Coursework: The origin of life on Earth. Theories of the origin of life Vernadsky's hypothesis about the origin of life

Introduction
Creationist concept
Panspermia theory
Evolutionist concept
Conclusion
Bibliography

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. In recent years, interest in this “eternal problem” has increased significantly.

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 about the origin of life on earth are varied and far from reliable. Most common theories of the origin of life on Earth are the following:

Life was created by a supernatural being (the Creator) at a specific time (creationism).
Life arose repeatedly from nonliving matter (spontaneous generation).
Life was brought to our planet from outside (panspermia).
Life arose as a result of processes that obey chemical and physical laws (biochemical evolution).

Creationist concept

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 Ussher 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. 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.

Theory of spontaneous generation (self-organization)

This theory of the origin of life on earth 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.

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.

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).

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, in sour milk, in feces, in dental plaque One has only to place perishable and easily rotting substances in a warm place for a while, and microscopic living creatures that were not there before immediately develop in them. The idea arose that in rotting decoctions and infusions the spontaneous generation of living microbes from inanimate matter occurs. This idea was strongly confirmed in the experiments of the Scottish priest Needham, who took meat broth or decoctions of plant substances, placed them in tightly closed vessels and boiled them for a short time, according to Needham, all new embryos should die. they 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.

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 high temperatures 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.

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.

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.

Panspermia theory

The theory of the origin of life on earth panspermia (Greek panspermía - a mixture of all kinds of seeds, from pán - all, everyone and spérma - seed) does not offer any mechanism to explain the initial emergence of life, but puts forward a theory about its non-terrestrial origin, therefore it cannot be considered theory of the origin of life, since it transfers the problem of origin to some other place in the universe. The theory convinces that life could have arisen one or more times at different times and in different parts of the galaxy or in the universe, multiple appearances of UFOs, rock art similar to rockets, astronauts and encounters with aliens are used to substantiate this theory. Russian and American followers in space believe that the formation of life within our solar system is negligible. However, they do not provide any information about the possibility of life in this system. Cyanide genes, hydrocyanic acid, and organic compounds were found in meteorites and comets - precursors of life, which may have played the role of seeds falling on the bare ground.

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. Indeed, in fact, in the end, the main question is precisely whether a 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.

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."

Modern adherents of the concept of panspermia (including Nobel Prize winner 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.

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.”

In general, interest in the theory of panspermia has not waned to this day.

Evolutionist concept

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:

The emergence of organic substances.
Formation of biopolymers (proteins, nucleic acids, polysaccharides, lipids, etc.) from simpler organic substances.
The emergence of primitive self-reproducing organisms.

The theory of biochemical evolution has the largest number of supporters among modern scientists. The earth 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 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.

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 of at least one DNA molecule during the entire existence of the Earth is 1/10800. 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.

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.

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 facts in the nature around us that convince us that life exists forever and has so little in common with inanimate nature that under no circumstances could it ever be formed or separated from it? 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 a grandiose System of 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 review main theories of the origin of life on Earth, the theory of creation seemed most likely to me personally. 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.

Bibliography

Bernal D. The emergence of life Appendix No. 1: Oparin A.I. "The Origin of Life". - M.: "Mir", 1969.
Vernadsky V.I. The beginning and eternity of life. - M., 1989.
Naydysh V. M. Concepts of modern natural science. – M., 1999.
Oparin A. N. The emergence of life on earth. – M., 1957.
Ponnamperuma S. Origin of life. - M.: "Mir", 1977.
Smirnov I.N., Titov V.F. Philosophy. Textbook for students of higher educational institutions. - M.: Russian Economic Academy named after. Plekhanov, 1998.
Yablokov A.V., Yusufov A.G. Evolutionary doctrine. - M.: Higher School, 1988.

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The question of the origin of life on Earth is one of the most difficult questions in modern natural science, to which there is still no clear answer.

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

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

Let us consider the main provisions of these theories.

Theory of spontaneous generation

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

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

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

Disputes about the possibility of spontaneous generation of life intensified in connection with the discovery of microorganisms. If complex living things cannot spontaneously generate, perhaps microorganisms can?

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

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

Rice. 1. Pasteur flask

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

Creation theory

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

The theory of creationism is still quite widespread today, not only in religious but also in scientific circles. It is usually used to explain the most complex issues of biochemical and biological evolution that currently have no solution, related to the emergence of proteins and nucleic acids, the formation of the mechanism of interaction between them, the emergence and formation of individual complex organelles or organs (such as the ribosome, the eye or brain). Acts of periodic “creation” also explain the absence of clear transitional links from one type of animal
to another, for example, from worms to arthropods, from monkeys to humans, etc. It must be emphasized that the philosophical dispute about the primacy of consciousness (supermind, absolute idea, deity) or matter is fundamentally insoluble, however, since the attempt to explain any difficulties of modern biochemistry and evolutionary theory by fundamentally incomprehensible supernatural acts of creation takes these issues beyond the scope of scientific research, the theory of creationism cannot be classified as a scientific theory of the origin of life on Earth.

Theories of steady state and panspermia

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

However, the steady state theory, which assumes an infinitely long existence of the universe, does not agree with the data of modern astrophysics, according to which the universe arose relatively recently (about 16 billion years ago) through a primary explosion.

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

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

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

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

Prebiological (chemical) evolution

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

Under the influence of compression forces, the particles from which the Earth is formed release enormous amounts of heat. Thermonuclear reactions begin in the depths of the Earth. As a result, the Earth is heating up greatly. Thus, 5 billion years so-called. The Earth was a hot ball rushing through outer space, the surface temperature of which reached 4000-8000 ° C (laughter. 2).

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

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

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

About 4 billion years so-called. - formation of the earth's crust and primary atmosphere

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

Energy for synthesis is provided by:

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

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

simple organic molecules - monomers
complex organic molecules - biopolymers

Scheme. 2. Main stages of chemical evolution

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

Recognition and wide dissemination of the theory of A.I. Oparin was largely promoted by the fact that the processes of abiogenic synthesis of organic molecules are easily reproduced in model experiments.

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

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

Rice. 3. Installation of S. Miller

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

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

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

However, the processes of polymerization of individual nucleotides, amino acids and sugars are condensation reactions; they occur with the elimination of water, therefore, the aqueous environment does not promote polymerization, but, on the contrary, the hydrolysis of biopolymers (i.e., their destruction with the addition of water).

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

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

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

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

Proteins are “worker molecules,” “engineer molecules” of a living cell. When characterizing their role in metabolism, biochemists often use figurative expressions such as “protein works,” “enzyme conducts a reaction.” The most important function of proteins is catalytic. As you know, catalysts are substances that accelerate chemical reactions, but are not themselves included in the final reaction products. Catalyst tanks are called enzymes. Enzymes bend and speed up metabolic reactions thousands of times. Metabolism, and therefore life, is impossible without them.

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

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

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

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

What follows is fairly well explained by a process that could be called “natural selection” at the molecular level. When self-copying (self-assembling) RNA molecules, inaccuracies and errors inevitably arise. The RNA copies containing errors are copied again. When copying again, errors may occur again. As a result, the population of RNA molecules in a certain area of the primary ocean will be heterogeneous.

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

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

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

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

It is obvious that at a certain stage of biochemical evolution, RNA molecules encoding not only protective proteins, but also catalyst proteins (enzymes) that sharply accelerate the speed of RNA copying received an advantage. Apparently, this is precisely how the process of interaction between proteins and nucleic acids, which we currently call life, arose.

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

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

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

The phenomenon of coacervation is that under certain conditions (for example, in the presence of electrolytes), high molecular weight substances are separated from the solution, but not in the form of a precipitate, but in the form of a more concentrated solution - coacervate. When shaken, the coacervate breaks up into individual small droplets. In water, such drops are covered with a hydration shell (a shell of water molecules) that stabilizes them - Fig. 5.

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

Coacervate droplets that arise as a result of concentrating protein solutions during mixing under the influence of waves and wind can become covered with a shell of lipids: a single shell, reminiscent of soap micelles (when a drop is lifted off the surface of water covered with a lipid layer once), or a double shell, reminiscent of a cell membrane ( when a drop covered with a single-layer lipid membrane repeatedly falls onto a lipid film covering the surface of a reservoir - Fig. 5).

The processes of the emergence of coacervate droplets, their growth and “budding”, as well as their “dressing” with a membrane of a lipid bilayer are easily simulated in laboratory conditions.

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

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

A possible path of transition from coacervate drops to primitive flares:

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

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

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

The Earth was probably formed 4.5-5 billion years ago from a giant cloud of cosmic dust. the particles of which were compressed into a hot ball. Water vapor was released from it into the atmosphere, and water fell from the atmosphere onto the slowly cooling Earth for millions of years in the form of rain. A prehistoric Ocean formed in the depressions of the earth's surface. The original life arose in it approximately 3.8 billion years ago.

The emergence of life on Earth

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

Millions of years passed, and the temperature of the Earth's surface dropped even more. Stormwater stopped evaporating and began to flow into huge puddles. Thus began the influence of water on the earth's surface. And then, due to the drop in temperature, a real flood occurred. The water, which had previously evaporated into the atmosphere and turned into its component, continuously fell to the Earth, with thunder and lightning, powerful showers fell from the clouds.

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

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

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

Life then existed in a thin bacterial film at the bottom of reservoirs and in damp places. This era of the development of life is called Archean. From bacteria, and perhaps in a completely independent way, tiny single-celled organisms arose - the most ancient protozoa.

What did the primitive Earth look like?

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

Theories of the origin of life on Earth

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

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

Biogenesis theory

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

Panspermia theory

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

To substantiate this theory, multiple sightings of UFOs, rock paintings of objects resembling rockets and “astronauts,” and reports of alleged encounters with aliens are used. When studying the materials of meteorites and comets, many “precursors of life” were discovered in them - substances such as cyanogens, hydrocyanic acid and organic compounds, which may have played the role of “seeds” that fell on the bare Earth.

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

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

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

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

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

Some scientists suggest that the result of this bombardment is the colonization of life in the Earth's oceans. However, several studies on this topic indicate that our planet has more water reserves than it should. And this excess is attributed to comets that came to us from the Oort Cloud, which is supposedly located one light year away from us.

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

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

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

Life on Earth could have arisen thanks to clay

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

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

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

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

In water, or more precisely in a solution, little could happen, because the processes in a solution are absolutely chaotic, and all compounds are very unstable. Modern science considers clay - more precisely, the surface of particles of clay minerals - as a matrix on which primary polymers could form. But this is also only one of many hypotheses, each of which has its own strengths and weaknesses. But to simulate the origin of life on a full scale, you really need to be God. Although in the West today articles with the titles “Cell Construction” or “Cell Modeling” are already appearing. For example, one of the last Nobel laureates, James Szostak, is now actively attempting to create effective cell models that multiply on their own, reproducing their own kind.

Theory of spontaneous generation

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

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

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

In this regard, in 1859, the French Academy announced the award of a prize to the one who would finally decide the question of the possibility or impossibility of the spontaneous generation of life. This prize was received in 1862 by the famous French chemist and microbiologist Louis Pasteur. Just like Spalanzani, he boiled the nutrient broth in a glass flask, but the flask was not an ordinary one, but with a neck in the form of a 5-shaped tube. Air, and therefore the “life force,” could penetrate the flask, but dust, and with it the microorganisms present in the air, settled in the lower leg of the 5-shaped tube, and the broth in the flask remained sterile (Fig. 2.1.1 ). However, as soon as the neck of the flask was broken or the lower leg of the 5-shaped tube was rinsed with sterile broth, the broth began to quickly become cloudy - microorganisms appeared in it.

Thus, thanks to the works of Louis Pasteur, the theory of spontaneous generation was recognized as untenable and the theory of biogenesis was established in the scientific world, the brief formulation of which is “all living things are from living things.”

Creation theory

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

Theories of steady state and panspermia

Prerequisites for the emergence of life. According to scientific data, the planet of the solar system, the Earth, was formed from a gas-dust cloud about 4.5-5 billion years ago. Such gas-dust matter is found in interstellar space at the present time.
For the emergence of life on Earth, certain cosmic and planetary conditions are necessary. One of these conditions is the size of the planet. The mass of the planet should not be too large, since the energy of the atomic decay of natural radioactive substances can lead to overheating of the planet or radioactive contamination of the environment. But if the mass of the planet is small, then it will not be able to maintain an atmosphere around itself. It is also necessary for the planet to move around the star in a circular orbit, allowing it to constantly and evenly receive the required amount of energy. For the development and emergence of life, a uniform flow of energy to the planet is important, because the existence of living organisms is possible within certain temperature conditions. Thus, the main conditions for the emergence of life on Earth include the size of the planet, energy, and certain temperature conditions. It has been scientifically proven that these conditions exist only on planet Earth.
The question of the origin of life has long been of concern to humanity; many hypotheses are known.
In ancient times, due to the lack of scientific data about the origin of life, there were different views. The great scientist of his time, Aristotle (IV century BC), was of the opinion that a louse arose from meat, a bug from animal juice, and a worm from silt.
In the Middle Ages, despite the expansion of scientific knowledge, there were different ideas about the origin of life. Later, with the discovery of the microscope, data on the structure of the organism were clarified. Accordingly, experiments appeared that shook the ideas about the origin of life from inanimate nature. However, until the middle of the 17th century. there were still many supporters of the view of spontaneous generation.
To understand the secrets of life, the English philosopher F. Bacon (1561-1626) proposed conducting research in the form of observations and experiments. The scientist’s views had a special influence on the development of natural science.
In the middle of the 17th century. Italian physician Francesco Redi (1626-1698) dealt a serious blow to the theory of spontaneous generation of life with the following experiment (1668). He placed meat in four vessels and left them open, and covered the other four vessels with meat with gauze. Larvae hatched in open vessels from eggs laid by flies. In a closed vessel, where the flies could not penetrate, the larvae did not appear. Based on this experiment, Redi proved that flies hatch from eggs laid by flies, i.e. flies do not spontaneously generate.
In 1775, M. M. Terekhovsky conducted the following experiment. He poured broth into two vessels. He boiled the first vessel with the broth and tightly closed the stopper, where he later observed no changes. M. M. Terekhovsky left the second vessel open. A few days later, he discovered a sour broth in an open vessel. However, at that time they did not yet know about the existence of microorganisms. According to the ideas of these scientists, living things arise from non-living things under the influence of supernatural “life forces.” The “life force” cannot penetrate into a closed vessel, and when boiled it dies. Such views are called vitalistic (Latin vitalis - “living, vital”).
On the issue of the origin of life on Earth, two opposing views have emerged.
The first (theory of abiogenesis) - living things arise from inanimate nature. The second view (biogenesis theory) - living things cannot arise spontaneously, they come from living things. The irreconcilable struggle between these views continues to this day.
To prove the impossibility of the spontaneous generation of life, the French microbiologist L. Pasteur (1822-1895) carried out such an experiment in I860. He modified the experiment of M. Terekhovsky and used a flask with an S-shaped narrow neck. L. Pasteur boiled the nutrient medium and placed it in a flask with a long curved neck; air passed into the flask freely. But the microbes could not get into it, since they settled in the curved part of the neck. In such a flask, the liquid was preserved for a long time without the appearance of microorganisms. With the help of such a simple experiment, L. Pasteur proved that the views of the vitalists were wrong. He convincingly proved the correctness of the theory of biogenesis - living things arise only from living things.
But supporters of the theory of abiogenesis did not recognize JI’s experiments. Pasteur.

Louis Pasteur (1822-1895). French microbiologist. Studied the processes of fermentation and decay. He proved the impossibility of spontaneous generation of microorganisms. Developed a method for pasteurizing food. Proved the spread of infectious diseases through microbes.

Alexander Ivanovich Oparin (1894-1980). Famous Russian biochemist. Founder of the hypothesis about the emergence of organic substances by abiogenic means. He developed a natural science theory of the origin of life on Earth. Founder of evolutionary biochemistry.

John Haldane (1892-1964). Famous English biochemist, geneticist and physiologist. Author of the "primordial soup" hypothesis, one of the founders of population genetics. He has many works in the field of determining the frequency of human mutation and the mathematical theory of selection.

Some of them argued that "there is some kind of life force, and life on Earth is eternal." This view is called creationism (Latin creatio - “creator”). Its supporters were K. Linnaeus, J. Cuvier and others. They argued that the germs of life were brought to Earth from other planets through meteorites and cosmic dust. This view is known in science as the theory of panspermia (Greek pan - “unity”, sperma - “embryo”). The “Theory of Panspermia” was first proposed in 1865 by the German scientist G. Richter. In his opinion, life on Earth did not appear from inorganic substances, but was brought from other planets through microorganisms and their spores. This theory was supported by famous scientists at that time G. Helmholtz, G. Thomson, S. Arrhenius, T. Lazarev. However, to date there is no scientific evidence of the introduction of microorganisms in meteorites from distant outer space.
In 1880, the German scientist W. Preyer proposed the theory of the eternity of life on Earth, which was supported by the famous Russian scientist V.I. Vernadsky. This theory denies the difference between living and inanimate nature.
The concept of the origin of life is closely related to the expansion and deepening of knowledge about living organisms. In this area, the German scientist E. Pfluger (1875) studied protein substances. He attached particular importance to protein as the main component of the cytoplasm, trying to explain the origin of life from a materialistic point of view.
The hypothesis of the Russian scientist A.I. Oparin (1924), which proves the emergence of life on Earth abiogenically from organic substances, is of great scientific importance. His views were supported by many foreign scientists. In 1928, the English biologist D. Haldane came to the conclusion that the energy required for the formation of organic compounds is the ultraviolet rays of the Sun.

John Bernal (1901-1971). English scientist, public figure. Founder of the theory of the origin of modern life on Earth. He created works on studying the composition of proteins using X-rays.

Currently, many scientists are of the opinion that life first appeared as a result of the isolation of amino acids and other organic compounds in sea water.
Vitalism. Abiogenesis. Biogenesis. Creationism. Panspermia.

According to the theory of abiogenesis, life emerged from inanimate nature as a result of the complication of chemical compounds.
The experiment of F. Redi convincingly proved the inconsistency of the theory of spontaneous generation.
The vitalistic theory means that life arose under the influence of the “vital force.”
According to the theory of panspermia, life on Earth was brought from another planet, and was not created from organic substances.
Modern definition of life: “Life is an open self-regulating and self-reproducing system built from biopolymers - proteins and nucleic acids.”

How did Aristotle explain the emergence of life?
What is the meaning of the panspermia theory?
What did F. Redi's experiment prove?

What conditions are necessary for life to arise?
How does creationism explain the origin of life?
Describe L. Pasteur's experience?

What mutually opposing points of view are there to explain the emergence of life?
What is the significance of E. Pfluger’s research?
What hypotheses were put forward by A. I. Oparin and D. Haldane?

Write an essay or report on different views on the origin of life.

In modern science they consider several theories the origin of life on Earth. Most modern models indicate that organic compounds - the first living organisms appeared on the planet approximately 4 billion years ago.

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Development of ideas about the emergence of life

At a certain historical period, scientists had different ideas about how life appeared on. Until the twentieth century, the following hypotheses played a huge role in scientific circles:

The theory of spontaneous generation.
The theory of the stationary state of life.
Oparin's theory (partially supported now).

Theory of spontaneous generation

It’s interesting, but the theory of the spontaneous generation of life on the planet arose ancient times. She existed with theory of divine origin all living organisms on the planet.

The ancient Greek scientist Aristotle believed that the spontaneous generation hypothesis is true, while the divine is only a deviation from reality. He believed that life began spontaneously.

According to his thoughts, the theory of spontaneous generation is that some “active principle” unknown to people under certain conditions capable of creating from an inorganic compound simple organism.

After the adoption of Christianity in Europe and its spread, this scientific assumption faded into the background - its place was taken by divine theory.

Steady State Theory

According to this scientific assumption, it is impossible to answer when life arose on Earth, since it existed forever. Thus, the followers of the theory testify that species never originated - they are only capable of disappearing or changing their numbers (). The stationary state of life hypothesis was quite popular until mid-20th century.

The so-called "theory of the eternity of life" suffered a general collapse when it was established that The universe didn't always exist either., but was created after the Big Bang. Answering the question: how many forms of life existed initially, the answer emerges that all four, including viruses, which contradicts generally accepted .

For this reason, the hypothesis is not discussed in academic scientific circles. The “Theory of the Eternity of Life” is of exclusively philosophical interest, since its conclusions are largely do not correspond with modern achievements Sciences.

Oparin's theory

In the twentieth century, the attention of scientists was attracted by an article by Academician Oparin, which returned interest in the theory spontaneous generation of life. He considered in it some “proto-organisms” - coacervate drops or simply “primary broth”, as they were dubbed in scientific circles.

These droplets were protein balls that attracted molecules and fats, which then bonded. This is how the first storage media were created - first brochures, which contain DNA.

This hypothesis does not answer where it came from, and therefore in academic circles many people refute it.

Previous theories of the origin of life on Earth are not considered fundamental in modern scientific thought. A small group of scientists also suggests that life could have originated in hot water, which surrounds underwater volcanoes. This hypothesis not main, but it has not yet been refuted, and therefore it is worthy of mention.

Basic theories of the origin of life on Earth

The main theories of the origin of life on Earth appeared not so long ago, namely in the twentieth century - a period when humanity made more discoveries than in its entire previous history.

Modern hypotheses of the origin of life on Earth have been confirmed to varying degrees by a number of studies, and are key for discussion in academic circles. Among them the following can be noted:

biochemical theory of the origin of life;
RNA world hypothesis;
PAH world theory.

Biochemical theory

Considered key biochemical theory the origin of life on the planet, which most scientists adhere to.

Chemical evolution preceded the appearance of organic life. It is during this stage that the first living organisms appear, which arose as a result chemical reactions from inorganic molecules.

The appearance of organic life forms 4 billion years ago as a result of reactions is very likely, since it was then that the most favorable environment.

A temperature of 1000 degrees is considered optimal. The oxygen content in the air was minimal, because in large quantities it destroys simple organic compounds.

RNA World

The RNA world is just a hypothesis, which indicates that before the emergence of DNA, genetic information was stored by RNA compounds.

In the 1980s, it was proven that RNA compounds could exist autonomously and self-replicate. Millions of years of RNA life cycle have led to the fact that During mutations, DNA connections arose, which acted as specialized gene repositories. The evolution of RNA was proven by many experiments, which partially explain the origin of life on Earth and answer the question of how life developed on Earth.

The world of PAHs (polyaromatic hydrocarbons)

The world of PAHs is considered stage of chemical evolution and indicates that the first RNAs arose from PAHs, which later led to the creation of DNA and life on the planet.

PAHs can still be observed today - they are widespread in the Universe and were first discovered in nebulae throughout the cosmos. A number of researchers call PAHs “seeds of life.”

Alternative theories

It just so happens that the most interesting theories are alternative, and many scientists even ridicule them. The reliability of alternative assumptions cannot yet be confirmed, and they are partially, or largely contradict modern scientific ideas, but their mention is mandatory.

Space hypothesis

According to this assumption, life never existed on Earth, and it could not have originated here, since there were no prerequisites. The first living organisms appeared on the planet after fall of a cosmic body, which brought them on itself from another galaxy.

This hypothesis does not answer the question: how many forms of life were there, what they were, and how they developed further.

It is also impossible to establish when this cosmic body fell. But the most important thing is scientists don't believe that any organism could survive on a falling cosmic body after it entered the Earth's atmosphere.

In recent years, scientists have discovered bacteria that can exist under extreme circumstances and even outer space, but if a meteorite or asteroid burned, they certainly would not have survived.

UFO hypothesis

When highlighting the most interesting hypotheses, one cannot fail to mention the assumption that life on Earth is the work of aliens. Proponents of this hypothesis believe that in such a vast Universe, the probability of the existence of other forms of intelligent life is very high. Science also does not deny this fact., since people have not yet explored 99% of space.

Followers of the UFO hypothesis say that one of the intelligent life forms we call aliens deliberately brought life to Earth. There are several theories as to why they created man.

Some say it's just part of the experiment, during which they observe people. Adherents of this assumption cannot give a reliable answer to why they need to observe people, and what is the meaning of this experiment.

The latter indicate that a certain race of cosmic beings is engaged in the spread of life in the Universe, and humans are one of the many races they created. Therefore, there are some the forefathers of all living things, which a person could take for gods.

The cosmic theory of the origin of life on Earth does not answer the main question: where did life originally originate before it was brought to Earth?

Theological hypothesis

Attention! The divine theory of the origin of life on the planet is the most ancient among all, and at the same time it is considered one of the most widespread in the 21st century.

Adherents of the hypothesis believe in some omnipotent being or beings, which are usually called gods.

In different religions, the gods have different names, as well as their number. Christianity speaks of only one god, like Islam, but the pagans believed in dozens, or even hundreds of gods, each of which is responsible for something specific.

For example, one god is considered the creator of love, and the second is considered the ruler of the seas.

Christians believe that God created the Earth and life on it in just seven days. It was he who created the first man and woman, who became the ancestors of humanity.

Since billions of people on the planet identify themselves with a particular religion, they believe that all life was created by the hands of a god or gods.

And although many religions share the same facts, in scientific circles deny the existence of an omnipotent being, which created the world and life in it, since this theory contradicts many scientific achievements and discoveries.

Also, the divine hypothesis does not make it possible to establish when life arose on Earth. Some scriptures do not contain this information at all; in others, the data simply does not coincide, which casts enormous doubt on the hypothesis.

None of the above theories not ideal and cannot comprehensively reveal the question of the origin of life on the planet. Which theory to follow is up to you to decide.

Creationist concept

Theory of spontaneous generation (self-organization)

Panspermia theory

Evolutionist concept

Conclusion

Bibliography

Theory of spontaneous generation

Creation theory

Theories of steady state and panspermia

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

Prebiological (chemical) evolution

The emergence of life on Earth

What did the primitive Earth look like?

Theories of the origin of life on Earth

Biogenesis theory

Panspermia theory

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

Life on Earth could have arisen thanks to clay

Theory of spontaneous generation

Creation theory

Theories of steady state and panspermia

Development of ideas about the emergence of life

Theory of spontaneous generation

Steady State Theory

Oparin's theory

Basic theories of the origin of life on Earth

Biochemical theory

RNA World

The world of PAHs (polyaromatic hydrocarbons)

Alternative theories

Space hypothesis

UFO hypothesis

Theological hypothesis

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