The main hypotheses of the origin of life on earth.
Biochemical evolution
Among astronomers, geologists and biologists, it is generally accepted that the age of the Earth is approximately 4.5 - 5 billion years.
According to many biologists, in the past the state of our planet was little like the current one: probably the temperature on the surface was very high (4000 - 8000 ° C), and as the Earth cooled, carbon and more refractory metals condensed and formed the earth's crust ; the surface of the planet was probably bare and uneven, since as a result of volcanic activity, shifts and contractions of the crust caused by cooling, folds and ruptures formed on it.
It is believed that the gravitational field of the still insufficiently dense planet could not hold light gases: hydrogen, oxygen, nitrogen, helium and argon, and they left the atmosphere. But simple compounds containing among others these elements (water, ammonia, CO2 and methane). Until the Earth's temperature dropped below 100°C, all water was in a vapor state. The absence of oxygen was probably a necessary condition for the origin of life; as laboratory experiments show, organic substances (the basis of life) are much easier to form in an oxygen-poor atmosphere.
In 1923 A.I. Oparin, based on theoretical considerations, expressed the opinion that organic substances, possibly hydrocarbons, could be created in the ocean from simpler compounds. The energy for these processes was supplied by intense solar radiation, mainly ultraviolet radiation, which fell on the Earth before the ozone layer formed, which began to trap most of it. According to Oparin, the variety of simple compounds found in the oceans, the surface area of the Earth, the availability of energy and time scales suggest that organic matter gradually accumulated in the oceans and formed a "primordial soup" in which life could arise.
It is impossible to understand the origin of man without understanding the origin of life. And to understand the origin of life is possible only by understanding the origin of the universe.
First there was a big bang. This explosion of energy took place fifteen billion years ago.
Evolution can be thought of as the Eiffel Tower. At the base - energy, above - matter, planets, then life. And finally, at the very top - a man, the most complex and the last animal to appear.
The course of evolution:
15 billion years ago: the birth of the universe;
5 billion years ago: birth of the solar system;
4 billion years ago: birth of the Earth;
3 billion years ago: the first traces of life on Earth;
500 million years ago: first vertebrates;
200 Ma: First mammals;
70 million years ago: the first primates.
According to this hypothesis, proposed in 1865. by the German scientist G. Richter and finally formulated by the Swedish scientist Arrhenius in 1895, life could be brought to Earth from space. The most likely hit of living organisms of extraterrestrial origin with meteorites and cosmic dust. This assumption is based on data on the high resistance of some organisms and their spores to radiation, high vacuum, low temperatures, and other influences.
In 1969, the Murchison meteorite was found in Australia. It contained 70 intact amino acids, eight of which are part of the human protein!
Many scientists could argue that the squirrels that petrified upon re-entry into the atmosphere were dead. However, a prion, a protein that can withstand very high temperatures, has recently been discovered. The prion is stronger than the virus and is able to transmit the disease much faster. According to the Panspermia theory, man somehow originates from a virus of extraterrestrial origin that struck monkeys, which mutated as a result.
Theory of spontaneous generation of life
This theory was circulated in ancient China, Babylon, and Egypt as an alternative to the creationism with which it coexisted.
Aristotle (384-322 BC), often hailed as the founder of biology, held to the theory of the spontaneous generation of life. Based on his own observations, he developed this theory further, linking all organisms in a continuous series - the "ladder of nature". “For nature makes the transition from lifeless objects to animals with such a smooth succession, placing between them creatures that live, while not being animals, that between neighboring groups, due to their close proximity, one can hardly notice the differences” (Aristotle).
According to Aristotle's hypothesis of spontaneous generation, certain "particles" of matter contain some kind of "active principle", which, under suitable conditions, can create a living organism. Aristotle was right in thinking that this active principle is contained in a fertilized egg, but mistakenly believed that it is also present in sunlight, mud and rotting meat.
“These are the facts - living things can arise not only by mating animals, but also by decomposition of the soil. The same is the case with plants: some develop from seeds, while others, as it were, spontaneously generate under the action of all nature, arising from the decaying earth or certain parts of plants ”(Aristotle).
With the spread of Christianity, the theory of the spontaneous origin of life was not honored: it was recognized only by those who believed in witchcraft and worshiped evil spirits, but this idea continued to exist somewhere in the background for many more centuries.
Steady State Theory
According to this theory, the Earth never originated, but existed forever, it is always capable of supporting life, and if it has changed, then very little. Species have also always existed.
Estimates of the age of the earth have varied greatly, from about 6,000 years according to Archbishop Ussher's calculations, to 5,000 106 years according to modern estimates based on radioactive decay rates. Improved dating methods give increasingly higher estimates of the age of the Earth, which allows the proponents of the steady state theory to believe that the Earth has existed forever. According to this theory, species also never arose, they have always existed, and each species has only two alternatives - either a change in numbers or extinction.
Proponents of this theory do not recognize that the presence or absence of certain fossil remains may indicate the time of the appearance or extinction of a particular species, and cite as an example a representative of lobe-finned fish - coelacanth. Proponents of the steady state theory argue that only by studying living species and comparing them with fossil remains can one conclude about extinction, and in this case it is very likely that it will turn out to be wrong. Using paleontological data to support the steady state theory, its few supporters interpret the appearance of fossils in an ecological aspect (increase in abundance, migration to places favorable for the preservation of remains, etc.). Much of the argument in favor of this theory has to do with obscure aspects of evolution, such as the significance of gaps in the fossil record, and it has been most elaborate in this direction.
creationism
Creationism (lat. sgea - creation). According to this concept, life and all species of living beings inhabiting the Earth are the result of a creative act of a higher being at some specific time. The main provisions of creationism are set out in the Bible, in the Book of Genesis. The process of the divine creation of the world is conceived as having taken place only once and therefore inaccessible to observation. This is enough to take the whole concept of divine creation out of the scope of scientific research. Science deals only with observable phenomena and therefore will never be able to either prove or reject this concept.
The theory of water origin of man
It says: man came directly from the water. Those. we were once something like marine primates, or humanoid fish.
The "Water Theory" of human origins was put forward by Alistair Hardy (1960) and developed by Elaine Morgan. After that, the idea was broadcast by many popularizers, for example, Jan Lindblad and the legendary submariner Jacques Maillol. According to Hardy and Morgan, one of our ancestors was a Miocene great ape of the proconsul family, which lived in the water for many millions of years before becoming terrestrial.
In favor of the origin of the "water monkey", the following human features are given:
1. The ability to hold your breath, apnea (including during vocalization) makes a person a diver.
2. Working with dexterous brushes and using tools is similar to the behavior of the raccoon and sea otter.
3. When wading water bodies, primates stand on their hind limbs. The semi-aquatic lifestyle contributed to the development of bipedal locomotion.
4. The loss of hair and the development of subcutaneous fat (in humans it is normally thicker than in other primates) are characteristic of aquatic mammals.
5. Large breasts helped keep the body in the water and warm the heart.
6. Hair on the head helped keep the baby.
7. An elongated foot helped swim.
8. There is a skin fold between the fingers.
9. By wrinkling the nose, a person can close the nostrils (monkeys - no)
10. The human ear takes in less water.
And for example, if a newborn is placed in water immediately after he leaves the mother's womb, he will feel great. He already knows how to swim. After all, in order for a newborn to move from the stage of a fish to the stage of an air-breathing mammal, it needs to be patted on the back.
50 million years ago, dolphins emerged from the water and became land animals. And then, for unknown reasons, they decided to return to the water. We just have to follow their example.
Transformism
Nominated in 1815 by Jean-Baptiste Lamarck
Changes in the external environment entail a change in cells.
The fault forced (!!) the first prehistoric people to live in a treeless savannah. They could no longer climb trees to escape predators. People were forced to stand on their hind legs in order to see the enemy from afar in the tall grass. Constantly fearing attack, people straightened up and changed from "animals mostly living in trees and sometimes upright" to "upright animals sometimes gazing up at trees".
The use of the lower limbs freed the upper paws, now it was possible to hold a stick in the hands and use it as a weapon.
Bipedalism opened an era of other changes, in particular in the skeleton. The pelvis became a basket for the insides. Previously, the connection of the spinal column and the skull was horizontal. Now it has become vertical, and the volume of the skull has increased, since the spinal cord no longer interferes with it.
Over 2 million years, the volume of the brain grows from 450 to 1000 cubic centimeters, then from 1000 to today's 1450.
We have almost no wool left. Wool was needed so that babies could cling to their mother's stomach. This became unnecessary when mothers were able to take their children in their arms. And the wool was left on the top of the skull to protect from the sun. Above the eyes (eyebrows) protection from the rain.
The difference from Darwinism is that, Darwinists believe that people are animals that accidentally had a gene that allowed them to stand on their hind legs. And the Lamarckians believe that any animal, if necessary, can transform its genes.
Lamarck's ideas give everyone hope for the best. And Darwin, if you are a representative of not the most successful species, does not leave you a chance.
Developing within 9 months, the human embryo lives through the entire history of its species.
The 12-day-old embryo resembled a tiny elongated worm with large eyes. Looks like a fish embryo.
When a human embryo is thirty-one days old, it looks like a lizard, at 9 weeks it looks like a baby shrew, at 18 weeks it is no different from a monkey embryo.
Darwinism
Materialistic theory of evolution (historical development) of the organic world of the Earth, based on the views of Charles Darwin.
Two main engines of evolution. The first is chance, the second is species selection. Nature put thousands of experiments at the same time. And natural selection then eliminates the least fit.
A picture of the history of human ancestors.
70 million years ago: The appearance of the first primates. They were insectivorous and very similar to shrews.
40 million years ago; the appearance of the first lemurs. These animals already had features characteristic of humans: a protruding thumb, sharp nails, and a flat face. The thumb, angled to the palm, allows you to grasp objects and use them as tools. Flat nails instead of claws make it possible to clench a fist. Lemurs were the first to have a hand. Thanks to flat faces, lemurs began to see in volume. Animals whose eyes are located on the sides of the muzzle cannot determine distance and distinguish relief. Ulemurov's muzzle ceased to be elongated, and his eyes were on the same plane. Lemurs gained the ability to see the world in three dimensions.
20 million years ago, lemurs were overtaken by apes, their much more dexterous mutated cousins.
Between about 4.4 and 2.8 million years ago, a branch of Australopithecus monkeys appears, from which humans later evolved. Man has become different from a gorilla or a chimpanzee due to climate change. Monkeys inhabited East Africa, where an earthquake occurred that provoked a break in the soil, the so-called rift. The fault caused the formation of three special climatic zones: a zone of dense forests, a mountainous zone, and a savanna zone with sparse vegetation. In dense forests, only the ancestors of chimpanzees survived, in the mountains, the ancestors of gorillas, and in the savannah zone with sparse vegetation, Australopithecus, that is, our ancestors.
The main difference between the australopithecine and the prehistoric gorilla or chimpanzee was the disappearance of the tail, which was necessary in order to maintain balance when jumping from branch to branch. Touch your coccyx. That useless little tail stump on the back is the last sign of the tree monkey that man was before the rift.
The absence of a tail is not the only difference between man and ape. The torso gradually straightened, the volume of the skull increased, the face became flat, and the person acquired stereoscopic vision. Let's not forget the lowering of the larynx. Previously, primates emitted only grunts, while lowering the larynx greatly expanded the range of sounds. Hair disappeared, the period of childhood lengthened, that is, the time for teaching children lengthened. More complex social relationships arose.
And here he is, Homo sapiens, that is, we. One of the perfect forms of creation of nature.
Do you know the origin of life?
3. What is the basic principle of the scientific method?
The problem of the origin of life on our planet is one of the central ones in modern natural science. Since ancient times, people have tried to find the answer to this question.
Creationism (lat, sgeatio - creation).
At different times, different peoples had their own ideas about the origin of life. They are reflected in the sacred books of various religions, which explain the emergence of life as an act of the Creator (the will of God). The hypothesis of the divine origin of living things can only be accepted on faith, since it cannot be experimentally verified or refuted. Therefore, it cannot be considered scientific points of view.
The hypothesis of spontaneous origin of life.
From ancient times to the middle of the 17th century. scientists did not doubt the possibility of spontaneous generation of life. It was believed that living beings can appear from inanimate matter, for example, fish - from silt, worms - from soil, mice - from rags, flies - from rotten meat, and also that some forms can give rise to others, for example, animals can also form from fruits. (see, p. 343).
So, the great Aristotle, studying eels, found that among them there are no individuals with caviar or milk. Based on this, he suggested that eels are born from "sausages" of silt, formed from the friction of an adult fish against the bottom.
The first blow to the concept of spontaneous generation came from the experiments of the Italian scientist Francesca Redi, who in 1668 proved the impossibility of spontaneous generation of flies in rotting meat.
Despite this, the ideas of spontaneous generation of life persisted until the middle of the 19th century. Only in 1862 did the French scientist Louis Pasteur finally disprove the hypothesis of spontaneous generation of life.
The works of the Master made it possible to assert that the principle "All living things - from living things" is true for all known organisms on our planet, but they did not resolve the question of the origin of life.
Panspermia hypothesis.
Proof of the impossibility of spontaneous generation of life gave rise to another problem. If another living organism is needed for the emergence of a living organism, then where did the first living organism come from? This gave impetus to the emergence of the panspermia hypothesis, which had and has many supporters, including among prominent scientists. They believe that for the first time life did not originate on Earth, but was somehow introduced to our planet.
However, the panspermia hypothesis only attempts to explain the emergence of life on Earth. It does not answer the question of how life began.
The denial of the fact of spontaneous generation of life at the present time does not contradict the ideas about the fundamental possibility of the development of life in the past from inorganic matter.
The hypothesis of biochemical evolution.
In the 1920s, the Russian scientist A. I. Oparin and the Englishman J. Haldane put forward a hypothesis about the origin of life in the process of biochemical evolution carbon compounds, which formed the basis of modern ideas.
In 1924, AI Oparin published the main provisions of his hypothesis of the origin of life on Earth. He proceeded from the fact that in modern conditions the emergence of living beings from inanimate nature is impossible. Abiogenic (i.e., without the participation of living organisms) the emergence of living matter was possible only in the conditions of the ancient atmosphere and the absence of living organisms.
According to A. I. Oparin, in the primary atmosphere of the planet, saturated with various gases, with powerful electric discharges, as well as under the influence of ultraviolet radiation (there was no oxygen in the atmosphere and, therefore, there was no protective ozone screen, the atmosphere was reducing) and high radiation organic compounds could be formed that accumulated in the ocean, forming a "primordial soup".
It is known that in concentrated solutions of organic substances (proteins, nucleic acids, lipids) under certain conditions, clots called coacervate drops, or coacervates, can form. Coacervates did not break down in a reducing atmosphere. From the solution, they received chemicals, they synthesized new compounds, as a result of which they grew and became more complex.
Coacervates already resembled living organisms, but they were not yet such, since they did not have an ordered internal structure inherent in living organisms, and were not able to reproduce. Protein coacervates were considered by A.I., Oparin as probionts - the precursors of a living organism. He assumed that at a certain stage, protein probionts included nucleic acids, creating single complexes.
The interaction of proteins and nucleic acids led to the emergence of such living properties as self-reproduction, the preservation of hereditary information and its transmission to subsequent generations.
Probionts, in which metabolism was combined with the ability to reproduce themselves, can already be considered as primitive procells.
In 1929, the English scientist J. Haldane also put forward the hypothesis of the abiogenic origin of life, but according to his views, the primary was not a coarcervate system capable of exchanging substances with the environment, but a macromolecular system capable of self-reproduction. In other words, A. I. Oparin gave priority to proteins, and J. Haldane - to nucleic acids.
The Oparin-Holdein hypothesis won many supporters, as it received experimental confirmation of the possibility of abiogenic synthesis of organic biopolymers.
In 1953, the American scientist Stanley Miller, in the installation he created (Fig. 141), simulated the conditions that presumably existed in the Earth's primary atmosphere. As a result of the experiments, amino acids were obtained. Similar experiments were repeated many times in various laboratories and made it possible to prove the fundamental possibility of synthesizing practically all monomers of the main biopolymers under such conditions. Subsequently, it was found that, under certain conditions, it is possible to synthesize more complex organic biopolymers from monomers: polypeptides, polynucleotides, polysaccharides, and lipids.
But the Oparin-Haldane hypothesis also has a weak side, which is pointed out by its opponents. Within the framework of this hypothesis, it is not possible to explain the main problem: how did the qualitative leap from inanimate to living occur. Indeed, for the self-reproduction of nucleic acids, enzyme proteins are needed, and for the synthesis of proteins, nucleic acids.
Creationism. Spontaneous generation. Panspermia hypothesis. The hypothesis of biochemical evolution. Coacervates. Probionts.
1. Why can the notion of the divine origin of life be neither confirmed nor refuted?
2. What are the main provisions of the Oparin-Haldane hypothesis?
3. What experimental evidence can be given in favor of this hypothesis?
4. What is the difference between the hypothesis of A. I. Oparin and the hypothesis of J. Haldane?
5. What arguments do opponents give when criticizing the Oparin-Haldane hypothesis?
Give possible arguments "for" and "against" the hypothesis of panspermia.
Ch. Darwin wrote in 1871: “But now ... in some warm reservoir containing all the necessary ammonium and phosphorus salts and accessible to light, heat, electricity, etc., a protein capable of to further, more and more complex transformations, then this substance would immediately be destroyed or absorbed, which was impossible in the period before the emergence of living beings.
Confirm or refute this statement of Charles Darwin.
In understanding the essence of life and its origin in the culture of human civilization, there have long been two ideas - biogenesis and abiogenesis. The idea of biogenesis (the origin of living things from living things) comes from ancient Eastern religious constructions, for which the idea of the absence of the beginning and end of natural phenomena was common. The reality of eternal life for these cultures is logically acceptable, as well as the eternity of matter, the Cosmos.
An alternative idea - abiogenesis (the origin of living things from non-living things) goes back to civilizations that existed long before our era in the valleys of the Tigris and Euphrates rivers. This area was subject to constant flooding, and it is not surprising that it became the birthplace of catastrophism, which influenced European civilization through Judaism and Christianity. Catastrophes, as it were, interrupt the connection, the chain of generations, suggest its creation, reappearance. In this regard, the belief in the periodic spontaneous generation of an organism under the influence of natural or supernatural causes was widespread in European culture.
Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology Grade 10
Submitted by readers from the website
The problem of life and the living is the object of study of many natural disciplines, starting with biology and ending with philosophy, mathematics, which consider abstract models of the living phenomenon, as well as physics, which defines life from the standpoint of physical laws.
All other more particular problems and questions are concentrated around this main problem, and philosophical generalizations and conclusions are also built.
In accordance with two worldview positions - materialistic and idealistic - even in ancient philosophy, opposite concepts of the origin of life were formed: creationism and materialistic theory of origin organic from inorganic.
Supporters creationism argue that life arose as a result of an act of divine creation, evidence of which is the presence in living organisms of a special force that controls all biological processes.
Proponents of the origin of life from inanimate nature argue that organic nature arose due to the action of natural laws. Later, this concept was concretized in the idea of spontaneous generation of life.
The concept of spontaneous generation, despite the fallacy, played a positive role; experiments designed to confirm it provided rich empirical material for the developing biological science. The final rejection of the idea of spontaneous generation occurred only in the 19th century.
In the 19th century was also put forward hypothesis of the eternal existence of life and its cosmic origin on Earth. It has been suggested that life exists in space and travels from one planet to another.
At the beginning of the XX century. idea cosmic origin biological systems on Earth and the eternity of the existence of life in space was developed by the Russian academician IN AND. Vernadsky.
The hypothesis of academician A.I. Oparina
A fundamentally new hypothesis of the origin of life was presented by Academician A.I. Oparin in the book "The origin of life”, published in 1924. He made the statement that Redi's principle, introducing a monopoly of the biotic synthesis of organic substances, is valid only for the modern era of the existence of our planet. At the beginning of its existence, when the Earth was lifeless, abiotic synthesis of carbon compounds and their subsequent prebiological evolution took place on it.
The essence of Oparin's hypothesis is as follows: the origin of life on Earth is a long evolutionary process of the formation of living matter in the depths of inanimate matter. This happened through chemical evolution, as a result of which the simplest organic substances were formed from inorganic substances under the influence of potent physical and chemical processes.
He considered the emergence of life as a single natural process, which consisted of the initial chemical evolution taking place under the conditions of the early Earth, which gradually passed to a qualitatively new level - biochemical evolution.
Considering the problem of the emergence of life through biochemical evolution, Oparin distinguishes three stages of the transition from inanimate to living matter.
The first stage is chemical evolution. When the Earth was still lifeless (about 4 billion years ago), abiotic synthesis of carbon compounds and their subsequent prebiological evolution.
This period of the Earth's evolution was characterized by numerous volcanic eruptions with the release of a huge amount of red-hot lava. As the planet cooled, the water vapor in the atmosphere condensed and fell on the Earth in showers, forming huge expanses of water (the primary ocean). These processes continued for many millions of years. Various inorganic salts were dissolved in the waters of the primary ocean. In addition, various organic compounds, which are continuously formed in the atmosphere under the influence of ultraviolet radiation, high temperature, and active volcanic activity, also entered the ocean.
The concentration of organic compounds was constantly increasing, and, in the end, the waters of the ocean became " broth»from protein-like substances — peptides.
The second stage is the appearance of proteins. As the conditions on Earth softened, under the influence of electrical discharges, thermal energy and ultraviolet rays on the chemical mixtures of the primary ocean, the formation of complex organic compounds - biopolymers and nucleotides, which, gradually combining and becoming more complex, turned into protobionts(precellular ancestors of living organisms). The result of the evolution of complex organic substances was the appearance coacervates, or co-acervate drops.
coacervates- complexes of colloidal particles, the solution of which is divided into two layers: a layer rich in colloidal particles and a liquid almost free of them. Coacervates had the ability to absorb various substances dissolved in the waters of the primary ocean. As a result, the internal structure of coacervates changed in the direction of increasing their stability in constantly changing conditions.
The theory of biochemical evolution considers coacervates as prebiological systems, which are groups of molecules surrounded by a water shell.
So, for example, coacervates are able to absorb substances from the environment, interact with each other, increase in size, etc. However, unlike living beings, coacervate drops are not capable of self-reproduction and self-regulation; therefore, they cannot be classified as biological systems.
The third stage is the formation of the ability to self-reproduce, the appearance of a living cell. During this period, natural selection began to act, i.e. in the mass of coacervate droplets, the coacervates most resistant to the given environmental conditions were selected. The selection process has been going on for many millions of years. The surviving coacervate drops already possessed the ability for primary metabolism, the main property of life.
At the same time, having reached a certain size, the parent drop broke up into child droplets that retained the features of the parent structure.
Thus, we can talk about the acquisition by coacervates of the property of self-production - one of the most important signs of life. In fact, at this stage, coacervates have become the simplest living organisms.
Further evolution of these prebiological structures was possible only with the complication of metabolic processes inside the coacervate.
The internal environment of the coacervate needed protection from environmental influences. Therefore, around the coacervates, rich in organic compounds, layers of lipids arose, separating the coacervates from the surrounding aqueous medium. In the process of evolution, lipids were transformed into the outer membrane, which significantly increased the viability and resistance of organisms.
The appearance of the membrane predetermined the direction of further biological evolution along the path of ever more perfect autoregulation, culminating in the formation of the primary cell, the archecell. A cell is an elementary biological unit, the structural and functional basis of all living things. Cells carry out an independent metabolism, are capable of division and self-regulation, i.e. have all the properties of living things. The formation of new cells from non-cellular material is impossible, cell reproduction occurs only due to division. Organic development is considered as a universal process of cell formation.
In the structure of the cell, there are: a membrane that delimits the contents of the cell from the external environment; cytoplasm, which is a saline solution with soluble and suspended enzymes and RNA molecules; a nucleus containing chromosomes, consisting of DNA molecules and proteins attached to them.
Therefore, the beginning of life should be considered the emergence of a stable self-reproducing organic system (cell) with a constant sequence of nucleotides. Only after the emergence of such systems can we speak of the beginning of biological evolution.
The possibility of abiogenic synthesis of biopolymers was experimentally proven in the middle of the 20th century. In 1953 an American scientist S. Miller modeled the Earth's primordial atmosphere and synthesized acetic and formic acids, urea and amino acids by passing electric charges through a mixture of inert gases. Thus, it was demonstrated how the synthesis of complex organic compounds is possible under the action of abiogenic factors.
Despite the theoretical and experimental validity, Oparin's concept has both strengths and weaknesses.
The strength of the concept is a fairly accurate experimental substantiation of chemical evolution, according to which the origin of life is a natural result of the prebiological evolution of matter.
A convincing argument in favor of this concept is also the possibility of experimental verification of its main provisions.
The weak side of the concept is the impossibility of explaining the very moment of the jump from complex organic compounds to living organisms.
One of the versions of the transition from prebiological to biological evolution is offered by the German scientist M. Eigen. According to his hypothesis, the origin of life is explained by the interaction of nucleic acids and proteins. Nucleic acids are carriers of genetic information, and proteins serve as catalysts for chemical reactions. Nucleic acids reproduce themselves and transmit information to proteins. A closed chain appears - a hypercycle, in which the processes of chemical reactions are self-accelerated due to the presence of catalysts and congestion.
In hypercycles, the reaction product simultaneously acts as both a catalyst and an initial reactant. Such reactions are called autocatalytic.
Synergetics is another theory that can explain the transition from prebiological to biological evolution. The patterns discovered by synergetics make it possible to clarify the mechanism of the emergence of organic matter from inorganic matter in terms of self-organization through the spontaneous emergence of new structures during the interaction of an open system with the environment.
Remarks on the theory of the origin of life and the emergence of the biosphere
In modern science, the hypothesis of the abiogenic (non-biological) origin of life under the influence of natural causes as a result of a long process of cosmic, geological and chemical evolution - abiogenesis, is accepted, the basis of which was the hypothesis of Academician A. I. Oparin. The abiogenesis concept does not exclude the possibility of the existence of life in space and its cosmic origin on Earth.
However, based on modern achievements of science, to the hypothesis of A.I. Oparin suggests the following clarifications.
Life could not have arisen on the surface (or near it) of the water of the Ocean, since in those distant times the Moon was much closer to the Earth than at present. The tidal waves had to be of great height, great destructive force. Protobionts simply could not form under these conditions.
Due to the lack of an ozone layer under the influence of hard ultraviolet radiation, protobionts also could not exist. This suggests that life could only appear in the water column.
Due to special conditions, life could appear only in the water of the primary Ocean, but not on the surface, but at the bottom in thin films of organic matter adsorbed by the surfaces of pyrite and apatite crystals, apparently, near geothermal sources. Since, it has been established that organic compounds are formed in the products of volcanic eruptions, and volcanic activity under the Ocean in ancient times was very active. There was no dissolved oxygen in the ancient Ocean capable of oxidizing organic compounds.
Today it is believed that protobionts were RNA molecules, but not DNA, since it has been proven that the evolutionary process went from RNA to protein, and then to the formation of a DNA molecule, in which C-H bonds were stronger than C-OH bonds in RNA. However, it is clear that RNA molecules could not have arisen as a result of smooth evolutionary development. Probably, there was a jump with all the features of the self-organization of matter, the mechanism of which is not clear at present.
The primary biosphere in the water column was probably represented by a rich functional diversity. And the first appearance of life should have occurred not in the form of any one type of organism, but in the totality of organisms. Many primary biocenoses should have appeared immediately. They consisted of the simplest unicellular organisms capable of performing all the functions of living matter in the biosphere without exception.
These simplest organisms were heterotrophs (they fed on ready-made organic compounds), were prokaryotes (organisms without a nucleus), were anaerobes (used yeast fermentation as an energy source).
Due to the special properties of carbon, life appeared on this basis. However, no modern data contradicts the possibility of the emergence of life not only on a carbon basis.
Some future directions for studying the origin of life
In the 21st century in order to clarify the problem of the origin of life, researchers are showing increased interest in two objects - to Jupiter's moon opened in 1610 G. Galileo. It is located at a distance from the Earth equal to 671,000 km. Its diameter is 3100 km. It is covered with many kilometers of ice. However, under the cover of ice is the ocean, and it may have preserved the simplest forms of ancient life.
Another object - east lake, which is called a relict reservoir. It is located in Antarctica under a four-kilometer layer of ice. Our researchers discovered it as a result of deep sea drilling. Currently, an international program is being developed, which aims to penetrate into the waters of this lake without violating its relict purity. It is possible that there are relic organisms several million years old.
There is also great interest in cave discovered in Romania without access to light. When they drilled the entrance to this cave, they discovered the existence of blind living organisms such as bugs that feed on microorganisms. These microorganisms use for their existence inorganic compounds containing hydrogen sulfide coming from inside the bottom of this cave. There is no light in this cave, but there is water.
Of particular interest are microorganisms, recently discovered by American scientists in the study one of the salt lakes. These micro-organisms exhibit exceptional resistance to the environment. They can live even on a purely arsenic medium.
The organisms living in the so-called "black smokers" also attract great attention (Fig. 2.1).
Rice. 2.1. "Black smokers" of the ocean floor (jets of hot water are shown by arrows)
"Black smokers" are numerous hydrothermal vents operating at the bottom of the oceans, confined to the axial parts of the mid-ocean ridges. Of these, into the oceans under high pressure of 250 atm. highly mineralized hot water (350 °C) enters. Their contribution to the Earth's heat flux is about 20%.
Hydrothermal ocean vents carry dissolved elements from the oceanic crust into the oceans, altering the crust and making a very significant contribution to the chemical composition of the oceans. Together with the cycle of oceanic crust generation at oceanic ridges and its recycling into the mantle, hydrothermal alteration represents a two-stage system for the transfer of elements between the mantle and the oceans. The oceanic crust recycled into the mantle is apparently responsible for part of the mantle inhomogeneities.
Hydrothermal vents at mid-ocean ridges are home to unusual biological communities that derive their energy from the decomposition of hydrothermal fluid compounds (jet black).
In the oceanic crust, apparently, there are the deepest parts of the biosphere, reaching a depth of 2500 m.
Hydrothermal springs make a significant contribution to the heat balance of the Earth. Beneath the median ridges, the mantle comes closest to the surface. Sea water penetrates through cracks into the oceanic crust to a considerable depth, is heated by mantle heat due to thermal conductivity, and is concentrated in magma chambers.
A deep study of the "special" objects listed above will undoubtedly lead scientists to a more objective understanding of the problem of the origin of life on our planet and the formation of its biosphere.
However, it should be pointed out that, to date, it has not been possible to obtain life experimentally.
Hypotheses of the origin of life on Earth. Life is one of the most complex natural phenomena. Since ancient times, it has seemed mysterious and unknowable - that is why there has always been a sharp struggle between materialists and idealists on questions of its origin. Adherents of idealistic views considered (and still consider) life to be a spiritual, non-material beginning that arose as a result of divine creation. Materialists, on the contrary, believed that life on Earth could arise from inanimate matter by spontaneous generation (abiogenesis) or by introduction from other worlds, i.e. is a product of other living organisms (biogenesis).
According to modern concepts, life is the process of the existence of complex systems consisting of large organic molecules and inorganic substances and capable of self-reproducing, self-developing and maintaining their existence as a result of the exchange of energy and matter with the environment.
With the accumulation of human knowledge about the world around us, the development of natural science, views on the origin of life changed, new hypotheses were put forward. However, even today the question of the origin of life has not yet been finally resolved. There are many hypotheses for the origin of life. The most important of them are the following:
Creationism (life was created by the Creator);
Hypotheses of spontaneous generation (spontaneous generation; life arose repeatedly from inanimate matter);
Steady state hypothesis (life has always existed);
Panspermia hypothesis (life brought to Earth from other planets);
Biochemical hypotheses (life arose under the conditions of the Earth as a result of processes that obey physical and chemical laws, i.e. as a result of biochemical evolution).
Creationism. According to this religious hypothesis, which has ancient roots, everything that exists in the Universe, including life, was created by a single Force - the Creator as a result of several acts of supernatural creation in the past. The organisms that inhabit the Earth today are descended from separately created basic types of living beings. The created species were from the very beginning excellently organized and endowed with the capacity for some variability within certain boundaries (microevolution). Followers of almost all the most common religious teachings adhere to this hypothesis.
The traditional Judeo-Christian idea of the creation of the world, set forth in the Book of Genesis, has caused and continues to cause controversy. However, the existing contradictions do not refute the concept of creation. Religion, considering the question of the origin of life, is looking for an answer mainly to the questions "why?" and “for what?”, and not to the question “how?”. If science makes extensive use of observation and experiment in search of truth, then theology comprehends the truth through divine revelation and faith.
The process of the divine creation of the world is presented as having taken place only once and therefore inaccessible to observation. In this regard, the hypothesis of creation can neither be proved nor refuted and will always exist along with scientific hypotheses of the origin of life.
Hypotheses of spontaneous generation. For thousands of years, people believed in the spontaneous generation of life, considering it the usual way for the appearance of living beings from inanimate matter. It was believed that the source of spontaneous generation is either inorganic compounds or decaying organic residues. (the concept of abiogenesis). This hypothesis was circulated in ancient China, Babylon, and Egypt as an alternative to the creationism with which it coexisted. The idea of spontaneous generation was also expressed by the philosophers of Ancient Greece and even by earlier thinkers, i.e. it seems to be as old as humanity itself. Throughout such a long history, this hypothesis has been modified, but still remained erroneous. Aristotle, often hailed as the founder of biology, wrote that frogs and insects thrive in damp soil. In the Middle Ages, many "managed" to observe the birth of various living creatures, such as insects, worms, eels, mice, in decaying or rotting remains of organisms. These "facts" were considered very convincing until the Italian physician Francesco Redi (1626-1697) approached the problem of the origin of life more rigorously and questioned the theory of spontaneous generation. In 1668 Redi made the following experiment. He placed the dead snakes in different vessels, covering some vessels with muslin and leaving others open. The swarming flies laid their eggs on dead snakes in open vessels; soon the larvae hatched from the eggs. There were no larvae in the covered vessels (Fig. 5.1). Thus, Redi proved that the white worms that appear in the meat of snakes are the larvae of the Florentine fly and that if the meat is closed and the access of the flies is prevented, then it will not "produce" worms. Refuting the concept of spontaneous generation, Redi suggested that life can only arise from a previous life. (the concept of biogenesis).
Similar views were held by the Dutch scientist Anthony van Leeuwen-hoek (1632-1723), who, using a microscope, discovered the smallest organisms invisible to the naked eye. They were bacteria and protists. Leeuwenhoek suggested that these tiny organisms, or "animalcules," as he called them, are descended from their own kind.
Leeuwenhoek's opinion was shared by the Italian scientist Lazzaro Spallanzani (1729-1799), who decided to prove experimentally that the microorganisms often found in meat broth do not spontaneously arise in it. To this end, he placed a liquid rich in organic matter (meat broth) into vessels, boiled this liquid over a fire, and then sealed the vessels hermetically. As a result, the broth in the vessels remained clean and free from microorganisms. With his experiments, Spallanzani proved the impossibility of spontaneous generation of microorganisms.
Opponents of this point of view argued that life did not arise in flasks for the reason that the air in them deteriorates during boiling, therefore they still recognized the hypothesis of spontaneous generation.
A crushing blow to this hypothesis was dealt in the 19th century. French microbiologist Louis Pasteur (1822-1895) and English biologist John Tyndale (1820-1893). They showed that bacteria spread through the air and that if they were not in the air entering the flasks with sterilized broth, then they would not arise in the broth itself. Pasteur used for this flasks with a curved S-shaped neck, which served as a trap for bacteria, while air freely entered and exited the flask (Fig. 5.3).
Tyndall sterilized the air entering the flasks by passing it through a flame or through cotton wool. By the end of the 70s. 19th century practically all scientists recognized that living organisms are descended only from other living organisms, which meant returning to the original question: where did the first organisms come from?
Steady State Hypothesis. According to this hypothesis, the Earth never came into being, but existed forever; it has always been capable of sustaining life, and if it has changed, it has changed very little; species have always existed. This hypothesis is sometimes called the hypothesis eternism (from lat. eternus- eternal).
The hypothesis of eternism was put forward by the German scientist W. Preyer in 1880. Preyer's views were supported by Academician V.I. Vernadsky, author of the doctrine of the biosphere.
Panspermia hypothesis. The hypothesis about the appearance of life on Earth as a result of the transfer of certain germs of life from other planets was called
panspermia (from Greek. pan- all, everyone and sperma- seed). This hypothesis is adjacent to the steady state hypothesis. Its adherents support the idea of the eternal existence of life and put forward the idea of its extraterrestrial origin. One of the first the idea of the cosmic (extraterrestrial) origin of life was expressed by the German scientist G. Richter in 1865. According to Richter, life on Earth did not arise from inorganic substances, but was introduced from other planets. In this regard, questions arose as to how possible such a transfer from one planet to another and how it could be carried out. The answers were sought primarily in physics, and it is not surprising that the first defenders of these views were the representatives of this science, the outstanding scientists G. Helmholtz, S. Arrhenius, J. Thomson, P.P. Lazarev and others.
According to the ideas of Thomson and Helmholtz, spores of bacteria and other organisms could have been brought to Earth with meteorites. Laboratory studies confirm the high resistance of living organisms to adverse effects, in particular to low temperatures. For example, spores and seeds of plants did not die even after prolonged exposure to liquid oxygen or nitrogen.
Other scientists have expressed the idea of transferring the "spores of life" to Earth by light.
Modern adherents of the concept of panspermia (including Nobel Prize winner English biophysicist F. Crick) believe that life on Earth was brought by accident or intentionally by space aliens.
The point of view of astronomers C. Vik-ramasingh (Sri Lanka) and F. Hoyle adjoins the panspermia hypothesis
(Great Britain). They believe that in outer space, mainly in gas and dust clouds, microorganisms are present in large numbers, where, according to scientists, they are formed. Further, these microorganisms are captured by comets, which then, passing near the planets, "sow the germs of life."
There are many hypotheses for the origin of life on Earth. The most important of these are: creationism, spontaneous generation, steady state, panspermia, biochemical hypotheses
If we analyze all the data that scientists managed to obtain in the course of various studies, it becomes obvious that life on Earth is an amazingly incredible fact. The chances of its occurrence in our universe are negligible. All stages of the emergence of life contained the possibility of an alternative development of events, as a result of which the world would have remained a cold cosmic abyss without a hint not only of the human mind, but even of the smallest microbe. Creationists attribute this incredible event to divine intervention. However, the existence of God cannot be proved or disproved, and modern ideas about the origin of life, like all science in general, are based on experimental data and theoretical developments that can be questioned or confirmed.
Vitalism
Human knowledge is undergoing an evolution somewhat similar in its main points to the process described by Darwin. Theories pass and survive the strongest, who managed to withstand the onslaught of counterarguments or adapt, change to match them. Hypotheses of the origin of life have also gone a long way of formation, the completion of which has not even been marked yet, since new facts are discovered daily, forcing to correct already established views.
Vitalism, the theory of constant spontaneous generation of life, became a major milestone on this road. According to its provisions, mice appeared in old rags, worms - in rotting food remnants. Vitalism dominated science until the experiments of Louis Pasteur in 1860, when he proved the impossibility of spontaneous generation of living organisms. The results triggered paradoxical events: they strengthened faith in the divine principle and forced scientists to look for evidence of what they had recently refuted. Science sought to explain that the independent origin of life took place, but a very long time ago and happened in stages, taking millions of years.
Synthesis of carbons
The situation seemed hopeless until, in 1864, A.M. Butlerov did not make an important discovery.
He managed to get (carbon) from inorganic (in his experiment it was formaldehyde). The data obtained destroyed the imposing wall that until now delimited living organisms and the world of dead matter. Over time, scientists were able to obtain other variants of organics from inorganic substances. From that moment, modern ideas about the origin of life began to form. They absorbed data not only from biology, but also from cosmology and physics.
Consequences of the Big Bang
Theories of the origin of life cover a huge period: scientists find the first prerequisites for the future formation of organisms even in the early stages of the birth of the Universe. Modern physics counts the existence of the world from the Big Bang, when almost everything appeared from nothing. In the rapidly expanding and cooling Universe, first atoms and molecules were formed, then they began to combine, forming the first generation of stars. They became the place of formation of most of the elements known to science today. New atoms filled space after the explosions of stars and became the basis for the next generation of objects, including our Sun. Modern data suggest that the first could have appeared in protoplanetary clouds surrounding new stars. Planets soon formed from them. It turns out that the first stages of the emergence of life on Earth took place even before its formation.
Autocatalytic cycles
The processes that took place on the Blue Planet in its “childhood years” were supported by substances that make up its interior and come from space as meteorites. Hypotheses of the origin of life One of the important foundations for the origin of organics on Earth is the catalysts for chemical reactions that came here with the fragments of these "aliens". They led to the fact that the fastest processes began to play an overwhelming role in the formation of new substances on the planet.
The next step is autocatalytic cycles. In such processes, substances are formed that increase the rate of the reaction, as well as renew the substrate - the elements that interact. The cycle thus closed: the processes accelerated themselves and “cooked food” for themselves, that is, substances that reacted again, again catalyzing themselves and again forming a substrate, and so on.
Doubts
Modern ideas about the origin of life have long contained conflicting opinions. The stumbling block is the chicken and egg problem. What came first: proteins that carry out all the processes in the cell, or DNA that determines the structure of these proteins, storing all hereditary information. The former are necessary for the body, as they contribute to the self-maintenance of the system, without which life is impossible. DNA contains a record of the structure of the cell, which also determines viability. The opinions of scientists were divided and there was no answer to the question until the moment when it became known that not DNA, but RNA, the third class of organic compounds, which was usually assigned only a secondary role in the theory of the origin of life, acts as a repository of hereditary information in viruses.
RNA world
Gradually, facts began to accumulate, and in the 80s of the last century, data appeared that overturned ideas about the initial stages of the formation of living matter. Ribozymes, RNA molecules, have been discovered that have the ability of proteins, in particular, to catalyze reactions. The first forms of life, therefore, could have arisen without the participation of proteins and DNA. In them, the function of storing information, as well as all the internal work, was performed by RNA. Life on Earth now descended from proto-organisms, which are autocatalytic cycles composed of self-replicating ribozymes. The theory was called "RNA World".
coacervates
Today it is difficult to imagine the life of that period, since it did not have one important feature - a shell or a border. In fact, it was a solution containing autocatalytic cycles from RNA. The problem of the lack of boundaries necessary for the correct flow of processes was solved by improvised methods. Protoorganisms found shelter near zeolite minerals, which had a network structure of the crystal lattice. Their surface was able to catalyze the formation of RNA chains and give them a certain configuration.
Further - more: coacervates or water-lipid drops appear on the stage. Hypotheses of both recent times and modernity are largely based on the theory of A.I. Oparin, who studied the properties of such formations. Coacervates are drops of solution enclosed in a shell of fats (lipids). Their membranes are also characterized by the ability to carry out metabolism. Some of them, apparently, combined with chains of self-replicating RNA, including those that catalyzed the synthesis of lipids themselves. Thus, new forms of life arose, having overcome the path from the pre-organismal level to the proper organismic one. The possibility of such formations was confirmed quite recently: scientists experimentally confirmed the ability of RNA in combination with calcium ions to attach to lipid membranes and regulate their permeability.
Skilled Helpers
The origin of life at the next stage was the process of improving the functions of the resulting organisms. RNA acquired the ability to catalyze the synthesis of amino acid polymers, initially quite simple. The crowning achievement of the new mechanism was the ability to synthesize proteins. The resulting formations coped with biological processes several times more effectively than ribozymes.
Initially, the synthesis of peptides was not ordered. The process happened "haphazardly", leaving the direction of the sequence of amino acids in new chains to chance. Over time, exact copying became entrenched, since it was it that contributed to the greater stability of the entire system. This is how it appeared allowing to synthesize certain proteins with the necessary functions.
Perfection
Honing the ability to synthesize the necessary proteins took place gradually. The first step was the emergence of a special type of RNA that could connect amino acids. The next phase was accompanied by the construction of the process of formation of peptide molecules with the help of bases lined up in a certain order. The sequence was set by the RNA template. Correlating the "instruction" of informative RNA and the elements of future proteins was taken up by a new type of RNA, called transport. As well as informational, it is still an important part of peptide synthesis to this day.
DNA
The complication of organisms further followed the path of improving the ways of storing information. It is assumed that originally DNA was one of the phases of the life cycle of RNA colonies. She had a more stable structure. Its degree of information protection was an order of magnitude higher, so after some, quite a long time, DNA became the main repository of the genetic code.
One of the properties of the new formation, which at one time did not allow placing DNA at the head of the theory of the origin of life, is the inability to take active actions. It has become a kind of payment for the improved functions of the information storage. All the "work" was left to proteins and RNA.
Symbiosis
Modern ideas about the origin of life do not deduce as an ancestor an organism that is closed and fenced off from the rest. Scientists are more in favor of the assumption that in the early stages there were communities of microscopic similarities of cells that performed different functions. Such a symbiosis is not difficult to find in nature today. The simplest example is cyano-bacterial mats, which are both a community of microorganisms and a single whole living being.
Biology at the present stage of its development sees a process characterized not by constant struggle and competition, but rather by an ever-increasing rallying of certain diverse structures, which eventually led to the appearance of a living cell, as we imagine it today.
Generalization
Summing up, we can briefly list all the stages of the formation of life, which, according to modern theories, seem to be the most probable version of the appearance and development of organisms on Earth:
Formation of primary organic compounds in protoplanetary clouds.
Gradual coming to the forefront of self-accelerating reactions and autocatalytic cycles.
Emergence of autocatalytic cycles consisting of RNA.
Union of RNA and lipid membranes.
The acquisition of RNA's ability to synthesize protein.
The emergence of DNA and its establishment as the main repository of information.
The formation of the first unicellular organisms based on symbiosis.
Understanding the processes that led to the emergence of life is still imperfect. Scientists are left with a lot of questions. It is not known exactly how RNA originated, many intermediate phases remain only theoretical. However, new experiments are being set up every day, facts and hypotheses are being tested. It is safe to say that our century will give the world a lot more discoveries related to the prehistoric era.
