Municipal educational institution
Average comprehensive school № 45
Theories of the origin of life on Earth
Performed : student of 11th grade "B"
Nigmatullina Maria
Proveila : biology teacher
Trapueva L. S.
Chelyabinsk
2010
1. Introduction
2. Hypotheses about the origin of life
3. Genobiosis and holobiosis
4. Oparin–Haldane theory
5. The RNA world as a precursor to modern life
6. Panspermia
7. Spontaneous generation of life
8. Steady State Theory
9. Creationism
10. Theory of evolution
11. Darwinian theory
12. Conclusion
Introduction
Theories concerning the origin of the Earth and life on it, and indeed the entire Universe, are varied and far from reliable. According to the steady state theory, the universe has existed forever. According to other hypotheses, the Universe could have arisen from a bunch of neutrons as a result of the “Big Bang”, was born in one of the black holes, or was created by the Creator. Contrary to popular belief, science cannot refute the thesis of the divine creation of the Universe, just as theological views do not necessarily reject the possibility that life in the process of its development acquired features that can be explained on the basis of the laws of nature.
Hypotheses about the origin of life
IN different time The following hypotheses have been put forward regarding the origin of life on Earth:
- Biochemical evolution hypothesis
- Panspermia hypothesis
- Stationary State of Life Hypothesis
- Spontaneous generation hypothesis
Theories spontaneous generation And steady state are of historical or philosophical interest only, since the results scientific research contradict the conclusions of these theories.
Theory panspermia does not solve the fundamental question of the origin of life, it only pushes it into the even more nebulous past of the Universe, although it cannot be excluded as a hypothesis about the beginning of life on Earth.
Genobiosis and holobiosis
Depending on what is considered primary, there are two methodological approaches to the question of the origin of life:
Genobiosis- a methodological approach to the question of the origin of life, based on the belief in the primacy of a molecular system with the properties of a primary genetic code.
Holobiosis- a methodological approach to the question of the origin of life, based on the idea of the primacy of structures endowed with the ability to elementary metabolism with the participation of an enzymatic mechanism.
Oparin–Haldane theory
In 1924, the future academician Oparin published an article “The Origin of Life,” which was translated into English in 1938 and revived interest in the theory of spontaneous generation. Oparin suggested that in solutions of high molecular weight compounds they can spontaneously zones of increased concentration are formed, which are relatively separated from the external environment and can maintain exchange with it. He called them Coacervate drops, or simply coacervates .
According to his theory, the process that led to the emergence of life on Earth can be divided into three stages:
- The emergence of organic substances
- The emergence of proteins
- The emergence of protein bodies
Astronomical studies show that both stars and planetary systems arose from gas and dust matter. Along with metals and their oxides, it contained hydrogen, ammonia, water and the simplest hydrocarbon - methane.
The conditions for the beginning of the process of formation of protein structures were established from the moment the primary ocean appeared. In the aquatic environment, hydrocarbon derivatives could undergo complex chemical changes and transformations. As a result of this complication of molecules, more complex organic substances could be formed, namely carbohydrates.
Science has proven that as a result of the use of ultraviolet rays, it is possible to artificially synthesize not only amino acids, but also other biochemical substances. According to Oparin's theory, a further step towards the emergence of protein bodies could be the formation of coacervate droplets. Under certain conditions, the aqueous shell of organic molecules acquired clear boundaries and separated the molecule from the surrounding solution. Molecules surrounded by a water shell united, forming multimolecular complexes - coacervates.
Coacervate droplets could also arise from simply mixing different polymers. In this case, self-assembly of polymer molecules into multimolecular formations occurred - droplets visible under an optical microscope.
The drops were capable of absorbing substances from the outside according to the type open systems. When various catalysts (including enzymes) were included in coacervate drops, various reactions, in particular the polymerization of monomers coming from the external environment. Due to this, the drops could increase in volume and weight, and then split into daughter formations. Thus, coacervates could grow, multiply, and carry out metabolism.
British biologist John Haldane also expressed similar views.
The theory was tested by Stanley Miller in 1953 in the Miller-Urey experiment. He placed a mixture of H 2 O, NH 3, CH 4, CO 2, CO in a closed vessel (Fig. 1) and began to pass electrical discharges through it. It turned out that amino acids are formed. Later in different conditions other sugars and nucleotides were obtained. He concluded that evolution can occur in a phase-separated state from solution (coacervates). However, such a system cannot reproduce itself.
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 was unable to provide a solution to the problem accurate reproduction- within the coacervate and in generations - single, randomly appearing effective protein structures. However, it was shown that the first coacervates could be formed spontaneously from lipids synthesized abiogenically, and they could enter into symbiosis with “living solutions” - colonies of self-replicating RNA molecules, among which were ribozymes that catalyze the synthesis of lipids, and such a community is already possible call it an organism.
Alexander Oparin (right) in the laboratory
The RNA World as a Precursor to Modern Life
TO XXI century the Oparin-Haldane theory, which assumes the initial emergence of proteins, has practically given way to a more modern one. The impetus for its development was the discovery of ribozymes - RNA molecules with enzymatic activity and therefore capable of combining functions that in real cells are mainly performed separately by proteins and DNA, that is, catalyzing biochemical reactions and storing hereditary information. Thus, it is assumed that the first living beings were RNA organisms without proteins and DNA, and their prototype could be an autocatalytic cycle formed by those very ribozymes capable of catalyzing the synthesis of their own copies.
Panspermia
According to the theory of Panspermia, proposed in 1865 by the German scientist G. Richter and finally formulated by the Swedish scientist Arrhenius in 1895, life could have been brought to Earth from space. Living organisms of extraterrestrial origin are most likely to enter with meteorites and cosmic dust. This assumption is based on data on the high resistance of some organisms and their spores to radiation, deep vacuum, low temperatures and other influences. However, there are still no reliable facts confirming the extraterrestrial origin of microorganisms found in meteorites. But even if they got to Earth and gave rise to life on our planet, the question of the original origin of life would remain unanswered.
Francis Crick and Leslie Orgel proposed another option in 1973 - controlled panspermia, that is, the deliberate “infection” of the Earth (along with other planetary systems) with microorganisms delivered on unmanned spacecraft an advanced alien civilization that may have been facing a global catastrophe or simply hoped to terraform other planets for future colonization. They gave two main arguments in favor of their theory - the universality of the genetic code (known other variations of the code are used much less frequently in the biosphere and differ little from the universal one) and the significant role of molybdenum in some enzymes. Molybdenum is a very rare element throughout solar system. According to the authors, the original civilization may have lived near a star enriched in molybdenum.
Against the objection that the theory of panspermia (including controlled) does not solve the question of the origin of life, they put forward the following argument: on planets of another type unknown to us, the probability of the origin of life may initially be much higher than on Earth, for example, due to the presence of special minerals with high catalytic activity.
In 1981, F. Crick wrote the book “Life itself: its origin and nature,” in which he sets out the hypothesis of controlled panspermia in more detail than in the article and in a popular form.
The origin of life on Earth is one of the most important problems of natural science. Even in ancient times, people asked themselves questions about where it came from. Live nature, how life appeared on Earth, where is the line of transition from inanimate to life, etc. Over the course of tens of centuries, views on the problem of life have changed, opinions have been expressed different ideas, hypotheses and concepts. This question worries humanity to this day.
Some ideas and hypotheses about the origin of life became widespread during different periods in the history of the development of natural science. Currently, there are five hypotheses for the origin of life:
1. Creationism is a hypothesis that states that life was created by a supernatural being as a result of an act of creation, that is, God.
2. The steady state hypothesis, according to which life has always existed.
3. The hypothesis of the spontaneous generation of life, which is based on the idea of the repeated emergence of life from nonliving matter.
4. The panspermia hypothesis, according to which life was brought to Earth from outer space.
5. Hypothesis of the historical origin of life through biochemical evolution.
According to creationist hypothesis which has the longest history, the creation of life is an act of divine creation. Evidence of this is the presence in living organisms of a special force, a “soul” that controls all life processes. The creationism hypothesis is inspired by religious views and has nothing to do with science.
According to steady state hypothesis, life never arose, but existed forever along with the Earth, distinguished by a great variety of living things. As living conditions on Earth changed, species also changed: some disappeared, others appeared. This hypothesis is based mainly on paleontological studies. In its essence, this hypothesis does not relate to the concepts of the origin of life, since it does not fundamentally affect the question of the origin of life.
Spontaneous origin of life hypothesis was promoted to ancient China and India as an alternative to creationism. This hypothesis was supported by thinkers Ancient Greece(Plato, Aristotle), as well as scientists of the New Age period (Galileo, Descartes, Lamarck). According to this hypothesis, living organisms (lower) can appear by spontaneous generation from non-living matter containing some kind of “active principle”. So, for example, according to Aristotle, insects and frogs, under certain conditions, can grow in silt and damp soil; worms and algae in stagnant water, but fly larvae in rotten meat as it rots.
However, already from the beginning of the 17th century. This understanding of the origin of life began to be questioned. A significant blow to this hypothesis was dealt by the Italian naturalist and physician F. Redi (1626–1698), who in 1688 revealed the essence of the emergence of life in rotting meat. F. Redi formulated his principle: “All living things come from living things” and became the founder of the concept of biogenesis, which argued that life can only arise from previous life.
The French microbiologist L. Pasteur (1822–1895) with his experiments with viruses finally proved the inconsistency of the idea of the spontaneous generation of life. However, having refuted this hypothesis, he did not propose his own and did not shed light on the question of the origin of life.
Nevertheless, L. Pasteur's experiments had great importance in obtaining rich empirical material in the field of microbiology of his time.
Panspermia hypothesis– about the unearthly origin of life by bringing the “embryos of life” from space to Earth – was first expressed by the German biologist and physician G. Richter at the end of the 19th century. The concept of panspermia (from the Greek. pan- all, sperma– seed) allows for the possibility of the origin of life at different times in different parts of the Universe and its transfer in different ways to Earth (meteorites, asteroids, cosmic dust).
Indeed, some data have now been obtained indicating the possibility of the formation of organic substances chemically in space conditions. Thus, in 1975, amino acid precursors were found in lunar soil. The simplest carbon compounds, including those close to amino acids, have been discovered in interstellar clouds. Aldehydes, water, alcohols, hydrocyanic acid, etc. were found in meteorites.
The concept of panspermia was shared by major scientists late XIX– beginning of the 20th century: German chemist and agronomist J. Liebig, English physicist W. Thomson, German naturalist G. Helmholtz, Swedish physical chemist S. Arrhenius. In 1907, S. Arrhenius even described in his writings how living spores of organisms escape into outer space with dust particles from other planets. Rushing through the vast expanses of space under the influence of starlight pressure, they ended up on planets and, where conditions were favorable (including on Earth), began new life. The ideas of panspermia were also supported by some Russian scientists: geophysicist P. Lazarev, biologist L. Berg, soil biologist S. Kostychev.
There is an idea about the emergence of life on Earth almost from the moment of its formation. As you know, the Earth was formed about 5 billion years ago. This means that life could have arisen during the formation of the Solar System, that is, in space. Since the duration of the evolution of the Earth and life on it varies slightly, there is a version that life on Earth is a continuation of its eternal existence. This position is close to the theory of the eternal existence of life in the Universe. On the scale of the global evolutionary process, it can be assumed that the emergence of life on Earth may apparently coincide with the formation and existence of matter. Academician V. Vernadsky shared the idea of the eternity of life not in the context of its redistribution in space, but in the sense of the inseparability and interconnectedness of matter and life. He wrote that “life and matter are inseparable, interconnected and there is no temporal sequence between them.” The Russian biologist and geneticist Timofeev-Resovsky (1900-1982) points to the same idea. In his brief outline of the theory of evolution (1977), he wittily observed: “We are all such materialists that we are all madly concerned about how life came to be. At the same time, we hardly care how matter arose. Everything is simple here. Matter is eternal, it has always been, and no questions are needed. Always was. But life, you see, must necessarily arise. Or maybe she has always been there too. And there’s no need for questions, it’s just always been there, that’s all.”
To substantiate panspermia, popular science literature provides “facts” about unidentified flying objects, the arrival of aliens on Earth, and rock topological paintings.
However, this concept does not have serious evidence, and many arguments oppose it. It is known that the range of living conditions for the existence of living things is quite narrow. Therefore, it is unlikely that living organisms would survive in space under the influence of ultraviolet rays, X-rays and cosmic radiation. But the possibility of introducing certain prerequisite factors of life onto our planet from space cannot be ruled out. It should be noted that this is not of fundamental importance, since the concept of panspermia does not fundamentally solve the problem of the origin of life, but only transfers it beyond the Earth, without revealing the very mechanism of its formation.
Thus, none of the four hypotheses listed has so far been confirmed by reliable experimental studies.
The fifth hypothesis looks the most convincing from the point of view of modern science - hypothesis of the origin of life in the historical past as a result of biochemical evolution. Its authors are the domestic biochemist academician A. Oparin (1923) and the English physiologist S. Haldane (1929). We will discuss this hypothesis in detail in the next section.
Hypothesis of the origin of life in the historical past as a result of biochemical evolution by A. I. Oparin
From the point of view of A. Oparin’s hypothesis, as well as from the point of view of modern science, the emergence of life from inanimate matter occurred as a result of natural processes in the Universe during the long evolution of matter. Life is a property of matter that appeared on Earth at a certain point in its history. This is the result of processes that take place first for many billions of years on the scale of the Universe, and then for hundreds of millions of years on Earth.
A. Oparin identified several stages of biochemical evolution, the ultimate goal of which was a primitive living cell. Evolution proceeded according to the following scheme:
1. Geochemical evolution of planet Earth, the synthesis of the simplest compounds, such as CO 2, 1 h[H 3, H 2 0, etc., the transition of water from a vapor to a liquid state as a result of the gradual cooling of the Earth. Evolution of the atmosphere and hydrosphere.
2. The formation of organic substances - amino acids - from inorganic compounds and their accumulation in the primary ocean as a result of the electromagnetic influence of the Sun, cosmic radiation and electrical discharges.
3. Gradual complication organic compounds and the formation of protein structures.
4. Isolation of protein structures from the medium, formation of aqueous complexes and creation of an aqueous shell around proteins.
5. The fusion of such complexes and the formation of coacervates (from lat. coacervus– clot, heap, accumulation), capable of exchanging matter and energy with environment.
6. Absorption of metals by coacervates, which led to the formation of enzymes that accelerate biochemical processes.
7. Formation of hydrophobic lipid boundaries between coacervates and the external environment, which led to the formation of semi-permeable membranes, which ensured the stability of the functioning of the coacervate.
8. Development in the course of evolution in these formations of processes of self-regulation and self-reproduction.
Thus, according to A. Oparin’s hypothesis, a primitive form of living matter appeared. This, in his opinion, is the prebiological evolution of matter.
Academician V. Vernadsky associated the emergence of life with a powerful leap that interrupted the lifeless evolution of the earth's crust. This leap (bifurcation) introduced so many contradictions into evolution that they created the conditions for the origin of life.
The origin of life on Earth is one of the most difficult and at the same time relevant and interest Ask 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 known in nature chemical elements, 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 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 have deeply eroded the earth's surface and valleys have 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 her upper layers the water washed away huge amounts of soluble minerals and salts, which ended up in the sea. The water from it continuously evaporated, forming clouds, and the salts settled, and over time, gradual salinization occurred 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 breathing, 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- the oldest simple animals.
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 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 - the original hypothesis modern theory 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, the American researcher S. Miller, passing electric charges through a mixture of gases and vapors, obtained the simplest fatty acids, urea, acetic and formic acid 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, microorganism spores 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 is 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.
The supporters of this hypothesis were the laureates Nobel Prize F. Crick, 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 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 trying to create efficient cell models that multiply on their own, reproducing their own kind.
The problem of the origin and evolution of life is one of the most interesting and at the same time least explored issues related to philosophy and religion. Throughout almost the entire history of the development of scientific thought, it was believed that life is a spontaneously generated phenomenon.
Main theories:
1) life was created by the Creator at a certain time - creationism (from lat. creatio - creation);
2) life arose spontaneously from nonliving matter;
3) life has always existed;
4) life was brought to Earth from Space;
5) life arose as a result of biochemical evolution.
According to theory creationism , the origin of life refers to a specific event in the past that can be calculated. The organisms that inhabit the Earth today are descended from the individually created basic types of living beings. The created species were from the very beginning superbly organized and endowed with the capacity for some variability within certain boundaries (microevolution).
Theory of spontaneous origin of life existed in Babylon, Egypt and China as an alternative to creationism. It goes back to Empedocles and Aristotle: certain “particles” of a substance contain a certain “active principle”, which, under certain conditions, can create a living organism. Aristotle believed that the active principle is in a fertilized egg, sunlight, and rotting meat. For Democritus, the beginning of life was in mud, for Thales - in water, for Anaxagoras - in the air.
With the spread of Christianity, the ideas of spontaneous generation were declared heretical, and for a long time they were not remembered. But Helmont came up with a recipe for producing mice from wheat and dirty laundry. Bacon believed that decay is the germ of a new birth. The ideas of spontaneous generation of life were supported by Copernicus, Galileo, Descartes, Harvey, Hegel, Lamarck, Goethe, and Schelling.
L. Pasteur finally showed in 1860 that bacteria can appear in organic solutions only if they were introduced there earlier. And to get rid of microorganisms, sterilization is necessary, called pasteurization . Hence, the idea was strengthened that a new organism can only come from a living one.
Supporters theories of eternal existence of life believe that on an ever-existing Earth, some species were forced to become extinct or sharply change their numbers in certain places due to changes external conditions. A clear concept on this path has not been developed, since there are some gaps and ambiguities in the fossil record of the Earth.
The hypothesis about the emergence of life on Earth as a result of the transfer of certain embryos of life from other planets is called panspermia (from Greek pan- all, every and sperma- seed). The panspermia theory does not offer a mechanism to explain the primary origin of life and shifts the problem to another place in the Universe. Having originated in space, life remained for a long time in suspended animation at almost T= O K and was brought to Earth by meteorites. At the beginning of the 20th century. Arrhenius came up with the idea of radiopanspermia. He described how particles of matter, grains of dust and living spores of microorganisms escape from inhabited planets into outer space. They, while maintaining vitality, fly in the Universe due to light pressure and, arriving on a planet with suitable conditions, begin a new life.
In the last century, when studying the substance of meteorites and comets, many “precursors of living things” were discovered - organic compounds, water, formaldehyde, cyanogens. Modern adherents of the concept of panspermia believe that life was brought to Earth by accident or intentionally space 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 in outer space, mainly in gas and dust clouds, in large quantities microorganisms are present, where, according to scientists, they are formed. Next, these microorganisms are captured by comets, which then, passing near the planets, “sow the germs of life.”
The first scientific theory regarding the origin of living organisms on Earth was created by the Soviet biochemist A.I. Oparin. In 1924, he published works in which he outlined ideas about how life on Earth could have arisen. According to this theory, life arose under specific conditions ancient earth, and is considered as a natural result of the chemical evolution of carbon compounds in the Universe. According to this theory, 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.
In ideas about the origin of life as a result of biochemical evolution The evolution of the planet itself plays an important role. The earth has existed for almost 4.5 billion years, and organic life for about 3.5 billion years. The young Earth was a hot planet with a temperature of 5...8 10 3 K. As it cooled, refractory metals and carbon condensed, forming the earth's crust. The atmosphere of the primordial Earth was very different from the modern one. Light gases - hydrogen, helium, nitrogen, oxygen, argon, etc. - were not yet retained sufficiently dense planet, and heavier compounds remained (water, ammonia, carbon dioxide, methane).
When the Earth's temperature dropped below 100ºC, water vapor began to condense, forming the World Ocean. At this time, abiogenic synthesis took place, that is, in the primary 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 environmental factors, the synthesis of more complex organic compounds began, 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 the modern theory of evolution is the transformation of complex organic substances into simple living organisms. Oparin believed that a vital 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 aquatic environment(coacervation). At the border between the coacervate (from lat. coacervus- clot, heap) and the environment lined up lipid molecules - primitive cell membrane. It is assumed that colloids could exchange molecules with the environment (a prototype of heterotrophic nutrition) and accumulate certain substances.
The first organisms on earth were single-celled - prokaryotes. After several billion years, eukaryotes formed, and with their appearance, a choice of plant or animal lifestyles emerged, the difference between which lies in the method of nutrition and is associated with the process of photosynthesis. It is accompanied by the entry of oxygen into the atmosphere; the current oxygen content in the atmosphere of 21% was achieved 25 million years ago as a result of the intensive development of plants.