MINISTRY OF EDUCATION OF THE RUSSIAN FEDERATION
ST. PETERSBURG STATE INSTITUTE OF SERVICE AND ECONOMICS
Department of Applied Physics
TEST
course: “Concepts of modern natural science”
on the topic: “Hypotheses of the origin of life”
Completed by: 1st year student
138 groups
Bykova I.B.
Teacher: Naydenova S.N.
Vyborg
2003
CONTENT :
1. Introduction …………………………………………………………. page 1
2. Concepts of the origin of life……………………………… page 2
3. Hypothesis of the origin of life A.I. Oparina……………….. page 5
- Natural scientific ideas about life and its evolution... page 8
5. Geological eras and the evolution of life ………………………… page 10
6. Literature used……………………………………….. page 12
INTRODUCTION
One of the most difficult and at the same time interesting in modern natural science is the question of the origin of life. It is difficult because when science approaches the problems of development as the creation of something new, it finds itself at the limit of its capabilities as a branch of culture based on evidence and experimental verification of statements.
Scientists today are unable to reproduce the process of the origin of life with the same accuracy as it was several billion years ago. Even the most carefully staged experiment will be only a model experiment, devoid of a number of factors that accompanied the appearance of life on Earth. The methodological difficulty lies in the impossibility of conducting a direct experiment on the origin of life (the uniqueness of this process prevents the use of the basic scientific method).
Life on Earth is represented by a huge variety of forms, which are characterized by increasing complexity of structure and functions. All living organisms are characterized by two characteristics: integrity and self-reproduction. During individual change (ontogenesis), organisms adapt to external conditions, and the change of generations takes on an evolutionary-historical character (phylogeny). Organisms have developed the ability to be relatively independent of the external environment (autonomy). One of the main properties of any living organism is metabolism. Along with it, the essential signs of life are irritability, growth, reproduction, variability, and heredity. Every living organism seems to strive for the main thing - the reproduction of its own kind.
2. Concepts of the origin of life.
There are five concepts of the origin of life:
- Life was created by the Creator at a certain time - creationism.
- Life arose spontaneously from inanimate matter (it was believed by Aristotle, who believed that living things could also arise as a result of the decomposition of the soil).
- The concept of a steady state according to which life has always existed.
- The concept of panspermia - the extraterrestrial origin of life;
- The concept of the origin of life on Earth in the historical past as a result of processes subject to physical and chemical laws.
According to creationism, the origin of life refers to a specific event in the past that can be calculated. In 1650, Archbishop Ussher from Ireland calculated that God created the world in October 4004 BC, and at 9 o'clock in the morning on October 23, man. He obtained this number from an analysis of the ages and relationships of all persons mentioned in the Bible. However, by that time there was already a developed civilization in the Middle East, as proven by archaeological research. However, the question of the creation of the world and man is not closed, since the texts of the Bible can be interpreted in different ways.
Aristotle, based on information about animals that came from the soldiers of Alexander the Great and merchant travelers, formulated the idea of the gradual and continuous development of living things from non-living things and created the idea of the “ladder of nature” in relation to the animal world. He had no doubt about the spontaneous generation of frogs, mice and other small animals. Plato spoke about the spontaneous generation of living beings from the earth through the process of decay.
With the spread of Christianity, the ideas of spontaneous generation were declared heretical, and for a long time they were not remembered. Helmont came up with a recipe for producing mice from wheat and dirty laundry. Bacon also believed that decay is the germ of a new birth. The ideas of spontaneous generation were supported by Galileo, Descartes, Harvey, Hegel, and Lamarck.
In 1688, the Italian biologist Francesco Redi, through a series of experiments with open and closed vessels, proved that the small white worms that appear in rotting meat are fly larvae, and formulated his principle: all living things are from living things. In 1860, Pasteur showed that bacteria can be everywhere and infect non-living substances; to get rid of them, sterilization is necessary, called pasteurization.
Theory panspermia(the hypothesis about the possibility of transferring Life in the Universe from one cosmic body to others) does not offer any mechanism to explain the primary 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 considered as eternal repositories of animated form, as eternal plantations of organic embryos,” from where life is dispersed in the form of these embryos in the Universe.
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 particles of matter, grains of dust and living spores of microorganisms escape into outer space from planets inhabited by other creatures. 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, they begin new life on this planet.
This hypothesis was supported by many, including Russian scientists academicians Sergei Pavlovich Kostychev (1877-1931), Lev Semenovich Berg (1876-1950) and Pyotr Petrovich Lazarev (1878-1942).
To substantiate panspermia, they usually use cave paintings depicting objects that look like rockets or astronauts, or the appearance of UFOs. Spacecraft flights destroyed the belief in the existence of intelligent life on the planets of the solar system, which appeared after Schiaparelli's discovery of canals on Mars (1877). But so far no traces of life have been found on Mars.
At the end of the 60s, interest in hypotheses of panspermia increased again. Thus, geologist B.I. Chuvashov (Questions of Philosophy. 1966) wrote that life in the Universe, in his opinion, exists forever.
When studying the substance of meteorites and comets, many “precursors of living things” were discovered - organic compounds, hydrocyanic acid, water, formaldehyde, cyanogens. Formaldehyde, in particular, was found in 60% of cases in 22 studied areas, its clouds with a concentration of approximately 1 thousand molecules per cubic cm filling vast areas. In 1975, amino acid precursors were found in lunar soil and meteorites. Proponents of the hypothesis of the introduction of life from space consider them to be “seeds” sown on Earth.
In ideas about the origin of life as a result of physical and chemical processes, the evolution of a living planet plays an important role. According to many biologists, geologists and physicists, the state of the Earth has changed all the time during its existence. In very ancient times, the Earth was a hot planet, its temperature reached 5-8 thousand degrees. As the planet cooled, refractory metals and carbon condensed and formed the earth's crust, which was not smooth due to active volcanic activity and all kinds of movements of the forming soil. The atmosphere of the primordial Earth was very different from the modern one. Light gases - hydrogen, helium, nitrogen, oxygen, argon and others - were not yet retained sufficiently dense planet, while their heavier compounds remained (water, ammonia, carbon dioxide, methane). The water remained in a gaseous state until the temperature dropped below 100°C.
The chemical composition of our planet was formed as a result of the cosmic evolution of the matter of the solar system, during which certain proportions of quantitative relationships of atoms arose. Therefore, modern data on the ratio of atoms of chemical elements are important. The cosmic abundance of oxygen and hydrogen was expressed in the abundance of water and its numerous oxides. The relatively higher abundance of carbon was one of the reasons that determined the greater likelihood of the emergence of life. The abundance of silicon, magnesium and iron contributed to the formation of silicates in the earth's crust and meteorites. Sources of information about the abundance of elements are data on the composition of the Sun, meteorites, surfaces of the Moon and planets. Age of meteorites
Approximately the age of Earth's rocks, their composition helps reconstruct the Earth's past chemistry and highlight changes caused by the emergence of life on Earth.
The scientific formulation of the problem of the origin of life belongs to Engels, who believed that life did not arise suddenly, but was formed during the evolution of matter. K.A. Timiryazev spoke in the same vein: “We are forced to admit that living matter was carried out in the same way as all other processes, through evolution... This process probably took place during the transition from non-life. organic world into organic" (1912).
3. Hypothesis of the origin of life A.I. Oparina
Even Charles Darwin realized that life can arise only in the absence of life. In 1871, he wrote: “But if now ... in some warm body of water containing all the necessary ammonium and phosphorus salts and accessible to the influence of light, heat, electricity, etc., a protein was chemically formed, capable of further, all more complex transformations, then this substance would immediately be destroyed or absorbed, which was impossible in the period before the emergence of living beings.” Heterotrophic organisms now common on earth would use newly emerging organic matter. Therefore, the emergence of life in the earthly conditions familiar to us is impossible.
The second condition under which life can arise is the absence of free oxygen in the atmosphere. This important discovery was made by the Russian scientist A.I. Oparin in 1924 (the English scientist J.B.S. Haldane came to the same conclusion in 1929). A.I. Oparin suggested that during powerful electrical discharges in the earth’s atmosphere, which 4-4.5 billion years ago consisted of nitrogen, hydrogen, carbon dioxide, water vapor and ammonia, possibly with the addition of hydrocyanic acid (it was discovered in the tails of comets), the simplest organic compounds necessary for the emergence of life could have arisen. Therefore, organic substances arising on the Earth's surface could accumulate without oxidizing. And now on our planet they accumulate only in oxygen-free conditions, which is how peat, coal and oil arise. The creator of the materialistic hypothesis of the origin of life on Earth, Russian biochemist, academician Alexander Ivanovich Oparin (1894-1980), devoted his entire life to the problem of the origin of living things.
In 1912, the American biologist J. Loeb was the first to obtain the simplest component of proteins - the amino acid glycine - from a mixture of gases under the influence of an electric discharge.
Perhaps, in addition to glycine, he received other amino acids, but at that time there were no methods to determine their small quantities.
Loeb's discovery went unnoticed, so the first abiogenic synthesis of organic substances (that is, occurring without the participation of living organisms) from a random mixture of gases is attributed to the American scientists S. Miller and G. Urey. In 1953, they carried out an experiment according to the program outlined by Oparin, and under the influence of electrical discharges with a voltage of up to 60 thousand V, simulating lightning, from hydrogen, methane, ammonia and water vapor under pressure of several Pascals at t = 80C, a complex mixture of many dozens of organic substances. Organic products predominated among them.
(carboxylic) acids - formic, acetic and malic, their aldehydes, as well as amino acids (including glycine and alanine). Miller and Urey's experiments were repeatedly tested on mixtures of different gases and with different energy sources (sunlight, ultraviolet and radioactive radiation, and just heat). Organic matter occurred in all cases. The results obtained by Miller and Urey prompted scientists from various countries to study possible paths of prebiological evolution. In 1957, the first International Symposium on the problem of the origin of life was held in Moscow.
According to data recently obtained by our scientists, the simplest organic substances can also appear in outer space at temperatures close to absolute zero. In principle, the Earth could have received abiogenic organic substances as a dowry upon its emergence.
As a result, the ocean turned into a complex solution of organic substances (the so-called primary ocean), which in principle could feed anaerobic bacteria
(organisms that are able to live and develop in the absence of free oxygen and obtain energy for life through the breakdown of organic or inorganic substances). In addition to amino acids, it also contained nucleic acid precursors - purine bases, sugars, phosphates, etc.
However, low molecular weight organic substances are not yet life. The basis of life is biopolymers - long molecules of proteins and nucleic acids, composed of units - amino acids and nucleotides. The polymerization reaction of the primary units does not occur in an aqueous solution, since when two amino acids or two nucleotides are combined with each other, a water molecule is split off. The reaction in water will go to reverse side. The rate of breakdown (hydrolysis) of biopolymers will be greater than the rate of their synthesis. In the cytoplasm of our cells, the synthesis of biopolymers is a complex process that requires the expenditure of ATP energy. For it to proceed, DNA, RNA and proteins are needed, which themselves are the result of this process. It is clear that biopolymers could not have arisen on their own in the primordial ocean.
Perhaps the primary synthesis of biopolymers occurred when the primary ocean was frozen or when its dry residue was heated. American researcher S.W. Fox, heating a dry mixture of amino acids to 130C, showed that in this case the polymerization reaction occurs (the released water evaporates) and artificial proteinoids are obtained, similar to proteins, having up to 200 or more amino acids in the chain. Dissolved in water, they had the properties of proteins, provided a nutrient medium for bacteria, and even catalyzed (accelerated) some chemical reactions, like real enzymes. Perhaps they arose in the pre-biological era on the hot slopes of volcanoes, and then rains washed them into the primordial ocean. There is also a point of view that the synthesis of biopolymers took place directly in the primary atmosphere and the resulting compounds fell into the primary ocean in the form of dust particles.
The next proposed stage in the origin of life is protocells. A.I. Oparin showed that in standing solutions of organic substances, coacervates are formed - microscopic “droplets” bounded by a semi-permeable shell - the primary membrane. Organic substances can be concentrated in coacervates, reactions and metabolism with the environment occur faster in them, and they can even divide like bacteria. Fox observed a similar process when dissolving artificial proteinoids; he called these balls microspheres.
In protocells like coacervates or microspheres, nucleotide polymerization reactions took place until a protogen was formed from them - a primary gene capable of catalyzing the emergence of a certain amino acid sequence - the first protein. Probably the first such protein was a precursor to an enzyme that catalyzes the synthesis of DNA or RNA. Those protocells in which the primitive mechanism of heredity and protein synthesis arose divided faster and took into themselves all the organic substances of the primary ocean. At this stage, natural selection was already underway for the speed of reproduction; any improvement in biosynthesis was picked up, and new protocells replaced all previous ones.
The final steps in the origin of life—the origin of ribosomes and transfer RNAs, the genetic code, and the cell's energy machinery using ATP—have not yet been replicated in the laboratory. All these structures and processes are already present in the most primitive microorganisms, and the principle of their structure and functioning has not changed throughout the history of the Earth. Therefore, for now we can only reconstruct the final stage of the origin of life only tentatively - until it can be recreated in experiments.
For now, we can only say that the emergence of life on earth took relatively little time - less than one billion years. Already 3.8 billion years ago, the first microorganisms existed, from which all the diversity of forms of earthly life originated.
Life arose on earth abiogenically. Currently, living things come only from living things (biogenic origin). The possibility of life re-emerging on earth is excluded.
4. Natural scientific ideas about life and its evolution
Darwin opened driving forces evolution of living nature. He tried to understand and explain the real nature of the internal contradictions of the organic world. His theory not only explains the nature of these contradictions, but also indicates the ways in which they are resolved in the world of animals and plants.
A significant place in all of Darwin’s works, and in particular in “The Origin of Species,” is occupied by evidence of the very fact of organic evolution.
It is now generally accepted that all living things are based on similar chemical compounds of a group of proteins, among which nucleoproteins have a special position. These are compounds of protein bodies and nucleic acids. Nucleoproteins constitute the main component of the cell nucleus of plants and animals. Research in the field of molecular biology has shown that nucleic acids are responsible for many important processes in the life of organisms. In this case, macromolecules of deoxyribonucleic acid (DNA) and ribonucleic acid play a special role. (RNA). The DNA molecule, in interaction with other cell substances, determines the synthesis of protein and enzymes that regulate metabolism in the body. Proteins and nucleoproteins (especially DNA and RNA) are an essential component of all biological organisms. Consequently, from the point of view of chemical evolution, they underlie the life of all biological forms known on Earth.
In addition, there is an eternal, continuous connection between inanimate and living nature. “There is a continuous, never-ending connection between inert and living matter, which can be expressed as a continuous biogenic flow of atoms from living matter to the inert matter of the biosphere, and back. This biogenic current of atoms is caused by living matter. It is expressed in never-ending breathing, nutrition, reproduction, etc.”
The unity of living nature is also indicated by the differentiation of the bodies of animals and plants. Thus, the unity of the world of organisms is manifested both in their chemical composition and in their structure and functioning. This fact could not escape the attention of natural scientists. The idea of the similarity of living organisms led J. Cuvier to the doctrine of the types of the animal kingdom. Subsequently, it was developed in the works of K. Baer, E. Haeckel, A. O. Kovalevsky, I. I. Mechnikov, who argued that the similarity of animals cannot be explained otherwise than by the commonality of their origin.
The unity of the organic world is also indicated by the existence of so-called intermediate forms, which include animals and plants that occupy a transitional, intermediate position between large taxa.
In the organic world there are no rigid boundaries between its divisions. At the same time, the boundaries between species are always real. Darwin devotes great attention to the problem of species and speciation. It is no coincidence that the title of his work includes the words “origin of species.” As the most important unit of systematization, the species occupies a central place in evolutionary theory. The task of evolutionary theory is to explain the mechanism of the origin of life and changes in real species of animals and plants inhabiting the Earth.
Evidence of evolution is also the similarity of animal organs, expressed in their position, relationship in the general plan of structure and in the development of an embryo from a similar rudiment. Similar organs are called homologous organs. Evolutionary theory explains the similarity of organs by the common origin of the compared forms, while supporters of creationist concepts interpreted this similarity as the will of the creator,
creating groups of animals according to a specific plan.
Confirmation of the idea of evolution is the reflection of the history of the development of organisms on their structure and on the processes of embryonic development, as well as the geographical distribution of organisms.
Genetics occupies a special place in the development and deepening of evolutionary concepts. The idea of the immutability of genes began to be overcome in the 20-30s of the 20th century. in connection with the emergence of population, evolutionary genetics. Elucidation of the structure of populations allowed us to take a new look at the evolutionary processes playing out at the population level. Genetics has made it possible to trace the main stages of the evolutionary process from the appearance of a new trait in a population to the emergence of a new species. She brought precise experimental methods to research at the intraspecific, microevolutionary level.
elementary unit heredity - a gene, which is a section of a DNA molecule that determines the development of the elementary characteristics of an individual. Elementary evolutionary unit must meet the following requirements: division limbs;
the ability of hereditary change in the change of biological generations; reality and concreteness of existence in natural conditions. The population is considered to be such a unit of evolution - elementary unit of the evolutionary process, and a heritable change in a population is an elementary evolutionary phenomenon. It reflects a change in the genotypic structure of the population. The gene is subject to mutations—hereditary changes in individual individuals. Mutation - discrete
changing the code of an individual's hereditary information. There are gene, chromosomal, genomic, and extranuclear types of mutations.
The process of mutations maintains a very high degree of genetic heterogeneity in natural populations. But, fulfilling the role of a “supplier” of elementary material, the mutation process itself does not direct the course of evolutionary changes; it has a probabilistic, statistical nature.
The laws of evolution find their expression in the life of an individual, but the driving forces of evolution are contained within a system of individuals, in this case a population. The resolution of the contradictions of the population serves as the basis for all evolution and at the same time determines the transformation of the organism as an integral part of the population. The relationships between organisms in a population are complex nature. Their study is complicated by the fact that in addition to intrapopulation interactions, organisms are influenced by other populations, other species, and, even more broadly, environmental conditions.
5. Geological eras and the evolution of life
Under the influence of evolutionary theory, geologists had to reconsider their ideas about the history of our planet. The organic world has developed over billions of years along with the environment in which it had to exist, i.e. together with the Earth. Therefore, the evolution of life cannot be understood without the evolution of the Earth, and vice versa. Brother A.O. Kovalevsky Vladimir Kovalevsky (1842-1883) based evolutionary theory paleontology- science of fossil organisms.
Geologists discover the first traces of organic remains in the most ancient sediments dating back to Proterozoic geological era , covering a huge period of time - 700 million years. The earth at that time was almost completely covered by ocean. It was inhabited by bacteria, protozoan algae, and primitive marine animals. Evolution then proceeded so slowly that tens of millions of years passed before the organic world changed any noticeably.
IN Paleozoic era(lasting about 365 million years), the evolution of all living things proceeded at a faster pace. Large expanses of land were formed, on which land plants appeared. Ferns developed especially rapidly: they formed giant dense forests. Marine animals also improved, which led to the formation of huge armored fish. In the Carboniferous (Carboniferous) period, which marked the heyday of Paleozoic fauna and flora, amphibians appeared. And in the Permian period, which ended the Paleozoic era and began the Mesozoic era (it is 185 million years removed from us), reptiles appeared.
The animal and plant world of the Earth began to develop even faster in Mesozoic era. Already at its very beginning, reptiles began to dominate the land. The first mammals, marsupials, also appeared. Coniferous trees became widespread, and a variety of birds and mammals arose.
About 70 million years ago came Cenozoic era. Species of mammals and birds continued to improve. IN flora the predominant role passed to flowering plants. The species of animals and plants that live on Earth today were formed.
With the emergence of man about 2 million years ago, the current period of the Cenozoic era begins - the Quaternary or anthropogen. Man on the geological scale of time is a perfect baby. After all, 2 million years is an extremely short period of time for nature. The most significant event in the Cenozoic era was the emergence of a large number of cultivated plants and domestic animals. All of them are the result of the creative activity of man, a rational being capable of purposeful activity.
If Darwin, while developing the theory of evolution, studied the experience of breeders, then, armed with scientific theory, breeders learned to develop new varieties much faster and more purposefully. Here, a special role belongs to the Russian scientist N.I. Vavilov (1887-1943), who developed the doctrine of the origin of cultivated plants. The evolution of living things continues, but under the influence of man.
We now know that the expediency of organic forms is not something given in advance, but the result of a long and complex process of development of matter, and, therefore, the expediency of organic forms is relative. Man is now actively changing living nature. Increasing human intervention in natural processes gives rise to new serious problems, which can be solved only on the condition that the person himself takes care of surrounding nature, about preserving those subtle
ratios in biosphere, which have developed in it over millions of years of the evolution of life on Earth.
The doctrine of the biosphere was created by the remarkable scientist V.I. Vernadsky (1863-1945). By the biosphere, the scientist understood that thin shell of the Earth in which processes occur under the direct influence of living organisms.
The biosphere is located at the junction of all other shells of the Earth - the lithosphere, hydrosphere and atmosphere and plays a vital role in the exchange of substances between them. Huge amounts of oxygen, carbon, nitrogen, hydrogen and other elements constantly pass through living organisms on Earth. V.I. Vernadsky showed that there is practically not a single element in the periodic table that would not be included in the living matter of the planet and would not be released from it during its decay. Therefore, the face of the Earth as a celestial body is actually shaped by life. Vernadsky was the first to show what a decisive geological role living matter played on our planet.
Vernadsky also focused on the enormous geological role of man. He showed that the future of the biosphere is noosphere, i.e. sphere of the mind. The scientist believed in the power of the human mind, believed that by increasingly interfering with natural evolutionary processes, man would be able to direct the evolution of living things in such a way as to make our planet even more beautiful and richer.
USED BOOKS
1. T.Ya.Dubnischeva “The Concept of Modern Natural Science” textbook., M., 2000.
2. S.Kh.Karpenkov “Concepts of modern natural science.” M., " graduate School» 2000
3. A.A. Gorelov “Concepts of modern natural science.” M. "Center" 1998
4. A.I. Oparin “Life, its nature, origin and development” M. 1960
5. Ponnamperuma S. “The Origin of Life”, M., “Mir”, 1977
6. Josip Klechek Universe and Earth - M. Artia 1985
7. Kesarev V.V. Evolution of matter in the universe - M. Atomizdat 1976
The question of the origin of life is one of the most difficult questions in modern natural science. However, great interest was attracted to him at all times. The difficulty in obtaining an answer to this question is that it is difficult to accurately reproduce the processes and phenomena that occurred in the Universe billions of years ago. At the same time, the current diversity of forms and manifestations of life on Earth attracts the closest attention to this problem. Today, the following main hypotheses of the origin of life are distinguished.
Creationism
According to this hypothesis, life and all species of living beings inhabiting the Earth were created by God. Moreover, the divine creation of the world occurred simultaneously, so the process of creating life itself is not accessible to observation in time. In addition, creationism does not provide a clear interpretation of the origin of God the Creator himself and therefore has the character of a postulate. The famous Swedish naturalist K. Linnaeus, as well as the outstanding Russian chemist M.V. Lomonosov, supported this dogma of the origin of life.
Spontaneous generation hypothesis
This hypothesis is a variation abiogenesis- the origin of life from nonliving matter. This hypothesis was an alternative to creationism, when the accumulated knowledge of people about living nature questioned the creation of life by God. Philosophers of Ancient Greece and naturalists of medieval Europe believed in the emergence of living organisms from inanimate matter. They believed and tried to prove that frogs and insects breed in damp soil, flies in rotten meat, etc. Views about the spontaneous origin of life were widespread almost until the end of the 18th century. Only in the middle of the 19th century. French scientist Louis Pasteur proved that bacteria are ubiquitous. Moreover, any non-living objects become “infected” with them if sterilization is not carried out. Thus, Pasteur confirmed the theory biogenesis- Life can only arise from a previous life. The scientist finally refuted the concept of the spontaneous origin of life.
Panspermia hypothesis
In 1865, the German scientist G. Richter proposed a hypothesis panspermia, according to which life could have been brought to Earth from space along with meteorites and cosmic dust. A supporter of this hypothesis was the great Russian scientist, creator of the modern doctrine of the biosphere, V. I. Vernadsky. Modern research confirms the high resistance of some microorganisms and their spores to radiation and low temperatures. Recently there have been reports that traces of organic matter have been found in meteorites. When studying the closest planet to Earth, Mars, structures similar to bacteria and traces of water were found. However, these findings do not answer the question of the origin of life.
Biochemical hypothesis of the origin of life is the most common at present. This hypothesis was proposed in the 20s. last century, Russian biochemist A.I. Oparin and English biologist J. Haldane. It formed the basis of scientific ideas about the origin of life.
The essence of this hypothesis is that in the early stages of the development of the Earth there was a long period of abiogenesis. Living organisms did not take part in it. For the synthesis of organic compounds, the energy source was ultraviolet radiation from the Sun. Solar radiation was not retained by the ozone layer because there was no ozone or oxygen in the atmosphere of the ancient Earth. Synthesized amino acids, sugars and other organic compounds were stored in the ancient ocean for tens of millions of years. Their accumulation eventually led to the formation of a homogeneous mass, which Oparin called the “primary broth.” According to Oparin, it was in the “primordial broth” that life arose.
Oparin believed that a vital role in the transformation of non-living things into living things belongs to proteins. It is proteins that are capable of forming colloidal complexes that attract water molecules. Such complexes, merging with each other, formed coacervates- structures isolated from the rest of the water mass.
Coacervates had some properties of life. They could selectively absorb substances from the surrounding solution and increase in size - a certain semblance of nutrition and growth. When the coacervates were crushed, new droplets were formed that retained the basic properties of the original formation - semblance of reproduction. But to transform into the first living organisms, coacervates lacked biological membranes and genetic information to ensure reproduction.
The next step in the origin of life was the appearance of membranes. They could be formed from lipid films covering the surface of water bodies. Next, proteins dissolved in water were added to such lipid formations. As a result, the surface of the coacervates acquired the structure and properties of a biological membrane. Such a membrane could already allow some substances to pass through and not others.
Further combination of coacervates with nucleic acids led to the formation of self-regulating and self-reproducing first living organisms - protobionts. These primitive primary organisms were anaerobes and heterotrophs that fed on substances from the “primordial broth.” Thus, after 1 billion years, according to this hypothesis, the origin of life on Earth was completed.
Currently, the following main hypotheses of the origin of life are distinguished: the hypotheses of creationism, spontaneous generation, panspermia and biochemical. Among modern views of scientists on the origin of life, the biochemical hypothesis occupies the most important place. According to it, life on Earth arose over a long period of time in the absence of oxygen in the presence chemical substances and a constant source of energy.
MINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS
BSPU IM. M. TANK
FACULTY OF SPECIAL EDUCATION
DEPARTMENT OF FUNDAMENTALS OF DEFECTOLOGY
Essay
in the discipline "Natural Science"
on the topic of:
"The main hypotheses about the origin of life on Earth."
Performed:
1st year student of group 101
correspondence department (budgetary
form of training)
………Irina Anatolyevna
INTRODUCTION………………………………………………………………………………..….1
1. CREATIONISM……………………………………………………….…….1
2. THEORY OF STEADY STATE…………..……………….….2
3. THEORY OF SPONTANEOUS GENERATION…………..…3
4. THE THEORY OF PANSPERMIA……………………………………………………......7
5. THEORY OF A.I. OPARIN……………...…………………………..……10
6. MODERN VIEWS ON THE ORIGIN OF LIFE ON EARTH……………………………………………………………………………………….....12
CONCLUSION…………………………………………………………...…..14
LITERATURE …………………………………………………………...……...15
INTRODUCTION
The problem of the origin of life on Earth and the possibility of its existence in other areas of the Universe has long attracted the attention of both scientists and philosophers, and ordinary people. Behind last years Interest in this “eternal problem” has increased significantly.
This is due to two circumstances: firstly, significant advances in laboratory modeling of some stages of the evolution of matter that led to the origin of life, and secondly, the rapid development of space research, making the direct search for any forms of life on the planets of the solar system more and more realistic , and in the future beyond.
The origin of life is one of the most mysterious questions, a comprehensive answer to which is unlikely to ever be obtained. Many hypotheses and even theories about the origin of life, explaining various aspects of this phenomenon, are so far unable to overcome the essential circumstance - 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.
Theories regarding the origin of life on Earth are varied and far from reliable. The most common theories of the origin of life on Earth are the following:
1. Life was created by a supernatural being (Creator) at a specific time (creationism).
2. Life has always existed (stationary state theory).
3. Life arose repeatedly from nonliving matter (spontaneous generation).
4. Life was brought to our planet from outside (panspermia).
5. Life arose as a result of processes that obey chemical and physical laws (biochemical evolution).
1. CREATIONISM.
Creationism (from the Latin creaсio - creation) is a philosophical and methodological concept within the framework of which the entire diversity of the organic world, humanity, planet Earth, as well as the world as a whole, are considered as intentionally created by some superbeing (Creator) or deity. There is no scientific evidence for this point of view: in religion, truth is comprehended through divine revelation and faith. The process of creation of the world is thought of as having taken place only once and therefore inaccessible to observation.
The theory of creationism is adhered to by followers of almost all the most common religious teachings (especially Christians, Muslims, Jews). According to this theory, the origin of life refers to some specific supernatural event in the past that can be calculated. In 1650, Archbishop Usher of Armagh (Ireland) calculated that God created the world in October 4004 BC. e. and finished his work on October 23 at 9 a.m., creating man. Asher obtained this date by adding up the ages of all the people mentioned in the Biblical genealogy, from Adam to Christ (“who begat whom”). From an arithmetic point of view, this makes sense, but it means that Adam lived at a time when, as archaeological finds show, a well-developed urban civilization already existed in the Middle East.
The traditional Judeo-Christian view of creation, as set out in the Book of Genesis, has been and continues to be controversial. However, existing contradictions do not refute the concept of creation. The creation hypothesis can neither be proven nor disproved and will always exist along with scientific hypotheses of the origin of life.
Creationism is thought of as God's Creation. However, at present, some view it as the result of the activity of a highly developed civilization, creating various forms of life and observing their development.
2. THEORY OF STATIONARY STATE.
According to this theory, the Earth never came into being, but existed forever; it was always capable of supporting life, and if it changed, it was 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.
According to modern estimates, based on the rate of radioactive decay, the age of the Earth is 4.6 billion years. More advanced dating methods provide ever higher estimates of the age of the Earth, leading proponents of the steady state theory to believe that the Earth has always existed.
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 lobe-finned fish - coelacanth (coelacanth). It was believed that the lobe-finned fish (coelacanth) was a transitional form from fish to amphibians and became extinct 60-90 million years ago (at the end Cretaceous period). However, this conclusion had to be revised when, in 1939, off the coast of the island. The first live coelacanth was caught in Madagascar, and then other specimens. Thus, the coelacanth is not a transitional form.
Many other animals that were considered extinct were also found, for example, the lingula - a small sea animal, supposedly extinct 500 million years ago, is alive today and like other "living fossils": the solendon - a shrew, the tuatara - a lizard. For millions of years they have not undergone any evolutionary changes.
Another example of a misconception is Archeopteryx - a creature that connects birds and reptiles, a transitional form on the way to transforming reptiles into birds. But in 1977, fossils of birds were discovered in Colorado, the age of which is commensurate with and even exceeds the age of the remains of Archeopteryx, i.e. it is not a transitional form.
Proponents of the steady state theory argue that only by studying living species and comparing them with fossil remains can one draw a conclusion about extinction, and even then it is very likely that it will be incorrect. Using paleontological data to support the steady state theory, its proponents interpret the appearance of fossils in ecological terms.
For example, they explain the sudden appearance of a fossil species in a certain layer by an increase in the size of its population or its movement to places favorable for the preservation of remains.
Much of the argument for this theory has to do with obscure aspects of evolution such as the significance of breaks in the fossil record, and it is along these lines that it has been most extensively developed.
The steady state hypothesis is sometimes called the eternism hypothesis (from the Latin eternus - eternal). The hypothesis of eternism was put forward by the German scientist W. Preyer in 1880.
Preyer's views were supported by academician Vladimir Ivanovich Vernadsky (1864 - 1945), the author of the doctrine of the biosphere. Vernadsky believed that life is the same eternal basis of the cosmos, which are matter and energy. “We know, and we know it scientifically,” he insisted, “that the Cosmos cannot exist without matter, without energy. And is there enough matter, even without the manifestation of life, to build the Cosmos, that Universe that is accessible to the human mind? He answered this question in the negative, referring specifically to scientific facts, and not on personal sympathies, philosophical or religious beliefs. “...We can talk about the eternity of life and the manifestations of its organisms, just as we can talk about the eternity of the material substrate of celestial bodies, their thermal, electrical, magnetic properties and their manifestations. From this point of view, the question of the beginning of life will be as far from scientific research as the question of the beginning of matter, heat, electricity, magnetism, and motion.”
Based on the idea of the biosphere as an earthly, but at the same time a cosmic mechanism, Vernadsky connected its formation and evolution with the organization of the Cosmos. “It becomes clear to us,” he wrote, “that life is a cosmic phenomenon, and not a purely earthly one.” Vernadsky repeated this idea many times: “... there was no beginning of life in the Cosmos that we observe, since there was no beginning of this Cosmos. Life is eternal because the Cosmos is eternal.”
3. THEORY OF SPONTANEOUS GENERATION.
This theory was common in ancient China, Babylon and Egypt as an alternative to 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 a deity. The first researchers of nature also resolved this issue very naively. Aristotle (384 – 322 BC), often hailed as the founder of biology, adhered to the theory of the spontaneous origin of life. Even for such an outstanding mind of antiquity as Aristotle, it was not particularly difficult to accept the idea that animals - worms, insects and even fish - could arise from silt. On the contrary, this philosopher argued that every dry body, becoming wet, and, conversely, every wet body, becoming dry, will give birth to animals.
According to Aristotle's hypothesis of spontaneous generation, certain “particles” of matter contain a certain “active principle” that, under suitable conditions, can create a living organism. Aristotle was right in believing that this active principle was contained in the fertilized egg, but he erroneously believed that it was also present in sunlight, mud and rotting meat.
“These are the facts - living things can arise not only through the mating of animals, but also through the decomposition of the soil. The same is the case with plants: some develop from seeds, while others seem to spontaneously generate under the influence of all nature, arising from decaying earth or certain parts of plants” (Aristotle).
The authority of Aristotle had an exceptional influence on the views of medieval scientists. The opinion of this philosopher in their minds was intricately intertwined with the teachings of the church fathers, often giving ideas that were absurd and even funny in modern eyes. The preparation of a living person or his likeness, a “homunculus,” in a flask, by mixing and distilling various chemicals, was considered in the Middle Ages, although very difficult and lawless, but, without a doubt, doable. The production of animals from non-living 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 you can artificially prepare mice 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. All you needed was a dirty shirt, a dark closet and a handful of wheat. Van Helmont considered human sweat to be the active principle in the process of mouse generation.
A number of works 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 gives a picture of frogs being formed from the May dew, and Aldrovand gives drawings showing how birds and insects are born from the branches and fruits of trees.
The further natural science developed, the more important accurate observation and experience, and not mere reasoning and philosophizing, acquired in the knowledge of nature, the more the scope of application of the theory of spontaneous generation narrowed. 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, through simple experiments, proved the unfoundedness of opinions about the spontaneous generation of worms in rotting meat. He established that the small white worms are fly larvae. After conducting a series of experiments, he obtained data supporting the idea that life can only arise from previous life (the concept of biogenesis).
“Conviction would be futile if it could not be confirmed by experiment. Therefore, in mid-July, I took four large wide-mouthed vessels, placed earth in one of them, some fish in another, eels from the Arno in the third, a piece of dairy veal in the fourth, closed them tightly and sealed them. Then I placed the same thing in four other vessels, leaving them open... Soon the meat and fish in the unsealed vessels were wormed; one could see flies freely flying into and out of the vessels. But I did not see a single worm in the sealed vessels, although many days had passed since the dead fish were placed in them” (Redi).
Thus, with regard to living beings visible to the naked eye, the assumption of spontaneous generation turned out to be untenable. But at the end of the 17th century. Kircher and Leeuwenhoek discovered a world of tiny creatures, invisible to the naked eye and visible only through a microscope. These “smallest living animals” (as Leeuwenhoek called the bacteria and ciliates he discovered) could be found wherever decay occurred, in long-standing decoctions and infusions of plants, in rotting meat, broth, sour milk, in feces, in dental plaque. “In my mouth,” Leeuwenhoek wrote, “there are more of them (microbes) than there are people in the United Kingdom.” One has only to place perishable and easily rotting substances in a warm place for a while, and microscopic living beings that were not there before immediately develop in them. Where do these creatures come from? Did they really come from embryos that accidentally fell into a rotting liquid? How many of these embryos there must be everywhere! The thought involuntarily appeared that it was here, in rotting decoctions and infusions, that the spontaneous generation of living microbes from inanimate matter took place. This is the 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 plant substances, placed them in tightly sealed vessels and boiled them for a short time. In this case, according to Needham, all the embryos should have died, but new ones could not enter from the outside, since the vessels were tightly closed. However, after some time, microbes appeared in the liquids. From this the said scientist concluded that it is present during the phenomenon of spontaneous generation.
However, another scientist, the Italian Spallanzani, opposed this opinion. Repeating Needham's experiments, he became convinced that longer heating of vessels containing organic liquids completely sterilizes them. In 1765, Lazzaro Spallanzani conducted the following experiment: after boiling meat and vegetable broths for several hours, he immediately sealed them and then removed them from the heat. Having examined the liquids a few days later, Spallanzani did not find any signs of life in them. From this he concluded that heat destroyed all forms of living beings and that without them nothing living could arise.
A fierce dispute broke out between representatives of two opposing views. Spallanzani argued that the liquids in Needham's experiments were not sufficiently heated and embryos of living beings remained there. To this, Needham objected that it was not he who heated the liquids too little, but, on the contrary, Spallanzani heated them too much and with such a crude method destroyed the “generative power” of organic infusions, which is very capricious and fickle.
Thus, each of the disputants remained unconvinced, and the question of the spontaneous generation of microbes in rotting liquids was not resolved in either direction for a whole century. During this time, many attempts were made to experimentally prove or disprove spontaneous generation, but none of them led to definite results.
The question became more and more confused, and only in the half of the 19th century. it was finally resolved thanks to the brilliant research of the brilliant French scientist Pasteur.
LOUIS PASTER
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 managed to solve 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. Through a series of experiments, he showed that everywhere, and especially near human habitation, tiny embryos are floating in the air. They are so light that they float freely in the air, only very slowly and gradually falling to the ground.
As a result of a series of experiments based on Splanzani'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 incomplete sterilization of the environment, or by insufficient protection of liquids from the penetration of germs. If you thoroughly boil the contents of the flask and then protect it from germs that could get in with the air flowing into the flask, then in one hundred cases out of a hundred, rotting of the liquid and the formation of microbes will not occur.
To dehydrate the air flowing into the flask, Pasteur used a variety of techniques: he either calcined the air in glass and metal tubes, or protected the neck of the flask with a cotton plug, in which all the smallest particles suspended in the air are retained, or, finally, he passed the air through a thin glass tube , curved in the shape of the letter S - in this case, all the embryos were mechanically retained on the wet surfaces of the bends of the tube.
S-neck flasks used in Louis Pasteur's experiments:
A – in a flask with a curved neck, the broth remains transparent (sterile) for a long time; B – after removing the S-shaped neck, rapid growth of microorganisms is observed in the flask (the broth becomes cloudy).
Wherever the protection was sufficiently reliable, the appearance of microbes in the liquid was not observed. But maybe prolonged heating chemically changed the environment and made it unsuitable for supporting life? Pasteur easily refuted this objection too. He threw a cotton plug into the liquid, deprived of heat, through which air was passed and which, therefore, contained embryos - the liquid quickly rotted. Consequently, boiled infusions are quite suitable soil for the development of microbes. This development does not occur just because there is no embryo. As soon as the embryo enters the liquid, it immediately germinates and produces a lush harvest.
Pasteur's experiments showed beyond doubt that spontaneous generation of microbes does not occur in organic infusions. All living organisms develop from embryos, that is, they originate from other living beings. However, confirmation of the biogenesis theory gave rise to another problem. Since another living organism is necessary for the emergence of a living organism, then where did the very first living organism come from? Only the steady state theory does not require an answer to this question, and all other theories imply that at some stage in the history of life there was a transition from nonliving to living. So how did life begin on Earth?
4. THEORY OF PANSPERMIA.
Pasteur is rightly considered the father of the science of simple organisms - microbiology. Thanks to his work, an impetus was given to extensive research into the world of the smallest creatures that inhabit the earth, water and air, invisible to the naked eye. These studies were no longer aimed, as before, at merely describing the forms of microorganisms; bacteria, yeast, ciliates, amoebas, etc. were studied from the point of view of their living conditions, their nutrition, breathing, reproduction, from the point of view of the changes that they make in their environment, and, finally, from the point of view of their internal structure, their finest structure. The further these studies went, the more and more it was discovered that the simplest organisms are not at all as simple as previously thought.
The body of every organism - plant, snail, worm, fish, bird, animal, human - consists of tiny bubbles, visible only through a microscope. It is made up of these bubble-cells, just like a house is made up of bricks. Different organs of different animals and plants contain cells that differ from each other in appearance. Adapting to the work assigned to a given organ, the cells that make it up, one way or another, change, but in principle, all cells of all organisms are similar to each other. Microorganisms differ only in that their entire body consists of just one single cell. This fundamental similarity of all organisms confirms the now generally accepted idea in science that everything living on Earth is connected, so to speak, by blood. More complex organisms evolved from simpler ones, gradually changing and improving. Thus, one has only to explain to oneself the formation of some simple organism - and the origin of all animals and plants becomes clear.
But, as already mentioned, even the simplest, consisting of just one cell, are very complex formations. Their main component, the so-called protoplasm, is a semi-liquid, viscous gelatinous substance, saturated with water, but insoluble in water. The composition of protoplasm includes a number of extremely complex chemical compounds (mainly proteins and their derivatives), which are not found anywhere else, only in organisms. These substances are not just mixed, but are in a special, little-studied state, due to which protoplasm has the finest structure, difficult to distinguish even with a microscope, but extremely complex. The assumption that such a complex formation with a well-defined fine organization could spontaneously arise within a few hours in structureless solutions, such as broths and infusions, is as wild as the assumption that frogs are formed from May dew or mice from grain.
The exceptional complexity of the structure of even the simplest organisms so amazed the minds of some scientists that they came to the conclusion that there was an impassable gap between living and nonliving things. The transition of the inanimate into the living, organized seemed to them absolutely impossible, either in the present or in the past. “The impossibility of spontaneous generation at any time,” says the famous English physicist W. Thomson, “should be considered as firmly established as the law of universal gravitation.”
But how then did life originate on Earth? After all, there was a time when the Earth, according to the now generally accepted view in science, was a white-hot ball. Data from astronomy, geology, mineralogy, and other exact sciences speak for this - this is certain. This means that conditions existed on Earth under which life was impossible and unthinkable. Only after the globe lost a significant part of its heat, dissipating it into cold interplanetary space, only after cooled water vapor formed the first thermal seas, did the existence of organisms like those that we now observe become possible. To clarify this contradiction, a theory was created that bears a rather complex name - the theory of panspermia (Greek panspermía - a mixture of all kinds of seeds, from pán - all, everyone and spérma - seed).
One of the first to express the idea of cosmic rudiments was in 1865 the German doctor G. E. Richter, who argued that life is eternal and its rudiments can be transferred from one planet to another. This hypothesis is closely related to the stationary state hypothesis. Based on the idea that small particles of solid matter (cosmozoans), separated from celestial bodies, are floating around everywhere in the cosmos, this author assumed that simultaneously with these particles, perhaps clinging to them, viable germs of microorganisms are flying around. Thus, these embryos can be transferred from one celestial body inhabited by organisms to another, where there is no life yet. If favorable living conditions have already been created on this latter, in the sense of suitable temperature and humidity, then the embryos begin to germinate, develop and subsequently become the ancestors of the entire organic world of a given planet.
This theory gained many supporters in the scientific world, among whom there were even such outstanding minds as G. Helmholtz, S. Arrhenius, J. Thomson, P. P. Lazarev and others. Its defenders sought mainly to scientifically substantiate the possibility of such a transfer embryos from one celestial body to another, which would preserve the viability of these embryos. Because in fact, in the end, main question The question is whether the spore can make such a long and dangerous journey as flying from one world to another without dying, retaining the ability to germinate and develop into a new organism. Let us examine in detail what dangers are encountered on the path of the embryo.
First of all, this is the cold of interplanetary space (220° below zero). Having separated from its home planet, the embryo is doomed to float for many years, centuries and even millennia at such a terrifying temperature before a lucky chance gives it the opportunity to land on a new earth. One cannot help but doubt whether the embryo is capable of withstanding such a test. To solve this issue, we turned to the study of resistance to cold in modern spores. Experiments carried out in this direction have shown that germs of microorganisms tolerate cold excellently. They remain viable even after six months at 200° below zero. Of course, 6 months is not 1000 years, but experience still gives us the right to assume that at least some of the embryos can survive the terrible cold of interplanetary space.
A much greater danger for embryos is their complete lack of protection from light rays. Their path between planets is penetrated by the rays of the suns, destructive for most microbes. Some bacteria die from direct sunlight within a few hours, others are more resistant, but very strong lighting has an adverse effect on all microbes without exception. However, this unfavorable effect is significantly weakened in the absence of atmospheric oxygen, and we know that there is no air in interplanetary space, and therefore we can reasonably assume that the embryos of life will withstand this test.
But a lucky chance makes it possible for the embryo to fall into the sphere of gravity of a planet with conditions of temperature and humidity favorable for the development of life. The wanderer could only, obeying the force of gravity, fall to his new Earth. But just here, almost already in a peaceful harbor, a terrible danger awaits him. Previously, the embryo rushed in airless space, but now, before falling on the surface of the planet, it must fly through a rather thick layer of air that envelops this planet on all sides.
Everyone, of course, is well aware of the phenomenon of “falling stars” - meteors. Modern science explains this phenomenon as follows. In interplanetary space, solid bodies and particles of various sizes are rushing around, possibly fragments of planets or comets that have flown into our solar system from the most distant places in the Universe. Flying close to the globe, they are attracted by this latter, but before falling on its surface, they must fly through air atmosphere. Due to friction with the air, a rapidly falling meteorite heats up to white heat and becomes visible in the dark vault of heaven. Only a few of the meteorites reach the earth; most burn up from intense heat while still far from its surface.
The embryos must suffer a similar fate. However, various considerations show that this kind of death is not necessary. There is reason to assume that at least some of the embryos that enter the atmosphere of a particular planet will reach its surface viable.
At the same time, we must not forget about those colossal astronomical periods of time during which the Earth could be seeded with embryos from other worlds. These intervals are calculated in millions of years! If during this time, out of many billions of embryos, at least one reached safely the surface of the Earth and found here conditions suitable for its development, then this would already be enough for the formation of the entire organic world. This possibility, given the current state of science, seems unlikely, but acceptable; in any case, we have no facts that would directly contradict it.
However, the theory of panspermia is an answer only to the question of the origin of earthly life, and not at all to the question of the origin of life in general, transferring the problem to another place in the Universe.
“One of two things,” says Helmholtz. “Organic life either ever began (originated) or exists forever.” If we admit the first, then the theory of panspermia loses all logical meaning, since if life could have originated anywhere in the Universe, then, based on the uniformity of the world, we have no reason to say that it could not have originated on Earth. Therefore, supporters of the theory under consideration accept the position of the eternity of life. They admit that “life only changes its form, but is never created from dead matter.”
In the late 60s, the popularity of this theory resumed. This was due to the fact that during the study of meteorites and comets, many “precursors of living things” were discovered - organic compounds, hydrocyanic acid, water, formaldehyde, cyanogens. In 1975, amino acid precursors were found in lunar soil and meteorites. Proponents of panspermia consider them "seeds sown on Earth." In 1992, works by American scientists appeared, where, based on a study of material collected in Antarctica, they describe the presence in meteorites of the remains of living creatures resembling bacteria.
Modern adherents of the concept of panspermia (including the laureate Nobel Prize English biophysicist F. Crick) believe that life was brought to Earth either accidentally or intentionally by space aliens using aircraft. Proof of this is the repeated appearances of UFOs, rock paintings of objects similar to spaceports, as well as reports of encounters with aliens.
The panspermia hypothesis is supported by the point of view of astronomers Ch. Wickramasinghe (Sri Lanka) and F. Hoyle (Great Britain). They believe that microorganisms are present in large numbers in outer space, mainly in gas and dust clouds. Next, these microorganisms are captured by comets, which then, passing near the planets, “sow the germs of life.”
Other scientists have expressed the idea of transferring “spores of life” to Earth by light (under the pressure of light).
In general, interest in the theory of panspermia has not waned to this day.
5. THEORY OF A.I. OPARIN.
The first scientific theory regarding the origin of living organisms on Earth was created by the Soviet biochemist A. I. Oparin (born 1894). In 1924, he published works in which he outlined ideas about how life on Earth could have arisen. 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. Formation of biopolymers (proteins, nucleic acids, polysaccharides, lipids, etc.) from simpler organic substances.
3. The emergence of primitive self-reproducing organisms.
The theory of biochemical evolution has the largest number of supporters among modern scientists. The earth originated about five billion years ago; Initially, its surface temperature was very high (4000 - 80000C). As it cooled, a solid surface (the earth's crust - lithosphere) formed. The atmosphere, originally consisting of light gases (hydrogen, helium), could not be effectively contained by the insufficiently dense Earth, and these gases were replaced by heavier ones: 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 broth” 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, primary living beings of microscopic size were synthesized.
The most difficult problem in modern theory evolution is the transformation of complex organic substances into simple living organisms. Oparin believed that the decisive role in the transformation of non-living things into living things belongs to proteins. Apparently, protein molecules, attracting water molecules, formed colloidal hydrophilic complexes. Further fusion of such complexes with each other led to the separation of colloids from the aqueous medium (coacervation). At the boundary between the coacervate (from the Latin coacervus - clot, heap) and the environment, lipid molecules were built - 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 justified, except for one problem, to which almost all experts in the field of the origin of life had long turned a blind eye. If spontaneously, through random template-free syntheses, single successful designs of protein molecules arose in the coacervate (for example, effective catalysts that provide an advantage for a given coacervate in growth and reproduction), then how could they be copied for distribution within the coacervate, and even more so for transmission to descendant coacervates? The theory turned out to be unable to offer a solution to the problem of exact reproduction - within a coacervate and in generations - of single, randomly appearing effective protein structures.
6. 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 even the simplest living organism from lifeless compounds. Thousands of attempts at such synthesis have been carried out in numerous laboratories around the world. For example, the American scientist S. Miller, based on assumptions regarding 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, and some scientists managed to obtain fairly long chains of peptides (simple proteins). But only! No one has been lucky enough to synthesize even the simplest living organism. Nowadays, Redi’s principle is popular among scientists: “Living things come only from living things.”
But let's assume that such attempts will one day be crowned with success. What will such an experience prove? Only that the synthesis of life requires the human mind, complex, developed science and modern technology. 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, occurred precisely in this direction. Here we observe nothing more than a creative process. The second law of thermodynamics is an immutable law, the only law that has never been questioned, violated or refuted. Therefore, 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 practically zero. Thus, L. Blumenfeld proved that the probability of the random formation during the entire existence of the Earth of at least one DNA molecule (deoxyribonucleic acid - one of the most important components of the genetic code) is 1/10800 Think about the negligible magnitude of this number! After all, in its denominator there is a figure where after one there is a row of 800 zeros, and this number is an incredible number of times greater than the total number of all atoms in the Universe. Contemporary American astrophysicist C. Wickramasinghe expressed the impossibility of abiogenic synthesis in the following way: “It’s faster for a hurricane that sweeps over an old airplane cemetery to assemble a brand new superliner from pieces of scrap than for life to emerge from its components as a result of a random process.”
The theories of abiogenic synthesis and geological data contradict. No matter how far we penetrate into the depths of geological history, we find no traces of the “Azoic era,” that is, the period when life did not exist on Earth.
Now paleontologists have found fossil remains of quite complexly organized creatures - bacteria, blue-green algae, simple fungi. V. Vernadsky was sure that life is geologically eternal, that is, in geological history there was no era when our planet was lifeless. “The problem of abiogenesis (spontaneous generation of living organisms),” the scientist wrote in 1938, “remains fruitless and paralyzes truly urgent scientific work.”
The terrestrial form of life is extremely closely related to the hydrosphere. This is evidenced by the fact that water is the main part of the mass of any terrestrial organism (a person, for example, consists of more than 70% water, and organisms such as jellyfish - 97-98%). It is obvious that life on Earth formed only when the hydrosphere appeared on it, and this, according to geological data, happened almost from the beginning of the existence of our planet. Many of the properties of living organisms are determined precisely by the properties of water, but water itself is a phenomenal compound. Thus, according to P. Privalov, water is a cooperative system in which any action spreads in a “relay race” way over thousands of interatomic distances, that is, “long-range action” takes place.
Some scientists believe that the entire hydrosphere of the Earth is, in essence, 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, all organisms are components, “drops” of this supermolecule of earthly water.
Although we still know only terrestrial protein-nucleic acid-water life, this does not mean that other forms cannot exist in the boundless Cosmos. Some scientists, in particular American ones, G. Feinberg and R. Shapiro, model the following hypothetically possible options:
plasmoids - life in stellar atmospheres due to magnetic forces associated with groups of moving electric charges;
radiobs - life in interstellar clouds based on aggregates of atoms that are in different states of excitation;
Lavobs - life based on silicon compounds, which can exist in lakes of molten lava on very hot planets;
water sparrows - life that can exist at low temperatures on planets covered with “reservoirs” of liquid methane, and draw energy from the transformation of orthohydrogen to parahydrogen;
Thermophages are a type of space life that obtains energy from the temperature gradient in the atmosphere or oceans of planets.
Of course, such exotic life forms currently exist only in the imagination of scientists and science fiction writers. However, the possibility of the real existence of some of them, in particular plasmoids, cannot be ruled out. There is some reason to believe that on Earth, in parallel with “our” form of life, there is another type of life, similar to the mentioned plasmoids. These include some types of UFOs (unidentified flying objects), formations similar to ball lightning, as well as energy “clumps” flying in the atmosphere invisible to the eye, but recorded by color photographic film, which in some cases exhibited intelligent behavior.
Thus, there is now reason to assert that life on Earth appeared from the very beginning of its existence and arose, in the words of Ch. Wickramasinghe, “from an all-pervasive pan-galactic living system.”
CONCLUSION.
Do we have a logical right to recognize the fundamental difference between living and nonliving? Are there any 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 never be formed from it, stand out? Can we recognize organisms as entities completely, fundamentally different from the rest of the world?
Biology of the XX century. deepened the understanding of the essential features of living things, revealing the molecular basis of life. The modern biological picture of the world is based on the idea that the living world is grandiose System highly organized systems.
Undoubtedly, new knowledge will be included in models of the origin of life, and it will become increasingly valid. But the more qualitatively the new differs from the old, the more difficult it is to explain its emergence.
After reviewing the main theories of the origin of life on Earth, the theory of creation seemed to me personally the most likely. The Bible states that God created everything out of nothing. Surprisingly, modern science admits that everything could have been created out of nothing. “Nothing” in scientific terminology is called a vacuum. Vacuum, which is the physics of the 19th century. considered emptiness, according to modern scientific concepts it is a unique form of matter, capable of “giving birth” to material particles under certain conditions. Modern quantum mechanics allows that the vacuum can come into an “excited state”, as a result of which a field can form in it, and from it - matter.
LITERATURE.
1. Bernal D. “The Emergence of Life” Appendix No. 1: Oparin A.I. "The Origin of Life". - M.: "Mir", 1969.
2. Vernadsky V.I. Living matter. - M., 1978.
3. Naydysh V. M. Concepts of modern natural science. – M., 1999.
4. General biology./ Ed. N. D. Lisova. – Mn., 1999.
5. Ponnamperuma S. “The Origin of Life.” - M.: "Mir", 1977.
6. Smirnov I.N., Titov V.F. Philosophy. Textbook for students of higher educational institutions. - M.: Russian Economic Academy named after. Plekhanov, 1998.
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The origin of life is a vast scientific problem. There has been a wealth of new data and research available over the past 10 years. Today, there are still unresolved questions, but the general picture of how life could have arisen from inanimate matter is becoming clearer very quickly. But, as you know, in science, every answer gives rise to 10 new questions.
Models of gradual evolution from inorganic compounds to the first organisms are now well developed. But the history of this issue dates back to the famous author .
The English naturalist and researcher did not write anything about this in his scientific works and did not seriously study theories and hypotheses of the origin of life. This topic was beyond the understanding of 19th century science. Charles was only talking about how the first living organisms that already existed gave rise to all the diversity of biological forms that we see.
Only from his letters to his best friend do we know that Darwin tried to think about this topic, but of course, at that level of knowledge, he could not specifically assume anything except the most general ideas, that somehow organic substances could still be generated from inorganic chemistry, ammonium salts, phosphorus using electricity in a small warm pond.
But it should be noted that even in this letter he guessed a lot very accurately. For example, chemists have discovered a plausible pathway for the abiogenic synthesis of nucleotides, the building blocks of RNA. It turned out that these nucleotides can be spontaneously synthesized under conditions similar to those of a small warm pond.
A huge number of versions of the origin of all life on Earth have been invented. Many of them were invented by conspiracy theorists and pseudoscientists. But still, the bulk of the theories are based on real facts and research.
Main theories of the origin of life:
— creationism;
- panspermia;
— steady state theory;
- spontaneous generation;
- biochemical evolution.
Creationist hypothesis adhered to by people who believe that life was created by a creator, God, the universal mind. It has no evidence, and its promotion is carried out not by scientists, but by journalists, theologians and theologians. They are also joined by people who want to earn extra money through deception.
These same creationists continue to argue that there is a mystery in the question of the origin of people, since archaeologists cannot find some missing link, that is, a transitional form from the ancient Cro-Magnon man to modern homo sapiens. Articles that are extremely important to understand:
» 100% Human Origins: Theories and Hypotheses
Steady State Theory is that living things, together with the universe, and accordingly the whole world, have existed and will always exist, regardless of time. Along with this, bodies and formations derived from the universe, such as stars, planetary systems, and living organisms, are limited in time: they are born and die.
At the moment, this hypothesis has only historical significance, and has not been discussed in scientific circles for a long time, since it has been refuted modern science at the key point: the universe arose thanks to the big bang and its subsequent expansion. An important article on this topic in a simple and in clear language: 100% Origin and evolution of the universe.
Panspermia theory already more scientific. It assumes the following: living organisms brought cosmic bodies such as meteorites or comets to our planet. Some especially dreamy supporters are sure that UFOs and aliens did this deliberately, pursuing their goals.
In our solar system, the probability of finding living organisms anywhere else is extremely small, but life could have flown to us from another star system. Astronomical data show that, according to the biochemical composition of meteorites, meteors and comets, organic compounds, for example, amino acids, can often be found in them. It was they who could become seeds when a cosmic body came into contact with the Earth, just as dandelion seeds scatter hundreds of meters around.
The main counterbalance to the panspermist statements is the logical question of where life came from on other planets from which this same asteroid or comet flew. Thus, the panspermic hypothesis of the alien origin of living organisms can only complement the main version - the biochemical one.
Abiogenesis theory through biochemical evolution, studies and successfully proves the formation of organic structures from inorganic matter, outside the body and without the use of special enzymes.
The synthesis of the simplest organic compounds from inorganic matter can take place in a wide variety of natural conditions: on the planet or in space (for example, in a protoplanetary disk - proplyd). In 1953, the famous classic Miller-Urey experiment was carried out, proving that organics such as amino acids can appear in a mixture of different gases that would imitate the atmospheric composition of the planet.
In nature, over time, it formed and acquired the ability to (by the way, today its synthesis by humans is very difficult). But this is the main building block, and the answer to the question of the origin of life on Earth lies precisely in it.
It is now absolutely clear how the deoxyribonucleic acid molecule arose. At first, biological creatures were based on another similar molecule called RNA. For a long time, there existed another living world in which organisms had hereditary information in the form of a ribonucleic acid molecule that acted as proteins. This molecule is capable of storing hereditary information like DNA and performing active work like proteins.
In modern cells, these functions are separated - DNA stores hereditary information, proteins do the work, and RNA serves as a kind of intermediary between them. In the very first ancient organisms there was only RNA, which coped with both tasks on its own.
An interesting pattern in the question of the origin of all living things is that over the past few years, dozens of new scientific articles have appeared that bring us as close as possible to solving the mystery, and no other theories or hypotheses of the origin of life other than the abiogenic one are currently required.
Life on Earth began three billion years ago. Since then, evolution has transformed elementary single-celled organisms into the variety of shapes, colors, sizes, and functions we see today. But how exactly did life arise in the primordial soup - water contained in shallow springs and saturated with amino acids and nucleotides?
There are many theoretical answers to the question of what exactly caused the emergence of life, from a lightning strike to a cosmic body. Here are just a few of them.
Spark of electricity
That very metaphorical spark of life could be a completely literal spark or many sparks, the source of which was lightning. Electrical sparks entering the water could cause the formation of amino acids and glucose, converting them from an atmosphere rich in methane, water, hydrogen and ammonia. This theory was even confirmed experimentally in 1953, proving that lightning could well have been the cause of the formation of the basic elements necessary for the emergence of the first forms of life.
After conducting the experiment, scientists were able to prove that the early atmosphere of our planet could not contain a sufficient amount of hydrogen, but the volcanic clouds covering the surface of the Earth could include all the necessary elements and, accordingly, enough electrons to cause lightning.
Underwater hydrothermal vents
Relatively strong deep-sea vents could have become a necessary source of hydrogen for the formation of the first living organisms on their rocky surfaces. Even today, a variety of ecosystems develop around hydrothermal vents, even at great depths.
Clay
The first organic molecules could have been found on a clay surface. Clay always contains a sufficient amount of organic components, in addition, it could become a kind of organizer of these components into more complex and effective structures, similar to DNA.
In fact, DNA is a kind of map for amino acids, indicating exactly how they should be organized in the cells of complex fats. A group of biologists from the University of Glasgow in Scotland argue that clay could be such a map for the simplest polymers and fats until they learned to “self-organize.”
Panspermia
This theory makes us think about the possibility of the cosmic origin of life. That is, according to its postulates, life did not originate on Earth, but was simply brought here with the help of a meteorite, for example, from Mars. Enough fragments have been found on earth that presumably came to us from the red planet. Another way of “space taxi” for unknown life forms is comets, which are capable of traveling between star systems.
Even if this is true, panspermia is still unable to answer the question of how exactly life originated where it was brought to planet Earth.
Under the ice cover
It is possible that the oceans and continents three billion years ago were covered with a thick layer of ice, because the Sun did not shine as brightly as it does today. Ice could become a protective layer for fragile organic molecules, blocking ultraviolet rays and cosmic bodies colliding with the surface, cause damage first and weak forms life. In addition, more low temperature could have caused the evolution of the first molecules into stronger and longer lasting ones.
RNA world
The RNA world theory is based on the philosophical question of the egg and the chicken. The fact is that for the formation (doubling) of DNA, proteins are needed, and proteins cannot self-reproduce without the very map embedded in the DNA. So how did life arise if one cannot appear without the other, but both exist perfectly in the present? The answer may be RNA, a ribonucleic acid that can store information like DNA and serve as protein enzymes. Based on RNA, more perfect DNA was formed, then more efficient proteins completely replaced RNA.
Today, RNA exists and performs several functions in complex organisms, for example, it is responsible for the functioning of certain genes. This theory is quite logical, but it does not answer the question of what served as the catalyst for the formation of ribonucleic acid itself. The assumption that it could have appeared by itself is rejected by most scientists. The theoretical explanation is the formation of the simplest acids PNA and TNA, which then developed into RNA.
The simplest beginning
This theory is called holobiosis and comes from the idea that life began not from complex RNA molecules and primary genetic code, but from simple particles interacting with each other for the sake of metabolism. Perhaps these particles over time developed a protective shell, like a membrane, and then evolved into one, more complex organism. This model is called the "enzyme model of metabolism", while the RNA world theory is called the "primary genetic code model".