Theory of the origin of life on Earth, proposed in 1924 by an outstanding Russian scientist, later an academician A.I. Oparin (1894-1980; fig. 78) was widely known.
The first stage, according to this theory, consisted in the formation of organic substances from inorganic ones. The reality of this stage was experimentally confirmed by American scientists S. Miller(1930-2007) and G. Urey(1893-1981) in 1953. By acting with electric charges on substances characteristic of the early atmosphere of the Earth, they obtained a whole mixture of several dozen organic compounds - organic acids (including amino acids), nitrogenous bases, carbohydrates and others. Even more actively stimulated the synthesis of organic substances from inorganic ultraviolet radiation. As a result, the World Ocean of the early Earth became a "primordial soup", i.e. a solution of organic substances in water. However, these substances themselves are not yet life. Let us remind you that its chemical basis is made up of biopolymers - proteins, nucleic acids, polysaccharides and their derivatives, which are composed of amino acids, nucleotides and monosaccharides. In order for biopolymers to arise, energy-consuming processes (for example, with the participation of ATP) are necessary, as well as DNA, RNA and enzymes, which are themselves products of such a process.
The second stage, according to Oparin's theory, is the stage of the emergence of life. So, he showed that in solutions of organic compounds, coacervates- small droplets, limited by a semi-permeable shell - the primary membrane. Organic substances can be concentrated in coacervates, reactions and metabolism with the environment are faster in them. They can even divide like bacteria. Experimentally, this assumption of Oparin was confirmed by an American researcher S. Fox(1912-1998), who called these droplets microspheres. material from the site
The third stage, according to Oparin, was that a primary gene could form in coacervates, carrying information about the first protein. Probably, the properties of heredity and even natural selection were inherent in such droplets-coacervates, because the more adapted and improved of them survived. As a result of this selection, life on Earth has chosen asymmetric organic molecules of amino acids and sugars. Such molecules are also called chiral. They are similar to each other, like the right hand of a person to the left (Fig. 79), that is, they are mirror images of each other. They were called right and left. The amino acids that make up the proteins of terrestrial organisms are always left-handed, and the carbohydrates (ribose and deoxyribose) that make up nucleic acids are always right-handed. It has been experimentally proven that coacervates-microspheres from asymmetric biopolymers grew faster than symmetrical ones and displaced them. However, as A. Einstein emphasized, the fact that we have left amino acids and right carbohydrates can be explained by mere chance.
It is easy to see that the assumption about the first stages of the emergence of life on Earth, according to Oparin's theory, has been proven experimentally, but the last stage is hypothetical. At the final stage, protein biosynthesis arose - a process that is characteristic of even the most primitive microorganisms. Its mechanism has not changed in the entire history of the Earth.
On this page, material on the topics:
Examples of irreversible and reversible processes from different areas of natural science
Briefly about Oparin's report on the origin of life on earth
How proteins polysaccharides are organized in terms of asymmetry
The theory of Academician Oparin. briefly
Theory of oparin report briefly
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The first scientific theory regarding the origin of living organisms on Earth was created by the Soviet biochemist A. I. Oparin (b. 1894). 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:
1. The emergence of organic substances.
2. The formation of biopolymers (proteins, nucleic acids, polysaccharides, lipids, etc.) from simpler organic substances.
3. 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 (4000 - 80000C). 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. When the Earth's temperature dropped below 1000C, water vapor began to condense, forming the world's oceans. At this time, in accordance with the ideas of A. I. Oparin, abiogenic synthesis took place, that is, in the original earth's oceans saturated with various simple chemical compounds, "in the primary soup" under the influence of volcanic heat, lightning discharges, intense ultraviolet radiation and other factors environment began the synthesis of more complex organic compounds, and then biopolymers. 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 Latin coacervus - clot, heap) and the environment, lipid molecules were 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.
A. I. Oparin’s system of views was called the “coacervate hypothesis”.
The theory was substantiated, except for one problem, which for a long time turned a blind eye to almost all experts in the field of the origin of life. If single successful constructions of protein molecules (for example, effective catalysts that provide an advantage for this coacervate in growth and reproduction) arose spontaneously, by means of random template-free syntheses in a coacervate, how could they be copied for distribution within the coacervate, and even more so for transmission to descendant coacervates? The theory has been unable to offer a solution to the problem of exact reproduction - within the coacervate and in generations - of single, randomly appearing effective protein structures.
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There are different points of view on the problem of the origin of life on Earth. For example, according to Vernadsky, it appeared simultaneously with the formation of the Earth. Richter believed that life was brought from space (the concept of panspermia). At present, the hypothesis formulated by the Soviet scientist Acad. A. I. Oparin and the English scientist J. Haldane. It proceeds from the assumption of the gradual emergence of life on Earth from inorganic substances through a long abiogenic (non-biological) molecular evolution. The views of these scientists are a generalization of evidence for the emergence of life on Earth as a result of a natural process of transition of the chemical form of the movement of matter into a biological one (Formation of simple organic compounds.) To justify this, they consider the conditions that existed on the planet several billion years ago: At the initial stages of their history The earth represented a hot planet. As a result of rotation with a gradual decrease in t, the atoms of heavy elements moved to the center, and atoms of light elements (hydrogen, carbon, oxygen, nitrogen) concentrated on the surface. With further cooling of the planet, chemical compounds appeared: methane, carbon dioxide, ammonia, hydrogen cyanide, oxygen, nitrogen, etc. Physical and chem. Holy Islands of water and carbon allowed them to stand out and find themselves at the cradle of life. At these initial stages, a primary atmosphere was formed, which was of a reducing nature, after which a second atmosphere formed in its place, consisting of the most chemically active gases. A further decrease in temperature led to the transition of a number of gaseous compounds into a liquid and solid state, i.e. formation of the earth's crust. As a result of active volcanic activity, a lot of hot mass containing carbon was brought to the surface from the inner layers of the Earth. It got into the ocean and formed hydrocarbon compounds. So the simplest organic compounds accumulated on the surface, and eventually, under the influence of synthesis, the energy of the Sun, they formed the primary broth in which life could arise.
Origin of life. The theory of panspermia. Theory of eternity of life.
There are several hypotheses that explain the emergence of life on Earth in different ways: 1. Creationism - the divine creation of living things; 2. the concept of multiple spontaneous generation of life from non-living matter (its supporter was Aristotle, who believed that life could also arise as a result of soil decomposition); 3. the concept of the origin of life as a result of processes that are subject to physical. and chem. laws; 4. the concept of a stationary state, according to which life is noun. forever; 5. the concept of panspermia - an extraterrestrial origin of life. A special place in natural science is given to the last two. According to panspermia hypothesis , life is brought from space either in the form of spores of microorganisms, or by deliberately “populating” the planet with intelligent aliens from other worlds. There is no direct evidence for this. And the theory of panspermia itself does not offer any mechanism for explaining the primary. the emergence of life and transfers the problem to another place in the universe. Liebig believed that the atmospheres of celestial bodies, as well as rotating cosmic nebulae, can be regarded as age-old repositories of a lively form, as eternal plantations of organic matter. germs, from where life is dispersed in the form of these germs in the Universe. In 1865 a German doctor G. Richter put forward the hypothesis of cosmozoans (cosmic germs), according to which life is eternal and the germs that inhabit the world space can be transferred from one planet to another. His hypothesis was supported by many eminent scientists. Kelvin, Helmholtz, and others thought in a similar way. At the beginning of our century, Arrhenius came up with the idea of radiopanspermia. He described how, from planets inhabited by other beings, particles of matter, dust grains, and living spores of microorganisms leave for the world space. They maintain their viability by flying in the space of the Universe due to light pressure. Once on a planet with suitable conditions for life, these disputes begin a new life on it. To justify panspermia, cave paintings resembling living organisms or the appearance of UFOs are usually used. Supporters theories of eternity of life (de Chardin and others) believe that on the ever-existing Earth, some species were forced to become extinct or dramatically change their numbers in certain places on the planet due to changes in external conditions. A clear concept on this path has not been developed, since there are some gaps and ambiguities in the paleontological record of the Earth. According to Chardin, at the moment of the origin of the universe, God merged with matter and gave it a vector of development. That. we see that this concept interacts closely with creationism.
It is known that scientific journals try not to accept for publication articles devoted to problems that attract everyone's attention, but do not have a clear solution - a serious publication in physics will not publish a perpetual motion machine project. This topic was the origin of life on Earth. The question of the origin of living nature, the appearance of man has been worrying thinking people for many millennia, and only creationists, supporters of the divine origin of all things, have found an unequivocal answer for themselves, but this theory is not scientific as unverifiable.
Views of the ancients
Ancient Chinese and Indian manuscripts tell about the appearance of living beings from water and rotting remains, about the birth of amphibious creatures in the muddy deposits of large rivers, it is written in ancient Egyptian hieroglyphs and the cuneiform 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 appearance 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 a 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 effect on lifeless matter of a higher principle that instills the soul into objects of nature.
The idea of the existence of some kind of "life force" that contributes to the emergence of living beings turned out to be very persistent. It formed 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 discovered by him the main subject of controversy between scientists who shared two main theories of the origin of life on Earth - biogenesis and abiogenesis. The former believed that all living things can be the product of only living things, the latter believed that spontaneous generation of organic matter in solutions placed under special conditions is possible. The essence of this dispute has not changed so far.
The experiments of some naturalists proved the possibility of the spontaneous emergence of the simplest microorganisms, the supporters of biogenesis completely denied such a possibility. Louis Pasteur (1822-1895), by strictly scientific methods, by the high correctness of his experiments, proved the absence of a mythical life force that is transmitted through the air and generates living bacteria. However, in his works, he admitted the possibility of spontaneous generation in some special conditions, which scientists of future generations had to find out.
Evolution theory
The works of the great Charles Darwin (1809-1882) shook the foundations of many natural sciences. The emergence of a huge variety of biological species from one common ancestor, proclaimed by him, again made the origin of life on Earth the most important issue of science. The theory of natural selection, at first, had difficulty finding its supporters, and is now being subjected to critical attacks that look quite reasonable, but it is Darwinism that underlies the modern natural sciences.
After Darwin, biology could not consider the origin of life on Earth from the same positions. Scientists in 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 respects, the truth of the general concept is unshakable.
Steady State Theory
The laboratory refutation of spontaneous spontaneous generation of bacteria and other microorganisms, the awareness of the complex biochemical structure of the cell, together with the ideas of Darwinism, had a particular impact 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 had no beginning as such, it is unchanging and constantly ready for rebirth in any suitable conditions.
The ideas of Preyer and his followers are only of purely historical and philosophical interest, because in the future, astronomers and physicists calculated the terms of the finite existence of planetary systems, fixed a constant but steady expansion of the Universe, i.e. it was never either eternal or constant.
The desire to consider 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 a young planet, Vernadsky called her contacts with space objects - comets, asteroids and meteorites. Here his theory merges 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 occurrence, but calls space the source of life germs 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 on living organisms of cosmic radiation and the temperature conditions of interplanetary space 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) suggested the extraterrestrial production of molecular living systems and their entry to Earth with meteorites and comets. At the same time, he estimated the chances of abiogenesis on our planet as very low. The prominent 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, similar traces have been found in soil samples brought from the Moon and Mars. On the other hand, numerous experiments are being carried out on the processing of biostructures by 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 probe-impactor, released by an automatic device. Analysis of the cometary material 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 in a different way those primary elements of life that could be delivered to our young planet by space objects. Research and experiments prove the viability of living cells under the conditions of interplanetary travel. All this makes the idea of an extraterrestrial origin of earthly life relevant. The main concepts of the origin of life on Earth are theories, in which panspermia is included either as the main part, or as a method of delivering components to Earth to create living matter.
Oparin-Haldane's theory of biochemical evolution
The idea of the 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 strength of a well-developed and substantiated 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 suggested 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. In the future, such molecules could form clots and clusters - coacervate drops, which are proto-organisms, around which water shirts are formed - the rudiments of a shell-membrane, stratification occurs, generating a charge difference, which means that movement is the beginning of metabolism, the rudiments of metabolism, etc. Coacervates were considered the basis for starting the evolutionary processes that led to the creation of the first life forms.
Haldane introduced the concept of "primordial soup" - the initial terrestrial 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 connected 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 origin of the Universe from a bunch 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 the formation of the atmosphere took place. 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 were 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 organics took place.
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, a membrane with variable permeability.
3 billion years BC e. - the emergence 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 circulating in the instrument was similar in composition to the primary Earth's atmosphere. The design of the device provided an imitation of volcanic activity, and electric discharges passed through the mixture created the effect of lightning.
After a week of circulation of the mixture through the system, the transition of a tenth of the carbon to organic compounds was noted, amino acids, sugars, lipids and compounds preceding amino acids were found. Repeated and modified experiments fully confirmed the possibility of abiogenesis under 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 ejecta, and other non-cardinal changes were made. In most cases, the experiment in the synthesis of 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 for 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 defining for a living organism - to multiply with the preservation of hereditary traits. With the discovery of genetic cellular structures, with the definition of the function and structure of DNA, with the development of microbiology, a new candidate for the role of the primordial life molecule appeared.
They became a molecule of ribonucleic acid - RNA. This macromolecule, which is part of all living cells, is a chain of nucleotides - the simplest organic links, 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 break 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, compared to DNA, structure (into one strand) made ribonucleic acid the main candidate for the role of the main element of prebiological systems.
The final new theory of the origin of living matter on the planet was 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 the “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 desired properties appeared, even if there was a huge amount of “building material” 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 Pascal Ehrenfreund. Polyaromatic hydrocarbons have been proposed as starting material 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 features of their ring-shaped structure, which contributes to the rapid connection with nitrogenous bases - key components of RNA. The PAH theory once again speaks of the topicality 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 - many of those who dealt with this problem come to this conclusion. The main concepts of the origin of life on Earth are: the theory of abiogenesis and the theory of panspermia. They can intersect in many ways, but most likely they will not be able to answer: how a surprisingly precisely balanced system of the Earth and its satellite, the Moon, appeared in the vast cosmos, how life originated on it ...
