Theories about the origin of life. Hypotheses about the origin of life

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 They believe that on an ever-existing Earth, some species were forced to become extinct or dramatically change their numbers in certain places due to changes in external conditions. A clear concept on this path has not been developed, since there are some gaps and ambiguities in the 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 their viability, fly in the Universe due to light pressure and, arriving on a planet with suitable conditions, begin new life.

In the last century, when studying the matter 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 either accidentally or intentionally by 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) Appearance organic matter.

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 to form 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 by the insufficiently dense planet, but 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 the decisive role in the transformation of non-living things into living things belongs to proteins. Apparently, protein molecules, attracting water molecules, formed colloidal hydrophilic complexes. Further fusion of such complexes with each other led to the separation of colloids from the aqueous medium (coacervation). At the border between the coacervate (from lat. coacervus- clot, heap) and the environment formed lipid molecules - a primitive cell membrane. It is assumed that colloids could exchange molecules with 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.

The idea of ​​life on Earth is ambiguous. There are several hypotheses about the origin of life on Earth.

Creationism – earthly life was created by the Creator. The idea of ​​the Divine creation of the world is held by followers of almost all the most widespread religious teachings. It is currently impossible to either prove or disprove the creationist concept.

The Eternity of Life Hypothesis – life, like the Universe itself, has always existed, and will exist forever, without beginning or end. At the same time, individual bodies and formations - galaxies, stars, planets, organisms - arise and die, i.e. existence is limited in time. Life could spread from one galaxy to another, and this idea of ​​“bringing” life to Earth from Space is called panspermia. The idea of ​​“eternity and beginninglessness” of life was adhered to by many scientists, among them S.P. Kostychev, V.I. Vernadsky.

The hypothesis of the spontaneous generation of life from inanimate matter. Ideas about the spontaneous generation of life have been expressed since antiquity. For thousands of years they believed in the possibility constant spontaneous generation of life, counting it in the usual way the emergence of living beings from inanimate matter. According to many medieval scientists, fish could be born from silt, worms from soil, mice from rags, flies from rotten meat.

In the 17th century Italian scientist F. Redi experimentally showed the impossibility of constant spontaneous generation of living things. He placed pieces of meat in several glass vessels. He left some of them open, and covered some with muslin. Fly larvae appeared only in open vessels; they were not present in closed ones. Redi's principle: “living from living.” The version of the constant spontaneous generation of living organisms was finally refuted in the middle of the 19th century. L. Pasteur. Experiments have convincingly shown that in the modern era, living organisms of any size descend from other living organisms.

Hypothesis of biochemical evolution. According to ideas expressed in the 20s. XX century A.I. Oparin, and then J. Haldane, life, or rather living things, arose from inanimate matter on Earth as a result biochemical evolution.

Conditions for the emergence of life during biochemical evolution

Currently, scientists have proposed more or less probable explanations of how, in the primary conditions of the Earth, various forms of life gradually, step by step, developed from inanimate matter. The following conditions contributed to the emergence of life through chemical evolution:

— initial absence of life;

— the presence in the atmosphere of compounds with reducing properties (in the almost complete absence of oxygen O 2);

— availability of water and nutrients;

— presence of an energy source (relatively high temperature, powerful electrical discharges, high level UV radiation).

The mechanism of the origin of life

The age of the Earth is about 4.6–4.7 billion years. Life has its own history, which began, according to paleontological data, 3–3.5 billion years ago.

In 1924, Russian academician A.I. Oparin put forward a hypothesis about the mechanism of the origin of life. In 1953, American scientists S. Miller And G. Yuri experimentally confirmed the hypothesis of the formation of organic substances (monomers) from gases present in the primary atmosphere of the Earth.

There is now quite a lot of indisputable evidence that primary atmosphere The Earth was oxygen-free and probably consisted mainly of water vapor H 2 O, hydrogen H 2 and carbon dioxide CO 2 with a small admixture of other gases (NH 3, CH 4, CO, H 2 S). Life that arose on Earth gradually changed these conditions and transformed the chemistry of the upper shells of the planet.

The origin of life on Earth - details for inquiring minds

According to biochemical theory of A.I. Oparina in the absence of oxygen and living organisms, abiogeno the simplest organic compounds were synthesized - monomers, precursors of biological macromolecules of living matter and a number of other organic compounds.

Possible sources of energy for the formation of organic substances without the participation of living organisms apparently included electrical discharges, ultraviolet radiation, radioactive particles, cosmic rays, shock waves from meteorites entering the earth's atmosphere, and heat from intense volcanic activity. In the absence of oxygen, which could destroy them, as well as living organisms that would use them as food, abiogenically formed organic substances accumulated in the World Ocean - “ primordial broth».

The next step was the formation of larger polymers from small organic monomers, again without the participation of living organisms. American scientist S. Fox obtained polypeptides of various lengths by heating a mixture of dry amino acids. They were called proteinoids, i.e. proteinaceous substances. Apparently, on the primitive Earth, the formation of such proteinoids and polynucleotides with a random sequence of amino acids or nucleotides could occur during the evaporation of water in reservoirs remaining after low tide.

Once a polymer is formed, it is able to influence the formation of other polymers. Some proteinoids are capable, like enzymes, of catalyzing certain chemical reactions: It was this ability that was probably the main feature that determined their subsequent evolution. Experiments show that one polynucleotide arising from a mixture of nucleotides can serve as a template for the synthesis of another.

Polypeptides, due to their amphotericity, formed colloidal hydrophilic complexes (i.e., water molecules, forming a shell around protein molecules, isolated them from the entire mass of water). In this case, individual complexes associated with each other, which led to the formation of droplets isolated from the primary environment coacervates, capable of absorbing and selectively accumulating various compounds. Natural selection contributed to the survival of the most stable coacervate systems capable of further complication.

Further self-organization of complex molecules, which occurred due to concentration at the boundary between coacervates and external environment lipid molecules, led to the formation of membrane-type partitions. In the internal cavities of coacervates, where molecules can only selectively penetrate, the evolution from chemical reactions to biochemical ones began. One of the most important stages of this theory was the combination of the ability of polynucleotides with the catalytic activity of enzyme proteins.

The point of view of Oparin and his supporters essentially shaped holobiosis hypothesis : the structural basis of the precellular ancestor (bioid) is made up of life-like open (coacervate) microsystems, like a cellular one, capable of elementary metabolism with the participation of an enzymatic mechanism. Primary protein substance.

Genobiosis hypothesis : the primary one was a macromolecular system, similar to a gene, capable of self-reproduction. The RNA molecule is recognized as primary.

Initial stages development of life on Earth

The modern idea of ​​life on Earth comes down to the fact that the first primitive cells appeared in the aquatic environment of the Earth 3.8 billion years ago - anaerobic, heterotrophic prokaryotes , they ate abiogenically synthesized organic substances or their less fortunate brethren; energy needs were satisfied through fermentation.

With an increase in the number of heterotrophic prokaryotic cells, the supply of organic compounds in the primary ocean was depleted. Under these conditions, organisms capable of autotrophy, i.e. to the synthesis of organic org. substances from inorganic. Apparently, the first autotrophic organisms were chemosynthetic bacteria. The next stage was the development of reactions using sunlight - photosynthesis.

For the first photosynthetic bacteria, the source of electrons was hydrogen sulfide. Much later, cyanobacteria (blue-green algae) developed a more complex process for obtaining electrons from water. As a by-product of photosynthesis in earth's atmosphere oxygen began to accumulate. This was a prerequisite for the emergence in the course of evolution aerobic respiration. Ability to synthesize during respiration large quantity ATP allowed organisms to grow and reproduce faster, as well as to increase the complexity of their structures and metabolism.

It is believed that the ancestors of eukaryotes were prokaryotic cells. According to cell theory symbiogenesis A eukaryotic cell is a complex structure consisting of several prokaryotic cells that complement each other. A number of data indicate the origin of mitochondria and chloroplasts, and possibly flagella, from early prokaryotic cells that became internal symbionts of a larger anaerobic cell.

Profound transformations in structure and functioning significantly increased the evolutionary capabilities of eukaryotes, which, having appeared only 0.9 billion years ago, were able to reach the multicellular level and form modern flora and fauna. For comparison, it should be said that from the appearance of the first prokaryotic cells (3.8 billion years ago) until the appearance of the first eukaryotic cells it took 2.5 billion years.

The origin of life on Earth: The main stages of the development of the biosphere

The diversity of living organisms is the basis of organization and

biosphere sustainability

Modern biological diversity: there are from 5 to 30 million species on Earth. Biological diversity– as a result of the interaction of two processes – speciation and extinction. Biological diversity is the most valuable “resource” on the planet. Biological diversity includes two concepts: genetic diversity, or the diversity of genetic properties among individuals of the same species, and species diversity, or the number various types within a community or the entire biosphere. Biodiversity provides new sources of food, energy, raw materials, chemicals and medicinal products. Genetic diversity allows species to improve, adapt, use the necessary resources, and find a place in the biogeochemical cycle of the Earth. Biodiversity is nature's insurance policy against disasters.

Structure of biological diversity. The units of the system are demes and populations. Gene pool of the population.

Evolution of biological diversity. A cross-cutting evolutionary trend—increasing diversity, interrupted by sharp declines as a result of mass extinctions of species.

Human impact on biological diversity. Direct damage resulting from human activity. Indirect damage from impacts that disrupt the balanced relationships and processes in ecosystems.

Conservation of biological diversity. Inventory and protection of biological diversity. Combining human rights with animal rights. Bioethics. Combination of ethical principles and economic interests. Conservation and natural evolution of biological diversity.

Biodiversity as an indicator of impacts. Both individual components of biological diversity and summary indicators are used. Violation of the structure of function or successional sequence of ecosystem development is usually expressed in a reduction in biological diversity.

Currently, about 3 million species of living organisms are described on Earth. In the modern taxonomy of living organisms, there is the following hierarchy of taxa: kingdom, division (type in the taxonomy of animals), class, order (order in the taxonomy of animals), family, genus, species. In addition, intermediate taxa are distinguished: super- and subkingdoms, super- and subdivisions, etc.

Throughout the history of natural science there have arisen various hypotheses origin of life on Earth. Some of them can be classified as idealistic; from the point of view of science, they are not valid. Others are quite materialistic, but among them there are also those who are completely rejected modern science.

Probably the very first hypothesis of the origin of life, based on human feelings and a limited amount of knowledge, should be considered creationism. According to him, life on Earth arose spontaneously, as a result of an act of divine creation. God is assumed to be a supernatural being. In creationism, by the will of God or gods, out of some chaos, the cosmos, planets, life, and man are born.

Creationism was adhered to by C. Linnaeus. He believed that species on Earth exist unchanged, the way God created them.

According to steady state hypothesis life never arose, it existed forever, like the Universe itself. But this does not mean that life did not change. Proponents of this hypothesis assumed both the development of life and its rebirth after various catastrophes (and the rebirth of life was often associated with the act of the same divine creation). This assumption made it possible to explain the remains of now non-existent living forms that were already discovered at that time.

The next hypothesis of the origin of life on Earth, refuted by modern science, is hypothesis of spontaneous, or spontaneous, origin of life. For centuries, people have observed how worms suddenly appear in meat, mushrooms grow from the soil after rain, and sometimes the number of frogs or fish in reservoirs sharply increases. All this suggested the idea that living things can arise in non-living things (soil, water) if there is some living energy, force, or substance in it. Similar views were held not only by many scientists Ancient world(including Aristotle), but also scientists of the 16th-17th centuries. And although this hypothesis was refuted by the experiments of other scientists, with the discovery of microorganisms its supporters increased again.

F. Redi proved in the 17th century that fly larvae appear only in open vessels. This means that they were brought there by the flies themselves, and did not spontaneously generate. In the 19th century, L. Pasteur finally proved the impossibility of the spontaneous origin of life. He did not boil the nutrient broth and did not even close the flask, but used a neck with a bend, which prevented microorganisms from entering the substrate, but could not prevent the penetration of a certain vital force, which seemed to be transmitted through the air. Such a broth did not turn sour (that is, microorganisms did not grow there), which means that for some reason the “grains” of life did not get there. Most likely because they did not exist in nature.

After Pasteur's experience in biology, the principle that all living things come only from living things began to gain popularity, which can be called a hypothesis biogenesis. But it did not solve the question of the original origin of life on Earth. Since at that time science was already sufficiently developed to refute creationism and the stationary state, the only logical assumption was the assumption of the introduction of life from space.

Panspermia is a hypothesis of the origin of life on Earth by its introduction from space. Similar views were held by scientists: Richter (who first put forward this hypothesis in the 19th century), Helmholtz, Arrhenius, Vernadsky, Crick, etc. Basically, panspermia is understood as the introduction of primitive organisms supposedly capable of surviving low temperatures and the impact of various radiations from space on meteorites, with cosmic dust, and not a visit to the Earth by aliens. Panspermia, like biogenesis, does not answer the question “how did life arise”; it only transfers this problem from Earth to space.

Currently the most popular in the scientific world is abiogenesis hypothesis, which refers to the origin of life on Earth through first chemical and then prebiological evolution under special conditions. These conditions existed on Earth in the past, when the planet first appeared (about 4.5 billion years ago) and existed for approximately its first 1 billion years. Later, conditions on Earth, including due to the emergence of living organisms, changed so that many chemical reactions and physicochemical processes became impossible. Therefore, today living things can only arise from living things.

The abiogenesis hypothesis has a certain evidence base, including that based on laboratory experiments. Therefore it is often called a theory. Abiogenesis was first described by A. Oparin in 1923-1924.

The origin of life on Earth is one of the most important problems of natural science. Even in ancient times, people asked themselves questions about where living nature came from, how life appeared on Earth, where is the line of transition from inanimate to life, etc. Over the course of dozens 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 together with the Earth, differing great variety alive. 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 early XVII V. 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 the Universe and its transfer in various ways to Earth (meteorites, asteroids, cosmic dust).

Indeed, some data have now been obtained indicating the possibility of the formation of organic substances by chemical means in space conditions. Thus, in 1975, amino acid precursors were found in lunar soil. The simplest carbon compounds, including those close to amino acids, have been discovered in interstellar clouds. Aldehydes, water, alcohols, hydrocyanic acid, etc. were found in meteorites.

The concept of panspermia was shared by the largest scientists of the late 19th and early 20th centuries: the German chemist and agronomist J. Liebig, the English physicist W. Thomson, the German naturalist G. Helmholtz, and the Swedish physical chemist S. Arrhenius. In 1907, S. Arrhenius even described in his writings how living spores of organisms escape 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 there were favorable conditions (including on Earth), began a new life. The ideas of panspermia were also supported by some Russian scientists: geophysicist P. Lazarev, biologist L. Berg, soil biologist S. Kostychev.

There is an idea about the emergence of life on Earth almost from the moment of its formation. As you know, the Earth was formed about 5 billion years ago. This means that life could have originated during the formation 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 ultraviolet rays, X-ray 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 electromagnetic influence The sun, cosmic radiation and electrical discharges.

3. Gradual complication of organic compounds and the formation of protein structures.

4. Isolation of protein structures from the medium, formation of aqueous complexes and creation of an aqueous shell around proteins.

5. The fusion of such complexes and the formation of coacervates (from lat. coacervus– clot, heap, accumulation) capable of exchanging matter and energy with the environment.

6. Absorption of metals by coacervates, which led to the formation of enzymes that accelerate biochemical processes.

7. Formation of hydrophobic lipid boundaries between coacervates and the external environment, which led to the formation of semi-permeable membranes, which ensured the stability of the functioning of the coacervate.

8. Development in the course of evolution in these formations of processes of self-regulation and self-reproduction.

Thus, according to A. Oparin’s hypothesis, a primitive form of living matter appeared. This, in his opinion, is the prebiological evolution of matter.

Academician V. Vernadsky associated the emergence of life with a powerful leap that interrupted lifeless evolution 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 it liquid surface, cooling down, began to harden. 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. Water that previously evaporated into the atmosphere and turned into it component, continuously fell to the Earth, with thunder and lightning, powerful showers fell from the clouds.

Little by little in the most deep depressions Water accumulated on 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 sushi was covered by the prehistoric Ocean. From its upper layers the water washed away great amount soluble minerals and salts that entered 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 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 conditions on Earth at that time, but they were destroyed long ago as a result 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 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 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 is a professor of geosciences at the University of Texas technological university(TTU) and curator of the museum of paleontology at the university, 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 in one light year from U.S.

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 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 strong and weak sides. 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 under the influence high temperature all living creatures that could cause spoilage of the broth died. 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.

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 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.”

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

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.

The theory of creationism is still quite widespread today, not only in religious circles, 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 cannot be resolved in principle, however, since an attempt to explain any difficulties of modern biochemistry and evolutionary theory fundamentally incomprehensible supernatural acts of creation takes these questions beyond scientific research, the theory of creationism cannot be classified as scientific theories 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).