Origin and initial stages of development of life on earth. Biochemical hypothesis of the origin of life

Origin of life hypotheses

The origin of life on Earth is one of the most important problems of natural science. Over the course of tens of centuries, views on the problem of life have changed, various ideas, hypotheses and concepts have been expressed. Some of them became widespread in different periods of the history of the development of natural science. Currently, there are five hypotheses for the origin of life:

1. Creationism is a hypothesis that states that life was created by a supernatural being as a result of an act of creation. Has the longest history. It is based on the presence in living organisms of a special power, the “soul”, which controls all life processes.

2. The hypothesis of a stationary state, according to which life never arose, but always existed. With the change in natural conditions, species also changed: some disappeared, others appeared. Based on research by paleontologists.

3. The hypothesis of spontaneous generation of life, which is based on the idea of ​​the repeated emergence of life from non-living matter, was put forward in ancient China and India as an alternative to creationism. This hypothesis was supported by Plato, Aristotle, Galileo, Descartes, Lamarck. The essence of the hypothesis: the lower living organisms arose from silt, damp soil, rotting meat. In refutation of this hypothesis, F. Redi formulated the principle: “All living things come from living things,” after he found the reason for the appearance of worms on rotting meat. L. Pasteur, with his experiments with viruses, finally proved the inconsistency of the idea of ​​spontaneous origin of life.

4. The hypothesis of panspermia, according to which life was brought to Earth from outer space. It was first expressed by G. Richter at the end of the 19th century. This concept allows for the possibility of the origin of life at different times in different parts of the Universe and its transfer to the Earth in various ways (meteorites, asteroids, cosmic dust).

5. The hypothesis of the historical origin of life through biochemical evolution. The authors are A. Oparin and S. Haldane. From the point of view of A. Oparin's hypothesis, as well as from the standpoint of modern science, the emergence of life from inanimate matter occurred as a result of natural processes in the Universe during the long evolution of matter. A. Oparin identified several stages of biochemical evolution, the ultimate goal of which was a primitive living cell. The evolution went according to the scheme:

A) the geochemical evolution of the planet Earth, the synthesis of the simplest compounds such as CO2, NH3, H2O, etc., the transition of water from a vapor to a liquid state as a result of the gradual cooling of the Earth. Evolution of the atmosphere and hydrosphere.

B) the formation of organic substances from inorganic compounds - amino acids - and their accumulation in the primary ocean as a result of the electromagnetic influence of the Sun, cosmic radiation and electrical discharges.

C) the gradual complication of organic compounds and the formation of protein structures.

D) the isolation of protein structures from the environment, the formation of water complexes and the creation of an aqueous shell around the proteins.

E) the fusion of such complexes and the formation of coacervates capable of exchanging matter and energy with the environment.

E) absorption of metals by coacervates, which led to the formation of enzymes that accelerate biochemical processes.

G) the formation of hydrophobic lipid boundaries between coacervates and the external environment, which led to the formation of semipermeable membranes, which ensured the stability of the functioning of the coacervate.

H) development in the course of evolution in these formations of processes of self-regulation and self-reproduction.

According to academician V. Vernadsky, the emergence of life is associated with a powerful leap, which introduced so many contradictions into evolution that they created the conditions for the birth of living matter. The extreme complexity of the organization of living matter is proof that the origin of life is the result of a long process of biological evolution.

6. Modern theory of biological evolution

Evolution is understood as one of the forms of movement, which is characterized by gradual, continuous, accumulating changes, leading to qualitative shifts in the development of living nature. In the process of formation of the evolutionary paradigm, there are three main stages:

· The first stage – traditional biology; its brightest representative is the Swedish scientist K. Linnaeus.

· The second stage is the classical theory of biological evolution; the creator is the English naturalist Ch. Darwin.

· The third stage is the synthetic theory of biological evolution. Its content was the result of the ideas of Charles Darwin and the Czech botanist, the founder of genetics G. Mendel.

The general theoretical basis of traditional biology, which dominated biological thought from ancient times until the 19th century, was the concept of creationism, which proceeded from the idea of ​​the simultaneous emergence of all forms of life on Earth. The task of traditional biology was to build a classification and systematization of all living beings. The most significant contribution to the solution of this problem was made by K. Linnaeus, who created a system of classification of living organisms, which revealed the integrity, unity, interconnection and continuity of organisms, which in turn led scientists to the idea that all the diversity of forms of wildlife is the result of biological evolution . Traditional biology accumulates its scientific material through direct observation of living nature, so it continues to develop at the present time.

Charles Darwin's theory was the result of summarizing a huge amount of various factual data. Darwin's explanation of the process of evolution can be summarized as follows:

1. Any group of animals and plants is characterized by variability. Variability is one of the properties inherent in living organisms.

2. The number of organisms of each species that are born into the world is much greater than the number that can find food, survive and leave offspring. Most of the offspring in each generation die.

3. Since more individuals are born than can survive, there is competition, a struggle for food and habitat.

4. Hereditary changes that make it easier for an organism to survive in a certain environment give their owners an advantage over other, less adapted organisms. Surviving individuals give rise to the next generation and, thus, the selection of the fittest representatives occurs (natural selection).

The impulse for the formation of a synthetic theory of evolution was the discovery of the law of inheritance and the deciphering of the structure of DNA. The synthetic theory of evolution in its content is a synthesis of Darwinism and the achievements of molecular biology. The essence of the theory lies in the presentation of the process of evolution as a competition of genetic programs, which determines the individual development of organisms. Moreover, an important role in determining the general direction of evolution is played by the main programming device, which is the biosphere as a whole. It is the biosphere that determines the speed and direction of the evolutionary transformation of the species included in its composition.

Bioethics

At first glance it seems that there is nothing in common between ethics and biology. After all, ethics is a branch of social and humanitarian knowledge that explores the ideal sphere of prescriptions, norms and principles of human behavior, while biology is one of the natural sciences that cognizes real facts that characterize the essence of life. Nevertheless, there is a connection between biology and ethics. After all, man is a product of a long biological evolution. And one of the sides of evolution is the struggle for existence, during which not only physical measures are applied, but also psychological, including ethical norms.

Bioethics is precisely the study of mental processes that, having arisen in the early stages of the evolution of the living, gradually developed and led to the emergence of a set of requirements and principles called human ethics. Bioethics in the direction of its interests most closely approaches the object of study of the social sciences and the humanities, studying the following main problems:

· Problems of the deep, biological origins of the ethical principles of human behavior, manifestations of the rudiments of these principles in the behavior of living organisms already at the early stages of biological evolution.

· Resolution on this basis of the issues of correlation in the ethical principles of human congenital and acquired, biological and social and unconscious.

· Development of a set of new ethical norms, the relevance of which is associated with the possibility of profound consequences for humans of the largest discoveries of modern biology, in particular genetics.

The complex behavioral programs inherent in the animal world and the norms of human ethics have a single biogenic origin. Based on this, bioethics as a central idea puts forward the idea that the principles of human behavior have not only social, but also biological prerequisites. Bioethics discovers in our inner world and in our behavior, in addition to forms generated by the mind, culture, society, there are also forms due to ancient genetic programs inherited from our animal ancestors. An important area of ​​modern bioethics is the search for new approaches to the moral assessment of such phenomena as euthanasia, violation of sexual certainty, cloning.



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, which makes the real search for any life forms on the planets of the solar system more and more real. , 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 various aspects of this phenomenon, are still unable to overcome the 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 the image of frogs allegedly arising from the May dew, and Aldrovand depicts the process of rebirth of birds and insects from the 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 vessels with wide mouths, put earth in one of them, some fish in another, eels from Arno in the third, a piece of dairy veal in the fourth, tightly closed them 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 “smallest 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 needed 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 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 Oparin "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 is considered by many biologists as an important distinguishing 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 so far nothing has appeared that would equally satisfy 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 so figuratively expressed the impossibility of abiogenic synthesis: “It is faster that a hurricane that sweeps over a cemetery of old aircraft will assemble a brand new superliner from pieces of scrap than life will arise from its components as a result of a random process.”

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 the latest 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%). Obviously, 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 around 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. From ancient times, it was 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

1. Oparin A. I. The emergence of life on Earth. - Tbilisi: Mincebra, 1985. - 270s.

2. Bernal D. The emergence of life Appendix No. 1: Oparin AI The origin of life. - Moscow: Mir, 1969. - 365s.

3.Vernadsky v. I. Living matter. - Moscow: Nauka, 1978. - 407s.

4. Naidysh V. M. Concepts of modern natural science - Moscow: Nauka, 1999. - 215s.

5. general biology. Ed. N. D. Lisova. - Minsk, 1999 - 190s.

6. Ponnamperuma S. The origin of life. - Moscow: Mir, 1977. - 234s.

7. Vologodin A. G. The origin of life on Earth. - Moscow: Knowledge, 1970. - 345s.

8. Ignatov AI The problem of the origin of life. - Moscow: Soviet Russia, 1962. - 538s.

9. Bernal J. The emergence of life. - Moscow: Mir, 1969. - 650s.

Hypotheses of the origin of life on Earth.

Currently, there are several concepts considering the origin of life on earth. Let us dwell only on some of the main theories that help to compose a fairly complete picture of this complex process.

Creationism (lat. cgea - creation).

According to this concept, life and all species of living beings inhabiting the Earth are the result of a creative act of a higher being at some specific time.

The main provisions of creationism are set out in the Bible, in the Book of Genesis. The process of the divine creation of the world is conceived as having taken place only once and therefore inaccessible to observation.

This is enough to take the whole concept of divine creation out of the scope of scientific research. Science deals only with observable phenomena and therefore will never be able to either prove or reject this concept.

Spontaneous(spontaneous) generation.

The ideas of the origin of living beings from inanimate matter were widespread in Ancient China, Babylon, and Egypt. The largest philosopher of ancient Greece, Aristotle, suggested that certain "particles" of matter contain some kind of "active principle", which, under suitable conditions, can create a living organism.

Van Helmont (1579–1644), a Dutch physician and natural philosopher, 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 process of the birth of a mouse.

In the 17th-18th centuries, thanks to successes in the study of lower organisms, the fertilization and development of animals, as well as the observations and experiments of the Italian naturalist F. Redi (1626-1697), the Dutch microscopist A. Leeuwenhoek (1632-1723), the Italian scientist L. Spallanzani ( 1729-1799), Russian microscopist M. M. Terekhovsky (1740-1796) and others, belief in spontaneous generation was thoroughly undermined.

However, until the appearance in the middle of the tenth century of the work of the founder of microbiology, Louis Pasteur, this doctrine continued to find adherents.

The development of the idea of ​​spontaneous generation refers, in essence, to the era when religious ideas dominated the public consciousness.

Those philosophers and naturalists who did not want to accept the Church's teaching on the "creation of life", with the then level of knowledge, easily came to the idea of ​​its spontaneous generation.

To the extent that, in contrast to the belief in creation, the idea of ​​the natural origin of organisms was emphasized, the idea of ​​spontaneous generation was at a certain stage of progressive significance. Therefore, this idea was often opposed by the Church and theologians.

The panspermia hypothesis.

According to this hypothesis, proposed in 1865. by the German scientist G. Richter and finally formulated by the Swedish scientist Arrhenius in 1895, life could be brought to Earth from space.

The most likely hit of living organisms of extraterrestrial origin with meteorites and cosmic dust. This assumption is based on data on the high resistance of some organisms and their spores to radiation, high vacuum, low temperatures, and other influences.

However, there are still no reliable facts confirming the extraterrestrial origin of microorganisms found in meteorites.

But even if they got to Earth and gave rise to life on our planet, the question of the original origin of life would remain unanswered.

Hypothesis biochemical evolution.

In 1924, the biochemist AI Oparin, and later the English scientist J. Haldane (1929), formulated a hypothesis that considers life as the result of a long evolution of carbon compounds.

The modern theory of the origin of life on Earth, called the theory of biopoiesis, was formulated in 1947 by the English scientist J. Bernal.

Currently, in the process of the formation of life, four stages are conventionally distinguished:

• 1. Synthesis of low molecular weight organic compounds (biological monomers) from gases of the primary atmosphere.
• 2. Formation of biological polymers.
• 3. Formation of phase-separated systems of organic substances separated from the external environment by membranes (protobionts).
• 4. The emergence of the simplest cells that have the properties of a living thing, including the reproductive apparatus, which ensures the transfer of the properties of parental cells to daughter cells.

The first three stages are attributed to the period of chemical evolution, and from the fourth, biological evolution begins.

Let us consider in more detail the processes as a result of which life could have arisen on Earth. According to modern concepts, the Earth was formed about 4.6 billion years ago. Its surface temperature was very high (4000-8000°C), and as the planet cooled and gravitational forces acted, the earth's crust was formed from compounds of various elements.

Degassing processes led to the creation of an atmosphere enriched, possibly, with nitrogen, ammonia, water vapor, carbon dioxide and carbon monoxide. Such an atmosphere was, apparently, reducing, as evidenced by the presence in the most ancient rocks of the Earth of metals in reduced form, such as, for example, ferrous iron.

It is important to note that the atmosphere contained hydrogen, carbon, oxygen and nitrogen atoms, which make up 99% of the atoms that make up the soft tissues of any living organism.

However, in order for atoms to turn into complex molecules, their simple collisions were not enough. Additional energy was needed, which was available on Earth as a result of volcanic activity, electrical lightning discharges, radioactivity, ultraviolet radiation from the Sun.

The absence of free oxygen was probably not a sufficient condition for the emergence of life. If free oxygen were present on the Earth in the prebiotic period, then, on the one hand, it would oxidize the synthesized organic substances, and on the other hand, forming an ozone layer in the upper horizons of the atmosphere, it would absorb the high-energy ultraviolet radiation of the Sun.

During the considered period of the emergence of life, which lasted approximately 1000 million years, ultraviolet radiation was probably the main source of energy for the synthesis of organic substances.

Oparin A.I.

From hydrogen, nitrogen and carbon compounds, in the presence of free energy on Earth, simple molecules (ammonia, methane and similar simple compounds) should first have arisen.

In the future, these simple molecules in the primary ocean could enter into reactions with each other and with other substances, forming new compounds.

In 1953, the American researcher Stanley Miller in a series of experiments simulated the conditions that existed on Earth approximately 4 billion years ago.

Passing electrical discharges through a mixture of ammonia, methane, hydrogen and water vapor, he obtained a number of amino acids, aldehydes, lactic, acetic and other organic acids. American biochemist Cyril Ponnaperuma achieved the formation of nucleotides and ATP. In the course of such and similar reactions, the waters of the primary ocean could be saturated with various substances, forming the so-called "primary soup".

The second stage consisted of further transformations of organic substances and the abiogenic formation of more complex organic compounds, including biological polymers.

The American chemist S. Fox composed mixtures of amino acids, subjected them to heating, and obtained proteo-like substances. On primitive earth, protein synthesis could take place on the surface of the earth's crust. In small depressions in the solidifying lava, reservoirs appeared containing small molecules dissolved in water, including amino acids.

When the water evaporated or splashed onto hot rocks, the amino acids reacted to form proteoids. The rains then washed the proteoids into the water. If some of these proteoids had catalytic activity, then the synthesis of polymers, i.e., protein-like molecules, could begin.

The third stage was characterized by the release of special coacervate droplets, which are groups of polymeric compounds, in the primary "nutrient broth". It has been shown in a number of experiments that the formation of coacervate suspensions, or microspheres, is typical of many biological polymers in solution.

Coacervate drops have some properties that are also characteristic of living protoplasm, such as, for example, selectively adsorbing substances from the surrounding solution and, due to this, "grow", increase their size.

Due to the fact that the concentration of substances in coacervate drops was ten times greater than in the surrounding solution, the possibility of interaction between individual molecules increased significantly.

It is known that the molecules of many substances, in particular polypeptides and fats, consist of parts that have a different relationship to water. The hydrophilic parts of the molecules located at the boundary between the coacervates and the solution turn towards the solution, where the water content is higher.

The hydrophobic parts are oriented inside the coacervates, where the water concentration is less. As a result, the surface of the coacervates acquires a certain structure and, in connection with this, the property of passing some substances in a certain direction and not letting others through.

Due to this property, the concentration of some substances inside the coacervates increases even more, while the concentration of others decreases, and the reactions between the components of the coacervates acquire a certain direction. Coacervate drops become systems isolated from the medium. Protocells, or protobionts, arise.

An important step in chemical evolution was the formation of a membrane structure. In parallel with the appearance of the membrane, there was an ordering and improvement of metabolism. Catalysts should have played a significant role in the further complication of metabolism in such systems.

One of the main features of a living thing is the ability to replicate, that is, to create copies that are indistinguishable from parent molecules. This property is possessed by nucleic acids, which, unlike proteins, are capable of replication.

A protenoid capable of catalyzing the polymerization of nucleotides with the formation of short RNA chains could form in coacervates. These chains could play the role of both a primitive gene and messenger RNA. Neither DNA, nor ribosomes, nor transfer RNAs, nor enzymes of protein synthesis have yet participated in this process. All of them appeared later.

Already at the stage of formation of protobionts, natural selection probably took place, i.e., the preservation of some forms and the elimination (death) of others. Thus, progressive changes in the structure of protobionts were fixed due to selection.

The appearance of structures capable of self-reproduction, replication, and variability apparently determines the fourth stage in the development of life.

So, in the late Archean (approximately 3.5 billion years ago), at the bottom of small reservoirs or shallow, warm and nutrient-rich seas, the first primitive living organisms arose that were heterotrophs by type of nutrition, that is, they fed on ready-made organic substances, synthesized in the course of chemical evolution.

Fermentation, a process of enzymatic transformation of organic substances, in which other organic substances serve as electron acceptors, served as a means of metabolism.

Part of the energy released in these processes is stored in the form of ATP. It is possible that some organisms also used the energy of redox reactions for life processes, that is, they were chemosynthetics.

Over time, there was a decrease in the reserves of free organic matter in the environment, and organisms capable of synthesizing organic compounds from inorganic ones gained an advantage.

In this way, probably about 2 billion years ago, the first phototrophic organisms of the cyanobacteria type arose, capable of using light energy for the synthesis of organic compounds from CO2 and H2O, while releasing free oxygen.

The transition to autotrophic nutrition was of great importance for the evolution of life on Earth, not only in terms of creating reserves of organic matter, but also for saturating the atmosphere with oxygen. At the same time, the atmosphere began to acquire an oxidizing character.

The appearance of the ozone screen protected the primary organisms from the harmful effects of ultraviolet rays and put an end to the abiogenic (non-biological) synthesis of organic substances.

These are the modern scientific ideas about the main stages of the origin and formation of life on Earth.

A visual diagram of the development of life on Earth (clickable)

Addition:

The wonderful world of "black smokers"

In science, it has long been believed that living organisms can exist only from the energy of the Sun. Jules Verne in his novel Journey to the Center of the Earth described the underworld with dinosaurs and ancient plants. However, this is fiction. But who would have thought that there would be a world isolated from the energy of the Sun with absolutely different living organisms. And he was found at the bottom of the Pacific Ocean.

Back in the fifties of the twentieth century, it was believed that there could be no life in the ocean depths. The invention of the bathyscaphe by Auguste Picard dispelled these doubts.

His son, Jacques Picard, together with Don Walsh, descended in the Trieste bathyscaphe into the Mariana Trench to a depth of more than ten thousand meters. At the very bottom, the participants of the dive saw a live fish.

After that, oceanographic expeditions of many countries began to comb the deep ocean abyss with deep-sea nets and discover new animal species, families, orders, and even classes!

Submersions in bathyscaphes improved. Jacques-Yves Cousteau and scientists from many countries made costly dives to the bottom of the oceans.
In the 70s, a discovery was made that turned many ideas of scientists upside down. Faults were discovered near the Galapagos Islands at a depth of two to four thousand meters.
And at the bottom were discovered small volcanoes - hydrotherms. Sea water, falling into the faults of the earth's crust, evaporated along with various minerals through small volcanoes up to 40 meters high.
These volcanoes were called "black smokers" due to the black water coming out of them.

However, the most incredible thing is that in such water, filled with hydrogen sulfide, heavy metals and various toxic substances, a vibrant life flourishes.

The temperature of the water coming out of the black smokers reaches 300°C. The sun's rays do not penetrate to a depth of four thousand meters, and therefore there cannot be a rich life.
Even in shallower depths, benthic organisms are very rare, not to mention deep abysses. There, animals feed on organic debris that falls from above. And the greater the depth, the less poorer the bottom life.
On the surfaces of black smokers, chemoautotrophic bacteria have been found that break down sulfur compounds erupted from the planet's interior. Bacteria cover the bottom surface in a continuous layer and live in aggressive conditions.
They have become food for many other animal species. In total, about 500 species of animals living in extreme conditions of "black smokers" have been described.

Another discovery was vestimentifera, which belong to the class of bizarre animals - pogonophores.

These are small tubes from which protrude long tubes at the ends with tentacles. The unusual thing about these animals is that they don't have a digestive system! They entered into symbiosis with bacteria. Inside the vestimentifer there is an organ - the trophosome, where many sulfurous bacteria live.

Bacteria receive hydrogen sulfide and carbon dioxide for life, the excess of breeding bacteria is eaten by vestimentifera itself. In addition, bivalve mollusks of the genera Calyptogena and Bathymodiolus were found nearby, which also entered into symbiosis with bacteria and ceased to depend on the search for food.

One of the most unusual creatures of the deep-sea world of hydrotherms is the Alvinella pompeii worms.

They are named because of the analogy with the eruption of the Pompeii volcano - these creatures live in a zone of hot water reaching 50 ° C, and ash from sulfur particles constantly falls on them. Worms, together with vestimentifera, form real "gardens" that provide food and shelter for many organisms.

Crabs and decapods live among colonies of vestimentifera and pompeii worms, which feed on them. Also among these "gardens" there are octopuses and fish from the eelpout family. The world of black smokers also harbored long-extinct animals that had been pushed out of other parts of the ocean, such as the barnacles Neolepas.

These animals were widespread 250 million years ago, but then became extinct. Here, representatives of barnacles feel calm.

The discovery of the ecosystems of "black smokers" has become the most significant event in biology. Such ecosystems have been found in different parts of the World Ocean and even at the bottom of Lake Baikal.

Pompeii worm. Photo life-grind-style.blogspot.com

The question of the origin of life on Earth is one of the most difficult questions of modern natural science, to which there is no unambiguous answer so far.

There are several theories about the origin of life on Earth, the most famous of which are:

• theory of spontaneous (spontaneous) generation;
• the theory of creationism (or creation);
• steady state theory;
• theory of panspermia;
• theory of biochemical evolution (the theory of A.I. Oparin).

Consider the main provisions of these theories.

Theory of spontaneous (spontaneous) generation

The theory of spontaneous generation of life was widespread in the ancient world - Babylon, China, Ancient Egypt and Ancient Greece (Aristotle, in particular, adhered to this theory).

Scientists of the ancient world and medieval Europe believed that living beings constantly arise from inanimate matter: worms from mud, frogs from mud, fireflies from morning dew, etc. So, the famous Dutch scientist of the 17th century. Van Helmont quite seriously described in his scientific treatise an experience in which he got mice in a locked dark closet directly from a dirty shirt and a handful of wheat in 3 weeks. For the first time, the Italian scientist Francesco Redi (1688) decided to subject a widely accepted theory to experimental verification. He placed several pieces of meat in vessels and covered some of them with muslin. In open vessels, white worms appeared on the surface of rotting meat - fly larvae. There were no fly larvae in the vessels covered with muslin. Thus, F. Redi managed to prove that fly larvae do not appear from rotting meat, but from eggs laid by flies on its surface.

In 1765, the famous Italian scientist and physician Lazzaro Spalanzani boiled meat and vegetable broths in sealed glass flasks. Broths in sealed flasks did not deteriorate. He concluded that under the influence of high temperature all living creatures capable of causing spoilage of the broth died. However, the experiments of F. Redi and L. Spalanzani did not convince everyone. Vitalist scientists (from lat. vita- life) believed that spontaneous generation of living beings does not occur in a boiled broth, since a special “life force” is destroyed in it, which cannot penetrate into a sealed vessel, since it is carried through the air.

Disputes about the possibility of spontaneous generation of life intensified in connection with the discovery of microorganisms. If complex living beings can't reproduce spontaneously, perhaps microorganisms can?

In this regard, in 1859, the French Academy announced the award of a prize to the one who finally decides the question of the possibility or impossibility of spontaneous generation of life. This award was received in 1862 by the famous French chemist and microbiologist Louis Pasteur. Just like Spalanzani, he boiled nutrient broth in a glass flask, but the flask was not ordinary, but with a neck in the form of a 5-shaped tube. Air, and hence the "life force", could penetrate into the flask, but the dust, and with it the microorganisms present in the air, settled in the lower elbow of the 5-shaped tube, and the broth in the flask remained sterile (Fig. 1). However, it was worth breaking the neck of the flask or rinsing the lower knee of the 5-shaped tube with sterile broth, as the broth began to quickly become cloudy - microorganisms appeared in it.

Thus, thanks to the work of Louis Pasteur, the theory of spontaneous generation was recognized as untenable and the theory of biogenesis was established in the scientific world, a brief formulation of which is - "everything living is from living things."

Rice. 1. Pasteur flask

However, if all living organisms in the historically foreseeable period of human development originate only from other living organisms, the question naturally arises: when and how did the first living organisms appear on Earth?

Creation theory

Creation theory assumes that all living organisms (or only their simplest forms) were created (“designed”) in a certain period of time by some supernatural being (deity, absolute idea, supermind, supercivilization, etc.). It is obvious that the followers of most of the leading religions of the world, in particular the Christian religion, adhered to this point of view from ancient times.

The theory of creationism is still quite widespread, not only in religious, but also in scientific circles. It is usually used to explain the most complex, unresolved issues of biochemical and biological evolution associated with the emergence of proteins and nucleic acids, the formation of the mechanism of interaction between them, the emergence and formation of individual complex organelles or organs (such as the ribosome, eye or brain). Acts of periodic "creation" also explain the absence of clear transitional links from one type of animal
to another, for example, from worms to arthropods, from monkeys to humans, etc. It must be emphasized that the philosophical dispute about the primacy of consciousness (supermind, absolute idea, deity) or matter is fundamentally unsolvable, however, since an attempt to explain any difficulties of modern biochemistry and evolutionary theory by fundamentally incomprehensible supernatural acts of creation takes these issues beyond the scope of scientific research, the theory of creationism can not be attributed to the category of scientific theories of the origin of life on Earth.

Steady state and panspermia theories

Both of these theories are complementary elements of a single picture of the world, the essence of which is as follows: the universe exists forever and life exists in it forever (stationary state). Life is carried from planet to planet by "seeds of life" traveling in outer space, which can be part of comets and meteorites (panspermia). Similar views on the origin of life were held, in particular, by Academician V.I. Vernadsky.

However, the theory of the stationary state, which assumes an infinitely long existence of the universe, is not consistent with the data of modern astrophysics, according to which the universe arose relatively recently (about 16 billion years ago) by means of a primary explosion.

It is obvious that both theories (panspermia and stationary state) do not offer an explanation of the mechanism of the primary origin of life at all, transferring it to other planets (panspermia) or moving it to infinity in time (the theory of a stationary state).

Theory of biochemical evolution (theory of A.I. Oparin)

Of all theories of the origin of life, the most common and recognized in the scientific world is the theory of biochemical evolution, proposed in 1924 by the Soviet biochemist Academician A.I. Oparin (in 1936 he described it in detail in his book The Emergence of Life).

The essence of this theory is that biological evolution - i.e. The emergence, development and complication of various forms of living organisms was preceded by chemical evolution - a long period in the history of the Earth associated with the emergence, complication and improvement of the interaction between elementary units, "bricks" that make up all living things - organic molecules.

Prebiological (chemical) evolution

According to most scientists (primarily astronomers and geologists), the Earth was formed as a celestial body about 5 billion years ago. by condensation of particles of a gas and dust cloud rotating around the Sun.

Under the influence of compressive forces, the particles from which the Earth is formed release a huge amount of heat. Thermonuclear reactions begin in the bowels of the Earth. As a result, the Earth gets very hot. Thus, 5 billion years ago The earth was a hot ball rushing through outer space, the surface temperature of which reached 4000-8000°C (laugh. 2).

Gradually, due to the radiation of thermal energy into outer space, the Earth begins to cool. About 4 billion years ago The earth cools so much that a hard crust forms on its surface; at the same time, light, gaseous substances escape from its bowels, rising up and forming the primary atmosphere. The composition of the primary atmosphere was significantly different from the modern one. Apparently, there was no free oxygen in the atmosphere of the ancient Earth, and its composition included substances in a reduced state, such as hydrogen (H 2), methane (CH 4), ammonia (NH 3), water vapor (H 2 O ), and possibly also nitrogen (N 2), carbon monoxide and carbon dioxide (CO and CO 2).

The reducing nature of the Earth's primary atmosphere is extremely important for the origin of life, since substances in a reduced state are highly reactive and, under certain conditions, are able to interact with each other, forming organic molecules. The absence of free oxygen in the atmosphere of the primary Earth (practically all of the Earth's oxygen was bound in the form of oxides) is also an important prerequisite for the emergence of life, since oxygen easily oxidizes and thereby destroys organic compounds. Therefore, in the presence of free oxygen in the atmosphere, the accumulation of a significant amount of organic matter on the ancient Earth would have been impossible.

About 5 billion years ago- the emergence of the Earth as a celestial body; surface temperature — 4000-8000°C

About 4 billion years ago - formation of the earth's crust and primary atmosphere

At 1000°C- in the primary atmosphere, the synthesis of simple organic molecules begins

The energy for synthesis is given by:

The temperature of the primary atmosphere is below 100 ° C - the formation of the primary ocean -

Synthesis of complex organic molecules - biopolymers from simple organic molecules:

• simple organic molecules - monomers
• complex organic molecules - biopolymers

Scheme. 2. Main stages of chemical evolution

When the temperature of the primary atmosphere reaches 1000°C, the synthesis of simple organic molecules begins in it, such as amino acids, nucleotides, fatty acids, simple sugars, polyhydric alcohols, organic acids, etc. The energy for synthesis is supplied by lightning discharges, volcanic activity, hard space radiation and, finally, the ultraviolet radiation of the Sun, from which the Earth is not yet protected by the ozone screen, and it is ultraviolet radiation that scientists consider the main source of energy for abiogenic (that is, passing without the participation of living organisms) synthesis of organic substances.

The recognition and wide dissemination of the theory of A.I. Oparin was greatly facilitated by the fact that the processes of abiogenic synthesis of organic molecules are easily reproduced in model experiments.

The possibility of synthesizing organic substances from inorganic substances has been known since the beginning of the 19th century. Already in 1828, the outstanding German chemist F. Wöhler synthesized an organic substance - urea from inorganic - ammonium cyanate. However, the possibility of abiogenic synthesis of organic substances under conditions close to those of the ancient Earth was first shown in the experiment of S. Miller.

In 1953, a young American researcher, a graduate student at the University of Chicago, Stanley Miller, reproduced in a glass flask with electrodes soldered into it the primary atmosphere of the Earth, which, according to scientists of that time, consisted of hydrogen, methane CH 4, ammonia NH, and water vapor H 2 0 (Fig. 3). Through this gas mixture, S. Miller passed electric discharges simulating thunderstorms for a week. At the end of the experiment, α-amino acids (glycine, alanine, asparagine, glutamine), organic acids (succinic, lactic, acetic, glycocolic), γ-hydroxybutyric acid and urea were found in the flask. When repeating the experiment, S. Miller managed to obtain individual nucleotides and short polynucleotide chains of five to six links.

Rice. 3. Installation by S. Miller

In further experiments on abiogenic synthesis conducted by various researchers, not only electrical discharges were used, but also other types of energy characteristic of the ancient Earth, such as cosmic, ultraviolet and radioactive radiation, high temperatures inherent in volcanic activity, as well as various options for gas mixtures, imitating the original atmosphere. As a result, almost the entire spectrum of organic molecules characteristic of living things was obtained: amino acids, nucleotides, fat-like substances, simple sugars, organic acids.

Moreover, abiogenic synthesis of organic molecules can also occur on Earth at the present time (for example, in the course of volcanic activity). At the same time, not only hydrocyanic acid HCN, which is a precursor of amino acids and nucleotides, but also individual amino acids, nucleotides, and even such complex organic substances as porphyrins can be found in volcanic emissions. Abiogenic synthesis of organic substances is possible not only on Earth, but also in outer space. The simplest amino acids are found in meteorites and comets.

When the temperature of the primary atmosphere dropped below 100 ° C, hot rains fell on the Earth and the primary ocean appeared. With streams of rain, abiogenically synthesized organic substances entered the primary ocean, which turned it, but in the figurative expression of the English biochemist John Haldane, into a dilute "primary soup". Apparently, it is in the primordial ocean that the processes of formation of simple organic molecules—monomers of complex organic molecules—biopolymers begin (see Fig. 2).

However, the processes of polymerization of individual nucleoside, amino acids and sugars are condensation reactions, they proceed with the elimination of water, therefore, the aqueous medium does not contribute to polymerization, but, on the contrary, to the hydrolysis of biopolymers (i.e., their destruction with the addition of water).

The formation of biopolymers (in particular, proteins from amino acids) could take place in the atmosphere at a temperature of about 180°C, from where they were washed into the primary ocean with atmospheric precipitation. In addition, it is possible that on the ancient Earth, amino acids were concentrated in drying up reservoirs and polymerized in a dry form under the influence of ultraviolet light and the heat of lava flows.

Despite the fact that water promotes the hydrolysis of biopolymers, the synthesis of biopolymers in a living cell occurs precisely in an aqueous medium. This process is catalyzed by special catalytic proteins - enzymes, and the energy necessary for synthesis is released during the breakdown of adenosine triphosphate - ATP. It is possible that the synthesis of biopolymers in the aquatic environment of the primary ocean was catalyzed by the surface of certain minerals. It has been experimentally shown that a solution of the amino acid alanine can polymerize in an aqueous medium in the presence of a special type of alumina. In this case, the peptide polyalanine is formed. The polymerization reaction of alanine is accompanied by the breakdown of ATP.

The polymerization of nucleotides is easier than the polymerization of amino acids. It has been shown that in solutions with a high salt concentration, individual nucleotides spontaneously polymerize, turning into nucleic acids.

The life of all modern living beings is a process of continuous interaction between the most important biopolymers of a living cell - proteins and nucleic acids.

Proteins are the "working molecules", "engineer molecules" of a living cell. Describing their role in metabolism, biochemists often use such figurative expressions as "the protein works", "the enzyme leads the reaction." The most important function of proteins is catalytic. As you know, catalysts are substances that speed up chemical reactions, but they themselves are not included in the final products of the reaction. Tanks-catalysts are called enzymes. Enzymes in bend and thousands of times accelerate metabolic reactions. Metabolism, and hence life without them, is impossible.

Nucleic acids- these are "molecules-computers", molecules are the keepers of hereditary information. Nucleic acids do not store information about all the substances of a living cell, but only about proteins. It is enough to reproduce in the daughter cell the proteins characteristic of the mother cell so that they accurately recreate all the chemical and structural features of the mother cell, as well as the nature and rate of metabolism inherent in it. Nucleic acids themselves are also reproduced due to the catalytic activity of proteins.

Thus, the mystery of the origin of life is the mystery of the emergence of the mechanism of interaction between proteins and nucleic acids. What information does modern science have about this process? What molecules were the primary basis of life - proteins or nucleic acids?

Scientists believe that despite the key role of proteins in the metabolism of modern living organisms, the first "living" molecules were not proteins, but nucleic acids, namely ribonucleic acids (RNA).

In 1982, American biochemist Thomas Check discovered the autocatalytic properties of RNA. He experimentally showed that in a medium containing a high concentration of mineral salts, ribonucleotides spontaneously (spontaneously) polymerize, forming polynucleotides - RNA molecules. On the original polynucleotide chains of RNA, as on a matrix, RNA copies are formed by pairing of complementary nitrogenous bases. The RNA template copying reaction is catalyzed by the original RNA molecule and does not require the participation of enzymes or other proteins.

What happened next is fairly well explained by what might be called "natural selection" at the molecular level. During self-copying (self-assembly) of RNA molecules, inaccuracies and errors inevitably arise. The erroneous RNA copies are copied again. When copying again, errors may occur again. As a result, the population of RNA molecules in a certain part of the primary ocean will be heterogeneous.

Since RNA decay processes are also taking place in parallel with the synthesis processes, molecules with either greater stability or better autocatalytic properties will accumulate in the reaction medium (i.e., molecules that copy themselves faster, “multiply” faster).

On some RNA molecules, as on a matrix, self-assembly of small protein fragments - peptides can occur. A protein "sheath" is formed around the RNA molecule.

Along with autocatalytic functions, Thomas Check discovered the phenomenon of self-splicing in RNA molecules. As a result of self-splicing, RNA regions that are not protected by peptides are spontaneously removed from RNA (they are, as it were, “cut out” and “ejected”), and the remaining RNA regions encoding protein fragments “grow together”, i.e. spontaneously combine into a single molecule. This new RNA molecule will already code for a large complex protein (Figure 4).

Apparently, initially protein sheaths performed primarily a protective function, protecting RNA from destruction and thereby increasing its stability in solution (this is the function of protein sheaths in the simplest modern viruses).

Obviously, at a certain stage of biochemical evolution, RNA molecules, which encode not only protective proteins, but also catalytic proteins (enzymes), sharply accelerating the rate of RNA copying, gained an advantage. Apparently, this is how the process of interaction between proteins and nucleic acids, which we now call life, arose.

In the process of further development, due to the appearance of a protein with the functions of an enzyme, reverse transcriptase, on single-stranded RNA molecules, molecules of deoxyribonucleic acid (DNA) consisting of two strands began to be synthesized. The absence of an OH group in the 2" position of deoxyribose makes DNA molecules more stable with respect to hydrolytic cleavage in slightly alkaline solutions, namely, the reaction of the medium in primary reservoirs was slightly alkaline (this reaction of the medium was also preserved in the cytoplasm of modern cells).

Where did the development of a complex process of interaction between proteins and nucleic acids take place? According to the theory of A.I. Oparin, the so-called coacervate drops became the birthplace of life.

Rice. 4. Hypothesis of the interaction of proteins and nucleic acids: a) in the process of self-copying of RNA, errors accumulate (1 - nucleotides corresponding to the original RNA; 2 - nucleotides that do not correspond to the original RNA - errors in copying); b) due to its physicochemical properties, amino acids “stick” to a part of the RNA molecule (3 - RNA molecule; 4 - amino acids), which, interacting with each other, turn into short protein molecules - peptides. As a result of self-splicing inherent in RNA molecules, the parts of the RNA molecule that are not protected by peptides are destroyed, and the remaining ones "grow" into a single molecule encoding a large protein. The result is an RNA molecule covered with a protein sheath (the most primitive modern viruses, for example, the tobacco mosaic virus, have a similar structure)

The phenomenon of coacervation consists in the fact that under certain conditions (for example, in the presence of electrolytes) macromolecular substances are separated from the solution, but not in the form of a precipitate, but in the form of a more concentrated solution - coacervate. When shaken, the coacervate breaks up into separate small droplets. In water, such drops are covered with a hydration shell (a shell of water molecules) that stabilizes them - fig. five.

Coacervate drops have some semblance of metabolism: under the influence of purely physical and chemical forces, they can selectively absorb certain substances from the solution and release their decay products into the environment. Due to the selective concentration of substances from the environment, they can grow, but when they reach a certain size, they begin to "multiply", budding small droplets, which, in turn, can grow and "bud".

The coacervate droplets resulting from the concentration of protein solutions in the process of mixing under the action of waves and wind can be covered with a lipid shell: a single membrane resembling soap micelles (with a single detachment of a droplet from the water surface covered with a lipid layer), or a double one resembling a cell membrane ( when a drop covered with a single-layer lipid membrane falls again onto the lipid film covering the surface of the reservoir - Fig. 5).

The processes of the emergence of coacervate droplets, their growth and "budding", as well as "clothing" them with a membrane from a double lipid layer are easily modeled in the laboratory.

For coacervate droplets, there is also a process of "natural selection" in which the most stable droplets remain in solution.

Despite the outward resemblance of coacervate drops to living cells, coacervate drops lack the main sign of a living thing - the ability to accurately reproduce, self-copy. Obviously, the precursors of living cells were such coacervate drops, which included complexes of replicator molecules (RNA or DNA) and the proteins they encode. It is possible that RNA-protein complexes existed for a long time outside coacervate droplets in the form of the so-called “free-living gene”, or it is possible that their formation took place directly inside some coacervate droplets.

Possible path of transition from coacervate drops to primitive flares:

a) the formation of a coacervate; 6) stabilization of coacervate drops in an aqueous solution; c) - formation of a double lipid layer around the drop, similar to a cell membrane: 1 - coacervate drop; 2 - monomolecular layer of lipid on the surface of the reservoir; 3 — formation of a single lipid layer around the drop; 4 — formation of a double lipid layer around the drop, similar to a cell membrane; d) - a coacervate drop surrounded by a double lipid layer, with a protein-nucleotide complex included in its composition - a prototype of the first living cell

From a historical point of view, the extremely complex process of the origin of life on Earth, which is not fully understood by modern science, passed extremely quickly. For 3.5 billion years, the so-called. chemical evolution ended with the appearance of the first living cells and biological evolution began.

The origin of life on Earth is one of the most difficult and at the same time topical and interesting question in modern natural science.

The Earth was formed probably 4.5-5 billion years ago from a giant cloud of cosmic dust. particles of which are compressed into a hot ball. Water vapor was released from it into the atmosphere, and water fell out of the atmosphere onto the slowly cooling Earth over millions of years in the form of rain. In the recesses of the earth's surface, the prehistoric Ocean was formed. In it, about 3.8 billion years ago, the original life was born.

Origin of life on earth

How did the planet itself come about and how did the seas appear on it? There is one widely accepted theory about this. In accordance with it, the Earth was formed from clouds of cosmic dust, containing all chemical elements known in nature, which were compressed into a ball. Hot water vapor escaped from the surface of this red-hot ball, enveloping it in a continuous cloud cover. The water vapor in the clouds slowly cooled and turned into water, which fell in the form of abundant continuous rains on the still hot, burning Earth. On its surface, it again turned into water vapor and returned to the atmosphere. Over millions of years, the Earth gradually lost so much heat that its liquid surface began to harden as it cooled. This is how the earth's crust was formed.

Millions of years have passed, and the temperature of the Earth's surface has dropped even more. Storm water stopped evaporating and began to flow into huge puddles. Thus began the impact of water on the earth's surface. And then, because of the drop in temperature, there was a real flood. Water, which had previously evaporated into the atmosphere and turned into its constituent part, continuously rushed down to the Earth, powerful showers fell from the clouds with thunder and lightning.

Little by little, in the deepest depressions of the earth's surface, water accumulated, which no longer had time to completely evaporate. There was so much of it that gradually a prehistoric Ocean was formed on the planet. Lightning cut the sky. But no one saw it. There was no life on Earth yet. The continuous downpour began to wash away the mountains. Water flowed from them in noisy streams and stormy rivers. Over millions of years, water flows have deeply corroded the earth's surface and in some places valleys have appeared. The content of water in the atmosphere decreased, and more and more accumulated on the surface of the planet.

The continuous cloud cover became thinner, until one day the first ray of the sun touched the Earth. The continuous rain is over. Most of the land was covered by the prehistoric Ocean. From its upper layers, water washed out a huge amount of soluble minerals and salts that fell into the sea. Water from it continuously evaporated, forming clouds, and the salts settled, and over time there was a gradual salinization of sea water. Apparently, under some conditions that existed in antiquity, substances were formed from which special crystalline forms arose. They grew, like all crystals, and gave rise to new crystals, which attached more and more new substances to themselves.

Sunlight and possibly very strong electrical discharges served as a source of energy in this process. Perhaps the first inhabitants of the Earth were born from such elements - prokaryotes, organisms without a formed nucleus, similar to modern bacteria. They were anaerobes, that is, they did not use free oxygen for respiration, which was not yet in the atmosphere at that time. The source of food for them was organic compounds that arose on the still lifeless Earth as a result of exposure to ultraviolet radiation from the Sun, lightning discharges and heat generated during volcanic eruptions.

Life then existed in a thin bacterial film at the bottom of reservoirs and in humid places. This era of the development of life is called the Archean. From bacteria, and possibly in a completely independent way, tiny unicellular organisms also arose - the oldest protozoa.

What did the primitive Earth look like?

Fast forward to 4 billion years ago. The atmosphere does not contain free oxygen, it is only in the composition of oxides. Almost no sounds, except for the whistle of the wind, the hiss of water erupting with lava and the impact of meteorites on the surface of the Earth. No plants, no animals, no bacteria. Maybe this is what the Earth looked like when life appeared on it? Although this problem has been of concern to many researchers for a long time, their opinions on this matter differ greatly. The conditions on the Earth of that time could be evidenced by rocks, but they have long been destroyed as a result of geological processes and movements of the earth's crust.

Theories about the origin of life on Earth

In this article, we will briefly talk about several hypotheses for the origin of life, reflecting modern scientific ideas. According to Stanley Miller, a well-known specialist in the field of the origin of life, one can speak about the origin of life and the beginning of its evolution from the moment when organic molecules self-organized into structures that could reproduce themselves. But this raises other questions: how did these molecules come about; why they could reproduce themselves and assemble into those structures that gave rise to living organisms; what are the conditions for this?

There are several theories about the origin of life on Earth. For example, one of the long-standing hypotheses says that it was brought to Earth from space, but there is no conclusive evidence for this. In addition, the life that we know is surprisingly adapted to exist precisely in terrestrial conditions, therefore, if it originated outside the Earth, then on a terrestrial-type planet. Most modern scientists believe that life originated on Earth, in its seas.

Theory of biogenesis

In the development of the teachings on the origin of life, an important place is occupied by the theory of biogenesis - the origin of the living only from the living. But many consider it untenable, since it fundamentally opposes the living to the inanimate and affirms the idea of ​​the eternity of life rejected by science. Abiogenesis - the idea of ​​the origin of living things from non-living things - is the initial hypothesis of the modern theory of the origin of life. In 1924, the famous biochemist A. I. Oparin suggested that with powerful electrical discharges in the earth's atmosphere, which 4-4.5 billion years ago consisted of ammonia, methane, carbon dioxide and water vapor, the simplest organic compounds could arise, necessary for the origin of life. Academician Oparin's prediction came true. In 1955, the American researcher S. Miller, passing electric charges through a mixture of gases and vapors, obtained the simplest fatty acids, urea, acetic and formic acids, and several amino acids. Thus, in the middle of the 20th century, the abiogenic synthesis of protein-like and other organic substances was experimentally carried out under conditions reproducing the conditions of the primitive Earth.

Panspermia theory

The theory of panspermia is the possibility of transferring organic compounds, spores of microorganisms from one cosmic body to another. But it does not at all give an answer to the question, how did life originate in the Universe? There is a need to justify the emergence of life at that point in the Universe, the age of which, according to the Big Bang theory, is limited to 12-14 billion years. Until that time, there were not even elementary particles. And if there are no nuclei and electrons, there are no chemicals. Then, within a few minutes, protons, neutrons, electrons arose, and matter entered the path of evolution.

This theory is based on multiple sightings of UFOs, rock carvings of things that look like rockets and "astronauts", and reports of alleged encounters with aliens. When studying the materials of meteorites and comets, many "precursors of life" were found in them - substances such as cyanogens, hydrocyanic acid and organic compounds, which, possibly, played the role of "seeds" that fell on the bare Earth.

Supporters of this hypothesis were Nobel Prize winners F. Crick, L. Orgel. F. Crick based on two indirect evidence: the universality of the genetic code: the need for the normal metabolism of all living beings of molybdenum, which is now extremely rare on the planet.

The origin of life on Earth is impossible without meteorites and comets

A researcher from Texas Tech University, after analyzing the vast amount of information collected, put forward a theory of how life could form on Earth. The scientist is sure that the appearance of early forms of the simplest life on our planet would have been impossible without the participation of comets and meteorites that fell on it. The researcher shared his work at the 125th annual meeting of the Geological Society of America, held on October 31 in Denver, Colorado.

The author of the work, a professor of geoscience at Texas Tech University (TTU) and curator of the museum of paleontology at the university, Sankar Chatterjee said that he came to this conclusion after analyzing information about the early geological history of our planet and comparing these data with various theories of chemical evolution.

The expert believes that this approach allows us to explain one of the most hidden and not fully understood periods in the history of our planet. According to many geologists, the bulk of space "bombardments" involving comets and meteorites occurred at a time of about 4 billion years ago. Chatterjee believes that the earliest life on Earth formed in craters left by impacts of meteorites and comets. And most likely this happened during the period of the "Late Heavy Bombardment" (3.8-4.1 billion years ago), when the collision of small space objects with our planet increased dramatically. At that time, there were several thousand cases of comets falling at once. Interestingly, this theory is indirectly supported by the Nice Model. According to it, the real number of comets and meteorites that should have fallen to the Earth at that time corresponds to the real number of craters on the Moon, which in turn was a kind of shield for our planet and did not allow the endless bombardment to destroy it.

Some scientists suggest that the result of this bombardment is the colonization of life in the oceans of the Earth. At the same time, several studies on this topic indicate that our planet has more water reserves than it should. And this surplus is attributed to comets that flew to us from the Oort Cloud, which is presumably one light year away from us.

Chatterjee points out that the craters formed by these collisions were filled with melted water from the comets themselves, as well as the necessary chemical building blocks necessary for the formation of the simplest organisms. At the same time, the scientist believes that those places where life did not appear even after such a bombardment simply turned out to be unsuitable for this.

“When the Earth formed about 4.5 billion years ago, it was completely unsuitable for the appearance of living organisms on it. It was a real boiling cauldron of volcanoes, poisonous hot gas and meteorites constantly falling on it, ”writes the online journal AstroBiology, referring to the scientist.

“And after one billion years, it became a quiet and calm planet, rich in huge reserves of water, inhabited by various representatives of microbial life - the ancestors of all living beings.”

Life on Earth could have originated from clay

A group of scientists led by Dan Luo from Cornell University came up with a hypothesis that ordinary clay could serve as a concentrator for the most ancient biomolecules.

Initially, the researchers were not concerned with the problem of the origin of life - they were looking for a way to increase the efficiency of cell-free protein synthesis systems. Instead of letting DNA and its supporting proteins float freely in the reaction mixture, the scientists tried to force them into hydrogel particles. This hydrogel, like a sponge, absorbed the reaction mixture, sorbed the necessary molecules, and as a result, all the necessary components were locked in a small volume - just as it happens in a cell.

The authors of the study then tried to use clay as an inexpensive substitute for hydrogel. Clay particles turned out to be similar to hydrogel particles, becoming a kind of microreactors for interacting biomolecules.

Having received such results, scientists could not help but recall the problem of the origin of life. Clay particles, with their ability to sorb biomolecules, could actually serve as the very first bioreactors for the very first biomolecules before they had membranes. This hypothesis is also supported by the fact that the leaching of silicates and other minerals from rocks with the formation of clay began, according to geological estimates, just before, according to biologists, the most ancient biomolecules began to combine into protocells.

In water, or rather in solution, little could happen, because the processes in solution are absolutely chaotic, and all compounds are very unstable. Clay by modern science - more precisely, the surface of particles of clay minerals - is considered as a matrix on which primary polymers could form. But this, too, is only one of many hypotheses, each with its own strengths and weaknesses. But in order to simulate the origin of life on a full scale, one must really be God. Although in the West today there are already articles with the titles "Cell Construction" or "Cell Modeling". For example, one of the last Nobel laureates, James Szostak, is now actively trying to create effective cell models that reproduce on their own, reproducing their own kind.