologists and paleontologists have proved that the record of life impressed in the terrestrial layers extends to 3.5 bln years back. The biosphere was a kingdom of microorganisms for a major part of its history. Compound eukaryotic cells with nuclei and organelles appeared more than 2 bln years ago, and communities of different animals came into being only at the end of the Proterozoic era, and their expansion began in the Vendian period (discovered by Academician Boris Sokolov), i.e. at least 50 mln years before the Cambrian.

 

My research was connected mainly with the Vendian period. When 1 was hired by the Geological Institute early in the 1970s, there was a description of one only imprint of a Vendian animal of about 1 cm size found when studying a core sample from a deep well in deposits of more than 550 mln years of age. Today the national collections number dozens of thousands of similar petrified remains varying in size from centimeter fractions to a meter and more. The ancient creatures were soft and elastic, their imprints, sometimes also traces of creeping, are found in thin marine deposits, clays and sandstones. We are indebted for our findings to ancient storms fatal for seabed inhabitants unable to get out of washed-up deposits. Thus trapped, the captives compacted in deposits, soft tissues of animals decomposed, but their imprints remained. Cleaving the tight sandstone, we can see traces of ancient life.

 

In the Vendian deposits both extinct species and distant ancestors of the now living organisms are preserved. We classified them according to morphological and anatomical characters and described a number of new types and classes of animals mostly lacking a mineral skeleton. This is a new page in the heretofore unknown protohistory of the animal kingdom.

 

When studying older deposits, we plunge deeper and further into the past, and the connection between the former and modern life is becoming ever more ephemeral. So far geologists have studied rocks of the last 3.5 bin years. A paleontologist, while studying a new object, tries to find out how it is related to the known organisms, but there comes a point when he encounters difficulties in interpreting the nature of remains found in ancient deposits and the class of organisms to which they belong. Sometimes it is difficult to understand, whether we have discovered a colony of microorganisms visible to the unaided eye or an animal, or perhaps algae. We have to resort to methods of electron microscopy, chemical and isotopic analysis of organic remains.

 
стр. 18

 

Further on, we detect fewer of the bodily signs, no coarse petrified remains at all, and the basic information on life is obtained from the remains of microorganisms, from biological minerals, biogenic deposits, isotope and biochemical signs.

 

In our travel back in time we, like Darwin, run into a blank wall, as in the most ancient sedimentary rocks on the Earth (3 bln 850 mln years) carbon in grains of mineral apatite has a light-weight isotope composition, which is indicative of life. Maybe it is older than the available geological records.

 

-- Then the question of its origin comes up inevitably?

 

-- A number of researchers are inclined to believe in the hypothesis of panspermia (life from space). But by "importing" life from other worlds we "export" the problem outside the Earth. Besides, there are two aspects complicating the problem, i.e. cell viability in outer space and adaptability of the "stranger's" biochemistry to the physicochemical parameters of the early Earth. It should be remembered that the organism and the habitat form an interactive system, and the biochemical evolution of the cell and the geochemical history of the planet are apparently mutually complementary processes.

 

For decades the mainstream of scientific inquiry into the origin of life included methods of the abiogenous emergence of RNA, DNA, proteins and other molecules biologically significant on our planet. Today a living cell synthesizes all these substances. Some of them are already created in laboratory. It has been proved that pyrite, calcite and aragonite (modification of calcium carbonate) possess catalytic properties and can act as a matrix ("the cradle of life"), which puts together compound organic molecules on its surface. Hundreds of their species are discovered in outer space. In this connection, two questions arise. First, whether it is possible in principle to assemble a functional cell from mature molecules. Second, whether the problem of the origin of life is well-formulated.

 

A few months ago American scientists found that some bacteria inhabiting oversalted lakes use arsenic instead of phosphorus, a most important element of life. It is part of an adenosine triphosphate molecule saving and giving up energy in every living cell, and of phospholipids forming all cell membranes and also the structure of DNA and RNA. Arsenic is poisonous for most organisms (by the way, due to the chemical properties similar to phosphorus). But, in the conditions of the early Earth, this element could act, because of better accessibility, as an electron acceptor in cell metabolism.

 

The discovery of the metabolic property of arsenic in the now living bacteria has proved the hypothesis for-mulated by the author of this article together with his Dutch colleague Robert Hengeveld in an extensive paper published in Acta Biotheoretica in 2007. We have shown that, apart from hydrogen, major elements of modern organisms (C, P, N, O, S) were preceded by elements of the same groups, but with a larger ionic radius placed below in the Mendeleev's Periodic Table. Such ions formed molecules with weak bonds and required no special enzymes for synthesis and cleavage. These ions appeared later on, with the involvement of C, P, N, O, S into vital activity, which are characterized by a small ionic radius and form more stable compounds. Thus, sulphur was preceded by selenium, phosphorus by arsenic, and nitrogen and oxygen became important components of a living substance at more recent stages.

 

When arsenic was found in bacteria instead of phosphorus, some of our colleagues spoke of the discovery of a new form of life, whose sources should be searched for in outer space. But I believe this was just a biochemical relict of the earliest life on earth. Similar discoveries are yet, to come especially in the extreme environmental conditions resembling the early biosphere 4.5 bln years ago.

 

-- Search for extraterrestrial life forms is one of the official targets of the US Space Program. On the other hand,

 
стр. 19

 

 

Imprint of an ancient animal body and traces of its movement on the muddy bottom. The Vendian period, the White Sea.

 

the plan of the RAS basic research for a period till 2025 includes the topic "Problems of the Origin and Evolution of the Earth's Biosphere". How can we come nearer to the truth here ?

 

-- I believe that we should try a risky method, i.e. one based not on what life was at the time of its origin, but on what life could not be at that time. Besides, emphasis should be put not so much on the abiogenic synthesis of biologically important compounds (proteins, fats, carbohydrates, amino acids), but on the physical mechanism of origination of prebiotic objects. It will be remembered that all chemical reactions in cells are connected with electron transfer. Where and in what media could prerequisites of this process arise?

 

For a long time scientists were looking for methods of the origin of building blocks of a living substance. I believe that this is a dead-end track. So far it has not been possible to create life from unit blocks of simple compounds of hydrogen, oxygen, nitrogen, sulphur and phosphorus formed under the effect of sun light, light-ning discharges, mineral catalysts or other factors. An exponential growth of hypotheses testifies to a crisis of this research trend. Unfortunately, specialists did not attempt to explain the energy flow phenomenon forming dynamically stable prebiotic systems. Energy sources should be looked for on our planet, since life and the environment are a unified system whose components coevolve and cannot be considered separately.

 

The earliest zircon crystals on the Earth counting 4 bln 400 mln years and bearing traces of erosion prove that water was present there at a very early time. It came from the degassing of planets and small comets. But the early hydrosphere differed from the modern one. Therefore, deep-water thermal sources in ocean rift valleys, or the so-called black smokers, are interesting objects in search of a mechanism of the origin of life*. It is a peculiar world. The ocean floor moves apart here, rock melts come up to the surface, under high pressure

 

See: A. Lisitsyn, A. Sagalevich, "Breakthrough Discovery of the Century", Science in Russia, No. 1, 2001.--Ed.

 
стр. 20

 

cold water infiltrates the boundary zone, it warms up and dissolves a solidified lava as if it were granulated sugar, carrying an immense amount of minerals upwards. Life is impossible at a temperature of 200-300 ºC, but thermophilic bacteria live at 115 ºC. Many of them absorb hydrogen and release methane, and are active in using dissolved iron, nickel, tungsten and other metals as activators (catalytic centers) of their enzymes. Bacteria proliferate quickly and form flocks which gravitate to the bottom and form sediments rich in organic matter and metal compounds.

 

-- A chemically rich medium of black smokers is a perfect paradise for these bacteria. But you mentioned the flow of energy without which no life is possible. Where do the inhabitants of thermal springs take it from?

 

-- When studying processes related to the origin of life, we have to use the language of physics rather than that of chemistry, as all reactions in a cell are connected with the electron transfer from a donor to an acceptor effected with the help of a proton (ion) gradient. Thermal springs rich in various ions and dissolved hydrogen, porous mineral crusts and sediments saturated with metal sulfides create conditions for osmotic and electrochemical gradients. This environment can be called a "geochemical storage battery". Being saturated with free electrons and ions, it could produce energy to support the existence of primary prebiotic systems.

 

We should point to the great importance of hydrogen. Waters of thermal sources are hydrogen saturated, and even today hydrogen serves as an "energy currency" for bacteria and Archaeota* living on chemically different substrates, some of them absorbing H2 and others producing it. Prokaryotes are the world's best "electro-chemists" capable of "building" their metabolic processes into natural gradients. Hydrogen binds them to become an ecosystemic factor.

 

Scientists are dealing with more than ten natural sources of hydrogen of different intensity but, of course, less potent than at the early stage of the Earth. However, 4.5 bln years ago our planet was hot, the atmosphere was reductive, the solar wind was very intensive; all these factors facilitated extraction of this gas. According to some calculations, H2 could amount to 30 percent of the pristine atmosphere. A great quantity of H2 escaped at the formative stage of the Earth's core, when it was being filled with iron and nickel. The serpentinization reaction of white-hot volcanic rocks rich in iron, nickel and tungsten, proceeding in interaction with thermal waters was also accompanied by H2 emission.

 

Hydrogen is a high-reactivity gas (its molecules have a low energy of activation), it is diffusion-mobile (it penetrates even through glass and metal), it is present everywhere and is, therefore, always accessible. I repeat that it was found in large amounts on the early Earth. It is proved also by tests with meteorites which release H2 and its simple compounds on heating. Interstellar dust provided a base for our planet's formation.

 

Methanogenic prokaryotes (Archaeota) are the most active users of hydrogen. They must be some of the ancient representatives of the organic world still inhabiting sites with a reducing environment corresponding to their nature and similar to the ancient biosphere.

 

-- In other words, if black smokers, which have a lot of "energy currency", have not been known yet to science, they shoud have been found in order to come nearer to the cradle of initial life?

 

-- Indeed, the above facts make us search for a medium rich in hydrogen and metals. These are thermal springs today, but on the early Earth it was in the form of the primary ocean. Furthermore, biochemical reactions with the participation of H2 are catalyzed by hydrogenase enzymes whose active site includes ions of iron and nickel. These microelements, making up fractions of one percent of all organisms, are no less important for life than biophil oxygen, hydrogen, nitrogen, phosphorus and sulphur. In fact, reactions proceeding within a cell with the participation of metals are thousands and sometimes millions of times faster than those outside the cell. But if we take out ions of iron or nickel from a large protein molecule, enzymes will cease to work. This speaks for the primary role of inorganic catalysts, and, consequently, the origin of life has to be searched for in a medium enriched with metals. Here again, thermal springs are an optimal model.

 

Metalloproteins constitute a major part of modern enzymes. The impression is that the objective of life is to protect in every way its chief asset, the metal, and prevent it from oxidation. Protein molecules are similar to the fingers of a hand controlling metal atoms during biocatalysis. Thus, thousands of reactions are carried out, and complex metabolic chains are built up in the organism just in one second. Cells of phytoplankton accumulate microelements in a concentration exceeding thousands of times that in seawater. Each of microelements (mainly transition metals) is necessary for vital activity, and, apart from the habitation medium, it cannot be obtained anywhere else.

 

In giant protein molecules of enzymes the active sites are often represented by small ferro-sulphuric clusters (cubanes). Their structure resembles a crystal lattice of pyrite orgreigit (ferric sulphides FeS2 and Fe3S4). Such resemblance may be not incidental, because in the medium of the said thermal springs metals, initially in a mobile condition, oxidized later to form sulphide deposits. In so doing, molecule fragments of sulphide ore compounds were involved also in other processes, which brings us back to the model of the life origin in the initial hydrosphere of the early Earth. Figuratively, there occurred a moment of bifurcation, namely, either to become a part of mineral or of future life.

 

* Archaeota-unicellular prokaryotes which differ both from bacteria and eukaryotes at the molecular level.--Ed.

 
стр. 21

 

 

Chemically rich medium of black smokers is a real paradise for bacteria.

 

-- Are there any hypotheses as to what exactly metals formed the first catalyst moleculesiron, nickel? Was the role of these chemical elements in the course of biological evolution invariable or it changed?

 

-- At present geochemical reactions with the participation of hydrogen are catalyzed by ironnickel enzymes of prokaryotes (microorganisms, whose cell has no distinct nucleus). Besides, most hydrogenases with Fe-Ni activators are found in Archaeota (including metanogens), but they occur more rarely in eukaryotes (whose cell has a nucleus). If we look at the phylogenetic tree*, which illustrates the direction of evolutionary transformations of microorganisms, and at the relatedness of different groups, we shall see that branches of hyperthermophils diverting from its roots are located mainly among the Archaeota. These strict anaerobes, consuming hydrogen, generating methane and somewhat more primitive than bacteria, live also now in the same conditions as on the ancient Earth, with iron and nickel, abundant at the dawn of life, as their activators. Since iron meteorites contain much nickel, up to 15 percent, its implication in biocatalysis can be regarded as a sign of antiquity. The remarkable fact is that both metals in the active site of the said enzymes are surrounded by sulphur atoms. This is also true of tungsten as part of proteins. Sulphur is occasionally replaced with selenium. These facts can be interpreted as evidence of the origin of microorganisms in the reducing conditions of the ancient ocean.

 

With oxygenation of the ocean other metals became more accessible, for example, molybdenum, copper and zinc. Synthesis of paleontological, geochemical and biochemical data on modern organisms leads to the conclusion that now, in the oxidizing atmosphere, molybdenum assumes greater importance than nickel or iron because it is less oxygensensitive and might have replaced "ancient" metals within enzymes in many cases. Molybdenum-activated enzymes help uptake nitrogen not only from nitrates, but also directly from the atmosphere and facilitate polymerization of a number of proteins. In the anoxic biosphere of the early Earth (4 bln years ago) it was less accessible, and its functions were performed by other metals, such as tungsten, iron and vanadium.

 

See: A. Martynov, "Biological Taxonomy Faces a Choice", Science in Russia, No. 3, 2011.--Ed.

 
стр. 22

 

Hypothetic sequence of the involvement of metals into enzymic evolution. Early history of the biosphere.

 

 

The following facts confirm this supposition. In the zone of well-being of archaebacteria-hyperthermophils (80-115 ºC) in the medium of "black smokers" there is a lot of tungsten but little of molybdenum which flocculates in the form of sulphide. Farther from thermal springs saturated with hydrogen sulphide, the role of oxygen grows, and Mo passes into solution, and W, on the contrary, becomes inaccessible for metabolic processes. The composition of microbial communities changes respectively. Likewise, molecular-phylogenetic analysis data support the version of the earlier appearance of organisms on the Earth, which used tungsten in their enzymatic systems. Meanwhile, W is attributable not only to hyperthermophilic prokaryotes, but also to other microorganisms. However, the former are incapable of "changing" it to any other microelements, which suggests that this metal was implicated in the sources of life.

 

Probably nickel and cobalt have also such a long history in biological evolution. This is confirmed by their limited consumption by eukaryotes, while cases of consumption of both metals by one organism are rare.

 

But what took place afterwards? With a lower volcanism, delivery of metals from the bowels of the earth and their appropriate supply to the biosphere was down. The proportion of magnesium, iron, nickel, cobalt and tungsten in volcanic lava decreased. The contribution of outer space likewise diminished. At the same time, the role of biota grew up to become a primary factor of mobilization, transport and isolation of microelements. The global temperature of the biosphere as an essential factor for chemosynthesis was going down. Not later than 2 bln 700 mln years ago oxygenic photosynthesis set in, and free oxygen, first produced by cyanobacteria, stepped up accumulation of ores and made iron, nickel and magnesium even less accessible.

 

Growing apace, the continents entrapped metals, as confirmed by ancient crusts of weathering and soils colored by ferrous oxides in reddish hues and above all by giant deposits of sedimentary ores of iron, manganese, uranium and other elements within 2.4-1.7 bln years ago. Worthy of note is a decrease in the proportion of nickel in products of ancient volcanism and, consequently, in the ocean of that time. If we remember that Ni alongside Fe acts as an activator of hydrogenases in prokaryotes generating methane and compare this fact with the history of the climate evolution on our planet, an interesting coincidence will become evident.

 

A decrease in nickel concentration in the ocean more than 100 times at the end of the Archaean and in the beginning of the Proterozoic weakened its role in catalysis of the greenhouse gas. Its generation decreased, which, together with other factors (for example, burial of enormous masses of biogenic carbon in sediments) contributed to climatic cooling: a global glaciation took place 2 bln 200 mln years ago. The temperature drop is seen in the isotopic ratio of oxygen in silicon oxide of ancient marine sediments, the pattern of sediments and other features. Starting with the end of the Proterozoic (750 mln years ago), the advance of glaciers became a regular phenomenon, and during deglaciation cold waters rich in oxygen came to the ocean which, therefore, was aerated to the floor already by the start of the Pharenozoic (542 mln years ago). Accordingly, the role of copper, zinc and molybdenum in the composition of enzymes and, consequently, in the ecosystem increased.

 

-- Thus, the atmospheric composition and the degree of accessibility of metals changed, and this had an effect on the biological community. Do the discovered tendencies help come to an understanding of the mechanisms implicated in the origin and evolution of life?

 

-- As I have already said, the objective of life is to extract metals from a medium, be it the ocean, lithosphere or soils. Microelements come regularly to the ocean with a river discharge. But their reserves in sea-water are well below the rated values, because microorganisms hunt for them and include into a biological

 
стр. 23

 

 

Ancient communities of Venetian multicellular organisms (585-543 mln years ago).

 

cycle. This is clearly seen in the concentration ratio of iron, zinc and aluminum in phytoplankton and seawa-ter: Fe-87,000, Zn-65,000, Al-25,000, N-19,000, P-15,000, Cu-17,000, Mn-9,400, Cd-910. This discovery was anticipated by the Russian poet Maximilian Voloshin, who wrote in 1923: "Our primogenitor, who took out his fishtail from the chilled waters, carried along the whole ancient Ocean in its wake...--the living blood running in veins." But specialists still keep wondering over the origin of the first living cells and the physico-chemical parameters in their first 'cradle'.

 

The high temperature of "black smokers" seems dangerous for early life to many researchers. Therefore, they showed a keen interest in research data on alkaline deep-water thermal springs with a temperature below 40-90 ºC discovered in the Atlantic Ocean in 2000. Surrounded by fanciful carbonaceous constructions rising up to dozens of meters (hence the name, Lost City), these objects are long-lived and emit fluids saturated with hydrogen and methane feeding microorganisms (mainly Archaeota) inside thermal springs and various biota (from bacteria oxidizing methane and sulphur to invertebrates) outside. It is believed that the semitrans-parent porous space of the mineral constructions could serve as a cataclave for the synthesis of compound organic molecules similar to adenosine triphosphate.

 

British geochemist Michael Russell proposed his model in 2006: layers of organic substance acting as membranes were formed on the walls of mineral crust pores near thermal springs on the ocean floor. They could include compounds of iron and sulphur (the role of Fe-S cubanes was discussed earlier). There emerged "chambers" partly isolated from an external environment as forerunners of a cell. In fact, the membrane is a key link for the ion gradient, as it protects to a great extent the uniformity of the inner medium, and this, according to the great French microbiologist of the 19th century Louis Pasteur, is the pledge of freedom in the variable external environment.

 

Russell's hypothesis (for all its shortcomings) allows for a bit of experimentation. Close to thermal springs many different minerals are formed; substances are in the ionic form and ready for reactions and transformations. A potential difference (the so-called geochemical battery) is generated inside porous rock, from which hot seawater seeps, in between media. Similar conditions are favorable for the germ of life, but we cannot understand yet, what molecular systems (not necessarily organic) were its precursor sustaining the substance and energy exchange. Therefore, we still remain on the level of hypotheses.

 

-- Nevertheless, some hypotheses are confirmed by practice. At the start of our discussion you said that ancient living organisms could use chemical elements rejected by modern plants and animals. In fact, at first scientific papers published your hypothesis, and then real bacteria were found, which preserved this ability.

 

-- Indeed, the theoretical considerations and studies of such kind are needed for understanding the nature of the present. We examine a cell and see that a set of coherent reactions proceed inside it. It cannot be ruled out that the historic sequence in the formation of these

 
стр. 24

 

complex interactions reflects the development of biochemical and geochemical processes on the early Earth. When reconstructing evolution on the molecular scale, we should understand what appeared later and what earlier. The initial stages are most interesting. In fact, the older certain biochemical features of life are, the more universal they are and, consequently, deserve special attention and delicate handling.

 

-- But the earthly conditions change all the time. On account of what are the primary mechanisms so stable?

 

-- The initial stable foundations of life are connected with an ability to retain energy and give it then for processes necessary for the organism. When studying the historic changes of volcanism, the ocean salinity, climate, the intensity and spectrum of sunlight, and the atmospheric composition, we can understand how and why changes took place in the cell and what is the nature of the formation of its organelles and complex membranes around them and also the nature of isolation and separation in its space and time of some biochemical reactions. All these structural and functional complications are connected with life continuity, which implies preservation of the basic mechanisms of metabolic processes.

 

-- For example, membranes protect "the ancient ocean" within the cell from the changed environment. But how is the presence of organelles explained evolutionally?

 

-- Their formation was also connected with changes of the external environment. Decreased was the accessibility of metals and hydrogen as well as the activating role of radiation, and temperature went down, too; free oxygen appeared at the same time, i.e. the dominant conditions of the "life cradle" were disappearing irreversibly. A "consortium" remained the only survival chance for the first organisms. In 1905, Russian biologist Konstantin Merezhkovsky formulated the theory of the origin of complex cells by symbiotic development of simpler cells. Based on cytology data, his theory is now confirmed by genetic and biochemical findings.

 

The eukaryote cell with its organelles is essentially an ecosystem formed on the basis of syntrophy (joint nutrition) of various prokaryote cells, whose consortiums were more stable in relation to the updating conditions of the environment. By exchanging vital products they synchronized their biochemical and reproductive cycles and formed stable exosymbiotic and endosymbiotic complexes. It appears that the most favorable are hypotheses which describe this process as aggregation of two cells, one producing hydrogen and the other uptaking it. This is how prokaryotes appeared. As to numerous cascades of exchange reactions in cells of modern eukaryotes, they can be the biosphere's memory about the arrival of new symbionts in the process of evolution.

 

Interpretation of this history opens up new opportunities in the spheres of medicine, ecology and biotechnology.

 

-- Is it possible to give practical recommendations to mankind proceeding from the available knowledge of biochemical trends in the ancient biosphere ?

 

-- All the above stated is topical for studies of the hydrogen metabolism, the most ancient line of the evolution of living being. It is predominant in anaerobic conditions including thermal springs and the "deep biosphere" several kilometers below the ocean floor. The role of biota in the mobilization and concentration of chemical elements in the most ancient ecosystems also becomes more clear (the largest deposits of Fe, Mn, U, Au, Ni, Cr, Cu and other metals are confined to Archean and Proterozoic deposits). Construction of metalloenzymes for biotechnologies with account of data on the metabolic system and its evolution will be possible in the future.

 

And yet another thing. Far from the continents there are the so-called blue waters of the ocean, a scanty region for the microflora, where the bacterial plankton is dormant in the form of spores. But American scientists have carried out an experiment--they enriched this environment with dissolved iron. Thereafter, a vigorous blooming of water could be observed even from orbital satellites. The point is that nitrogen fixation and photosynthesis could not be efficient in the absence of iron, though other biogenic elements were present. Meanwhile, people "inject" more metals into the biosphere than they get in naturally. But with the arrival of any particular microelements, specific groups of primary producers or certain types of physiology have priority. Where will the man-induced imbalance lead to?

 

We are still enthralled by the global ecological paradigm oriented to microelements. But the time has come to evaluate the consequences of environmental pollution with microelements, for they carry out the circulation of matter in the cell, organism and ecosystem.

 

The aforesaid results are obtained under the RAS Presidium Program of fundamental research "The Origin of the Biosphere and Evolution of Geobiological Systems ".


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© Mikhail FEDONKIN () Источник: Science in Russia, №6, 2011, C.17-25

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