by Academician Nikolai KOLCHANOV, Director of the Institute of Cytology and Genetics, RAS Siberian Branch (Novosibirsk), Valentin SUSLOV, staff member of the Laboratory of Theoretical Genetics of the same institute

In 2009 the Publishing House of the RAS Paleontological Institute issued a collection of articles "Problems of the Origin of Life" based on the materials of the colloquium of the same name held in Moscow a year before. The collection includes reports on different aspects of the origin and early evolution of the Earth biosphere and its relations with the world of organic molecules in the Universe.

Scientific progress proves a necessity for specialization. But there is also a reverse side of the medal, i.e. narrowing of the range of interest, when accumulation of facts outstrips their comprehension and leads to stagnation. It is well known that the so-called "eternal" problems always existed in science. Their solution sometimes took centuries, they are often perceived as "abstract", but scientists of different generations revert to them again and again. However, the striving "to grasp the unbounded" is not the main problem here. The "eternal problems" are interdisciplinary, they require a wide range of interests and intensive exchange between very remote spheres of knowledge. In short, their importance in the structure of science is not limited only by the scope of a specific content. They com-

Schemes of cell division (left) and disjunctive multiplication of viruses (grey background-recombinant viruses) (according to Agol, 2009, revised).

Combinatorics of matrix processes during self-reproduction of viruses. The options on a grey background are predicted theoretically and then found (according to Agol, 2009).

bine separate directions into encyclopedic knowledge there, where it cannot be achieved either by research in special aspects or borrowing of experimental methods. The origin of life is one of such "eternal" problems. The above-mentioned collection is devoted entirely to this issue.

Its authors are representatives of different fields of science: astronomers—Leonid Ksanfomaliti and Leo Mukhin, both Drs. Sc. (Phys. & Math.) from the Institute for Space Research, the Russian Academy of Sciences, and Nikolai Bochkarev, Dr. Sc. (Phys. & Math.) from the Sternberg State Astronomic Institute, Moscow State University, geologists—Academician Nikolai Dobretsov, Andrei Vityazev and Galina Pechernikova, both Drs. Sc. (Phys. & Math.) from the Institute of Geosphere Dynamics, RAS Siberian Branch, paleontologists—Academician Alexei Rozanov, chemists—Valery Snytnikov, Cand. Sc. (Phys. & Math.) from the Boreskov Institute of Catalysis, RAS Siberian Branch, biochemists—Academician Alexander Spirin and RAS Corresponding Member Alexander Chetverin, molecular biologists—RAS and RAMS Corresponding Member Vadim Agol, microbiologists-Academician Georgy Zavar-zin and Yelizaveta Bonch-Osmolovskaya, Dr. Sc. (Biology) from the RAS Vinogradsky Institute of Microbiology, and physiologists—Academician Yuri Natochin. Actually, the number of the authors was much more (36 persons participated in the discussion), as each chapter of the collection is supplemented with a shorthand report of the discussion. The latter cements the heterogeneity of subjects under discussion and makes clear issues specific for one or another science, thus adding integrity to the book and, what is more important, making it interesting not only for a particular specialist.

The event took place under the program of the RAS Presidium "The Origin and Evolution of Biosphere". But unlike the previous conferences and collective monographs, published according to their results, in this particu-

lar case a considerable part of the materials is devoted to astrobiology.

The authors focused on eight problems, whose solution revealed a lot of new ideas for the last 20 years, such as: possibility to get a cell out of its components; the origin of viruses before and after a cell; the importance of organic matters of the Universe for life; the world of RNA and a possibility of its existence at the pre-Earth stage; living conditions on the early Earth 4.6-4.0 bln years ago and later on, when biosphere traces are expressly present; deep-laid biosphere of our planet as a possible analogue of primary ancient ecosystems, and finally, the origin of membranes, or a lipid cellular cover, through which metabolism between a cell and an external medium takes place.

The above-mentioned first, second, fourth and eighth problems can be united as a scenario of organismogenesis, i.e. how the organism was formed (in particular, the simplest one or a cell). The third and fifth problems deal with the conditions of an external medium, in which the aforesaid process took place. Finally, the sixth problem is the theory of ecogenesis: how organism as such interacted with the medium and similar organisms.

Now let us consider all these problems in succession. Tasks of complete decoding of genomes have become routine in molecular biology. The impressive progress has been achieved in sequencing for the last 20 years: the widely used sequencers of the second generation reduced the cost and time of works by 2-3 orders. Foreign scientists started speaking about synthetic genomics* designed to construct new types either by combining different types of genome fragments or by their artificial synthesis de novo (i.e. from the very beginning).

In the chapter "Is it Possible to Get a Cell From its Components?", the well-known scientist in physicochem-ical biology Alexander Chetverin appraised prospects of laboratory synthesis and considered a possibility of this event in the nature, pointing out a fundamental contradiction on the one side. The self-assembly of separate elements of a cell is well studied (lipid membranes, proteins, nucleoprotein complexes including such compound complexes as viruses and ribosomes). But as soon as a membrane is formed (its self-assembly is very simple), the advance of large multimolecular components is stopped and that of low-molecular components, such as amino acids, nucleotides, sugars, etc., without which metabolism is impossible, is hindered. In other words, the self-assembly requires an unobstructed advance of components, but quick formation of closed membrane cavities, or compartments, will violate a duct (ecosystem—a flow system).

On the other hand, efficient evolution is complicated without compartmentalization. After all, selection is assessed not by genes themselves, but by their products, namely, a phenotype. Consequently, the more tightly a gene and a product are bound in space and time, the more efficient is refinement of protocells. But the duct required for self-assembly gives no guarantee that the product will not be carried away from its parent and serve foreign genes at best or be lost totally at worst. A similar situation is observed in viruses with their disjunctive (separate) multiplication, when DNA (RNA) and proteins are synthesized separately, and only then, after mixing, we observe self-assembly, which provides both parent and different

* Genomics is a section of molecular genetics dealing with decoding and comparative studies of genomes as a whole.—Auth.

Infrared strips in dust spectra of the astration area W33A, which allow to form an opinion on its composition. Ox-wave lengths, Oy-spectral density of radiation fluxes in JANSKE (Jy), (1 Jy=10^-23 W/m² H).

recombinant viruses. It appears that it is impossible to form an organism with compartmentalization, and it is impossible without it. According to the author, the solution of this paradox lies in the effect of formation of RNA molecular nanocolonies on a substrate with nanometer pores, discovered by him. In his laboratory studies, he used a gel as a substrate, while in nature it could be mont-morillonite, a widely used clayey mineral, which forms pores of an appropriate size.

In the experiments conducted by Chetverin, large molecules on a substrate with nanopores behave like flies in a cobweb-"anchored", they remain in place (non-membrane compartmentalization) but can bend, roll up and unroll within wide limits, changing their configuration in space or conformation. Changes of the latter is the basis for replication, transcription and other enzymatic reactions, which provide doubling of DNA and metabolism. As a result, descendants of one molecule form a nanocolony. One can carry out selection among them by changing of conditions (wetting and drying of a substrate) and a duct of low-molecular components. Sometimes separate RNA leave the "nanocobweb" and, as experiments prove, are transferred by air, thus infecting a new substrate. However, dehiscence of the latter and transfer of nanocolonial fragments on its pieces is a potentially best way of multiplication. Thus, unlike the viewpoint of Craig Venter (USA), "the father" of synthetic genomics, according to Chetverin, direct self-assembly of cells in nature is impossible. The origin of life has to take place via an intermediate stage of molecular nanocolonies.

It should be noted that though the eighth problem discussed in the book, namely, the origin of membranes, is placed at the end of it, as a whole it continues the first problem, as both of them are integral components of the cell.

For example, in the shorthand report of the discussion, Valery Snytnikov pointed out: alumosilicate clays of the montmorillonite type are good catalysts. Besides, it has been proved by the experiment recently that non-matrix synthesis of RNA can take place in the pores of this mineral. But the catalyst will become emaciated, when RNA blocks up pores. As a result, the nanocolony will grow on its edges by using pure montmorillonite. But if the nanocolony is surrounded by a membrane, its growth will stop. It appears that membranes hinder both the self-assembly and existence of nanocolonies. What then is the use of membranes, if compartmentalization is possible without them?

As it is the case with the "eternal" problems, the answer came from an unexpected field of knowledge. Yuri Nato-chin ("The Origin of Membranes"), an authority in kidney physiology, assumed that an evolutionary advantage should be energy-based. It is well known that the membrane stabilizes the ion composition inside a cell medium and creates asymmetry of ion concentrations between the inner and outer media. This asymmetry is a main energy accumulator for the synthesis of adenosine triphosphate (ATP)*. On the contrary, there are no distinctions between internal and external media for molecular nanocolonies, as the ion concentration is easily changed.

* Adenosine triphosphate (ATP) is a nucleotide acting as a universal energy source for all biochemical processes in living systems. -Ed.

Graphs of logarithm of particle density for different constants of their coagulation (C) in a self-gravitating disk obtained by computer modeling (according to Snytnikov, 2006).

The enzymatic activity of macromolecules depends on their conformation, while the latter depends, in its turn, on the number of different ions in a medium. Therefore, frequent variations of their composition reduce metabolism efficiency of nanocolonies and hamper their evolution. We can say that the nanocolony "does not know" its evolutionary direction, as the ion concentration can change faster than mutations are fixed. When a membrane with transmembrane proteins-pumps forms an internal medium, it stabilizes the ion composition thus canalyzing* enzyme evolution. It immediately affects the evolution, as only those enzymes are selected, which are efficient in the given medium. Such evolution is much more efficient than noncanalized one, as, first, selection sorts out less "victims" and, secondly, by adjusting to one and the same conditions, enzymes become more complicated. At the expense of selective transport of ions, the asymmetry of their composition is formed automatically as an energy accumulator, which is subsequently utilized by evolution for the synthesis of ATP and, in case of animals, also for nerve impulse transmission.

Virologist and molecular biologist Vadim Agol ("Virus Before and After a Cell") considered three hypotheses of the virus origin: cell descendants degenerated under the action of parasitism; or derivatives of separate genes, or pre-cellular genetic elements. The first two theories dominated at the end of the 20th century, but now factual data are accumulating in favor of the third theory. The point is that virus multiplication differs fundamentally from cytokinesis, and is not produced from the latter. Besides, according to the latest data, vimses realized all imaginable combinatorial schemes of matrix processes of self-reproduction of nucleic acids (including those predicted theoretically beginning from the 1970s, plus Vadim Agol's laboratory).

Molecular genetics of cellular organisms testifies to conservatism of fission schemes and matrix self-reproduction. Consequently, it stands to reason to suggest that should viruses be derived from cells, they would reveal similar conservatism.

If we accept Alexander Chetverin's nanocolony as a proto-organism, we can assume that viruses are the first attempt of evolution to tear such colony away from the substrate. Probably there were several similar attempts, in that

* Canalization of evolution is a stable tendency to change one or another character due to permanent action of selection under stable conditions of the medium as for this or that parameter (in the given case, for the ion concentration and composition). Canalization of evolution should not be confused with orthogenesis, when a tendency to change the character is limited by its structure. -Ed.

case their origin is polyphyletic, i.e., they originate from different forbears. Originally protoviruses could present a mechanism of multiplication of nanocolonies independent of clay dehiscence. Incapable of synthesizing ATP, they could drift in search of montmorillonite enriched with abiogenic phosphates or other substrate. But when a more successful attempt of nanocolonies to tear away created first cells, protoviruses used them as a substrate. From this moment on the evolutionary ways of both of them deeply interweaved: parasitizing on the cells, viruses participated (and participate up to now!) in the formation of prokaryotes and eukaryotes-unicellular protists, and also animals, mushrooms and plants. Moreover, probably it were viruses, which helped overcome the evolutionary boundary between pre-nucleic prokaryotes and eukaryotes—organisms with a nucleus. Organization and control of the genome in eukaryotes are much complicated than in prokaryotes. Besides, a number of appropriate genes have no prokaryot-ic analogs and probably were "borrowed" by the forbears of eukaryotes from viruses, which got "stuck" in their genomes as a result of mutations. It turns out that an answer to the question "origin of viruses: before or after a cell" is somewhere in the middle, i.e. their formation started before a cell and ended together with it.

Thus, the authors reached an elegant compromise between three main scenarios of the origin of life: homeostasis (self-regulation), matrix synthesis of macromole-cules, and individualization of metabolism.

Another problem of this collection deals with the conditions, in which organisms could originate. It should be noted that the origin of life includes a "preliminary" stage of chemical evolution. The data of radioastronomy and spectroscopic astrophysics (discussed in the chapter "Molecules and Their Migration in the Universe" by Nikolai Bochkarev) testify that simple organic molecules (size-up to 13 carbon atoms) exist in the atmosphere of cold stars, planets, their satellites and in interstellar gas-dust and molecular clouds. But if a complicated molecule is not observed, it does not mean that it does not exist. Perhaps we just have no instruments sensitive enough to identify it. Besides, different galaxies can be dissimilar in organic composition.

Astrophysicists assume that molecular clouds and cir-cumstellar environment are permanent chemical reactors of an organic synthesis. And ice shells of small bodies, from particles of dust to comets, are main "finished products storerooms". The exchange of organic molecules takes place most probably in the zones of collision of galaxies.

In a word, the Universe permanently synthesizes organic matter. According to Valery Snytnikov, a specialist in chemical catalysis, the paradox is in incommensurable scales of "astronomic" and "chemical" time. Thus, the chemical period of a multistage synthesis of complicated organic compounds, taking into account reduction of catalysts, transition between intermediate stages, etc., lasts from several hours to dozens of years, while the astronomic period begins at the least from dozens of thousands of years. The similar gap between intermediate stages of the synthesis leads to the fact that the whole complicated organic structure has time to decompose.

Thus, a compact chemical reactor and a mechanism for concentration in it of the organic matter of the Universe are needed. Valery Snytnikov, after experiments with a real meteorite substance as a chemist-technologist, and after simulating astrophysical processes in accretion disks of stars, suggested compression zones of gas-dust environment for use as similar reactors. The key role in the formation of the latter is played by gravitational instability of accretion disk*. According to computer modeling, the lifetime of such ephemeral astronomic objects is comparable with "chemical" time. When rotating around a star, they concentrate simple scattered organic matter (this process is interrelated in a certain manner) and provide a catalytic synthesis of compound substances, such as amino acids, sugars, etc. If such dense cloud becomes a foetus of the planet, there can be quickly formed the life at least of the type of a nanocolony. Thus, at the interface of the theories of catalysis and astrophysics, there emerged astrocatalysis, an original theory, which united the "preliminary" stage of chemical evolution of life and planetogenesis into a single process.

According to the data of astrophysicists Andrei Vityazev and Galina Pechernikova ("The Early Earth in the Midst of Young Stars"), young stars emerge in groups or clusters in the centers of astration. Therefore, the Sun was in the enriched interstellar environment during the first dozens of millions of years after its birth. When developing a standard model of the origin of Solar system, the authors demonstrated that already in the first millions of years of its existence, the formation of planets and differentiation of their depths into a core, mantle and crust, was quite possible. The well-known meteorite bombardment, whose traces are found on the Moon (～3.7-3.9 bln years ago), is probably a consequence of the fact that the Sun left the celestial cluster. Besides, the absence of significant eccentricity (deviations from the circle) of the Earth's orbit proves that the latter happily escaped megaimpacts destructive to life, i.e. collisions with a cosmic body like Mars. However, during discussions the scientists pointed out that in the presence of the World Ocean on our planet, an asteroid of about 400-500 km in diameter was quite enough to boil it and practically destroy its biosphere.

In the section "Conditions on the Earth Surface 4-4.6 bln Years Ago", the physicist Lev Mukhin showed that despite tectonic activity and meteorite bombardment, even on the early planet it is probable to preserve the areas of the Earth crust with a temperature sufficient for existence of liquid water. Here the main problem of the origin of life should be deficiency of phosphorus. It is the rarest element

* Accretion is a process of falling out of the substance on a cosmic body from the environment or concentration of the substance around a cosmic body,—Ed.

Fossil PECHENGIA MELEZHIKI. Size ~130 µm, its morphological characteristics do not allow to interpret it as a prokaryote (according to Rozanov, 2009).

in the Universe. It turns out that its "islands" should be searched for in the Galaxy.

Thus, already at the accretion stage or immediately after its completion, our future Earth seemed rather comfortable for the formation of life or bringing it from without. However, this also holds true for all planets of the Earth group. Consequently, there could also be found traces of life.

But Mukhin's colleague, the astronomer Leonid Ksan-fomaliti disappointed the colloquium participants with this idea ("From Mars to Europe: Search for Biosphere on Satellites of Giant Planets"). Though there was an ocean on the ancient Mars and there still exists liquid water on this planet today, no traces of life are found there.

The magnetic field disappeared there about 4 bln years ago, and large permanent water reservoirs existed approximately 2 bln years ago. As was mentioned above, at that time the prokaryotic biosphere already existed on the Earth. The American rovers in the 20th century found genuine meteorites on the Red Planet, but they could not determine their origin. But then secondary meteorites from Mars were found on our planet, i.e. fragments of the Martian rock, thrown out to outer space by a strong explosion (probably in collisions of large meteorites, which left their traces in the form of craters on the surface). The Martian origin was first established by methods of fine chemical and isotopic analysis during studies of Nakhla meteorite in Egypt. Ever since approximately 30 secondary meteorites have been found for a quarter of the century.

Supposing that Mars and Earth had exchanged a certain rock, the terrestrial prokaryotes could get to the Red Planet in the pores of this rock. How come they did not get acclimatized there? Does the Earth possess a special physical property or their combination, which is necessary for life (to be more precise, for life of cells with a chemical composition known to us)?

The prominent paleontologist Alexei Rozanov in the chapter "Microbe Pseudomorphoses in Meteorites" demonstrated a lot of photographs of microfossils from carbonaceous hondrites (they represent an overwhelming majority of stony meteorites. -Ed.), which cannot be distinguished from fossilized remains of terrestrial prokaryotes, eukaryotes and ecosystems or prokaryotic mats. The isotope data do not contradict their biogenicity. Experiments on survival of bacteria and viruses in the conditions of short-term heating to 200°C prove that the cosmic travelers had chances to survive even in case of "rough landing" (as meteorites of a medium size are seldom warmed up very much inside). If the age of carbonaceous hondrites is about 4.5 bln years, the organisms, whose fossils are preserved up till now, are older than the Earth and could exist only on other Earth-like planets. However, Ksanfomaliti emphasized the uniqueness of our planet, as no similar planets exist in near space.

Though the authors of the collection agreed not to give a definition of life, it was understood that it comprised at the least two complementary factors, i.e. organisms and the ecosystem. The former reproduce genetic information by

means of matrix processes. The latter, consisting of functionally heterogeneous organisms, which form linear and/or closed trophic chains, stabilize fluctuations of the duct of primary substance and energy. These fluctuations are connected with geochemical cycles, and their dynamics differs greatly among different planets. Comparative plane -tology testifies that Mars practically left "a corridor of hab-itability" for biosphere of the terrestrial type, while Venus never entered it. As the leading microbiologist-ecologist Georgy Zavarzin concludes in the chapter "The First Ecosystems on the Earth", functioning of life on the "astronomic" time scale is possible, if ecosystems "fit well" into the geochemical cycles of the planet, and the more well-balanced ample species it possesses, the more chances it has for functioning. Here follow two important conclusions. In case of the origin of life on the planet, functional diversity should appear together with life, i.e. ecosystems and organisms are formed not in sequence but in parallel (even on a nanocolony level). In case of bringing life from outer space, a ready-made ecosystem has maximum chances. Therefore, it is extremely important to find fossils of prokaryotic ecosystems in meteorites, which Alexei Rozanov mentioned in his report.

Zavarzin's idea of the unity of biosphere was discussed by his colleague Yelizaveta Bonch-Osmolovskaya in her review "High-Temperature Deep-Laid Microbial Communities as a Probable Analog of Ancient Ecosystems?". Deep-water chemotrophic communities of oceanic thermal springs ("black smokers") are a part of the photoautotrophic biosphere, as they intensively exchange chemical elements and microbial population with the latter. It turned out that ecosystems of natural oil fields exist at the expense of a buried organic substance of old biospheres. Only deep-water hydtolithospheric ecosystems of interstitial waters (the latter are formed in rock fissures) can be considered as trophic-independent. But they also exchange microbial population with the surface now and then.

Alexei Rozanov showed how ancient the land and shallow-water autotrophic ecosystems could be ("Conditions of Life on the Early Earth After 4 bln Years Ago") by revising the geological and paleontological data of the Lower Pre-Cambrian*. Comparison of fossilized** remains of modern prokaryotic ecosystems with the Pre-Cambrian ones revealed no fundamental distinctions. This makes us suppose that the trophic structure of microbial communities and conditions of their fossilization, and consequently of their existence, should not differ fundamentally from modern ones.

The prokaryotic biosphere in the interval between 4 and 2 bln years ago assumed a planetary character with inhabited shallow-water seas of the continental shelf and then spreading to continents (here Georgy Zavarzin is at one with Alexei Rozanov and believes that a thin layer of reduced rocks is sufficient for ultraviolet protection, and local high concentrations of oxygen shall appear on the Earth together with cyanobacterial mats, i.e. bacterial ecosystems based on cyanobacteria-the first organisms, which assimilated an oxygen photosynthesis). The same is testified by early (2.04 bln years) findings of eukaryote-like fossils (Pechengia melezhiki) on the Kola Peninsula.

The history of interrelations of our planet and the existing biosphere has been traced in detail by the prominent geologist Nikolai Dobretsov in the chapter "Correlations Between Irreversible and Recurrent Events of Deep-Laid Geotectonics of the Earth, Global Tectonics of Platforms and Key Moments of Biosphere Evolution". In his opinion, the evolution of the Earth as a planet is connected with a temperature drop of its depths and viscosity increase of its mantle. The process of heat transfer is unstable, as cyclic changes of temperature are observed against the background of gradual cooling down of the mantle. This determines respectively the peculiarities of tectonic plates (in particular, the Wilson cycle frequency, from formation to disintegration of supercontinents—Pangaea) and through volcanic activity contributes to global geochemical cycles, characteristic dynamics of glaciations, change of composition of eruptive rocks and, as a result, affects rates of biota evolution. In particular, frequency of global extinctions, beginning from the Cambrian/Ordovician and ending by the recent Cretaceous/Palaeogene, is well in keeping with the frequency of mantle plumes*** (through which the excessive heat in the mantle is released) calculated at the laboratory of Nikolai Dobretsov.

Biosphere cannot affect in any way the temperature periodicity of the mantle on our planet, but it can accelerate or decelerate extinction or overcome its consequences, reacting to these processes in its turn by evolution of species or reconstruction of ecosystems. As we come nearer to our time, the biodiversity grows and destructiveness of crises falls.

In short, a fairly consistent scenario can be drawn from the articles of different specialists included in the collection under consideration. Of course, not all problems have been solved (for example, it is not clear where had 4 bln year old rocks disappeared, if there remained cold areas on the ancient Earth). However, it means only one thing, i.e. there is a new direction of scientific studies, which require further experiments, and, accordingly, important discoveries are still ahead.

* Pre-Cambrian covers a major part of the geological history of the Earth of approximately 4 bln years. -Ed.

** Fossilization is a complete or partial substitution of organic matter of dead organisms by inorganic compounds of the environment. -Ed.

*** Plume is a hot flow of the mantle substance, relatively independent of a general pattern of convective currents in the mantle. "Rising" from the core to the crust, it can change outlines of a continent, activate or create new volcanoes, etc.-Auth.