Modern hypotheses of the origin of life on earth. Concepts of the origin of life on earth
At present, life on Earth cannot arise in an abiogenic way. Even Darwin wrote in 1871: “But if now ... in any warm reservoir containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, a protein was chemically formed, capable of further more and more complex transformations, then this the substance would immediately be destroyed and absorbed, which was impossible in the period of the emergence of living beings. " Life arose on Earth in an abiogenic way. At present, living things come only from living things (biogenic origin). The possibility of the re-emergence of life on Earth is excluded.
The theory of panspermia.
In 1865 the German doctor G. Richter put forward the cosmozoan hypothesis
( cosmic rudiments), in accordance with which life is eternal and the rudiments that inhabit world space, can be transferred from one planet to another.
A similar hypothesis was put forward in 1907 by the Swedish naturalist S. Arrhenius, suggesting that the embryos of life eternally exist in the Universe - hypothesis of panspermia. He described how particles of matter, dust particles and living spores of microorganisms leave in world space from planets inhabited by other creatures. They retain their viability, flying in the space of the Universe due to light pressure. Getting on a planet with suitable conditions for life, they begin a new life on this planet. This hypothesis was supported by many, including the Russian scientists S. P. Kostychev, L. S. Berg and P. P. Lazarev.
This hypothesis does not suggest any mechanism for explaining the primary origin of life and transfers the problem to another place in the Universe. Liebig believed that “the atmosphere celestial bodies, as well as rotating cosmic nebulae, can be considered as the eternal repositories of a revitalized form, as the eternal plantations of organic embryos ", from where life scatters in the form of these embryos in the Universe.
To substantiate panspermia, rock carvings are used depicting objects similar to rockets or astronauts, or the appearance of UFOs. Spacecraft flights destroyed the belief in the existence of intelligent life on planets Solar system which appeared after the discovery of the canals on Mars by Schiparelli in 1877.
Lovell counted 700 channels on Mars. The network of channels covered all continents. In 1924, the canals were photographed, and most scientists saw in them evidence of the existence of intelligent life. Photographs of 500 channels also recorded seasonal color changes, which confirmed the ideas of the Soviet astronomer G.A.Tikhov about vegetation on Mars, since the lakes and channels were green.
Valuable information about the physical conditions on Mars was obtained by the Soviet Mars spacecraft and the American Viking-1 and Viking-2 landing stations. Thus, the polar caps, experiencing seasonal changes, turned out to be composed of water vapor with an admixture of mineral dust and solid carbon dioxide from dry ice). But so far no traces of life have been found on Mars.
The study of the surface from aboard artificial satellites suggested that the channels and rivers of Mars could arise as a result of melting under the surface water ice in zones of increased activity or internal heat of the planet, or during periodic climate changes.
At the end of the sixties of the twentieth century, interest in the hypotheses of panspermia increased again. When studying the substance of meteorites and comets, the “precursors of living things” were discovered - organic compounds, hydrocyanic acid, water, formaldehyde, cyanogens.
Formaldehyde is found in 60% of cases in 22 regions studied, its clouds with a concentration of about 1000 molecules / cm. cub. fill vast spaces.
In 1975, amino acid precursors were found in lunar soil and meteorites.
The concept of a stationary state of life.
According to V.I. Vernadsky, it is necessary to talk about the eternity of life and the manifestations of its organisms, as we talk about the eternity of the material substrate of celestial bodies, their thermal electrical, magnetic properties and their manifestations. All living things came from living things (Redi's principle).
Primitive unicellular organisms could arise only in the biosphere of the Earth, as well as in the biosphere of the Universe. According to Vernadsky, natural sciences are built on the assumption that life with its special qualities does not take any part in the life of the Universe. But the biosphere must be taken as a whole, as a single living cosmic organism (then the question of the beginning of the living, of the jump from non-living to living, disappears).
Hypothesis of "holobiasis".
It concerns the prototype of the precellular ancestor and its abilities.
There are various forms of the precellular ancestor - "bioid", "biomonad", "microsphere".
According to the biochemist P. Dekker, the structural basis of the "bioid" is made up of viable nonequilibrium dissipative structures, that is, the opening of a microsystem with an enzymatic apparatus that catalyzes the metabolism of the "bioid".
This hypothesis interprets the activity up to the cellular ancestor in an exchange-metabolic spirit.
Biochemists S. Fox and K. Dose modeled their biopolymers capable of metabolism - complex protein synthesis within the framework of the hypothesis of "holobiose".
The main drawback of this hypothesis is the absence of a genetic system for such a synthesis. Hence the preference for the "molecular progenitor" of every living thing, rather than the primary protocellular structure.
Genobiosis hypothesis.
The American scientist Haldane believed that the primary was not a structure capable of metabolism with environment, but a wet molecular system, similar to a gene and capable of reproduction, and therefore named "naked gene" by him. This hypothesis received general recognition after the discovery of RNA and DNA and their phenomenal properties.
According to this genetic hypothesis, nucleic acids appeared in the beginning as the matrix basis for protein synthesis. It was first put forward in 1929 by G. Möller.
It has been experimentally proven that simple nucleic acids can be replicated without enzymes. The synthesis of proteins on ribosomes takes place with the participation of t - RNA and p - RNA. They are able to build not just random combinations of amino acids, but ordered polymers by protein. It is possible that the primary ribosomes consisted only of RNA. Such protein-free ribosomes could synthesize ordered peptides with the participation of t-RNA molecules, which bind to r-RNA through base pairing.
At the next stage of chemical evolution, matrices appeared that determined the sequence of t-RNA molecules, and thus the sequence of amino acids that are bound by t-RNA molecules. The ability of nucleic acids to serve as templates for the formation of complementary chains (for example, synthesis of and - RNA on DNA) is the most convincing argument in favor of the concept of the leading role in the process of biogenesis of the hereditary apparatus and, therefore, in favor of the genetic hypothesis of the origin of life.
3. How life appeared on Earth
The modern concept of the origin of life on Earth is the result of a wide synthesis natural sciences, many theories and hypotheses put forward by researchers of various specialties.
1. What is life?
Answer. Life is a way of being for entities (living organisms) endowed with internal activity, the process of development of bodies organic structure with a stable predominance of synthesis processes over decay processes, a special state of matter, achieved due to the following properties. Life is a way of existence of protein bodies and nucleic acids, an essential point of which is a constant exchange of substances with the environment, and with the termination of this exchange, life also stops.
2. What hypotheses about the origin of life do you know?
Answer. Various ideas about the origin of life can be combined into five hypotheses:
1) creationism - the Divine creation of the living;
2) spontaneous generation - living organisms arise spontaneously from non-living matter;
3) the hypothesis of a stationary state - life has always existed;
4) the hypothesis of panspermia - life is brought to our planet from the outside;
5) the hypothesis of biochemical evolution - life arose as a result of processes obeying chemical and physical laws. Currently, most scientists support the idea of the abiogenic origin of life in the process of biochemical evolution.
3. What is the main principle scientific method?
Answer. The scientific method is a set of techniques and operations used to build a system of scientific knowledge. The basic principle of the scientific method is not to take anything for granted. Any statement or refutation of something should be checked.
Questions after § 89
1. Why can the idea of the divine origin of life be neither confirmed nor refuted?
Answer. The process of the Divine creation of the world is thought of as having taken place only once and therefore inaccessible for research. Science deals only with those phenomena that are observable and experimental research... Therefore, from a scientific point of view, the hypothesis of the Divine origin of the living can neither be proved nor disproved. The main principle of the scientific method is "don't take anything for granted." Therefore, logically there can be no contradiction between the scientific and religious explanation of the origin of life, since these two spheres of thinking are mutually exclusive.
2. What are the main provisions of the Oparin - Haldane hypothesis?
Answer. In modern conditions, the emergence of living things from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only under conditions of an ancient atmosphere and the absence of living organisms. The ancient atmosphere included methane, ammonia, carbon dioxide, hydrogen, water vapor and other inorganic compounds. Under the influence of powerful electrical discharges, ultraviolet radiation and high radiation, organic compounds could arise from these substances, which accumulated in the ocean, forming a "primary soup". In the "primary broth" of biopolymers, multimolecular complexes - coacervates - were formed. Metal ions, which acted as the first catalysts, got into the coacervate drops from the external environment. From the huge number of chemical compounds present in the "primary broth", the most catalytically effective combinations of molecules were selected, which ultimately led to the appearance of enzymes. On the border between the coacervates and the external environment, lipid molecules lined up, which led to the formation of a primitive cell membrane. At a certain stage, protein probionts included nucleic acids, creating unified complexes, which led to the emergence of such properties of living things as self-reproduction, preservation of hereditary information and its transmission to subsequent generations. Probionts, in which metabolism is combined with the ability to reproduce itself, can already be considered as primitive procells, further development which took place according to the laws of evolution of living matter.
3. What experimental evidence can be given to support this hypothesis?
Answer. In 1953, this hypothesis of A.I. Oparin was experimentally confirmed by the experiments of the American scientist S. Miller. In the installation he created, the conditions that supposedly existed in the primary atmosphere of the Earth were simulated. As a result of the experiments, amino acids were obtained. Similar experiments were repeated many times in different laboratories and made it possible to prove the fundamental possibility of synthesizing practically all monomers of basic biopolymers under such conditions. Later it was found that, under certain conditions, more complex organic biopolymers can be synthesized from monomers: polypeptides, polynucleotides, polysaccharides and lipids.
4. What are the differences between A. I. Oparin's hypothesis and J. Haldane's hypothesis?
Answer. J. Haldane also put forward the hypothesis of the abiogenic origin of life, but, unlike AI Oparin, he gave priority not to proteins - coacervate systems capable of metabolism, but to nucleic acids, that is, macromolecular systems capable of self-reproduction.
5. What arguments do opponents give when criticizing the Oparin-Haldane hypothesis?
Answer. The Oparin - Haldane hypothesis has and weak side, pointed to by her opponents. Within the framework of this hypothesis, it is not possible to explain the main problem: how there was a qualitative leap from the inanimate to the living. Indeed, for the self-reproduction of nucleic acids, enzymatic proteins are needed, and for the synthesis of proteins, nucleic acids.
Provide possible pros and cons of the panspermia hypothesis.
Answer. Arguments for:
Life at the level of prokaryotes appeared on Earth almost immediately after its formation, although the distance (in terms of the difference in the level of complexity of organization) between prokaryotes and mammals is comparable to the distance from the primordial soup to pokaryotes;
In the event of the origin of life on any planet of our galaxy, it, as, for example, estimates by A.D. Panov show, for a period of only a few hundred million years can "infect" the entire galaxy;
Finds in some meteorites of artifacts that can be interpreted as the result of the activity of microorganisms (even before the meteorite hits the Earth).
The panspermia hypothesis (life is brought to our planet from the outside) does not answer the main question of how life arose, but transfers this problem to some other place in the Universe;
Complete radio silence of the Universe;
Since it turned out that our entire Universe is only 13 billion years old (i.e., our entire Universe is only 3 times older (!) Than planet Earth), then there is very little time left for the origin of life somewhere far away ... The distance to the nearest star a-centaurus is 4 sv. of the year. A modern fighter (4 speeds of sound) will fly to this star for ~ 800,000 years.
Ch. Darwin wrote in 1871: “But if now ... in some warm water body containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, etc., a protein capable of further , more and more complex transformations, then this substance would be immediately destroyed or absorbed, which was impossible in the period before the emergence of living beings. "
Confirm or refute this statement of Charles Darwin.
Answer. The process of the emergence of living organisms from simple organic compounds was extremely long. For life to arise on Earth, it took an evolutionary process that lasted for many millions of years, during which complex molecular structures, primarily nucleic acids and proteins, were selected for resistance, for the ability to reproduce their own kind.
If now on Earth somewhere in areas of intense volcanic activity, and sufficiently complex organic compounds can arise, then the probability of any prolonged existence of these compounds is negligible. The possibility of the re-emergence of life on Earth is excluded. Now living things appear only as a result of reproduction.
A.I. Oparin's hypothesis. The most essential feature of A.I. Oparin's hypothesis is the gradual complication of the chemical structure and morphological appearance of life precursors (probionts) on the way to living organisms.
A large amount of data suggests that the environment for the origin of life could be the coastal regions of the seas and oceans. Here, at the junction of sea, land and air, favorable conditions were created for the formation of complex organic compounds. For example, solutions of some organic substances (sugars, alcohols) are highly stable and can exist indefinitely. In concentrated solutions of proteins, nucleic acids, clots can form, similar to gelatin clots in aqueous solutions. Such clots are called coacervate drops or coacervates (Fig. 70). Coacervates are able to adsorb various substances... From the solution, chemical compounds enter them, which are transformed as a result of reactions occurring in coacervate drops, and are released into the environment.
Coacervates are not yet living things. They show only superficial resemblance to such signs of living organisms as growth and metabolism with the environment. Therefore, the emergence of coacervates is considered as a stage in the development of pre-life.
Rice. 70. Formation of a coacervate drop
Coacervates have undergone a very long-term selection for structural stability. Stability was achieved due to the creation of enzymes that control the synthesis of certain compounds. The most important stage in the origin of life was the emergence of the mechanism of reproduction of their own kind and the inheritance of the properties of previous generations. This became possible due to the formation of complex complexes of nucleic acids and proteins. Nucleic acids capable of self-reproduction began to control the synthesis of proteins, determining the order of amino acids in them. And proteins-enzymes carried out the process of creating new copies of nucleic acids. This is how the main property characteristic of life arose - the ability to reproduce molecules similar to themselves.
Living beings are so-called open systems, that is, systems into which energy comes from the outside. Life cannot exist without the supply of energy. As you know, according to the methods of energy consumption (see Chapter III), organisms are divided into two large groups: autotrophic and heterotrophic. Autotrophic organisms directly use solar energy in the process of photosynthesis (green plants), heterotrophic ones use energy that is released during the decay of organic matter.
Obviously, the first organisms were heterotrophs, receiving energy by anoxic decomposition of organic compounds. At the dawn of life, there was no free oxygen in the Earth's atmosphere. The emergence of an atmosphere of modern chemical composition is closely connected with the development of life. The appearance of organisms capable of photosynthesis led to the release of oxygen into the atmosphere and water. In its presence, oxygen decomposition of organic substances became possible, in which many times more energy is obtained than with anoxic.
From the moment of its origin, life forms a single biological system - the biosphere (see. chapter XVI). In other words, life did not arise in the form of separate isolated organisms, but immediately in the form of communities. The evolution of the biosphere as a whole is characterized by constant complication, that is, the emergence of more and more complex structures.
Is the emergence of life on Earth possible now? From what we know about the origin of life on Earth, it is clear that the process of the emergence of living organisms from simple organic compounds was extremely long. For life to arise on Earth, it took an evolutionary process that lasted for many millions of years, during which complex molecular structures, primarily nucleic acids and proteins, were selected for resistance, for the ability to reproduce their own kind.
If now on Earth somewhere in areas of intense volcanic activity, and sufficiently complex organic compounds can arise, then the probability of any prolonged existence of these compounds is negligible. They will be immediately oxidized or used by heterotrophic organisms. Charles Darwin understood this perfectly well. In 1871, he wrote: “But if now ... in some warm body of water containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, etc., a protein capable of further , more and more complex transformations, then this substance would be immediately destroyed or absorbed, which was impossible in the period before the emergence of living beings. "
Life arose on Earth in an abiogenic way. At present, living things come only from living things (biogenic origin). The possibility of the re-emergence of life on Earth is excluded.
- Name the main stages from which the process of the emergence of life on Earth could be composed.
- How, in your opinion, influenced the further evolution of the depletion of nutrient reserves in the waters of the primary ocean?
- Expand the evolutionary significance of photosynthesis.
- Why do you think man is trying to answer the question about the origin of life on Earth?
- Why is the re-emergence of life on Earth impossible?
- Give a definition of the concept of "life".
