It is known that scientific journals try not to accept for publication articles devoted to problems that attract general attention, but do not have a clear solution - a serious publication on physics will not publish a project for a perpetual motion machine. This topic was the origin of life on Earth. The question of the emergence of living nature, the appearance of man has worried thinking people for many millennia, and only creationists - supporters of the divine origin of all things - have found a definite answer, but this theory is not scientific as it cannot be verified.
Views of the ancients
Ancient Chinese and ancient Indian manuscripts tell about the emergence of living creatures from water and rotting remains; the birth of amphibious creatures in the muddy sediments of large rivers is written in ancient Egyptian hieroglyphs and the cuneiform script of Ancient Babylon. The hypotheses of the origin of life on Earth through spontaneous generation were obvious to the sages of the distant past.
Ancient philosophers also gave examples of the emergence of animals from inanimate matter, but their theoretical justifications were of a different nature: materialistic and idealistic. Democritus (460-370 BC) found the reason for the emergence of life in the special interaction of the smallest, eternal and indivisible particles - atoms. Plato (428-347 BC) and Aristotle (384-322 BC) explained the origin of life on Earth by the miraculous influence of a higher principle on lifeless matter, infusing souls into natural objects.
The idea of the existence of some kind of “life force” that contributes to the emergence of living beings has proven to be very persistent. It shaped the views on the origin of life on Earth among many scientists who lived in the Middle Ages and later, until the end of the 19th century.
Theory of spontaneous generation
Anthony van Leeuwenhoek (1632-1723), with the invention of the microscope, made the smallest microorganisms he discovered the main subject of dispute between scientists who shared two main theories of the origin of life on Earth - biogenesis and abiogenesis. The former believed that all living things could be the product of only living things, the latter believed that the spontaneous generation of organic matter in solutions placed under special conditions was possible. The essence of this dispute has not changed to this day.
The experiments of some naturalists proved the possibility of spontaneous emergence of the simplest microorganisms; supporters of biogenesis completely denied this possibility. Louis Pasteur (1822-1895), using strictly scientific methods and the high correctness of his experiments, proved the absence of a mythical vital force transmitted through the air and generating living bacteria. However, in his works he allowed for the possibility of spontaneous generation in some special conditions, which scientists of future generations had to find out.
Theory of evolution
The works of the great Charles Darwin (1809-1882) shook the foundations of many natural sciences. The emergence of a huge diversity of biological species from one common ancestor, proclaimed by him, again made the origin of life on Earth the most important question of science. The theory of natural selection had difficulty finding its supporters in the beginning, and is now subject to critical attacks that seem quite reasonable, but it is Darwinism that lies at the basis of modern natural sciences.
After Darwin, biology could not consider the origin of life on Earth from its previous positions. Scientists from many branches of biological science were convinced of the truth of the evolutionary path of development of organisms. Although modern views on the common ancestor placed by Darwin at the base of the Tree of Life have changed in many ways, the truth of the general concept is unshakable.
Steady State Theory
Laboratory refutation of the spontaneous generation of bacteria and other microorganisms, awareness of the complex biochemical structure of the cell, together with the ideas of Darwinism, had a particular influence on the emergence of alternative versions of the theory of the origin of life on Earth. In 1880, one of the new judgments was proposed by William Preyer (1841-1897). He believed that there was no need to talk about the birth of life on our planet, since it exists forever, and it did not have a beginning as such, it is unchanging and constantly ready for rebirth in any suitable conditions.
The ideas of Preyer and his followers are of only purely historical and philosophical interest, because later astronomers and physicists calculated the timing of the final existence of planetary systems, recorded the constant but steady expansion of the Universe, i.e. it was never eternal or constant.
The desire to view the world as a single global living entity echoed the views of the great scientist and philosopher from Russia, Vladimir Ivanovich Vernadsky (1863-1945), who also had his own idea of the origin of life on Earth. It was based on the understanding of life as an integral characteristic of the Universe, the cosmos. According to Vernadsky, the fact that science could not find layers that did not contain traces of organic substances spoke of the geological eternity of life. One of the ways in which life appeared on the young planet, Vernadsky called its contacts with space objects - comets, asteroids and meteorites. Here his theory merged with another version, which explained the origin of life on Earth by the method of panspermia.
The cradle of life is space
Panspermia (Greek - “seed mixture”, “seeds everywhere”) considers life to be a fundamental property of matter and does not explain the ways of its origin, but calls the cosmos the source of the germs of life that fall on celestial bodies with conditions suitable for their “germination”.
The first mention of the basic concepts of panspermia can be found in the writings of the ancient Greek philosopher Anaxagoras (500-428 BC), and in the 18th century the French diplomat and geologist Benoit de Maillet (1656-1738) spoke about it. These ideas were revived by Svante August Arrhenius (1859-1927), Lord Kelvin William Thomson (1824-1907) and Hermann von Helmholtz (1821-1894).
The study of the cruel influence of cosmic radiation and temperature conditions of interplanetary space on living organisms made such hypotheses of the origin of life on Earth not very relevant, but with the beginning of the space age, interest in panspermia increased.
In 1973, Nobel laureate Francis Crick (1916-2004) expressed the idea of the extraterrestrial production of molecular living systems and their arrival on Earth with meteorites and comets. At the same time, he assessed the chances of abiogenesis on our planet as very low. The eminent scientist did not consider the origin and development of life on Earth by the method of self-assembly of high-level organic matter to be a reality.
Fossilized biological structures have been found in meteorites all over the planet, and similar traces have been found in soil samples brought back from the Moon and Mars. On the other hand, numerous experiments are being carried out on the treatment of biological structures with influences that are possible when they are in outer space and when passing through an atmosphere similar to the earth’s.
An important experiment was carried out in 2006 as part of the Deep Impact mission. Comet Tempel was rammed by a special impactor probe launched by an automatic device. Analysis of the cometary substance that was released as a result of the impact showed the presence of water and various organic compounds in it.
Conclusion: Since its inception, the theory of panspermia has changed significantly. Modern science interprets differently those primary elements of life that could have been delivered to our young planet by space objects. Research and experiments prove the viability of living cells during interplanetary travel. All this makes the idea of the extraterrestrial origin of earthly life relevant. The main concepts of the origin of life on Earth are theories that include panspermia either as the main part or as a method of delivering components to Earth to create living matter.
Oparin-Haldane theory of biochemical evolution
The idea of spontaneous generation of living organisms from inorganic substances has always remained almost the only alternative to creationism, and in 1924 a 70-page monograph was published, giving this idea the force of a well-developed and well-founded theory. This work was called “The Origin of Life”, its author was a Russian scientist - Alexander Ivanovich Oparin (1894-1980). In 1929, when Oparin’s works had not yet been translated into English, similar concepts of the origin of life on Earth were expressed by the English biologist John Haldane (1860-1936).
Oparin proposed that if the primitive atmosphere of the young planet Earth was reducing (that is, containing no oxygen), a powerful burst of energy (such as lightning or ultraviolet radiation) could promote the synthesis of organic compounds from inorganic matter. Subsequently, such molecules could form clots and clusters - coacervate drops, which are proto-organisms, around which water jackets are formed - the rudiments of a shell-membrane, separation occurs, generating a charge difference, which means movement - the beginning of metabolism, the rudiments of metabolism, etc. Coacervates were considered to be the basis for the beginning of the evolutionary processes that led to the creation of the first life forms.
Haldane introduced the concept of the “primordial soup” - the initial earth's ocean, which became a huge chemical laboratory connected to a powerful power source - sunlight. The combination of carbon dioxide, ammonia and ultraviolet radiation resulted in a concentrated population of organic monomers and polymers. Subsequently, such formations were combined with the appearance of a lipid membrane around them, and their development led to the formation of a living cell.
The main stages of the origin of life on Earth (according to Oparin-Haldane)
According to the theory of the emergence of the Universe from a clot of energy, the Big Bang occurred about 14 billion years ago, and about 4.6 billion years ago the creation of the planets of the solar system was completed.
The young Earth, gradually cooling, acquired a solid shell around which an atmosphere formed. The primary atmosphere contained water vapor and gases, which later served as raw materials for organic synthesis: carbon monoxide and dioxide, hydrogen sulfide, methane, ammonia, and cyanide compounds.
Bombardment by space objects containing frozen water and condensation of water vapor in the atmosphere led to the formation of the World Ocean, in which various chemical compounds dissolved. Powerful thunderstorms accompanied the formation of an atmosphere through which strong ultraviolet radiation penetrated. Under such conditions, the synthesis of amino acids, sugars and other simple organic matter occurred.
At the end of the first billion years of the Earth's existence, the process of polymerization in water of the simplest monomers into proteins (polypeptides) and nucleic acids (polynucleotides) began. They began to form prebiological compounds - coacervates (with the rudiments of the nucleus, metabolism and membrane).
3.5-3 billion years BC - the stage of formation of protobionts with self-reproduction, regulated metabolism, and a membrane with variable permeability.
3 billion years BC e. - the appearance of cellular organisms, nucleic acids, primary bacteria, the beginning of biological evolution.
Experimental evidence for the Oparin-Haldane hypothesis
Many scientists positively assessed the basic concepts of the origin of life on Earth based on abiogenesis, although from the very beginning they found bottlenecks and inconsistencies in the Oparin-Haldane theory. In different countries, work began on conducting test studies of the hypothesis, of which the most famous is the classic experiment conducted in 1953 by American scientists Stanley Miller (1930-2007) and Harold Urey (1893-1981).
The essence of the experiment was to simulate in the laboratory the conditions of the early Earth, in which the synthesis of the simplest organic compounds could occur. A gas mixture similar in composition to the primary earth's atmosphere circulated in the device. The design of the device provided an imitation of volcanic activity, and electrical discharges passed through the mixture created the effect of lightning.
After circulating the mixture through the system for a week, the transition of a tenth of carbon into organic compounds was noted, amino acids, sugars, lipids and compounds preceding amino acids were discovered. Repeated and modified experiments fully confirmed the possibility of abiogenesis in simulated conditions of the early Earth. In subsequent years, repeated experiments were carried out in other laboratories. Hydrogen sulfide was added to the composition of the gas mixture as a possible component of volcanic emissions, and other non-drastic changes were made. In most cases, the experience of synthesizing organic compounds was successful, although attempts to go further and obtain more complex elements approaching the composition of a living cell were unsuccessful.
RNA world
By the end of the 20th century, many scientists who never ceased to be interested in the problem of the origin of life on Earth, it became clear that, with all the harmony of theoretical constructions and clear experimental confirmation, the Oparin-Haldane theory has obvious, perhaps insurmountable, flaws. The main one was the impossibility of explaining the appearance in protobionts of the properties that define a living organism - to reproduce while maintaining hereditary characteristics. With the discovery of genetic cellular structures, with the determination of the function and structure of DNA, with the development of microbiology, a new candidate for the role of the molecule of primordial life appeared.
It became a ribonucleic acid molecule - RNA. This macromolecule, which is part of all living cells, is a chain of nucleotides - the simplest organic units consisting of nitrogen atoms, a monosaccharide - ribose and a phosphate group. It is the sequence of nucleotides that is the code for hereditary information, and in viruses, for example, RNA plays the role that DNA plays in complex cellular structures.
In addition, scientists have discovered the unique ability of some RNA molecules to introduce breaks in other chains or glue individual RNA elements, and some play the role of autocatalysts - that is, they contribute to rapid self-reproduction. The relatively small size of the RNA macromolecule and its simplified structure compared to DNA (one strand) made ribonucleic acid the main candidate for the role of the main element of prebiological systems.
The new theory of the emergence of living matter on the planet was finally formulated in 1986 by Walter Gilbert (born 1932), an American physicist, microbiologist and biochemist. Not all experts agreed with this view of the origin of life on Earth. Briefly called “RNA World,” the theory of the structure of the prebiological world of our planet cannot answer the simple question of how the first RNA molecule with the given properties appeared, even if a huge amount of “building material” was present in the form of nucleotides, etc.
PAH world
Simon Nicholas Platts tried to find the answer in May 2004, and in 2006 a group of scientists led by Pascale Ehrenfreund. Polyaromatic hydrocarbons have been proposed as starting materials for RNA with catalytic properties.
The world of PAHs was based on the high abundance of these compounds in visible space (they were probably present in the “primordial soup” of the young Earth) and the peculiarities of their ring-shaped structure, which facilitates rapid combination with nitrogenous bases - key components of RNA. The PAH theory once again speaks of the relevance of some provisions of panspermia.
Unique life on a unique planet
Until scientists have the opportunity to go back 3 billion years ago, the mystery of the origin of life on our planet will not be revealed - this is the conclusion that many of those who have studied this problem come to. The main concepts of the origin of life on Earth are: the theory of abiogenesis and the theory of panspermia. They may overlap in many ways, but most likely they will not be able to answer: how, in the midst of the vast cosmos, an amazingly precisely balanced system of the Earth and its satellite, the Moon, appeared, how life originated on it...
Life is the greatest miracle that exists on our planet. The problems of its study are currently occupied not only by biologists, but also by physicists, mathematicians, philosophers and other scientists. Of course, the most difficult mystery is the very origin of life on Earth.
Researchers are still arguing about how this happened. Oddly enough, philosophy has made a significant contribution to the study of this phenomenon: this science allows one to draw correct conclusions by summarizing huge amounts of information. What versions are guiding scientists around the world today? Here are the current theories of the origin of life on Earth:
- The concept of spontaneous generation.
- Creationism, or the theory of divine creation.
- The principle of stationary state.
- Panspermia, whose proponents claim the natural “productivity” of any planet where suitable conditions exist. In particular, this idea was once developed by the well-known academician Vernadsky.
- Biochemical evolution according to A.I. Oparin.
Let us consider all these theories of the origin of life on Earth in a little more detail.
Materialism and idealism
Back in the Middle Ages and earlier, in the Arab world, some scientists, even at the risk of their own lives, assumed that the world could have been created as a result of some natural processes, without the participation of a divine essence. These were the first materialists. Accordingly, all other points of view that provided for Divine intervention in the creation of all things were considered idealistic. Accordingly, it is quite possible to consider the origin of life on Earth from these two positions.
Creationists argue that life could only have been created by God, while materialists promote the theory of the emergence of the first organic compounds and life from inorganic substances. Their version is based on the complexity or impossibility of understanding those processes that resulted in life in its modern form. Interestingly, the modern Church only partially supports this hypothesis. From the point of view of the most scientist-friendly figures, it is truly impossible to understand the main Plan of the Creator, but we can determine the phenomena and processes due to which life arose. However, this is still very far from a truly scientific approach.
Currently, the materialist point of view prevails. However, they did not always put forward modern theories of the origin of life. Thus, the hypothesis that the origin and evolution of life on Earth occurred spontaneously was initially popular, and supporters of this phenomenon met at the beginning of the 19th century.
Proponents of this concept argued that there are certain laws of natural nature that determine the possibility of the arbitrary transition of inorganic compounds into organic ones with the subsequent arbitrary formation of life. This also includes the theory of the creation of a “homunculus,” an artificial person. In general, the spontaneous origin of life on Earth is still considered by some “experts” seriously... At least it’s good that they talk about bacteria and viruses.
Of course, this approach was later proven to be wrong, but it played an important role, providing a huge amount of valuable empirical material. Note that the final rejection of the version of the independent origin of life occurred only in the middle of the 19th century. In principle, the impossibility of such a process was proven by Louis Pasteur. For this, the scientist even received a considerable prize from the French Academy of Sciences. Soon the main theories of the origin of life on Earth come to the fore, which we will describe below.
Academician Oparin's theory
Modern ideas about the origin of life on Earth are based on a theory that was put forward by a domestic researcher, Academician Oparin, back in 1924. He refuted Redi's principle, which spoke about the possibility of only biogenic synthesis of organic substances, pointing out that this concept is valid only for the current state of affairs. The scientist pointed out that at the very beginning of its existence, our planet was a giant rocky ball, on which, in principle, there was no organic matter.
Oparin's hypothesis was that the origin of life on planet Earth is a long-term biochemical process, the raw materials for which are common compounds that can be found on any planet. The academician suggested that the transition of these substances into more complex ones was possible under the influence of extremely strong physical and chemical factors. Oparin was the first to put forward a hypothesis about the continuous transformation and interaction of organic and inorganic compounds. He called it "biochemical evolution." Below are the main stages of the origin of life on Earth according to Oparin.
Stage of chemical evolution
About four billion years ago, when our planet was a huge and lifeless rock in the depths of space, the process of non-biological synthesis of carbon compounds was already underway on its surface. During this period, volcanoes emitted titanic amounts of lava and hot gases. Cooling in the primary atmosphere, the gases turned into clouds, from which torrential rains fell incessantly. All these processes took place over millions of years. But, excuse me, when did the origin of life on Earth begin?
At the same time, the showers gave rise to huge primary oceans, the waters of which were extremely saturated with salts. The first organic compounds got there, the formation of which took place in the atmosphere under the influence of strong electrical discharges and UV irradiation. Gradually their concentration increased until the seas turned into a kind of “broth” saturated with peptides. But what happened next and how did the first cells arise from this “soup”?
Formation of protein compounds, fats and carbohydrates
And only at the second stage do true proteins and other compounds from which life is built appear in the “broth”. Conditions on Earth softened, carbohydrates, proteins and fats, the first biopolymers, and nucleotides appeared. This is how coacervate droplets formed, which were the prototype of real cells. Roughly speaking, this was the name given to drops of proteins, fats, and carbohydrates (as in soup). These formations could absorb and absorb those substances that were dissolved in the waters of the primary oceans. At the same time, a peculiar evolution took place, the result of which were drops with increased resistance and stability to environmental influences.
Appearance of the first cells
Actually, at the third stage, this amorphous formation turned into something more “meaningful.” That is, into a living cell capable of the process of self-reproduction. The natural selection of drops, which we have already discussed above, became more and more stringent. The first “advanced” coacervates already had, albeit primitive, metabolism. Scientists suggest that the drop, having reached a certain size, disintegrated into smaller formations that had all the features of the mother “cell”.
Gradually, a layer of lipids appeared around the core of the coacervate, giving rise to a full-fledged cell membrane. This is how the primary cells, archecells, were formed. It is this moment that can rightfully be considered as the origin of life on Earth.
Is non-biological synthesis of organic matter real?
As for the hypothesis of the origin of life on Earth from Oparin... Many people immediately have a question: “How realistic is the formation of organic matter from inorganic matter under natural conditions?” Many researchers have had such thoughts!
In 1953, American scientist Miller modeled the Earth's primordial atmosphere, with its incredible temperatures and electrical discharges. Simple inorganic compounds were placed in this medium. As a result, acetic and formic acids and other organic compounds were formed there. This is how the origin of life on Earth took place. Briefly, this process can be characterized by the philosophical law of “Transition of quantity into quality.” Simply put, with the accumulation of a certain amount of proteins and other substances in the primary ocean, these compounds acquire different properties and the ability to self-organize.
Strengths and weaknesses of Oparin's theory
The concept we have considered has not only strong but also weak points. The strength of the theory is its logic and experimental confirmation of the abiotic synthesis of organic compounds. In principle, this could be the origin and development of life on Earth. A huge weakness is the fact that so far no one can explain how coacervates were able to degenerate into a complex biological structure. Even supporters of the theory admit that the transition from a protein-fat drop to a full-fledged cell is very doubtful. We are probably missing something by not taking into account factors unknown to us. Currently, all scientists recognize that there was some kind of sharp jump, as a result of which the self-organization of matter became possible. How could this even happen? It is still unclear... What other main theories of the origin of life on Earth exist?
Theory of panspermia and steady state
As we have already said, at one time this version was ardently supported and “promoted” by the famous academician Vernadsky. In general, the theory of panspermia cannot be discussed in isolation from the concept of a stationary state, since they consider the principle of the origin of life from the same point of view. You should know that this concept was first proposed by the German Richter at the end of the 19th century. In 1907, he was supported by the Swedish researcher Arrhenius.
Scientists who adhere to this concept believe that life simply existed in the Universe and will always exist. It is transferred from planet to planet with the help of comets and meteorites, which play the role of peculiar “seeds”. The disadvantage of this theory is that the Universe itself is believed to have formed approximately 15-25 billion years ago. It doesn't look like Eternity at all. Considering that the planets potentially suitable for the formation of life are many times smaller than ordinary rocky planetoids, it is quite natural for the question to arise: “When and where did life form and how did it spread throughout the Universe at such a speed, taking into account the unrealistic distances?”
It should be remembered that the age of our planet is no more than 5 billion years. Comets and asteroids fly much slower than the speed of light, so they simply might not have enough time to plant the “seeds” of life on Earth. Proponents of panspermia suggest that certain seeds (spores of microorganisms, for example) are transported “on light rays” at an appropriate speed... But decades of spacecraft have made it possible to prove that there are quite a few free particles in space. The probability of this method of spreading living organisms is too low.
Some researchers today suggest that any planet that is suitable for life may eventually form protein bodies, but the mechanism of this process is unknown to us. Other scientists say that in the Universe, perhaps, there are some “cradles”, planets on which life can form. It sounds, of course, like some kind of science fiction... However, who knows. In recent years, here and abroad, a theory has gradually begun to take shape, the provisions of which speak about the information initially encoded in the atoms of substances...
Allegedly, these data provide the very impetus that leads to the transformation of the simplest coacervates into archecells. If we think logically, then this is the same theory of the spontaneous origin of life on Earth! In general, the concept of panspermia is difficult to consider as a complete scientific thesis. Its supporters can only say that life was brought to Earth from other planets. But how did it form there? There is no answer to this.
"Gift" from Mars?
Today it is known for certain that there was indeed water on the Red Planet and there were all conditions favorable to the development of protein life. The data that confirms this was obtained thanks to the work on the surface of two landers at once: Spirit and Curiosity. But scientists are still passionately arguing: was there life there? The fact is that information received from the same rovers indicates the short-term (in geological aspect) existence of water on this planet. How high is the probability that, in principle, full-fledged protein organisms managed to develop there? Again, there is no answer to this question. Again, even if life came to our planet from Mars, this in no way explains the process of its development there (which we have already written about).
So, we have examined the basic concepts of the origin of life on Earth. Which of them are absolutely true is unknown. The problem is that there is not yet a single experimentally confirmed test that could confirm or refute at least Oparin’s concept, not to mention other theses. Yes, we can synthesize protein without any problems, but we cannot obtain protein life. So scientists have work in store for many decades to come.
There is another problem. The fact is that we are intensely searching for carbon-based life and trying to understand exactly how it came to be. What if the concept of life is much broader? What if it could be based on silicon? In principle, this point of view does not contradict the principles of chemistry and biology. So on the way to finding answers we are met with more and more new questions. Currently, scientists have put forward several fundamental theses, guided by which people are looking for potentially habitable planets. Here they are:
- The planet must orbit in the so-called “comfort zone” around the star: its surface should not be too hot or too cold. In principle, at least one or two planets in each star system meet this requirement (Earth and Mars, in particular).
- The mass of such a body should be average (within one and a half times the size of the Earth). Planets that are too large either have unrealistically high gravity or are gas giants.
- More or less highly organized life can only exist near fairly old stars (at least three to four billion years old).
- The star should not seriously change its parameters. It is useless to look for life near white dwarfs or red giants: if it was there, it would have died long ago due to extremely unfavorable environmental conditions.
- It is desirable that the star system be single. In principle, modern researchers object to this thesis. It is possible that a binary system with two stars located at opposite ends could contain even more potentially habitable planets. Moreover, today there is more and more talk that somewhere on the outskirts of the solar system there is a gas-dust cloud, the forerunner of the unborn second Sun.
Final conclusions
So, what can we say in conclusion? First, we urgently lack data on the exact environmental conditions on the newly formed Earth. To obtain this information, ideally one should observe the development of a planet that is similar to ours in other respects. In addition, researchers are still finding it difficult to say exactly what factors stimulate the transition of coacervate archecapelles into full-fledged cells. Perhaps further in-depth studies of the genome of living beings will provide some answers.
There is a hypothesis about the possible introduction of bacteria, microbes and other small organisms through celestial bodies. Organisms developed and, as a result of long-term transformations, life gradually appeared on Earth. The hypothesis considers organisms that can function even in oxygen-free environments and in abnormally high or low temperatures.
This is due to the presence of migrating bacteria on asteroids and meteorites, which are fragments from collisions of planets or other bodies. Due to the presence of a wear-resistant outer shell, as well as the ability to slow down all life processes (sometimes turning into a spore), this kind of life is capable of moving for a very long time and over very long distances.
When they find themselves in more hospitable conditions, “intergalactic travelers” activate basic life-support functions. And without realizing it, over time they form life on Earth.
The fact of the existence of synthetic and organic substances today is undeniable. Moreover, back in the nineteenth century, the German scientist Friedrich Wöhler synthesized an organic substance (urea) from an inorganic substance (ammonium cyanate). Hydrocarbons were then synthesized. Thus, life on planet Earth very likely arose through synthesis from inorganic material. Through abiogenesis, theories of the origin of life are put forward.
Since the main role in the structure of any organic organism is played by amino acids. It would be logical to assume their involvement in the settlement of life on the Earth. Based on the data obtained from the experiment of Stanley Miller and Harold Urey (the formation of amino acids by passing an electric charge through gases), we can talk about the possibility of the formation of amino acids. After all, amino acids are the building blocks with the help of which complex systems of the body and any life are built, respectively.
Cosmogonic hypothesis
Probably the most popular interpretation of all, which every schoolchild knows. The Big Bang Theory has been and remains a very hot topic for heated discussions. The Big Bang occurred from a singular point of accumulation of energy, as a result of the release of which the Universe expanded significantly. Cosmic bodies were formed. Despite all its consistency, the Big Bang Theory does not explain the formation of the Universe itself. As, in fact, no existing hypothesis can explain.
Symbiosis of organelles of nuclear organisms
This version of the origin of life on Earth is also called endosymbiosis. The clear provisions of the system were drawn up by the Russian botanist and zoologist K. S. Merezhkovsky. The essence of this concept is the mutually beneficial coexistence of an organelle with a cell. Which in turn suggests endosymbiosis as a symbiosis beneficial for both parties with the formation of eukaryotic cells (cells in which a nucleus is present). Then, using the transfer of genetic information between bacteria, their development and population increase were carried out. According to this version, all further development of life and life forms is due to the previous ancestor of modern species.
Spontaneous generation
This kind of statement in the nineteenth century could not but be perceived without a grain of skepticism. The sudden appearance of species, namely the formation of life from non-living things, seemed fantastic to the people of that time. Moreover, heterogenesis (a method of reproduction, as a result of which individuals are born that are very different from their parents) was recognized as a reasonable explanation of life. A simple example would be the formation of a complex viable system from decomposing substances.
For example, in the same Egypt, Egyptian hieroglyphs report the emergence of diverse life from water, sand, decomposing and rotting plant remains. This news would not have surprised the ancient Greek philosophers at all. There, the belief about the origin of life from non-living things was perceived as a fact that did not require justification. The great Greek philosopher Aristotle spoke about visible truth: “Aphids are formed from rotten food, Crocodile is the result of processes in rotting logs under water.” It’s mysterious, but despite all sorts of persecution from the church, the conviction, hidden in the bosom of secrecy, lived for a whole century.
The debate about life on Earth cannot continue forever. That is why, at the end of the nineteenth century, the French microbiologist and chemist Louis Pasteur carried out his analyzes. His research was strictly scientific in nature. The experiment was carried out in 1860-1862. Thanks to the removal of spores from a sleepy state, Pasteur was able to solve the question of the spontaneous generation of life. (For which he was awarded a prize by the French Academy of Sciences)
Creation of things from ordinary clay
It sounds crazy, but in reality this topic has the right to life. It’s not for nothing that the Scottish research scientist A.J. Cairns-Smith put forward the protein theory of life. Firmly building on the basis of similar studies, he spoke of the interaction at the molecular level between organic components and simple clay... Under its influence, the components formed stable systems in which changes occurred in the structure of both components, and then the formation of wealthy life. This is how Kerns-Smith explained his position in such a unique and original way. Clay crystals, with biological inclusions in it, gave rise to life together, after which their “cooperation” ended.
The theory of constant catastrophes
According to the concept developed by Georges Cuvier, the world that can be seen right now is not at all primary. What it is is just another link in a successively breaking chain. This means we live in a world that will eventually undergo a mass extinction of life. At the same time, not everything on Earth was subjected to global destruction (for example, a flood occurred). Some species, in the course of their adaptability, survived, thereby populating the Earth. The structure of species and life, according to Georges Cuvier, remained unchanged.
Matter as an objective reality
The main theme of the teaching is various areas and areas that bring closer to the understanding of evolution from the point of view of the exact sciences. (materialism is a worldview in philosophy that reveals all cause-and-effect circumstances, phenomena and factors of reality. The laws apply to man, society, and the Earth). The theory was put forward by well-known adherents of materialism, who believe that life on Earth originated from transformations at the level of chemistry. Moreover, they took place almost 4 billion years ago. The explanation of life has a direct connection with DNA, (deoxyribonucleic acid) RNA (ribonucleic acid), as well as some HMCs (high molecular weight compounds, in this case proteins.)
The concept was formed through scientific research that reveals the essence of molecular and genetic biology and genetics. The sources are reputable, especially considering their youth. After all, research into the hypothesis about the RNA world began to be carried out at the end of the twentieth century. Carl Richard Woese made a huge contribution to the theory.
Charles Darwin's teachings
Speaking about the origin of species, it is impossible not to mention such a truly brilliant person as Charles Darwin. His life's work, natural selection, marked the beginning of mass atheist movements. On the other hand, it gave an unprecedented impetus to science, inexhaustible soil for research and experimentation. The essence of the teaching was the survival of species throughout history, through the adaptation of organisms to local conditions, the formation of new characteristics that help in competitive conditions.
Evolution refers to certain processes aimed at changing the life of an organism and the organism itself over time. By hereditary traits, they mean the transfer of behavioral, genetic, or other types of information (transfer from mother to daughter.)
The main forces of evolution, according to Darwin, is the struggle for the right to exist through selection and variability of species. Under the influence of Darwinian ideas, at the beginning of the twentieth century, research was actively carried out in ecology, as well as genetics. The teaching of zoology changed radically.
God's creation
Many people from all over the globe still profess faith in God. Creationism is an interpretation of the formation of life on Earth. The interpretation consists of a system of statements based on the Bible and views life as a creature created by a creator god. Data is taken from the “Old Testament”, “Gospel” and other sacred scriptures.
Interpretations of the creation of life in different religions are somewhat similar. According to the Bible, the Earth was created in seven days. The sky, heavenly lights, water and the like took five days to be created. On the sixth, God created Adam from clay. Seeing a bored, lonely man, God decided to create another miracle. Taking Adam's rib, he created Eve. The seventh day was recognized as a day off.
Adam and Eve lived without troubles, until the malicious devil in the form of a snake decided to tempt Eve. After all, in the middle of paradise stood the tree of the knowledge of good and evil. The first mother invited Adam to share the meal, thereby breaking the word given to God (he forbade touching the forbidden fruits.)
The first people are expelled into our world, thereby beginning the history of all humanity and life on Earth.
The origin of life on Earth is one of the most important problems of natural science. Even in ancient times, people asked themselves questions about where living nature came from, how life appeared on Earth, where is the line of transition from lifeless to life, etc. Over the course of dozens of centuries, views on the problem of life have changed, different ideas, hypotheses and concepts have been expressed. This question worries humanity to this day.
Some ideas and hypotheses about the origin of life became widespread during different periods in 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, that is, God.
2. The steady state hypothesis, according to which life has always existed.
3. The hypothesis of the spontaneous generation of life, which is based on the idea of the repeated emergence of life from nonliving matter.
4. The panspermia hypothesis, according to which life was brought to Earth from outer space.
5. Hypothesis of the historical origin of life through biochemical evolution.
According to creationist hypothesis which has the longest history, the creation of life is an act of divine creation. Evidence of this is the presence in living organisms of a special force, a “soul” that controls all life processes. The creationism hypothesis is inspired by religious views and has nothing to do with science.
According to steady state hypothesis, life never arose, but existed forever along with the Earth, distinguished by a great variety of living things. As living conditions on Earth changed, species also changed: some disappeared, others appeared. This hypothesis is based mainly on paleontological studies. In its essence, this hypothesis does not relate to the concepts of the origin of life, since it does not fundamentally affect the question of the origin of life.
Spontaneous origin of life hypothesis was put forward in ancient China and India as an alternative to creationism. The ideas of this hypothesis were supported by thinkers of Ancient Greece (Plato, Aristotle), as well as scientists of the modern period (Galileo, Descartes, Lamarck). According to this hypothesis, living organisms (lower) can appear by spontaneous generation from non-living matter containing some kind of “active principle”. So, for example, according to Aristotle, insects and frogs, under certain conditions, can grow in silt and damp soil; worms and algae in stagnant water, but fly larvae in rotten meat as it rots.
However, already from the beginning of the 17th century. This understanding of the origin of life began to be questioned. A significant blow to this hypothesis was dealt by the Italian naturalist and physician F. Redi (1626–1698), who in 1688 revealed the essence of the emergence of life in rotting meat. F. Redi formulated his principle: “All living things come from living things” and became the founder of the concept of biogenesis, which argued that life can only arise from previous life.
The French microbiologist L. Pasteur (1822–1895) with his experiments with viruses finally proved the inconsistency of the idea of the spontaneous generation of life. However, having refuted this hypothesis, he did not propose his own and did not shed light on the question of the origin of life.
Nevertheless, the experiments of L. Pasteur were of great importance in obtaining rich empirical material in the field of microbiology of his time.
Panspermia hypothesis– about the unearthly origin of life by bringing the “embryos of life” from space to Earth – was first expressed by the German biologist and physician G. Richter at the end of the 19th century. The concept of panspermia (from the Greek. pan- all, sperma– seed) allows for the possibility of the origin of life at different times in different parts of the Universe and its transfer in different ways to Earth (meteorites, asteroids, cosmic dust).
Indeed, some data have now been obtained indicating the possibility of the formation of organic substances by chemical means in space conditions. Thus, in 1975, amino acid precursors were found in lunar soil. The simplest carbon compounds, including those close to amino acids, have been discovered in interstellar clouds. Aldehydes, water, alcohols, hydrocyanic acid, etc. were found in meteorites.
The concept of panspermia was shared by the largest scientists of the late 19th and early 20th centuries: the German chemist and agronomist J. Liebig, the English physicist W. Thomson, the German naturalist G. Helmholtz, and the Swedish physical chemist S. Arrhenius. In 1907, S. Arrhenius even described in his writings how living spores of organisms escape from other planets into outer space with dust particles. Rushing through the vast expanses of space under the influence of starlight pressure, they ended up on planets and, where there were favorable conditions (including on Earth), began a new life. The ideas of panspermia were also supported by some Russian scientists: geophysicist P. Lazarev, biologist L. Berg, soil biologist S. Kostychev.
There is an idea about the emergence of life on Earth almost from the moment of its formation. As you know, the Earth was formed about 5 billion years ago. This means that life could have arisen during the formation of the Solar System, that is, in space. Since the duration of the evolution of the Earth and life on it varies slightly, there is a version that life on Earth is a continuation of its eternal existence. This position is close to the theory of the eternal existence of life in the Universe. On the scale of the global evolutionary process, we can believe that the emergence of life on Earth may apparently coincide with the formation and existence of matter. Academician V. Vernadsky shared the idea of the eternity of life not in the context of its redistribution in space, but in the sense of the inseparability and interconnectedness of matter and life. He wrote that “life and matter are inseparable, interconnected and there is no temporal sequence between them.” The Russian biologist and geneticist Timofeev-Resovsky (1900-1982) points to the same idea. In his brief outline of the theory of evolution (1977), he wittily observed: “We are all such materialists that we are all madly concerned about how life came to be. At the same time, we hardly care how matter arose. Everything is simple here. Matter is eternal, it has always been, and no questions are needed. Always was. But life, you see, must necessarily arise. Or maybe she has always been there too. And there’s no need for questions, it’s just always been there, that’s all.”
To substantiate panspermia, popular science literature provides “facts” about unidentified flying objects, the arrival of aliens on Earth, and rock topological paintings.
However, this concept does not have serious evidence, and many arguments oppose it. It is known that the range of living conditions for the existence of living things is quite narrow. Therefore, it is unlikely that living organisms would survive in space under the influence of ultraviolet rays, X-rays and cosmic radiation. But the possibility of introducing certain prerequisite factors of life onto our planet from space cannot be ruled out. It should be noted that this is not of fundamental importance, since the concept of panspermia does not fundamentally solve the problem of the origin of life, but only transfers it beyond the Earth, without revealing the very mechanism of its formation.
Thus, none of the four hypotheses listed has so far been confirmed by reliable experimental studies.
The fifth hypothesis looks the most convincing from the point of view of modern science - hypothesis of the origin of life in the historical past as a result of biochemical evolution. Its authors are the domestic biochemist, academician A. Oparin (1923) and the English physiologist S. Haldane (1929). We will discuss this hypothesis in detail in the next section.
Hypothesis of the origin of life in the historical past as a result of biochemical evolution by A. I. Oparin
From the point of view of A. Oparin’s hypothesis, as well as from the point of view 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. Life is a property of matter that appeared on Earth at a certain point in its history. This is the result of processes that take place first for many billions of years on the scale of the Universe, and then for hundreds of millions of years on Earth.
A. Oparin identified several stages of biochemical evolution, the ultimate goal of which was a primitive living cell. Evolution proceeded according to the following scheme:
1. Geochemical evolution of planet Earth, the synthesis of the simplest compounds, such as CO 2, 1 h[H 3, H 2 0, 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.
2. The formation of organic substances - amino acids - from inorganic compounds and their accumulation in the primary ocean as a result of the electromagnetic influence of the Sun, cosmic radiation and electrical discharges.
3. Gradual complication of organic compounds and the formation of protein structures.
4. Isolation of protein structures from the medium, formation of aqueous complexes and creation of an aqueous shell around proteins.
5. The fusion of such complexes and the formation of coacervates (from lat. coacervus– clot, heap, accumulation) capable of exchanging matter and energy with the environment.
6. Absorption of metals by coacervates, which led to the formation of enzymes that accelerate biochemical processes.
7. Formation of hydrophobic lipid boundaries between coacervates and the external environment, which led to the formation of semi-permeable membranes, which ensured the stability of the functioning of the coacervate.
8. Development in the course of evolution in these formations of processes of self-regulation and self-reproduction.
Thus, according to A. Oparin’s hypothesis, a primitive form of living matter appeared. This, in his opinion, is the prebiological evolution of matter.
Academician V. Vernadsky associated the emergence of life with a powerful leap that interrupted the lifeless evolution of the earth's crust. This leap (bifurcation) introduced so many contradictions into evolution that they created the conditions for the origin of life.
Problem origin of life on Earth has long interested and worried people. There are several hypotheses about the origin of life on our planet:
life was created by God;
life on Earth was brought from outside;
living things on the planet have repeatedly spontaneously generated from non-living things;
life has always existed;
life arose as a consequence of the biochemical revolution.
The whole variety of different hypotheses comes down to two mutually exclusive points of view. Proponents of the theory of biogenesis believed that all living things come only from living things. Their opponents defended the theory of abiogenesis - they believed that the origin of living things from non-living things was possible.
Many scientists assumed the possibility of spontaneous generation of life. The impossibility of the spontaneous generation of life was proven by Louis Pasteur.
The second stage is the formation of proteins, fats, carbohydrates, and nucleic acids from simple organic compounds in the waters of the primary ocean. The isolated molecules of these compounds concentrated and formed coacervates, acting as open systems capable of exchange of substances with the environment and growth.
The third stage - as a result of the interaction of coacervates with nucleic acids, the first living beings were formed - probionts, capable, in addition to growth and metabolism, of self-reproduction.
