To appreciate this miracle at its true worth, you need to get acquainted with a number of modern theories that describe different options and stages of the birth of life. From a lively but lifeless set of simple organic compounds to proto-organisms that have known death and entered into an endless race of biological variability. After all, aren't these two terms - variability and death - giving rise to the whole sum of life? ..
1. Panspermia
The hypothesis of bringing life to Earth from other cosmic bodies has a lot of authoritative defenders. This position was held by the great German scientist Hermann Helmholtz and the Swedish chemist Svante Arrhenius, the Russian thinker Vladimir Vernadsky and the British Lord Physicist Kelvin. However, science is the realm of facts, and after the discovery of cosmic radiation and its destructive effect on all living things, panspermia seemed to have died.
But the deeper scientists dive into the question, the more nuances emerge. So, now - including having set up numerous experiments on spacecraft - we are much more serious about the ability of living organisms to endure radiation and cold, lack of water and other "charms" of being in outer space. Findings of various organic compounds on asteroids and comets, in distant gas and dust accumulations and protoplanetary clouds are numerous and beyond doubt. But claims that they contained traces of something suspiciously resembling microbes remain unproven.
It is easy to see that, for all its fascination, the theory of panspermia only transfers the question of the origin of life to another place and another time. Whatever brought the first organisms to Earth - whether it was an accidental meteorite or a cunning plan of highly developed aliens, they had to be born somewhere and somehow. Let not here and much further in the past - but life had to grow out of lifeless matter. The question "How?" remains.
1.Unscientific: Spontaneous Generation
The spontaneous origin of highly developed living matter from inanimate matter - like the birth of fly larvae in rotting meat - can be associated with Aristotle, who generalized the thoughts of many predecessors and formed a holistic doctrine of spontaneous generation. Like other elements of Aristotle's philosophy, spontaneous generation was the dominant doctrine in Medieval Europe and enjoyed some support until the experiments of Louis Pasteur, who finally showed that even fly larvae require parent flies to produce. Spontaneous generation should not be confused with modern theories of the abiogenic origin of life: the difference between them is fundamental.
2. Primary broth
This notion is closely related to the classic experiments performed in the 1950s by Stanley Miller and Harold Urey. In the laboratory, scientists simulated the conditions that could exist at the surface of the young Earth - a mixture of methane, carbon monoxide and molecular hydrogen, numerous electrical discharges, ultraviolet radiation - and soon more than 10% of the carbon from methane passed into the form of various organic molecules. In the experiments of Miller - Urey, more than 20 amino acids, sugars, lipids and precursors of nucleic acids were obtained.
Modern variations of these classic experiments use much more complex settings that more closely match the conditions of the early Earth. The effects of volcanoes are simulated with their emissions of hydrogen sulfide and sulfur dioxide, the presence of nitrogen, etc. In this way, scientists manage to obtain a huge and diverse amount of organic matter - potential building blocks of potential life. The main problem of these experiments remains the racemate: isomers of optically active molecules (such as amino acids) are formed in a mixture in equal amounts, while all life known to us (with isolated and strange exceptions) includes only L-isomers.
However, we will return to this problem later. Here it is worth adding that recently - in 2015 - the Cambridge professor John Sutherland (John Sutherland) and his team showed the possibility of the formation of all the basic "molecules of life", the components of DNA, RNA and proteins from a very simple set of initial components. The main characters of this mixture are hydrogen cyanide and hydrogen sulfide, which are not so rare in space. To them it remains to add some mineral substances and metals, which are available in sufficient quantities on Earth, such as phosphates, salts of copper and iron. Scientists have built a detailed reaction scheme that could well create a rich "primordial soup" in order for polymers to appear in it and full-fledged chemical evolution come into play.
The hypothesis of the abiogenic origin of life from the "organic soup", which was tested by the experiments of Miller and Urey, was put forward in 1924 by the Soviet biochemist Alexander Oparin. And although in the "dark years" of the heyday of Lysenkoism, the scientist took the side of the opponents of scientific genetics, his merits are great. In recognition of the role of the academician, the main award given by the International Scientific Society for the Study of the Origin of Life (ISSOL), the Oparin Medal, bears his name. The prize is awarded every six years, and at different times it was awarded to both Stanley Miller and the great chromosome researcher, Nobel laureate Jack Szostak. In recognition of the enormous contributions of Harold Urey, ISSOL awards the Urey Medal between the Oparin Medals (also every six years). The result was a unique, real evolutionary award - with a changeable name.
3.Chemical evolution
The theory attempts to describe the transformation of relatively simple organic substances into rather complex chemical systems, the precursors of life itself, under the influence of external factors, selection and self-organization mechanisms. The basic concept of this approach is "water-carbon chauvinism", which presents these two components (water and carbon - NS) as absolutely necessary and key for the emergence and development of life, whether on Earth or somewhere beyond its borders. And the main problem remains the conditions under which "water-carbon chauvinism" can develop into very sophisticated chemical complexes, capable - above all - of self-replication.
According to one of the hypotheses, the primary organization of molecules could occur in the micropores of clay minerals, which played a structural role. The Scottish chemist Alexander Graham Cairns-Smith put forward this idea a few years ago. On their inner surface, as on a matrix, complex biomolecules could settle and polymerize: Israeli scientists showed that such conditions make it possible to grow sufficiently long protein chains. The necessary amounts of metal salts, which play an important role as catalysts for chemical reactions, could also accumulate here. Clay walls could serve as cell membranes, separating the "internal" space, in which more and more complex chemical reactions take place, and separating it from external chaos.
The surfaces of crystalline minerals could serve as “matrices” for the growth of polymeric molecules: the spatial structure of their crystal lattice is capable of selecting only optical isomers of the same type, for example, L-amino acids, solving the problem discussed above. Energy for the primary "metabolism" could be supplied by inorganic reactions - such as the reduction of the mineral pyrite (FeS2) with hydrogen (to iron sulfide and hydrogen sulfide). In this case, neither lightning nor ultraviolet light is required for the appearance of complex biomolecules, as in the Miller-Urey experiments. So, we can get rid of the harmful aspects of their action.
The young Earth was not protected from harmful - and even deadly - components of solar radiation. Even modern, evolutionary organisms would be unable to withstand this harsh ultraviolet light - despite the fact that the Sun itself was much younger and did not give enough heat to the planet. From this arose the hypothesis that in the era when the miracle of the origin of life was happening, the whole Earth could be covered with a thick layer of ice - hundreds of meters; and that's for the best. Hiding under this ice sheet, life could feel quite safe from both ultraviolet radiation and frequent meteorite impacts that threatened to kill it in the bud. The relatively cool environment could also stabilize the structure of the first macromolecules.
4. Black smokers
Indeed, ultraviolet radiation on the young Earth, whose atmosphere did not yet contain oxygen and did not have such a wonderful thing as an ozone layer, should have been deadly for any nascent life. From this grew the assumption that the fragile ancestors of living organisms were forced to exist somewhere, hiding from the continuous stream of sterilizing rays. For example, deep under water - of course, where there are enough minerals, mixing, heat and energy for chemical reactions. And there are such places.
Toward the end of the 20th century, it became clear that the ocean floor could in no way be a haven for medieval monsters: the conditions here are too difficult, the temperature is low, there is no radiation, and rare organic matter can only settle from the surface. In fact, these are the vastest semi-deserts - with some notable exceptions: right there, deep under water, close to the outlets of geothermal sources, life is literally in full swing. Sulphide-rich black water is hot, agitated, and full of minerals.
Black ocean smokers are very rich and distinctive ecosystems: the bacteria that feed on them use the iron-sulphur reactions that we have already talked about. They are the basis for a thriving life including a host of unique worms and shrimp. Perhaps they were the basis and the origin of life on the planet: at least theoretically, such systems carry everything necessary for this.
2.Unscientific: Spirits, gods, ancestors
Any cosmological myths about the origin of the world are always crowned with anthropogonic ones - about the origin of man. And in these fantasies one can only envy the imagination of the ancient authors: on the question of what, how and why the cosmos arose, where and how life appeared - and people - the versions sounded very different and almost always beautiful. Plants, fish and animals were caught from the seabed by a huge crow, people crawled out like worms from the body of the first ancestor Pangu, were molded from clay and ashes, were born from the marriages of gods and monsters. All this is surprisingly poetic, but, of course, it has nothing to do with science.
In accordance with the principles of dialectical materialism, life is a "unity and struggle" of two principles: changing and inherited information, on the one hand, and biochemical, structural functions, on the other. One is impossible without the other - and the question of where life began, with information and nucleic acids, or with functions and proteins, remains one of the most difficult. And one of the well-known solutions to this paradoxical problem is the “RNA world” hypothesis, which appeared back in the late 1960s and finally took shape in the late 1980s.
RNA - macromolecules, in the storage and transmission of information is not as efficient as DNA, and in the performance of enzymatic functions - not as impressive as proteins. But RNA molecules are capable of both, and so far they serve as a transmission link in the information exchange of the cell, and catalyze a number of reactions in it. Proteins are unable to replicate without the information of DNA, and DNA is unable to replicate without protein "skills". RNA, on the other hand, can be completely autonomous: it is able to catalyze its own "reproduction" - and this is enough for a start.
Studies within the framework of the “RNA World” hypothesis have shown that these macromolecules are also capable of full-fledged chemical evolution. To take at least a clear example demonstrated by Californian biophysicists led by Lesley Orgel: if ethidium bromide, which serves as a poison for this system that blocks RNA synthesis, is added to a solution of self-replicating RNA, then little by little, with a change in generations of macromolecules, in a mixture RNAs appear that are resistant even to very high concentrations of the toxin. Approximately in this way, while evolving, the first RNA molecules could find a way to synthesize the first protein tools, and then, in combination with them, “discover” for themselves the DNA double helix, an ideal carrier of hereditary information.
3.Unscientific: Immutability
No more scientific than the stories about the ancestors can be called the views that bear the big name of the Steady State Theory. According to its supporters, no life has ever arisen at all - just as the Earth was not born, the cosmos did not appear either: they simply have always been, always will be. All this is no more justified than the Pangu worms: in order to take such a “theory” seriously, one will have to forget about the countless discoveries of paleontology, geology and astronomy. And in fact, to abandon the entire grandiose building of modern science - but then, probably, it is worth abandoning everything that is supposed to be for its inhabitants, including computers and painless dental treatment.
6.Protocells
However, simple replication is not enough for “normal life”: any life is, first of all, a spatially isolated area of the environment, separating metabolic processes, facilitating the course of some reactions and allowing the exclusion of others. In other words, life is a cell limited by a semi-permeable membrane consisting of lipids. And "protocells" should have appeared already at the earliest stages of the existence of life on Earth - the first hypothesis about their origin was expressed by Alexander Oparin, well known to us. In his view, “protomembranes” could be droplets of hydrophobic lipids, reminiscent of yellow drops of oil floating in water.
In general, the ideas of the scientist are accepted by modern science, and Jack Shostak, who received the Oparin Medal for his work, also dealt with this topic. Together with Katarzyna Adamala, he managed to create a kind of “protocell” model, the analogue of the membrane of which did not consist of modern lipids, but of even simpler organic molecules, fatty acids, which could well accumulate in the places of origin of the first proto-organisms. Shostak and Adamala even managed to “revive” their structures by adding magnesium ions (stimulating the work of RNA polymerases) and citric acid (stabilizing the structure of fatty membranes) to the medium.
As a result, they got a completely simple, but somewhat living system; in any case, it was a normal protocell that contained a membrane-protected environment for RNA propagation. From this moment, you can close the last chapter of the prehistory of life - and begin the first chapters of its history. However, this is a completely different topic, so we will talk about only one, but extremely important concept related to the first steps in the evolution of life and the emergence of a huge variety of organisms.
4. Unscientific: Eternal return
A "brand" representation of Indian philosophy, in Western philosophy associated with the works of Immanuel Kant, Friedrich Nietzsche and Mircea Eliade. A poetic picture of the eternal wandering of every living soul through an infinite number of worlds and their inhabitants, its rebirth either into an insignificant insect, or into an exalted poet, or even into a creature unknown to us, a demon or a god. Despite the absence of ideas of reincarnation, this idea is really close to Nietzsche: eternity is eternal, which means that any event in it can - and must be repeated again. And every being revolves endlessly on this carousel of universal return, so that only the head is spinning, and the very problem of primary origin disappears somewhere in a kaleidoscope of countless repetitions.
7. Endosymbiosis
Take a look at yourself in the mirror, look into your eyes: the creature with whom you exchange glances is the most complex hybrid that arose from time immemorial. Back in the late 19th century, the German-English naturalist Andreas Schimper noticed that chloroplasts, the plant cell organelles responsible for photosynthesis, replicate separately from the cell itself. Soon there was a hypothesis that chloroplasts are symbionts, cells of photosynthetic bacteria, once swallowed by the host - and left to live here forever.
Of course, we do not have chloroplasts, otherwise we could eat sunlight, as some pseudo-religious sects suggest. However, in the 1920s, the endosymbiosis hypothesis was expanded to include mitochondria, the organelles that consume oxygen and supply energy to all of our cells. To date, this hypothesis has acquired the status of a full-fledged, repeatedly proven theory - suffice it to say that mitochondria and plastids have their own genome, more or less cell-independent division mechanisms, and their own protein synthesis systems.
In nature, other endosymbionts have also been found that do not have billions of years of joint evolution behind them and are at a less deep level of integration in the cell. For example, some amoebae do not have their own mitochondria, but there are bacteria included inside and performing their role. There are hypotheses about the endosymbiotic origin of other organelles - including flagella and cilia, and even the cell nucleus: according to some researchers, all of us, eukaryotes, were the result of an unprecedented merger between bacteria and archaea. These versions have not yet found strict confirmation, but one thing is clear: as soon as it arose, life began to absorb neighbors and interact with them, giving birth to new life.
5. Unscientific: Creationism
The very concept of creationism arose in the 19th century, when supporters of various versions of the appearance of the world and life, proposed by the authors of the Torah, the Bible and other sacred books of monotheistic religions, began to be called this word. However, in essence, the creationists did not offer anything new in comparison with these books, over and over again trying to refute the strict and thorough findings of science - but in fact, over and over again losing one position after another. Unfortunately, the ideas of modern pseudo-creationist scientists are much easier to understand: understanding the theories of real science requires a lot of effort.
The origin of life on Earth is a key and unresolved problem of natural science, often serving as a ground for a clash between science and religion. If the existence of the evolution of living matter in nature can be considered proven, since its mechanisms were discovered, archaeologists discovered ancient, more simply arranged organisms, then no hypothesis of the origin of life has such an extensive evidence base. We can observe evolution with our own eyes, at least in selection. No one has been able to create a living thing from an inanimate one.
Despite the large number of hypotheses about the origin of life, only one of them has an acceptable scientific explanation. It's a hypothesis abiogenesis- a long chemical evolution that took place in the special conditions of the ancient Earth and preceded biological evolution. At the same time, simple organic substances were first synthesized from inorganic substances, of which more complex ones, then biopolymers appeared, the following stages are more speculative and hardly proven. The hypothesis of abiogenesis has many unresolved problems, different views on certain stages of chemical evolution. However, some of its points were confirmed empirically.
Other hypotheses for the origin of life - panspermia(introduction of life from space), creationism(creation by the creator), spontaneous generation(living organisms suddenly appear in inanimate matter), steady state(life has always existed). The impossibility of spontaneous generation of life in the inanimate was proved by Louis Pasteur (XIX century) and a number of scientists before him, but not so categorically (F. Redi - XVII century). The panspermia hypothesis does not solve the problem of the origin of life, but transfers it from Earth to outer space or to other planets. However, it is difficult to refute this hypothesis, especially those of its representatives who claim that life was brought to Earth not by meteorites (in this case, living things could burn out in the layers of the atmosphere, be subjected to the destructive action of cosmic radiation, etc.), but by intelligent beings. But how did they get to Earth? From the point of view of physics (the huge size of the Universe and the inability to overcome the speed of light), this is hardly possible.
For the first time, possible abiogenesis was substantiated by A.I. Oparin (1923-1924), later this hypothesis was developed by J. Haldane (1928). However, the idea that life on Earth could be preceded by the abiogenic formation of organic compounds was expressed by Darwin. The theory of abiogenesis has been finalized and is being finalized by other scientists to this day. Its main unresolved problem is the details of the transition from complex non-living systems to simple living organisms.
In 1947, J. Bernal, based on the developments of Oparin and Haldane, formulated the theory of biopoiesis, distinguishing three stages in abiogenesis: 1) the abiogenic occurrence of biological monomers; 2) formation of biopolymers; 3) the formation of membranes and the formation of primary organisms (protobionts).
Abiogenesis
The hypothetical scenario of the origin of life according to the theory of abiogenesis is described below in general terms.
The age of the Earth is about 4.5 billion years. Liquid water on the planet, so necessary for life, according to scientists, appeared no earlier than 4 billion years ago. At the same time, life on Earth already existed 3.5 billion years ago, which is proved by the discovery of rocks of such ages with traces of the vital activity of microorganisms. Thus, the first simple organisms arose relatively quickly - in less than 500 million years.
When the Earth first formed, its temperature could reach 8000 °C. When the planet cooled, metals and carbon, as the heaviest elements, condensed and formed the earth's crust. At the same time, volcanic activity was taking place, the crust was moving and contracting, folds and ruptures formed on it. Gravitational forces led to the compaction of the crust, while energy was released in the form of heat.
Light gases (hydrogen, helium, nitrogen, oxygen, etc.) were not retained by the planet and escaped into space. But these elements remained in the composition of other substances. Until the temperature on Earth dropped below 100°C, all water was in a vapor state. After the temperature dropped, evaporation and condensation repeated many times, there were heavy showers with thunderstorms. Hot lava and volcanic ash, once in the water, created different environmental conditions. In some, certain reactions could take place.
Thus, the physical and chemical conditions on the early Earth were favorable for the formation of organic substances from inorganic ones. The atmosphere was of a reducing type, there was no free oxygen and no ozone layer. Therefore, ultraviolet and cosmic radiation penetrated the Earth. Other sources of energy were the warmth of the earth's crust, which has not yet cooled down, erupting volcanoes, thunderstorms, radioactive decay.
Methane, carbon oxides, ammonia, hydrogen sulfide, cyanide compounds, and water vapor were present in the atmosphere. A number of the simplest organic substances were synthesized from them. Further, amino acids, sugars, nitrogenous bases, nucleotides and other more complex organic compounds could be formed. Many of them served as monomers for future biological polymers. The absence of free oxygen in the atmosphere favored the reactions.
Chemical experiments (for the first time in 1953 by S. Miller and G. Urey), simulating the conditions of the ancient Earth, proved the possibility of abiogenic synthesis of organic substances from inorganic ones. By passing electric discharges through a gas mixture that imitated the primitive atmosphere, in the presence of water vapor, amino acids, organic acids, nitrogenous bases, ATP, etc. were obtained.
It should be noted that in the ancient atmosphere of the Earth, the simplest organic substances could be formed not only abiogenically. They were also brought from space, contained in volcanic dust. Moreover, it could be quite large amounts of organic matter.
Low molecular weight organic compounds accumulated in the ocean, creating the so-called primordial soup. Substances were adsorbed on the surface of clay deposits, which increased their concentration.
Under certain conditions of the ancient Earth (for example, on clay, the slopes of cooling volcanoes), polymerization of monomers could occur. This is how proteins and nucleic acids were formed - biopolymers, which later became the chemical basis of life. In an aqueous environment, polymerization is unlikely, since depolymerization usually occurs in water. Experience has proven the possibility of synthesizing a polypeptide from amino acids in contact with pieces of hot lava.
The next important step towards the origin of life is the formation of coacervate drops in water ( coacervates) from polypeptides, polynucleotides, other organic compounds. Such complexes could have a layer on the outside that imitated a membrane and preserved their stability. Coacervates were obtained experimentally in colloidal solutions.
Protein molecules are amphoteric. They attract water molecules to themselves so that a shell forms around them. Colloidal hydrophilic complexes are obtained, isolated from the water mass. As a result, an emulsion is formed in water. Further, the colloids merge with each other and form coacervates (the process is called coacervation). The colloidal composition of the coacervate depended on the composition of the medium in which it was formed. In different reservoirs of the ancient Earth, coacervates of different chemical composition were formed. Some of them were more stable and could, to a certain extent, carry out selective metabolism with the environment. There was a kind of biochemical natural selection.
Coacervates are able to selectively absorb certain substances from the environment and release into it some products of chemical reactions occurring in them. It's like metabolism. As the substances accumulated, the coacervates grew, and when they reached a critical size, they broke up into parts, each of which retained the features of the original organization.
In the coacervates themselves, chemical reactions could take place. During the absorption of metal ions by coacervates, enzymes could be formed.
In the process of evolution, only such systems remained that were capable of self-regulation and self-reproduction. This marked the onset of the next stage in the origin of life - the emergence protobionts(according to some sources, this is the same as coacervates) - bodies that have a complex chemical composition and a number of properties of living beings. Protobionts can be considered as the most stable and successful coacervates.
The membrane could be formed in the following way. Fatty acids combine with alcohols to form lipids. Lipids formed films on the surface of water bodies. Their charged heads face into the water, while the non-polar ends face out. Protein molecules floating in water were attracted to the heads of lipids, resulting in the formation of double lipoprotein films. From the wind, such a film could bend, and bubbles formed. Coacervates may have been accidentally trapped in these vesicles. When such complexes again appeared on the surface of the water, they were already covered with a second lipoprotein layer (due to hydrophobic interactions of non-polar ends of lipids facing each other). The general layout of the membrane of today's living organisms is two layers of lipids inside and two layers of proteins located at the edges. But over millions of years of evolution, the membrane became more complex due to the inclusion of proteins immersed in the lipid layer and penetrating it, protrusion and protrusion of individual sections of the membrane, etc.
Coacervates (or protobionts) could get already existing nucleic acid molecules capable of self-reproduction. Further, in some protobionts, such a rearrangement could occur that the nucleic acid began to encode the protein.
The evolution of protobionts is no longer chemical, but prebiological evolution. It led to an improvement in the catalytic function of proteins (they began to play the role of enzymes), membranes and their selective permeability (which makes the protobiont a stable set of polymers), the emergence of matrix synthesis (transfer of information from nucleic acid to nucleic acid and from nucleic acid to protein).
| Evolution | results | |
|---|---|---|
| 1 | Chemical evolution - synthesis of compounds |
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| 2 | Prebiological evolution - chemical selection: the most stable, self-reproducing protobionts remain |
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| 3 | Biological evolution - biological selection: the struggle for existence, the survival of the most adapted to environmental conditions |
|
One of the biggest mysteries about the origin of life is how RNA came to code for the amino acid sequence of proteins. The question refers to RNA, not DNA, since it is believed that at first ribonucleic acid played not only a role in the implementation of hereditary information, but was also responsible for its storage. DNA replaced it later, emerging from RNA by reverse transcription. DNA is better at storing information and is more stable (less prone to reactions). Therefore, in the process of evolution, it was she who was left as the custodian of information.
In 1982, T. Chek discovered the catalytic activity of RNA. In addition, RNA can be synthesized under certain conditions even in the absence of enzymes, and also form copies of themselves. Therefore, it can be assumed that RNAs were the first biopolymers (the RNA world hypothesis). Some sections of RNA could accidentally encode peptides useful for the protobiont, while other sections of RNA became excised introns in the course of evolution.
A feedback appeared in protobionts - RNA encodes enzyme proteins, enzyme proteins increase the amount of nucleic acids.
Beginning of biological evolution
Chemical evolution and the evolution of protobionts lasted more than 1 billion years. Life arose, and its biological evolution began.
Some protobionts gave rise to primitive cells, which include the totality of the properties of living things that we observe today. They implemented the storage and transmission of hereditary information, its use to create structures and metabolism. Energy for vital processes was provided by ATP molecules, and membranes typical of cells appeared.
The first organisms were anaerobic heterotrophs. They obtained the energy stored in ATP through fermentation. An example is glycolysis - the oxygen-free breakdown of sugars. These organisms ate at the expense of organic substances of the primary broth.
But the reserves of organic molecules were gradually depleted, as the conditions on the Earth changed, and the new organics were almost no longer synthesized abiogenically. Under conditions of competition for food resources, the evolution of heterotrophs accelerated.
The advantage was gained by bacteria, which turned out to be able to fix carbon dioxide with the formation of organic substances. Autotrophic synthesis of nutrients is more complex than heterotrophic nutrition, so it could not have arisen in early life forms. From some substances, under the influence of the energy of solar radiation, compounds necessary for the cell were formed.
The first photosynthetic organisms did not produce oxygen. Photosynthesis with its release most likely appeared later in organisms similar to the current blue-green algae.
The accumulation of oxygen in the atmosphere, the appearance of an ozone screen, and a decrease in the amount of ultraviolet radiation led to the almost impossibility of the abiogenic synthesis of complex organic substances. On the other hand, emerging life forms have become more resilient under such conditions.
Oxygen respiration spread on Earth. Anaerobic organisms have survived only in a few places (for example, there are anaerobic bacteria living in hot underground springs).
INTRODUCTION SECTION 1. BASIC THEORIES OF THE ORIGIN OF LIFE ON EARTH.
1.1 Creationism.
1.2 Hypothesis of spontaneous generation.
1.3 Theory of a stationary state.
1.4 Panspermia hypothesis.
SECTION 2. PROTEIN-COACERVATE THEORY OPARINA.
2.1 The essence of the theory.
2.2 Alexander Ivanovich Oparin.
2.3 Origins of chemical evolution "Primary soup".
2.4 Stages of the process of origin of life.
SECTION 3. THE NEED TO STUDY THE ORIGIN OF LIFE.
SECTION 4. MODERN INTRODUCTIONS ON THE ORIGIN OF LIFE.
CONCLUSION.
LITERATURE.
INTRODUCTION
The question of the origin of life on Earth and the likelihood of its existence on other planets of the Universe has long attracted the interest of both scientists and philosophers, as well as ordinary people. In recent years, attention to this "eternal problem" has increased significantly.
This is due to two circumstances: firstly, significant progress in laboratory modeling of some stages of the evolution of matter, which led to the origin of life, and, secondly, the rapid development of space research, making it more and more real to actually search for any life forms on the planets of the solar system. , but in the future and beyond.
The origin of life is one of the most mysterious questions, an exhaustive answer that is unlikely to ever be received. Many hypotheses and even theories about the origin of life, explaining the various aspects of this phenomenon, are not yet able to overcome an essential circumstance - to experimentally confirm the fact of the appearance of life. Modern science does not have direct evidence of how and where life arose. There are only logical constructions and indirect evidence obtained through model experiments, and data in the field of paleontology, geology, astronomy, etc.
At the same time, the question of the origin of life has not yet been finally resolved. There are many hypotheses for the origin of life.
At different times and in different cultures, the following ideas were considered:
Creationism (life was created by the Creator);
Spontaneous generation (spontaneous generation; life arose repeatedly from inanimate matter);
Steady state hypothesis (life has always existed);
Panspermia hypothesis (life brought to Earth from other planets);
Biochemical hypotheses (life arose under terrestrial conditions in the course of processes that obey physical and chemical laws, i.e. as a result of biochemical evolution);
The purpose of the work is to consider the main theories of the origin of life on Earth.
It is important to note that in order to achieve the goal, the following tasks are considered:
Review the main theories
creationism
Theory of spontaneous generation of life
Steady State Theory
Pansermia hypothesis
To explore the basic protein-coacervate theory of A.I. Oparina
Read the biography of A.I. Oparina
Describe the origins of chemical evolution "primordial soup"
Determine the stages of the process of the emergence of life on Earth
The need to study the origin of life on Earth
Modern views on the origin of life
When performing the work, the following methods were used: comparative geographical, analysis of literary sources, historical.
The work was written on the basis of such materials: monographs, translated editions, articles from a collection of scientific papers, components of books, literature from the Internet.
SECTION 1. MAIN THEORIES OF THE ORIGIN OF LIFE ON EARTH
1.1creationism
Creationism (from the English. creation - creation) is a religious and philosophical concept, within which the entire diversity of the organic world, humanity, the planet Earth, as well as the world as a whole, are considered so intentionally created by some supreme being or deity. The theory of creationism, referring the answer to the question of the origin of life to religion (the creation of life by God), according to Popper's criterion, is outside the field of scientific research (since it is irrefutable: it is impossible to prove by scientific methods both that God created life and that God created it.) In addition, this theory does not give a satisfactory answer to the question of the causes of the emergence and existence of the supreme being itself, usually simply postulating its beginninglessness.
1.2Spontaneous generation hypothesis
This theory gained currency in ancient China, Babylon, and Egypt as an alternative to the creationism with which it coexisted. Religious teachings of all times and all peoples usually attributed the appearance of life to one or another creative act of the deity. Very naively solved this question and the first researchers of nature. Aristotle (384-322 BC), who is often hailed as the founder of biology, held to the theory of the spontaneous generation of life. Even for such an outstanding mind of antiquity as Aristotle, it was not difficult to accept the idea that animals - worms, insects, and even fish - could arise from mud. On the contrary, this philosopher argued that every dry body, becoming wet, and, conversely, every wet body, becoming dry, give birth to animals.
According to Aristotle's hypothesis of spontaneous generation, certain "particles" of matter contain some kind of "active principle", which, under suitable conditions, can create a living organism. Aristotle was right in thinking that this active principle is contained in a fertilized egg, but mistakenly believed that it is also present in solar wind, mud and rotting meat.
“These are the facts - living things can arise not only by mating animals, but also by decomposition of the soil. The same is the case with plants: some develop from seeds, while others, as it were, spontaneously generate under the action of all nature, arising from the decaying earth or certain parts of plants ”(Aristotle).
The authority of Aristotle had an exceptional influence on the views of medieval scholars. The opinion of this philosopher in their minds was bizarrely intertwined with religious concepts, often giving ridiculous and even frankly stupid conclusions in modern terms. The preparation of a living person or his likeness, "homunculus", in a flask, by mixing and distilling various chemicals, was considered in the Middle Ages, although very difficult and lawless, but no doubt doable. Obtaining animals from inanimate materials seemed so simple and common to scientists of that time that the famous alchemist and physician Van Helmont (1577-1644) directly gives a recipe, following which mice can be artificially prepared by covering a vessel with grain with wet and dirty rags. This very successful scientist described an experiment in which he allegedly created mice in three weeks. For this, a dirty shirt, a dark closet and a handful of wheat were needed. Van Helmont considered human sweat to be the active principle in the mouse process.
A number of sources dating back to the 16th and 17th centuries describe in detail the transformation of water, stones and other inanimate objects into reptiles, birds and animals. Grindel von Ach even shows frogs, allegedly emerging from May dew, and Aldrovand depicts the process of rebirth of birds and insects from branches and fruits of trees.
The further natural science developed, the more important accurate observation and experience became in the knowledge of nature, and not just reasoning and sophistication, the more narrowed was the scope of the theory of spontaneous generation. Already in 1688, the Italian biologist and physician Francesco Redi, who lived in Florence, approached the problem of the origin of life more strictly and questioned the theory of spontaneous generation. Dr. Redi, by simple experiments, proved the groundlessness of opinions about the spontaneous generation of worms in rotting meat. He found that the little white worms were fly larvae. After conducting a series of experiments, he received data confirming the idea that life can only arise from a previous life (the concept of biogenesis).
“Conviction would be futile if it could not be confirmed by experiment. So in the middle of July I took four large wide-mouthed vessels, put earth in one of them, some fish in another, eels from Arno in the third, a piece of veal in the fourth, closed them tightly and sealed them. Then I placed the same in four other vessels, leaving them open... Soon the meat and fish in the unsealed vessels were wormed; flies could be seen flying freely into and out of the vessels. But I did not see a single worm in the sealed vessels, although many days had passed after the dead fish had been placed in them ”(Redi).
Thus, with regard to living beings visible to the naked eye, the proposition of spontaneous generation turned out to be untenable. But at the end of the XVII century. Kircher and Leeuwenhoek discovered the world of the smallest creatures, invisible to the naked eye and distinguishable only through a microscope. These “tiniest living animals” (as Leeuwenhoek called the bacteria and ciliates he discovered) could be found wherever decay occurred, in decoctions and infusions of plants that had stood for a long time, in rotting meat, broth, in sour milk, in feces, in plaque . “In my mouth,” Leeuwenhoek wrote, “there are more of them (germs) than there are people in the United Kingdom.” One has only to put perishable and easily rotting substances in a warm place for some time, as microscopic living creatures immediately develop in them, which were not there before. Where do these creatures come from? Did they come from embryos that accidentally fell into the rotting liquid? How many of these germs must be everywhere! The thought involuntarily appeared that it was here, in rotting decoctions and infusions, that spontaneous generation of living microbes from inanimate matter took place. This opinion in the middle of the 18th century received strong confirmation in the experiments of the Scottish priest Needham. Needham took meat broth or decoctions of vegetable substances, placed them in tightly closed vessels and boiled them for a short time. At the same time, according to Needham, all the embryos should have died, while new ones could not get in from the outside, since the vessels were tightly closed. However, after a while, microbes appeared in the liquids. From this, the said scientist concluded that he was present at the phenomenon of spontaneous generation.
At the same time, another scientist, the Italian Spallanzani, opposed this opinion. Repeating Needham's experiments, he became convinced that a longer heating of vessels containing organic liquids completely dehydrates them. In 1765, Lazzaro Spallanzani conducted the following experiment: having boiled meat and vegetable broths for several hours, he immediately sealed them, after which he removed them from the fire. After examining the liquids a few days later, Spallanzani did not find any signs of life in them. From this, he concluded that the high temperature destroyed all forms of living beings, and that without them, nothing living could have arisen.
A fierce dispute broke out between representatives of two opposing views. Spallanzani argued that the liquids in Needham's experiments were not heated enough and the embryos of living beings remained there. To this, Needham objected that he did not heat the liquids too little, but, on the contrary, Spallanzani heated them too much and by such a rude method destroyed the "generating force" of organic infusions, which is very capricious and fickle.
Consequently, each of the disputants remained on their original positions, and the question of the spontaneous generation of microbes in decaying liquids was not resolved either way for a whole century. During this time, many attempts have been made empirically to prove or disprove spontaneous generation, but none of them has led to definite results.
The question became more and more confused, and only in the middle of the 19th century was it finally resolved thanks to the brilliant research of the brilliant French scientist.
Louis Pasteur took up the problem of the origin of life in 1860. By this time, he had already done a lot in the field of microbiology and was able to solve the problems that threatened sericulture and winemaking. He also proved that bacteria are ubiquitous and that non-living materials can easily be contaminated by living things if they are not properly sterilized. In a number of experiments, he showed that everywhere, and especially near human habitation, the smallest germs rush in the air. They are so light that they float freely in the air, only very slowly and gradually sinking to the ground.
As a result of a series of experiments based on Spallanzani's methods, Pasteur proved the validity of the theory of biogenesis and finally refuted the theory of spontaneous generation.
Pasteur explained the mysterious appearance of microorganisms in the experiments of previous researchers either by the incomplete deconditioning of the medium, or by the insufficient protection of liquids from the penetration of germs. If the contents of the flask are thoroughly boiled and then protected from germs that could get into the flask with air flowing into the flask, then in a hundred cases out of a hundred the liquid will not rot and the formation of microbes does not occur.
It is important to note that Pasteur used a wide variety of methods to depressurize the air flowing into the flask: he either calcined the air in glass and metal tubes, or protected the neck of the flask with a cotton plug, which retained all the smallest particles suspended in the air, or, finally, passed air through a thin glass tube bent in the shape of the letter S; in this case, all the nuclei were mechanically retained on the wet surfaces of the tube bends.
Wherever the protection was sufficiently reliable, the appearance of microbes in the liquid was not observed. But perhaps prolonged heating has chemically altered the environment and made it unsuitable for life? Pasteur easily refuted this objection as well. He threw a cotton plug into the heat-depleted liquid, through which air was passed and which, consequently, contained germs - the liquid quickly rotted. Therefore, boiled infusions are quite suitable soil for the development of microbes. This development does not take place just because there is no germ. As soon as the embryo enters the liquid, it immediately germinates and gives a lush harvest.
Pasteur's experiments showed with certainty that spontaneous generation of microbes in organic infusions does not occur. All living organisms develop from embryos, i.e. originate from other living beings. At the same time, the confirmation of the theory of biogenesis gave rise to another problem. Since another living organism is necessary for the emergence of a living organism, then where did the very first living organism come from? Only the steady state theory does not require an answer to this question, and in all other theories it is assumed that at some stage in the history of life there was a transition from inanimate to living.
1.3Steady State Theory.
According to this theory, the Earth never came into being, but existed forever; it has always been capable of sustaining life, and if it has changed, it has changed very little. According to this version, species also never arose, they always existed, and each species has only two possibilities - either a change in numbers or extinction.
At the same time, the hypothesis of a stationary state fundamentally contradicts the data of modern astronomy, which indicate the finite time of existence of any stars and, accordingly, planetary systems around stars. According to modern estimates based on radioactive decay rates, the age of the Earth, the Sun, and the Solar System is ~4.6 billion years. Therefore, this hypothesis is not usually considered by academic science.
Proponents of this theory do not recognize that the presence or absence of certain fossil remains may indicate the time of appearance or extinction of a particular species, and cite as an example a representative of the lobe-finned fish - coelacanth (coelacanth). According to paleontological data, the crossopterans became extinct at the end of the Cretaceous. At the same time, this conclusion had to be revised when living representatives of the crossopterygians were found in the Madagascar region. Proponents of the steady state theory argue that only by studying living species and comparing them with fossil remains can one conclude extinction, and in this case it is very likely that it will turn out to be wrong. Using paleontological data to support the steady state theory, its proponents interpret the appearance of fossils in an ecological sense. Thus, for example, the sudden appearance of a fossil species in a particular stratum is explained by an increase in its population or its movement to places favorable for the preservation of remains.
1.4Pansermia hypothesis
The hypothesis about the appearance of life on Earth as a result of the transfer of certain germs of life from other planets is called the theory of pansermia (from the Greek παν - all, everyone and σπερμα - seed). This hypothesis is adjacent to the steady state hypothesis. Its adherents support the idea of the eternal existence of life and put forward the idea of its sudden origin. One of the first to express the idea of a cosmic (sudden) origin of life was the German scientist G. Richter in 1865. According to Richter, life on Earth did not originate from inorganic substances, but was introduced from other planets. In this regard, questions arose as to how possible such a transfer from one planet to another and how it could be carried out. The answers were sought primarily in physics, and it is not surprising that the first defenders of these views were the representatives of this science, the outstanding scientists G. Helmholtz, S. Arrhenius, J. Thomson, P.P. Lazarev and others.
According to the ideas of Thomson and Helmholtz, spores of bacteria and other organisms could have been brought to Earth with meteorites. Laboratory studies confirm the high resistance of living organisms to adverse effects, in particular to low temperatures. For example, spores and seeds of plants did not die even after prolonged exposure to liquid oxygen or nitrogen.
Modern adherents of the concept of pansermia (including the Nobel Prize winner English biophysicist F. Crick) believe that life on Earth was brought to Earth by accident or intentionally by space aliens. The point of view of astronomers C. Wickramasingh (Sri Lanka) and F. Hoyle (Great Britain) adjoins the pansermia hypothesis. They believe that in outer space, mainly in gas and dust clouds, microorganisms are present in large numbers, where, according to scientists, they are formed. Further, these microorganisms are captured by comets, which then, passing near the planets, "sow the germs of life."
SECTION 2. PROTEIN-COACERVATE THEORY OPARINA
2.1The essence of the theory
The first scientific theory regarding the origin of living organisms on Earth was created by the Soviet biochemist A.I. Oparin (1894-1980). In 1924, he published works in which he outlined ideas about how life could have arisen on Earth. According to this theory, life arose in the specific conditions of the ancient Earth, and is considered by Oparin as a natural result of the chemical evolution of carbon compounds in the Universe.
According to Oparin, the process that led to the emergence of life on Earth can be divided into three stages:
The emergence of organic matter.
The formation of biopolymers (proteins, nucleic acids, polysaccharides, lipids, etc.) from simpler organic substances.
The emergence of primitive self-reproducing organisms.
The theory of biochemical evolution has the largest number of supporters among modern scientists. The earth arose about five billion years ago; Initially, its surface temperature was very high (up to several thousand degrees). As it cooled, a solid surface was formed (the earth's crust - the lithosphere).
The atmosphere, which originally consisted of light gases (hydrogen, helium), could not be effectively retained by the insufficiently dense Earth, and these gases were replaced by heavier gases: water vapor, carbon dioxide, ammonia and methane. As the Earth's temperature dropped below 100 degrees Celsius, water vapor began to condense to form the world's oceans. At this time, in accordance with the ideas of A.I. Oparin, an abiogenic synthesis took place, that is, in the primary terrestrial oceans saturated with various simple chemical compounds, “in the primary broth” under the influence of volcanic heat, lightning discharges, intense ultraviolet radiation and other environmental factors, the synthesis of more complex organic compounds, and then biopolymers began . The formation of organic substances was facilitated by the absence of living organisms - consumers of organic matter - and the main oxidizing agent - oxygen. Complex amino acid molecules randomly combined into peptides, which in turn created the original proteins. From these proteins, the primary living creatures of microscopic size were synthesized.
The most difficult problem in the modern theory of evolution is the transformation of complex organic substances into simple living organisms. Oparin believed that the decisive role in the transformation of the inanimate into the living belongs to proteins. Apparently, protein molecules, attracting water molecules, formed colloidal hydrophilic complexes. Further merging of such complexes with each other led to the separation of colloids from the aqueous medium (coacervation). On the border between the coacervate (from the Latin Coacervus - clot, heap) and the environment, lipid molecules lined up - a primitive cell membrane. It is assumed that colloids could exchange molecules with the environment (a prototype of heterotrophic nutrition) and accumulate certain substances. Another type of molecule provided the ability to reproduce itself. The system of views of A.I. Oparin was called the "coacervate hypothesis".
Oparin's hypothesis was only the first step in the development of biochemical ideas about the origin of life. The next step was the experiments of L.S. Miller, who in 1953 showed how amino acids and other organic molecules can be formed from the inorganic components of the earth's primary atmosphere under the influence of electrical discharges and ultraviolet radiation.
Academician of the Russian Academy of Sciences V.N. Parmon and a number of other scientists suggest various models to explain how autocatalytic processes can occur in a medium saturated with organic molecules, replicating some of these molecules. Some molecules replicate more successfully than others. This starts the process of chemical evolution, which precedes biological evolution.
Today, the RNA world hypothesis prevails among biologists, stating that between chemical evolution, in which individual molecules multiplied and competed, and a full-fledged life based on the DNA-RNA-protein model, there was an intermediate stage at which individual molecules multiplied and competed with each other. RNA molecules. There are already studies showing that some RNA molecules have autocatalytic properties and can reproduce themselves without the involvement of complex protein molecules.
Modern science is still far from an exhaustive explanation of how specifically inorganic matter has reached a high level of organization, characteristic of life processes. However, it is clear that this was a multi-stage process, during which the level of organization of matter increased step by step. To restore the specific mechanisms of this stepwise complication is the task of future scientific research. This research follows two main areas:
From top to bottom: analysis of biological objects and study of possible mechanisms for the formation of their individual elements;
From bottom to top: the complication of "chemistry" - the study of more and more complex chemical compounds.
So far, it has not been possible to achieve a full-fledged combination of these two approaches. Nevertheless, bioengineers have already managed to "according to the blueprints", that is, according to the known genetic code and the structure of the protein shell, assemble the simplest living organism - the virus - from the simplest biological molecules. Thus, it is proved that supernatural influence is not required to create a living organism from inanimate matter. So it is only necessary to answer the question of how this process could take place without human participation, in the natural environment.
There is a widespread "statistical" objection to the abiogenic mechanism of the origin of life. For example, in 1996, the German biochemist Schram calculated that the probability of a random combination of 6000 nucleotides in the tobacco mosaic RNA virus: 1 chance in 102,000. This is an extremely low probability, which indicates the complete impossibility of random formation of such RNA. In fact, however, this objection is constructed incorrectly. It proceeds from the assumption that the viral RNA molecule must be formed "from scratch" from disparate amino acids. In the case of stepwise complication of chemical and biochemical systems, the probability is calculated in a completely different way. In addition, there is no need to get just such a virus, and not some other. Taking into account these objections, it turns out that the estimates of the probability of the synthesis of the emergence of viral RNA are underestimated to the point of complete inadequacy and cannot be considered as a convincing objection to the abiogenic theory of the origin of life.
2.2 Alexander Ivanovich Oparin and his theory of the origin of life
From the beginning of 1935, the Institute of Biochemistry of the Academy of Sciences of the USSR began its work, founded by Oparin together with A.N. Bach. From the very foundation of the Institute, Oparin directed the Laboratory of Enzymology, which in the future was transformed into a laboratory of evolutionary biochemistry and subcellular structures. Until 1946 he was deputy director, after the death of A.N. Bach is the director of this institute.
On May 3, 1924, at a meeting of the Russian Botanical Society, he delivered a report "On the Origin of Life", in which he proposed a theory of the origin of life from a broth of organic substances. In the middle of the 20th century, complex organic substances were experimentally obtained by passing electric charges through a mixture of gases and vapors, which hypothetically coincides with the composition of the ancient Earth's atmosphere. As procells, Oparin considered coacervates - organic structures surrounded by fatty membranes.
After the death in 1951 S.I. Vavilova A.I. Oparin became the second chairman of the board of the All-Union Educational Society "Knowledge". He remained in this post until 1956, when M.B. Mitin.
In 1970, the International Society for the Study of the Origin of Life was organized, the first president and then the honorary president of which Oparin was elected. The ISSOL Executive Committee in 1977 established the Gold Medal named after A.I. Oparin (Eng. Oparin Medal), awarded for the most important experimental research in this area.
2.3 The origins of chemical evolution "Primary soup"
Despite some gaps in our knowledge about the first stage of the origin of life, we are able to draw fairly definite conclusions. After all, we know that the synthesis of compounds containing up to 24 carbon and nitrogen atoms is possible within the solar system. Perhaps, the synthesis of more complex compounds, including polymers, is also possible, although there are no data on the existence of polymers with an ordered sequence. This is all we can say about the composition of the medium known as the "primordial broth".
With the accumulation of new information, it becomes more and more obvious that the products of primary synthesis from molecules of simple hybrids will necessarily be formed under appropriate conditions. These conditions can be extremely diverse, and therefore the syntheses under consideration are not associated with any strictly defined time and place.
Facts, experiments and observations speak of the possibility of synthesizing rather complex chemical compounds in the vicinity of any star, provided there is a sufficient amount of "raw materials" - dust and gases. Thus, the first stage is not so much the emergence of life as preparation for it. It all starts with materials formed by normal astrophysical processes; further transformations are carried out in full accordance with the laws of chemistry, without involving any new principles. At the same time, already at this stage, there is a certain preliminary selection of those types of compounds that will subsequently be used to build living beings. Consequently, since the processes occurring at this first stage affect the entire subsequent course of biosynthesis, they themselves depend on the specific conditions existing on the planets. That is why the Earth - the only planet in the solar system that has oceans on its surface - turned out to be at the same time the only planet with developed life.
2.4 Stages of the origin of life
Stage 1. This stage corresponds to the increasing complexity of molecules and molecular systems that were destined to eventually be included in living systems. At the first stage, the formation of pre-organism molecules from hybrids of carbon, nitrogen and oxygen (ie from methane, ammonia and water) took place. These gases are found in molecular form in outer space (in the colder parts of the universe) even now. It seems obvious that the first stage could take place in many places - of which we know for sure only the Earth and meteorites of asteroid origin. Such a place could also be a primary field cloud. It also turned out to be possible to simulate these processes in the laboratory, which was done by Miller and his followers. In these experiments, the most important biological molecules were obtained: some organic bases (for example, adeine), which are part of proteins; some sugars, notably rabose and their phosphates; and, finally, some more complex nitrogen-containing compounds, such as porphyrins, which are important constituents of oxidative enzymes and energy carriers.
Stage 2. In the second stage, polymers were formed from the components of the Oparan “primordial soup”, which consisted mainly of the molecules just mentioned, as well as from more complex molecules, by combining similar or identical monomers or submolecules in a linear order. At some crucial stage in the evolution of such polymers, which appear to be simpler analogues of present-day nucleic acids and proteins, the mechanism of strict reproduction and replication, which many biologists regard as an important feature of life itself, must have arisen. So far, we can only logically reconstruct those processes that could lead to this under the conditions that apparently existed on Earth at that time, i.e. in the presence of free water, as well as gas molecules and metal ions in solution. It is difficult to imagine that all this could take place on such anhydrous celestial bodies as the Moon, and even more so on meteorites of asteroid origin, containing water only in a bound state - in the form of hydrates or ice.
SECTION 3. THE NEED FOR RESEARCH ON THE ORIGIN OF LIFE
The main practical motive for studying the origin of life is that without it we will not be able to understand modern life, and therefore we will not be able to control it. It is necessary to study the emergence of life in order to understand its essence, its possibilities and limitations, and then only in order to develop the first and overcome the second. In a broader sense, the study of the origin of life is a further attempt to find the meaning of life. From ancient times, the meaning of life was seen in a variety of things, but over time, the falsity of various paths of the meaning of life, their ultimate failure, became more and more clear. Until the Middle Ages and even later, the purpose of life in the general system of the world order was considered known. Different people in different civilizations solved this question in different ways, but these solutions were so similar that they can be considered variants of the same answer - the simplest answer was that life makes sense in the plans of an omniscient and omnipotent God. The will of the Lord should be fulfilled, and if it is sometimes difficult to understand what it consists of, then various interpretations are allowed. But of all such answers, only one can be correct. And what this answer is - it is given to know not to everyone, but only to true believers.
The scientific revolution that began in the 17th century gradually undermined the foundations of faith. But even in the minds of those who, one way or another, with their discoveries and intellectual insights destroyed the stronghold of faith (sometimes completely unconsciously), faith still continued to exist. Paradoxically, the more powerful the attack, the more people's minds clung to this belief. Hence the resistance to further researchers, who, naturally, had to put an end to religious views on the Universe. Although resistance to new ideas has ceased to be as fierce as it was in the days of Copernicus and even Darwin, it still exists. Yet what little is known about the possible origin of life is enough to shake the foundations of faith much more deeply than any other discovery in the past has been able to do. The structure of the Universe as a whole and the processes taking place in it begin to become clear for us, even if only in rough outline, and after that nothing can remain unchanged.
The need for myths explaining the origin and fate of man arose at the dawn of history, and a great many such myths have been known since ancient times, but nothing has yet appeared that equally satisfies the mind and heart. On the one hand, faith was called upon to correct the imperfection of the human mind and its observations, and on the other hand, what was considered a scientific picture of the Universe began to seem meaningless, dry and unsatisfactory. Now, finally, we are beginning to see the desired meaning, and this is not due to the creation of a "comforting philosophy", but practically due to the reduction of life's burdens and the increase in human capabilities.
SECTION 4. MODERN VIEWS ON THE ORIGIN OF LIFE ON EARTH
The theory of A.I. Oparin and other similar hypotheses have one significant drawback: there is not a single fact that would confirm the possibility of abiogenic synthesis on Earth of at least the simplest living organism from lifeless compounds. Thousands of attempts at such a synthesis have been made in numerous laboratories around the world. For example, the American scientist S. Miller, based on assumptions about the composition of the Earth's primary atmosphere, passed electrical discharges through a mixture of methane, ammonia, hydrogen and water vapor in a special device. He managed to obtain molecules of amino acids - those basic "building blocks" that make up the basis of life - proteins. These experiments were repeated many times, some of the scientists managed to get quite long chains of peptides (simple proteins). Only! No one has been lucky enough to synthesize even the simplest living organism. Nowadays Redi's principle is popular among scientists: "The living - only from the living."
But suppose that such attempts will someday be crowned with success. What will such an experience prove? Only that for the synthesis of life, the human mind, complex advanced science and modern technology are needed. None of this existed on the original Earth. Moreover, the synthesis of complex organic compounds from simple ones contradicts the second law of thermodynamics, which prohibits the transition of material systems from a state of greater probability to a state of lesser probability, and the development from simple organic compounds to complex ones, then from bacteria to humans, took place in this direction. Here we observe nothing but the creative process. The second law of thermodynamics is an immutable law, the only law that has never been questioned, violated or refuted. Therefore, the order (gene information) cannot spontaneously arise from the disorder of random processes, which is confirmed by the theory of probability.
Recently, mathematical research has dealt a crushing blow to the hypothesis of abiogenic synthesis. Mathematicians have calculated that the probability of spontaneous generation of a living organism from lifeless blocks is almost zero. So, L. Blumenfeld proved that the probability of random formation of at least one DNA molecule (deoxyribonucleic acid - one of the most important components of the genetic code) during the entire existence of the Earth is 1/10800. think about the negligible small amount of this number! Indeed, in its denominator there is a figure, where after one there is a series of 800 zeros, and this number is an incredible number of times greater than the total number of all atoms in the Universe. The modern American astrophysicist C. Wickramasinghe figuratively expressed the impossibility of abiogenic synthesis: “It is faster for a hurricane that sweeps over a cemetery of old aircraft to assemble a brand new superliner from pieces of scrap than as a result of a random process life will arise from its components.”
Contradict the theory of abiogenic synthesis and geological data. No matter how far we penetrate into the depths of geological history, we do not find traces of the "Azoic era", that is, the period when life did not exist on Earth.
Now paleontologists in rocks whose age reaches 3.8 billion years, that is, close to the time of the formation of the Earth (4-4.5 billion years ago, according to recent estimates), have found fossils of rather complexly organized creatures - bacteria, blue-green algae, simple fungi . V. Vernadsky was sure that life is geologically eternal, that is, there was no era in geological history when our planet was lifeless. "The problem of abiogenesis (spontaneous generation of living organisms)," the scientist wrote in 1938, "remains fruitless and paralyzes really overdue scientific work."
Now the form of life is extremely closely connected with the hydrosphere. This is evidenced by at least the fact that water is the main part of the mass of any terrestrial organism (a person, for example, consists of more than 70% water, and organisms such as jellyfish - 97-98%). It is obvious that life on Earth was formed only when the hydrosphere appeared on it, and this, according to geological information, happened almost from the beginning of the existence of our planet. Many of the properties of living organisms are due precisely to the properties of water, while water itself is a phenomenal compound. So, according to P. Privalov, water is a cooperative system in which any action is distributed in a "relay" way, that is, there is a "far action".
Some scientists believe that the entire hydrosphere of the Earth, in essence, is one giant "molecule" of water. It has been established that water can be activated by natural electromagnetic fields of terrestrial and cosmic origin (in particular, artificial). The recent discovery by French scientists of the "memory of water" was extremely interesting. Perhaps the fact that the Earth's biosphere is a single superorganism is due to these properties of water? After all, organisms are constituent parts, “drops” of this supermolecule of terrestrial water.
Although we still know only terrestrial protein-nucleic-aquatic life, this does not mean that its other forms cannot exist in the boundless Cosmos. Some scientists, in particular American ones, G. Feinberg and R. Shapiro, model such hypothetically possible variants of it:
Plasmoids - life in stellar atmospheres due to magnetic forces associated with groups of mobile electrical discharges;
Radiobes - life in interstellar clouds based on aggregates of atoms that are in different states of excitation;
Lavobs are silicon-based life that can exist in molten lava lakes on very hot planets;
Hydrogen - life that can exist at low temperatures on planets covered with "reservoirs" of liquid methane, and draw energy from the conversion of orthohydrogen to parahydrogen;
Thermophages are a species of cosmic life that draws energy from the temperature gradient in the atmosphere or oceans of planets.
Of course, such exotic life forms so far exist only in the imagination of scientists and science fiction writers. Nevertheless, the possibility of the real existence of some of them, in particular plasmoids, is not ruled out. There are some reasons to believe that on Earth, in parallel with "our" form of life, there is another kind of it, similar to the mentioned plasmoids. These include some types of UFOs (unidentified flying objects), formations similar to ball lightning, as well as invisible to the eye, but fixed by color photographic film, energy “clots” flying in the atmosphere, which in some cases showed reasonable behavior.
Thus, now there is reason to assert that life on Earth appeared from the very beginning of its existence and arose, according to C. Wickramasinghe, “from an all-penetrating general galactic living system.”
CONCLUSION
Do we have a logical right to recognize the fundamental difference between the living and the non-living? Are there facts in the nature surrounding us that convince us that life exists forever and has so little in common with inanimate nature that under no circumstances could it ever form, stand out from it? Can we recognize organisms as formations completely, fundamentally different from the rest of the world?
The biology of the 20th century deepened the understanding of the essential features of living things, revealing the molecular foundations of life. At the heart of the modern biological picture of the world is the idea that the living world is a grandiose system of highly organized systems.
Undoubtedly, new knowledge will be included in the models of the origin of life, and they will be more and more justified. But the more qualitatively the new differs from the old, the more difficult it is to explain its origin.
It is necessary to study the emergence of life in order to understand its essence, its possibilities and limitations, and then only in order to develop the first and overcome the second.
Life is one of the most complex natural phenomena. Since ancient times, it has been perceived as mysterious and unknowable - that is why there has always been a sharp struggle between materialists and idealists regarding the issues of its origin. Some adherents of idealistic views consider life to be a spiritual, non-material beginning that arose as a result of divine creation. Materialists, on the contrary, believe that life on Earth arose from inanimate matter by spontaneous generation (abiogenesis) or was brought from other worlds, i.e. is a product of other living organisms (biogenesis).
According to modern scientific concepts, life is the process of the existence of complex systems consisting of large organic molecules and inorganic substances and capable of self-reproducing, self-developing and maintaining their existence as a result of the exchange of energy and matter with the environment. Thus, biological science stands on materialistic positions.
At the same time, the question of the origin of life has not yet been finally resolved.
LITERATURE
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9. Bernal J. The emergence of life. - Moscow: Mir, 1969. - 650s.
There is a hypothesis about the possible introduction of bacteria, microbes and other tiny organisms through the introduction of celestial bodies. Organisms developed and as a result of long-term transformations, life gradually appeared on Earth. The hypothesis considers organisms that can function even in an anoxic environment and at abnormally high or low temperatures.
This is due to the presence of migrant bacteria on asteroids and meteorites, which are fragments from collisions of planets or other bodies. Due to the presence of a wear-resistant outer shell, as well as due to the ability to slow down all life processes (sometimes turning into a spore), this kind of life is able to move for a very long time and over very long distances.
When getting into more hospitable conditions, “intergalactic travelers” activate the main life-supporting functions. And without realizing it, they form, over time, life on Earth.
The fact of the existence of synthetic and organic substances today is undeniable. Moreover, back in the nineteenth century, the German scientist Friedrich Wöhler synthesized organic matter (urea) from inorganic matter (ammonium cyanate). Then hydrocarbons were synthesized. Thus, life on planet Earth quite likely originated by synthesis from inorganic material. Through abiogenesis, theories of the origin of life are put forward.
Since the main role in the structure of any organic organism is played by amino acids. It would be logical to assume that they were involved in the settlement of the Earth with life. Based on the data obtained from the experiment of Stanley Miller and Harold Urey (the formation of amino acids by passing an electric charge through gases), we can talk about the possibility of the formation of amino acids. After all, amino acids are the building blocks with which complex systems of the body and any life, respectively, are built.
Cosmogonic hypothesis
Probably the most popular interpretation of all, which every student knows. The Big Bang Theory has been and remains a hot topic of discussion. The Big Bang came from a singular point of energy accumulation, as a result of which the Universe expanded significantly. Cosmic bodies were formed. Despite all the consistency, the Big Bang Theory does not explain the formation of the universe itself. As a matter of fact, no existing hypothesis can explain it.
Symbiosis of organelles of nuclear organisms
This version of the origin of life on Earth is also called endosymbiosis. The clear provisions of the system were drawn up by the Russian botanist and zoologist K. S. Merezhkovsky. The essence of this concept lies in the mutually beneficial cohabitation of the organelle with the cell. Which, in turn, suggests endosymbiosis, as a symbiosis beneficial for both parties with the formation of eukaryotic cells (cells in which a nucleus is present). Then, with the help of the transfer of genetic information between bacteria, their development and population increase were carried out. According to this version, all further development of life and life forms is due to the previous ancestor of modern species.
Spontaneous generation
This kind of statement in the nineteenth century, could not be taken without a share of skepticism. The sudden appearance of species, namely the formation of life from non-living things, seemed like a fantasy for people of that time. At the same time, heterogenesis (the method of reproduction, as a result of which individuals are born that are very different from the parents) was recognized as a reasonable explanation of life. A simple example would be the formation of a complex viable system from decaying substances.
For example, in the same Egypt, Egyptian hieroglyphs report the appearance of a diverse life from water, sand, decaying and rotting plant remains. This news would not have surprised the ancient Greek philosophers. There, the belief about the origin of life from the inanimate was perceived as a fact that did not require substantiation. The great Greek philosopher Aristotle spoke of the visible truth in this way: “aphids are formed from rotten food, Crocodile is the result of processes in rotting logs under water.” Mysteriously, but despite all sorts of persecution from the church, the conviction under the bosom of mystery lived for a century.
Debates about life on Earth cannot go on forever. That is why, at the end of the nineteenth century, the French microbiologist and chemist Louis Pasteur carried out his analyzes. His research was strictly scientific. The experiment was carried out in 1860-1862. Thanks to the removal of disputes from a sleepy state, Pasteur was able to solve the problem of the spontaneous generation of life. (For which he was awarded the prize by the French Academy of Sciences)
Creation of existence from ordinary clay
It sounds like madness, but in reality this topic has the right to life. After all, it is not in vain that the Scottish scientist, A.J. Cairns-Smith, put forward a protein theory about life. Strongly forming the basis of similar studies, he talked about the interaction at the molecular level between organic constituents and simple clay ... Being under its influence, the components formed stable systems in which changes occurred in the structure of both components, and then the formation of a sustainable life. In such a unique and original way, Kearns-Smith explained his position. Clay crystals, with biological inclusions in it, gave birth to life together, after which their “cooperation” ended.
Theory of permanent catastrophes
According to the concept developed by Georges Cuvier, the world that you can see right now is not at all primary. And what he is, so it's just another link in a consistently torn chain. This means that we live in a world that will eventually undergo a mass extinction of life. At the same time, not everything on Earth was subjected to global destruction (for example, there was a flood). Some species, in the course of their adaptability, survived, thereby populating the Earth. The structure of species and life, according to Georges Cuvier, remained unchanged.
Matter as an objective reality
The main theme of the teaching is various spheres and areas that bring closer to understanding evolution from the point of view of the exact sciences. (materialism is a worldview in philosophy that reveals all causal circumstances, phenomena and factors of reality. Laws are applicable to man, society, the Earth). The theory was put forward by well-known adherents of materialism, who believe that life on Earth originated from transformations at the level of chemistry. Moreover, they occurred almost 4 billion years ago. The explanation of life is directly related to DNA, (deoxyribonucleic acid) RNA (ribonucleic acid), as well as to some HMCs (high molecular weight compounds, in this case proteins.)
The concept was formed through scientific research, revealing the essence of molecular and genetic biology, genetics. The sources are authoritative, especially given their youth. After all, studies of the hypothesis about the world of RNA began to be carried out at the end of the twentieth century. A huge contribution to the theory was made by Carl Richard Woese.
Teachings of Charles Darwin
Speaking about the origin of species, it is impossible not to mention such a truly brilliant person as Charles Darwin. His life's work, natural selection, laid the foundation for mass atheist movements. On the other hand, it gave an unprecedented impetus to science, an inexhaustible ground for research and experimentation. The essence of the doctrine was the survival of species throughout history, by adapting organisms to local conditions, the formation of new features that help in a competitive environment.
Evolution refers to some processes aimed at changing the life of an organism and the organism itself over time. Under hereditary traits, they mean the transfer of behavioral, genetic, or other kind of information (transmission from maternal to child.)
The main forces of the movement of evolution, according to Darwin, is the struggle for the right to exist, through the selection and variability of species. Under the influence of Darwinian ideas, at the beginning of the twentieth century, research was actively carried out in terms of ecology, as well as genetics. The teaching of zoology has changed radically.
Creation of God
Many people from all over the globe still profess faith in God. Creationism is an interpretation of the formation of life on Earth. The interpretation consists of a system of statements based on the Bible and considers life as a being created by a creator god. The data is taken from the "Old Testament", "Gospel" and other sacred writings.
Interpretations of the creation of life in different religions are somewhat similar. According to the Bible, the earth was created in seven days. The sky, the celestial body, water and the like, were created in five days. On the sixth day, God created Adam from clay. Seeing a bored, lonely man, God decided to create another miracle. Taking Adam's rib, he created Eve. The seventh day was recognized as a day off.
Adam and Eve lived without trouble, until the malevolent devil in the form of a snake decided to tempt Eve. After all, in the middle of paradise stood the tree of the knowledge of good and evil. The first mother invited Adam to share the meal, thereby violating the word given to God (he forbade touching the forbidden fruits.)
The first people are expelled into our world, thereby starting the history of all mankind and life on Earth.
Do you know the origin of life?
3. What is the basic principle of the scientific method?
The problem of the origin of life on our planet is one of the central ones in modern natural science. Since ancient times, people have tried to find the answer to this question.
Creationism (lat, sgeatio - creation).
At different times, different peoples had their own ideas about the origin of life. They are reflected in the sacred books of various religions, which explain the emergence of life as an act of the Creator (the will of God). The hypothesis of the divine origin of living things can only be accepted on faith, since it cannot be experimentally verified or refuted. Therefore, it cannot be considered scientific points of view.
The hypothesis of spontaneous origin of life.
From ancient times to the middle of the 17th century. scientists did not doubt the possibility of spontaneous generation of life. It was believed that living beings can appear from inanimate matter, for example, fish - from silt, worms - from soil, mice - from rags, flies - from rotten meat, and also that some forms can give rise to others, for example, animals can form from fruits (see, p. 343).
So, the great Aristotle, studying eels, found that among them there are no individuals with caviar or milk. Based on this, he suggested that eels are born from "sausages" of silt, formed from the friction of an adult fish against the bottom.
The first blow to the idea of spontaneous generation was caused by the experiments of the Italian scientist Francesc Redi, who in 1668 proved the impossibility of spontaneous generation of flies in rotting meat.
Despite this, the ideas of spontaneous generation of life persisted until the middle of the 19th century. Only in 1862 did the French scientist Louis Pasteur finally disprove the hypothesis of spontaneous generation of life.
The works of the Master made it possible to assert that the principle "All living things - from living things" is true for all known organisms on our planet, but they did not resolve the question of the origin of life.
Panspermia hypothesis.
Proof of the impossibility of spontaneous generation of life gave rise to another problem. If another living organism is needed for the emergence of a living organism, then where did the first living organism come from? This gave impetus to the emergence of the panspermia hypothesis, which had and has many supporters, including among prominent scientists. They believe that for the first time life did not originate on Earth, but was somehow introduced to our planet.
However, the panspermia hypothesis only attempts to explain the emergence of life on Earth. It does not answer the question of how life began.
The denial of the fact of spontaneous generation of life at the present time does not contradict the ideas about the fundamental possibility of the development of life in the past from inorganic matter.
The hypothesis of biochemical evolution.
In the 1920s, the Russian scientist A. I. Oparin and the Englishman J. Haldane put forward a hypothesis about the origin of life in the process of biochemical evolution carbon compounds, which formed the basis of modern ideas.
In 1924, AI Oparin published the main provisions of his hypothesis of the origin of life on Earth. He proceeded from the fact that in modern conditions the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only in the conditions of the ancient atmosphere and the absence of living organisms.
According to A. I. Oparin, in the primary atmosphere of the planet, saturated with various gases, with powerful electrical discharges, as well as under the influence of ultraviolet radiation (there was no oxygen in the atmosphere and, therefore, there was no protective ozone screen, the atmosphere was reducing) and high radiation organic compounds could be formed that accumulated in the ocean, forming a "primordial soup".
It is known that in concentrated solutions of organic substances (proteins, nucleic acids, lipids) under certain conditions, clots called coacervate drops, or coacervates, can form. Coacervates did not break down in a reducing atmosphere. From the solution, they received chemicals, they synthesized new compounds, as a result of which they grew and became more complex.
Coacervates already resembled living organisms, but they were not yet such, since they did not have an ordered internal structure inherent in living organisms, and were not able to reproduce. Protein coacervates were considered by A.I., Oparin as probionts - the precursors of a living organism. He assumed that at a certain stage, protein probionts included nucleic acids, creating single complexes.
The interaction of proteins and nucleic acids has led to the emergence of such living properties as self-reproduction, the preservation of hereditary information and its transmission to subsequent generations.
Probionts, in which metabolism was combined with the ability to reproduce themselves, can already be considered as primitive procells.
In 1929, the English scientist J. Haldane also put forward the hypothesis of the abiogenic origin of life, but according to his views, the primary was not a coarcervate system capable of exchanging substances with the environment, but a macromolecular system capable of self-reproduction. In other words, A. I. Oparin gave priority to proteins, and J. Haldane - to nucleic acids.
The Oparin-Holdein hypothesis won many supporters, as it received experimental confirmation of the possibility of abiogenic synthesis of organic biopolymers.
In 1953, the American scientist Stanley Miller, in the installation he created (Fig. 141), simulated the conditions that presumably existed in the Earth's primary atmosphere. As a result of the experiments, amino acids were obtained. Similar experiments were repeated many times in various laboratories and made it possible to prove the fundamental possibility of synthesizing practically all monomers of the main biopolymers under such conditions. Subsequently, it was found that, under certain conditions, it is possible to synthesize more complex organic biopolymers from monomers: polypeptides, polynucleotides, polysaccharides, and lipids.
But the Oparin-Haldane hypothesis also has a weak side, which is pointed out by its opponents. Within the framework of this hypothesis, it is not possible to explain the main problem: how did the qualitative leap from inanimate to living occur. Indeed, for the self-reproduction of nucleic acids, enzyme proteins are needed, and for the synthesis of proteins, nucleic acids.
Creationism. Spontaneous generation. Panspermia hypothesis. The hypothesis of biochemical evolution. Coacervates. Probionts.
1. Why can the notion of the divine origin of life be neither confirmed nor refuted?
2. What are the main provisions of the Oparin-Haldane hypothesis?
3. What experimental evidence can be given in favor of this hypothesis?
4. What is the difference between the hypothesis of A. I. Oparin and the hypothesis of J. Haldane?
5. What arguments do opponents give when criticizing the Oparin-Haldane hypothesis?
Give possible arguments "for" and "against" the hypothesis of panspermia.
C. Darwin wrote in 1871: “But now ... in some warm reservoir containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, etc., a protein capable of to further, more and more complex transformations, then this substance would immediately be destroyed or absorbed, which was impossible in the period before the emergence of living beings.
Confirm or refute this statement of Charles Darwin.
In understanding the essence of life and its origin in the culture of human civilization, there have long been two ideas - biogenesis and abiogenesis. The idea of biogenesis (the origin of living things from living things) comes from ancient Eastern religious constructions, for which the idea of the absence of the beginning and end of natural phenomena was common. The reality of eternal life for these cultures is logically acceptable, as well as the eternity of matter, the Cosmos.
An alternative idea - abiogenesis (the origin of life from non-life) goes back to civilizations that existed long before our era in the valleys of the Tigris and Euphrates rivers. This area was subject to constant flooding, and it is not surprising that it became the birthplace of catastrophism, which influenced European civilization through Judaism and Christianity. Catastrophes, as it were, interrupt the connection, the chain of generations, suggest its creation, reappearance. In this regard, the belief in the periodic spontaneous generation of an organism under the influence of natural or supernatural causes was widespread in European culture.
Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology Grade 10
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