If we analyze all the data that scientists have been able to obtain in the course of various studies, it becomes obvious that life on Earth is an amazingly incredible fact. The chances of its appearance 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 explain such an incredible event as divine intervention. However, the existence of God cannot be proven 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 that is somewhat similar in its main points to the process described by Darwin. Theories pass and the strongest survive, those who managed to withstand the onslaught of counterarguments or adapt and change to suit them. Hypotheses about the origin of life have also gone through a long journey of development, the completion of which has not yet even been indicated, since new facts are being discovered every day, forcing the correction of already established views.
A major milestone on this road was vitalism - the theory of the constant spontaneous generation of life. According to her provisions, mice appeared in old rags, worms - in rotting food remains. Vitalism dominated science until the experiments of Louis Pasteur in 1860, when he proved the impossibility of spontaneous generation of living organisms. The results created a paradox: they strengthened faith in the divine and forced scientists to look for evidence of what they had recently disproved. Science sought to explain that the independent origin of life took place, but a very long time ago and occurred in stages, taking millions of years.
Carbon synthesis
The situation seemed hopeless until in 1864 A.M. Butlerov did not make an important discovery.
He managed to obtain (carbon) from inorganic (in his experiment it was formaldehyde). The data obtained destroyed the impressive wall that had previously separated living organisms from the world of dead matter. Over time, scientists were able to obtain other variants of organic matter from inorganic substances. From this moment on, modern ideas about the origin of life began to form. They incorporated 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 in the early stages of the origin of the Universe. Modern physics dates the existence of the world from the Big Bang, when everything appeared from practically nothing. In the rapidly expanding and cooling Universe, atoms and molecules were first formed, then they began to unite, forming stars of the first generation. They became the place of formation of most of the elements known to science today. New atoms filled space after stellar explosions and became the basis for the next generation of objects, including our Sun. Modern data suggest that the first ones 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 were part of its interior and coming from space as meteorites. Hypotheses about the origin of life important basics For the origin of organic matter on Earth, catalysts for chemical reactions that came here with the fragments of these “aliens” are called. 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 stage is autocatalytic cycles. In such processes, substances are formed that help increase the reaction rate, 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 again reacted, 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 a chicken and egg problem. What came first: proteins that carry out all processes in the cell, or DNA, which determines the structure of these proteins and stores 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 cell's structure, which also determines viability. The opinions of scientists were divided and there was no answer to the question until the moment it became known that the storage of hereditary information in viruses is not DNA, but RNA, third class organic compounds, which was usually assigned only a secondary role in the theory of the origin of life.
RNA world
Gradually, facts began to accumulate, and in the 80s of the last century, data appeared that changed ideas about initial stages formation of living matter. Ribozymes were discovered, RNA molecules 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 evolved from proto-organisms that were autocatalytic cycles consisting of self-replicating ribozymes. The theory was called the “RNA world”.
Coacervates
Today it is difficult to imagine life of that period, since it did not have one important feature - a shell or border. Essentially, 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 using 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 scene. Hypotheses of both recent times and modern times are largely based on the theory of A.I. Oparin, who studied the properties of such formations. Coacervates are droplets 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 the lipids themselves. This is how new forms of life arose, overcoming the path from the pre-organismic level to the actual organismic level. 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.
Skillful helpers
The origin of life at the next stage was a 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 setting up the new mechanism was the ability to synthesize proteins. The emerging formations were several times more effective in coping with biological processes than ribozymes.
Initially, peptide synthesis was not ordered. The process occurred “haphazardly,” leaving chance to guide the sequence of amino acids in new chains. Over time, exact copying took hold because it contributed to greater stability of the entire system. This is how it became possible to synthesize certain proteins with the necessary functions.
Improvement
The ability to synthesize the necessary proteins was honed gradually. The first stage 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 using bases arranged in a certain order. The sequence was specified by the RNA template. A new type of RNA, called transport RNA, was involved in the correlation of the “instructions” of informative RNA and the elements of future proteins. Like information, it is still an important part of peptide synthesis.
DNA
The complication of organisms further followed the path of improving methods of storing information. It is believed that DNA was originally one of the phases life cycle RNA colonies. It had a more stable structure. Its level of information protection was an order of magnitude higher, so after some quite a long time DNA became the main repository genetic code.
One of the properties of the new formation, which at one time did not allow DNA to be placed at the head of the theory of the origin of life, is the inability to take active action. It became 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 identify an organism that is closed and fenced off from the rest as an ancestor. Scientists are more inclined to believe 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 cyanobacterial mats, which are both a community of microorganisms and a single 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 unification of certain diverse structures, which ultimately led to the emergence of a living cell, as we imagine it today.
Generalization
To summarize, we can briefly list all the stages of life formation that are represented within the framework modern theories the most probable version of the appearance and development of organisms on Earth:
Formation of primary organic compounds in protoplanetary clouds.
The gradual emergence of reactions with the ability to self-accelerate and autocatalytic cycles to the fore.
The emergence of autocatalytic cycles consisting of RNA.
Union of RNA and lipid membranes.
Acquisition of RNA ability to synthesize protein.
The emergence of DNA and its establishment as the main repository of information.
Formation of the first unicellular organisms based on symbiosis.
Understanding of the processes that led to the emergence of life is still imperfect. Scientists still have a lot of questions. It is not known exactly how RNA originated; many intermediate phases remain only theoretical. However, every day new experiments are performed, facts and hypotheses are tested. It is safe to say that our century will give the world many more discoveries related to the prehistoric era.
Valery Spiridonov, the first candidate for a head transplant, for RIA Novosti
For many years, humanity has been trying to unravel the real reason and the history of the emergence of life on our planet. Just over a hundred years ago, in almost all countries, people did not even think of questioning the theory of divine intervention and the creation of the world by a supreme spiritual being.
The situation changed after the release in November 1859 greatest work Charles Darwin, and now there is a lot of controversy around this topic. The number of supporters of Darwin's theory of evolution in Europe and Asia amounts to more than 60-70%, approximately 20% in the USA and about 19% in Russia according to the end of the last decade.
In many countries today there are calls to exclude Darwin's work from school curriculum or at least study it along with other plausible theories. If we don’t talk about the religious version, which one is inclined to most of population of the planet, today there are several basic theories of the origin and evolution of life, describing its development at various stages.
Panspermia
Proponents of the idea of panspermia are convinced that the first microorganisms were brought to Earth from space. This was the opinion of the famous German encyclopedist Hermann Helmholtz, the English physicist Kelvin, the Russian scientist Vladimir Vernadsky and the Swedish chemist Svante Arrhenius, who is considered today the founder of this theory.
It has been scientifically confirmed that meteorites from Mars and other planets, possibly from comets that could even come from alien star systems, have been repeatedly discovered on Earth. No one doubts this today, but it is not yet clear how life could have arisen on other worlds. In essence, apologists for panspermia shift the “responsibility” for what is happening to alien civilizations.
The Primal Soup Theory
The birth of this hypothesis was facilitated by the experiments of Harold Urey and Stanley Miller conducted in the 1950s. They were able to recreate almost the same conditions that existed on the surface of our planet before the origin of life. Small electrical discharges and ultraviolet light were passed through a mixture of molecular hydrogen, carbon monoxide and methane.
As a result, methane and other primitive molecules turned into complex organic substances, including dozens of amino acids, sugar, lipids, and even the beginnings of nucleic acids.
Relatively recently, in March 2015, scientists at the University of Cambridge, led by John Sutherland, showed that all types of “molecules of life”, including RNA, proteins, fats and carbohydrates, can be obtained through similar reactions in which simple inorganic carbon compounds, hydrogen sulfide, metal salts and phosphates.
Clay breath of life
One of the main problems with the previous version of the evolution of life is that many organic molecules, including sugars, DNA and RNA, are too fragile to accumulate in sufficient quantities in the waters of the Earth's primordial ocean, where it was previously thought most evolutionists, the first living beings arose.
British chemist Alexander Cairns-Smith believes that life is of "clay" rather than water origin - the optimal environment for the accumulation and complication of complex organic molecules found within pores and crystals in clay minerals, rather than in Darwin's "primordial pond" or the ocean of the Miller-Urey theories.
In fact, evolution began at the level of crystals, and only then, when the compounds became sufficiently complex and stable, did the first living organisms set off on an “open voyage” into the primary ocean of the Earth.
Life at the bottom of the ocean
Competing with this idea is the popular idea today that life did not originate on the surface of the ocean, but in the deepest regions of its bottom, in the vicinity of “black smokers”, underwater geysers, and other geothermal sources.
Their emissions are rich in hydrogen and other substances, which, according to scientists, could accumulate on the rock slopes and provide the first life with all the necessary food resources and reaction catalysts.
Proof of this can be recognized in the modern ecosystems that exist in the vicinity of similar sources at the bottom of all the Earth’s oceans - they include not only microbes, but even multicellular living beings.
RNA Universe
The theory of dialectical materialism is based on the simultaneous unity and endless struggle of a pair of principles. It's about about heredity information and structural biochemical changes. The version of the origin of life in which RNA plays a key role has come a long way from its appearance in the 1960s until the late 1980s, when it acquired its modern features.
On the one hand, RNA molecules are not as efficient at storing information as DNA, but they are capable of simultaneously accelerating chemical reactions and collect your own copies. It should be understood that scientists have not yet been able to show how the entire chain of evolution of RNA life worked, and therefore this theory has not yet received universal acceptance.
Protocells
Another important question in the evolution of life is the mystery of how such molecules of RNA or DNA and proteins “fenced off” from outside world and turned into the first isolated cells, the contents of which are protected by a flexible membrane or semi-permeable hard shell.
The pioneer in this field was the famous Soviet chemist Alexander Oparin, who showed that drops of water surrounded by a double layer of fat molecules could have similar properties.
His ideas were brought to life by Canadian biologists under the leadership of Jack Szostak, winner of the 2009 Nobel Prize in Physiology or Medicine. His team was able to “package” a simple set of RNA molecules capable of self-replication into a membrane of fat molecules by adding magnesium ions and citric acid inside the first “protocell.”
Endosymbiosis
Another mystery of the evolution of life is how multicellular creatures arose and why the cells of humans, animals and plants include special bodies, such as mitochondria and chloroplasts, which have an unusually complex structure.
The German botanist Andreas Schimper first thought about this problem, suggesting that chloroplasts in the past were independent organisms similar to cyanobacteria, which “became friends” with the cells of plant ancestors and began to live inside them.
This idea was later developed by the Russian botanist Konstantin Merezhkovsky and the American evolutionist Lynn Margulis, who showed that mitochondria and potentially all other complex organelles of our cells have a similar origin.
As with the theories of the “RNA world” and the “clay” evolution of life, the idea of endosymbiosis initially attracted a lot of criticism from most scientists, but today almost all evolutionists do not doubt its correctness.
Who is right and who is wrong?
A lot has been found in favor of Darwinian hypotheses. scientific works and specialized research, in particular in the field of “transitional forms”. Darwin did not have the required number of archaeological artifacts to support his scientific works, since for the most part he was guided by personal guesses.
For example, in the last ten years alone, scientists have found the remains of several similar "lost links" of evolution, such as Tiktaalik and Indohyus, which allow us to draw a line between land animals and fish, and whales and hippos.
On the other hand, skeptics often argue that such animal species are not true transitional forms, which gives rise to constant endless disputes between supporters of Darwinism and their opponents.
On the other hand, experiments on ordinary E. coli and on various multicellular creatures clearly show that evolution is real, and that animals can quickly adapt to new living conditions, acquiring new features that their ancestors did not have 100-200 generations ago.
It is worth remembering, however, that a significant part modern society is still inclined to believe in the existence of a higher divine intelligence or extraterrestrial civilizations that founded life on Earth. So far, there is no single correct theory, and humanity has yet to answer this question in the future.
From the archives of "Continent"
It is well known that our Universe was formed about 14 billion years ago as a result of a giant explosion known in science as the Big Bang. The emergence of the Universe “out of nothing” does not contradict the known laws of physics: the positive energy of the substance formed after the explosion is exactly equal to the negative energy of gravity, so the total energy of such a process is zero. IN Lately Scientists are also discussing the possibility of the formation of other universes - “bubbles”. The world, according to these theories, consists of an infinite number of universes about which we still know nothing. It is interesting that at the moment of the explosion not only three-dimensional space was formed, but, and what is very important, time associated with space. Time is the reason for all the changes that have occurred in the Universe after Big Bang. These changes occurred sequentially, step by step as the arrow of time increased, and included the formation of a huge number of galaxies (on the order of 100 billion), stars (the number of galaxies multiplied by 100 billion), planetary systems and, ultimately, life itself, including intelligent life. To imagine how many stars there are in the Universe, astronomers make this interesting comparison: the number of stars in our Universe is comparable to the number of grains of sand on all the beaches of the Earth, including seas, rivers and oceans. A universe frozen in time would be unchanged and of little interest and there would be no development in it, i.e. all those changes that occurred later and ultimately led to the existing picture of the world.
Our Galaxy is 12.4 billion years old, and our solar system is 4.6 billion years old. The age of meteorites and the oldest rocks on Earth is slightly less than 3.8-4.4 billion years. First single-celled organisms, devoid of prokaryotic nuclei and green-blue bacteria, appeared 3.0-3.5 billion years ago. These are the simplest biological systems, capable of forming proteins, amino acid chains consisting of the basic elements of life C, H, O, N, S, and leading an independent lifestyle. Simple green-blue “algae”, i.e. aquatic plants without vascular tissues and “archaebacteria” or old bacteria (used for the preparation of medicines) are still an important part of our biosphere. These bacteria are the first successful adaptation of life on Earth. It is interesting that green-blue bacteria and other prokaryotes have remained almost unchanged for billions of years, while extinct dinosaurs and other species can never be reborn again, because conditions on Earth have changed greatly, and they can no longer go through all the stages of development that they went through in those distant years. If for one reason or another life on Earth ceases (due to a collision with a giant meteorite, as a result of the explosion of a supernova adjacent to the solar system, or our own self-destruction), it cannot begin again in the same form, because current conditions are fundamentally different from those that were about four billion years ago (for example, the presence of free oxygen in the atmosphere, as well as changes in the Earth's fauna). Evolution, unique in its essence, can no longer repeat itself in the same form and go through all the stages through which it has passed over the past billions of years. Dr. Payson from the Los Alamos National Laboratory in the USA expressed a very interesting idea about the role of evolution in the organization of a system of living structures: “Life is a sequence of molecular interactions. If we discover a principle other than evolution in biology, we will learn to create living systems in the laboratory and thus understand the mechanism of the formation of life.” The reason why we cannot carry out the transformation of species in the laboratory (for example, the Drosophila fly into some other species) is that under natural conditions it took millions of years, and today we do not know any other principle how to cause such a transformation .
As the number of prokaryotes increased, they “invented” the phenomenon of photosynthesis, i.e. a complex chain of chemical reactions in which the energy of sunlight, along with carbon dioxide and water, is converted into oxygen and glucose. In plants, photosynthesis occurs in chloroplasts, which are contained in their leaves, resulting in atmospheric oxygen. An oxygen-saturated atmosphere appeared 2-2.5 billion ago. Eukaryotes, multicellular cells containing a nucleus with genetic information, as well as organelles, formed 1-2 billion years ago. Organelles are found in prokaryotic cells, as well as in animal and plant cells. DNA is the genetic material of any living cell that contains hereditary information. Hereditary genes are located on chromosomes, which contain proteins bound to DNA. All organisms - bacteria, plant and animal world s - despite the enormous diversity of species, they have a common origin, i.e. have a common ancestor. The tree of life consists of three main branches - Bacteria, Archaea, Eukaria. IN last group includes the entire flora and fauna. All known living organisms make proteins using only 20 basic amino acids (although the total number of amino acids in nature is 70), and also use the same molecule ATP energy to store energy in cells. They also use DNA molecules to pass genes from one generation to the next. A gene is the fundamental unit of heredity, a piece of DNA that contains the information necessary for protein synthesis. Various organisms have similar genes that may undergo mutation or improve over long evolution. From bacteria to amoebae and from amoebae to humans, genes are responsible for the characteristics of organisms and the improvement of species, while proteins support life. All living organisms use DNA to pass on their genes to the next generation. Genetic information is transferred from DNA to protein through a complex chain of transformations through RNA, which is similar to DNA, but differs from it in its structure. In the chain of transformations chemistry®biology®life, an organic molecule is synthesized. Biologists are well aware of all these transformations. The most amazing of them is the deciphering of the genetic code (The Human Genome Project), which amazes the imagination with both complexity and perfection. The genetic code is universal for all three branches of the tree of life.
The most interesting question that some humanity has been looking for an answer to throughout its history is how the first life arose and, in particular, whether it originated on Earth or was brought from the interstellar medium with the help of meteorites. All the basic molecules of life, including amino acids and DNA, are also found in meteorites. The theory of directed panspermia suggests that life arose in interstellar space (I wonder where from?), migrates through vast space, but this theory cannot explain how life can survive in the harsh conditions of space (dangerous radiation, low temperatures, lack of atmosphere, etc.). Scientists subscribe to the theory that natural, albeit primitive conditions on Earth led to the formation of simple organic molecules, as well as the development of forms of varying chemical activity, which ultimately launched the tree of life. Very interesting experiment Miller and Urey, carried out in 1953, they proved the formation of complex organic molecules (aldehydes, carboxyls and amino acids) by passing a powerful electrical discharge - an analogue of lightning in natural conditions - through a mixture of gases CH4, NH3, H2O, H2, which were present in the primary atmosphere Earth. This experiment demonstrated that the basic chemical components of life, i.e. biological molecules can be naturally formed by simulating primitive conditions on Earth. However, no forms of life, including the polymerization of DNA molecules, were discovered, which, apparently, could only arise as a result of long-term evolution.
Meanwhile, more complex structures began to appear, huge cells - organs and large living formations consisting of millions and billions of cells (for example, a person consists of ten trillion cells). The complexity of the system depended on the passage of time and the depth of natural selection, which preserved species most adapted to new living conditions. Although all simple eukaryotes reproduced by fission, more complex systems formed sexually. In the latter case, each new cell takes half the genes from one parent and the other half from the other.
Life for a very long period of its history (almost 90%) existed in microscopic and invisible forms. Approximately 540 million years ago, a completely new revolutionary period began, known in science as the Cambrian era. This is a period of rapid emergence of a huge number of multicellular species with a hard shell, skeleton and powerful shell. The first fish and vertebrates appeared, plants from the oceans began to migrate throughout the Earth. The first insects and their descendants contributed to the spread of the animal world across the Earth. Insects with wings, amphibians, the first trees, reptiles, dinosaurs and mammoths, the first birds and the first flowers began to appear successively (dinosaurs disappeared 65 million years ago, apparently due to a giant collision of the Earth with a massive meteorite). Then came the period of dolphins, whales, sharks and primates, the ancestors of monkeys. About 3 million years ago, creatures with an unusually large and highly developed brain, hominids (the first ancestors of humans), appeared. The appearance of the first man ( homo sapiens) dates back 200,000 years ago. According to some theories, the appearance of the first man, who is qualitatively different from all other species of the animal world, may be the result of a strong mutation of hominids, which was the source of the formation of a new allele (allele) - a modified form of one of the genes. Appearance modern man dates back approximately 100,000 years ago, the historical and cultural evidence of our history does not exceed 3000-74000 years, but we became a technologically advanced civilization only recently, only 200 years ago!
Life on Earth is the product of biological evolution dating back approximately 3.5 billion years. The emergence of life on Earth is the result of a large number of favorable conditions - astronomical, geological, chemical and biological. All living organisms, from bacteria to humans, have a common ancestor and consist of several basic molecules that are common to all objects in our Universe. The main properties of living organisms are that they react, grow, reproduce and transmit information from one generation to another. We, the earthly civilization, despite our youthful age, have achieved a lot: we have mastered atomic energy, deciphered the human genetic code, created complex technologies, and began to experiment in the field of genetic engineering(synthetic life), are engaged in cloning, are working to increase our life expectancy (even today scientists are discussing the possibility of increasing life expectancy to 800 years or more), began to fly into space, invented computers and are even trying to make contact with extraterrestrial civilization (SETI program, Search for Extraterrestrial Intelligence). Because another civilization will go through a completely different path of development, it will be completely different from ours. In this sense, each civilization is unique in its own way - perhaps this is one of the reasons why the SETI program was unsuccessful. We began to interfere in the holy of holies, i.e. into processes that natural environment would take millions and millions of years.
To better understand how young we are, let's assume that full story Earth is equal to one year and that our history began on January 1st. In this scale, prokaryotes and blue-green bacteria appeared as early as June 1, which soon led to an oxygenated atmosphere. The Cambrion era began on November 13th. Dinosaurs lived on Earth from December 13 to December 26, and the first hominids appeared on the afternoon of December 31. By the New Year we are already modern people, sent the first message into space - to another part of our Galaxy. Only in about 100,000 years (or in 15 minutes on our scale) will our message (not yet read by anyone) leave our Galaxy and rush to other galaxies. Will it ever be read? We won't know. Most likely not.
It would not only take billions of years for a civilization similar to ours to emerge in another part of the Universe. It is important that such a civilization has enough time for its development and transformation into a technological one, and most importantly does not destroy itself (this is another reason why we cannot find another civilization, although we have been looking for it for more than 50 years: it may perish before manages to become technological). Our technology can help harmful influence to the atmosphere. Already today we are concerned about the appearance of ozone holes in our atmosphere, which have greatly increased over the past 50 years (ozone is a triatomic oxygen molecule, which, in general, is poison). This is the result of our technological activity. The ozone shell protects us from dangerous ultraviolet radiation from the Sun. Such radiation, in the presence of ozone holes, will lead to an increase in the earth's temperature and, as a result, to global warming. The surface of Mars today is sterile due to the absence of an ozone layer. Over the past 20 years, the ozone hole in the Earth's atmosphere has grown to the size of a large continent. An increase in temperature of even 2 degrees will lead to melting ice, rising ocean levels, as well as their evaporation and dangerous increase carbon dioxide in the atmosphere. Then a new warming of the atmosphere will occur, and this process will continue until all the seas and oceans evaporate (scientists call this phenomenon the runaway greenhouse effect). After the evaporation of the oceans, the amount of carbon dioxide in the atmosphere will increase by about 100,000 times and amount to about 100%, which will lead to the complete and irreversible destruction of not only the ozone layer of the earth's atmosphere, but also all life on Earth. This development of events has already taken place in the history of our solar system on Venus. 4 billion years ago, conditions on Venus were close to those on Earth and, perhaps, there was even life there, because... The sun in those distant times did not shine so brightly (it is known that the intensity of solar radiation gradually increases). It is possible that life from Venus migrated to Earth, and from Earth, as solar radiation increases, migrates to Mars, although, apparently, such a development is unlikely due to the problems of living cell migration through space. The amount of carbon dioxide in the atmosphere of Venus today is 98%, and the atmospheric pressure is almost a hundred times higher than on Earth. Perhaps this is the result global warming and the evaporation of the Venusian oceans. Venus and Mars teach us important lesson, i.e. we know today what can happen to our planet if no measures are taken. Another problem is related to the increase in solar radiation, which will ultimately cause a runaway greenhouse effect on Earth with a known result.
Our development is exponential, accelerating. The Earth's population doubles every 40 years and has increased from approximately 200 thousand to 6 billion over the past 2000 years. However, do not such rapid development contain the seeds of danger to our existence? Will we destroy our civilization? Will we have time to become highly developed civilization and understand our history? Will we be able to fly deep into space and find another civilization like ours? According to Einstein, the most amazing thing in the world is that the world is knowable. Perhaps this is one of the most intriguing features of human civilization - the ability to reveal the secrets of the world. We can understand the world we live in and understand the laws that govern it. However, why do these laws exist? Why is the speed of light, for example, equal to 300,000 km/sec or why the well-known number i in mathematics (the ratio of the circumference of a circle to its diameter) is exactly 3.14159...? American physicist A. Michelson received the Nobel Prize for measuring the speed of light with unprecedented accuracy (let me remind you that this is a gigantic value: moving at such a speed we would find ourselves on the Moon in about one second, on the Sun in 8 minutes, and in the center of the Galaxy in 28,000 years ). Another example is that decoding the genetic code, consisting of 30 million pieces, each 500-600 letters long, required 15 years of work using complex programs and computers. It turned out that the length of the entire code is equal to the length of 100 million letters. This discovery was made at the turn of the two millennia and showed that we may be able to treat diseases of any complexity by correcting errors in the corresponding section of the damaged gene. Mathematicians, with the help of fast computers, calculated the number I with incredible accuracy to a trillion decimal places in order to know its exact value and describe this number using some simple formula. Who came up with these numbers and why are they what they are? How could the genetic code be so perfect? How are physical constants related to our universe? Of course, they reflect the geometric structure of our Universe and apparently have different meanings for different universes. We do not know this today, as well as many other things. But we strive to find general laws of our world or even a single law from which all other laws in a particular case could be derived, and also, which is very important, to understand the meaning of world constants. We also do not know whether our existence is connected with the fulfillment of some kind of mission.
But let's return to our history and our evolution. Has it ended and what is its meaning? What will happen to us in millions of years, if, of course, we manage to solve our technological problems and do not destroy ourselves? What is the meaning of the appearance in our history of such brilliant personalities as Einstein, Shakespeare or Mozart? Is it possible to have a new mutation and create another more perfect species than humans? Can this one the new kind solve the problems of the universe and understand the meaning of our history? We have discovered the laws and measured the constants of the world with breathtaking precision, but we do not understand why they are the way they are or what their role is in the universe. If those constants were changed just a little, then our whole history would look different. Despite all the complexity and mystery of the genetic code, the mysteries of the Universe itself seem endless. What is the essence of these mysteries and will we be able to decipher them? Of course we will change. But how? Are we the highest and last link in the long history of our development? Is our history the result of some ingenious plan or is it simply the result of hundreds and thousands of favorable conditions made possible by time and long evolution? There is no doubt that there is no limit to our development and it is also endless, just as the world is endless, consisting of millions and millions of universes that are constantly being destroyed and formed again.
Ilya Gulkarov, Professor, Doctor of Physical and Mathematical Sciences, Chicago
June 18, 2005
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Problem origin of life on Earth has long interested and worried people. There are several hypotheses about the origin of life on our planet:
life was created by God;
life on Earth was brought from outside;
living things on the planet have repeatedly spontaneously generated from non-living things;
life has always existed;
life arose as a consequence of the biochemical revolution.
The whole variety of different hypotheses comes down to two mutually exclusive points of view. Proponents of the theory of biogenesis believed that all living things come only from living things. Their opponents defended the theory of abiogenesis - they believed that the origin of living things from non-living things was possible.
Many scientists assumed the possibility of spontaneous generation of life. Impossibility spontaneous generation life was proven by Louis Pasteur.
The second stage is the formation of proteins, fats, carbohydrates, and nucleic acids from simple organic compounds in the waters of the primary ocean. The isolated molecules of these compounds concentrated and formed coacervates, acting as open systems, capable of metabolism with environment and growth.
The third stage - as a result of the interaction of coacervates with nucleic acids, the first living beings were formed - probionts, capable, in addition to growth and metabolism, of self-reproduction.
The question of when life appeared on Earth has always worried not only scientists, but also all people. Answers to it
almost all religions. Although there is still no exact scientific answer to this question, some facts allow us to make more or less reasonable hypotheses. Researchers found a rock sample in Greenland
with a tiny splash of carbon. The age of the sample is more than 3.8 billion years. The source of carbon was most likely some kind of organic matter - during this time it completely lost its structure. Scientists believe this lump of carbon may be the oldest trace of life on Earth.
What did the primitive Earth look like?
Let's fast forward to 4 billion years ago. The atmosphere does not contain free oxygen; it is found only in oxides. Almost no sounds except the whistle of the wind, the hiss of water erupting with lava and the impacts of meteorites on the surface of the Earth. No plants, no animals, no bacteria. Maybe this is what the Earth looked like when life appeared on it? Although this problem has long been of concern to many researchers, their opinions on this matter vary greatly. Rocks could indicate conditions on Earth at that time, but they were destroyed long ago as a result of geological processes and movements of the earth's crust.
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?
According to one hypothesis, life began in a piece of ice. Although many scientists believe that carbon dioxide in the atmosphere maintained greenhouse conditions, others believe that winter reigned on Earth. At low temperatures, all chemical compounds are more stable and can therefore accumulate in larger quantities than at high temperatures. Meteorite fragments brought from space, emissions from hydrothermal vents, and chemical reactions occurring during electrical discharges in the atmosphere were sources of ammonia and organic compounds such as formaldehyde and cyanide. Getting into the water of the World Ocean, they froze along with it. In the ice column, molecules of organic substances came closely together and entered into interactions that led to the formation of glycine and other amino acids. The ocean was covered with ice, which protected the newly formed compounds from destruction by ultraviolet radiation. This icy world could melt, for example, if a huge meteorite fell on the planet (Fig. 1).
Charles Darwin and his contemporaries believed that life could have arisen in a body of water. Many scientists still adhere to this point of view. In a closed and relatively small reservoir, organic substances brought by the waters flowing into it could accumulate in the required quantities. These compounds were then further concentrated on the inner surfaces of layered minerals, which could catalyze the reactions. For example, two molecules of phosphaldehyde that met on the surface of a mineral reacted with each other to form a phosphorylated carbohydrate molecule, a possible precursor to ribonucleic acid (Fig. 2).
Or maybe life arose in areas of volcanic activity? Immediately after its formation, the Earth was a fire-breathing ball of magma. During volcanic eruptions and with gases released from molten magma, earth's surface a variety of chemicals necessary for the synthesis of organic molecules were removed. Thus, carbon monoxide molecules, once on the surface of the mineral pyrite, which has catalytic properties, could react with compounds that had methyl groups and form acetic acid, from which other organic compounds were then synthesized (Fig. 3).
For the first time, obtain organic molecules - amino acids - in laboratory conditions American scientist Stanley Miller succeeded in simulating those that were on the primitive Earth in 1952. Then these experiments became a sensation, and their author gained worldwide fame. He currently continues to conduct research in the field of prebiotic (before life) chemistry at the University of California. The installation on which the first experiment was carried out was a system of flasks, in one of which it was possible to obtain a powerful electric discharge at a voltage of 100,000 V.
Miller filled this flask with natural gases - methane, hydrogen and ammonia, which were present in the atmosphere of the primitive Earth. In the flask below there was a small amount of water simulating the ocean. The electric discharge was close to lightning in strength, and Miller expected that under its action chemical compounds were formed, which, when they got into the water, would react with each other and form more complex molecules.
The result exceeded all expectations. After turning off the installation in the evening and returning the next morning, Miller discovered that the water in the flask had acquired a yellowish color. What emerged was a soup of amino acids, the building blocks of proteins. Thus, this experiment showed how easily the primary ingredients of life could be formed. All that was needed was a mixture of gases, a small ocean and a little lightning.
Other scientists are inclined to believe that the ancient atmosphere of the Earth was different from the one that Miller modeled, and most likely consisted of carbon dioxide and nitrogen. Using this gas mixture and Miller's experimental setup, chemists attempted to produce organic compounds. However, their concentration in water was as insignificant as if a drop of food coloring were dissolved in a swimming pool. Naturally, it is difficult to imagine how life could arise in such a dilute solution.
If indeed the contribution of earthly processes to the creation of reserves of primary organic matter was so insignificant, then where did it even come from? Maybe from space? Asteroids, comets, meteorites and even particles of interplanetary dust could carry organic compounds, including amino acids. These extraterrestrial objects could provide sufficient amounts of organic compounds for the origin of life to enter the primordial ocean or small body of water.
The sequence and time interval of events, starting from the formation of primary organic matter and ending with the appearance of life as such, remains and, probably, will forever remain a mystery that worries many researchers, as well as the question of what. in fact, consider it life.
Currently, there are several scientific definitions of life, but all of them are not accurate. Some of them are so wide that they include such inanimate objects like fire or mineral crystals. Others are too narrow, and according to them, mules that do not give birth to offspring are not recognized as living.
One of the most successful defines life as self-sustaining chemical system, capable of behaving in accordance with the laws of Darwinian evolution. This means that, firstly, a group of living individuals must produce descendants similar to themselves, which inherit the characteristics of their parents. Secondly, generations of descendants must show the consequences of mutations - genetic changes that are inherited by subsequent generations and cause population variability. And thirdly, it is necessary for a system of natural selection to operate, as a result of which some individuals gain an advantage over others and survive in changed conditions, producing offspring.
What elements of the system were necessary for it to have the characteristics of a living organism? Big number biochemists and molecular biologists believe that RNA molecules had the necessary properties. RNA - ribonucleic acids - are special molecules. Some of them can replicate, mutate, thus transmitting information, and, therefore, they could participate in natural selection. True, they are not capable of catalyzing the replication process themselves, although scientists hope that in the near future an RNA fragment with such a function will be found. Other RNA molecules are involved in “reading” genetic information and transferring it to ribosomes, where the synthesis of protein molecules occurs, in which the third type of RNA molecules takes part.
Thus, the most primitive living system could be represented by RNA molecules duplicating, undergoing mutations and being subject to natural selection. In the course of evolution, based on RNA, specialized DNA molecules arose - the custodians of genetic information - and no less specialized protein molecules, which took on the functions of catalysts for the synthesis of all currently known biological molecules.
At some point in time, a “living system” of DNA, RNA and protein found shelter inside a sac formed by a lipid membrane, and this structure, more protected from external influences, served as the prototype of the very first cells that gave rise to the three main branches of life, which are represented in the modern world by bacteria , archaea and eukaryotes. As for the date and sequence of appearance of such primary cells, this remains a mystery. In addition, according to simple probabilistic estimates, there is not enough time for the evolutionary transition from organic molecules to the first organisms - the first simplest organisms appeared too suddenly.
For many years, scientists believed that it was unlikely that life could have emerged and developed during the period when the Earth was constantly subject to collisions with large comets and meteorites, a period that ended approximately 3.8 billion years ago. However, recently, traces of complex cellular structures dating back at least 3.86 billion years have been discovered in the oldest sedimentary rocks on Earth, found in southwestern Greenland. This means that the first forms of life could have arisen millions of years before the bombardment of our planet by large cosmic bodies stopped. But then a completely different scenario is possible (Fig. 4).
Fallen to Earth space objects could have played a central role in the emergence of life on our planet, since, according to a number of researchers, cells similar to bacteria could have arisen on another planet and then arrived on Earth along with asteroids. One piece of evidence supporting the theory of extraterrestrial origins of life was found inside a meteorite shaped like a potato and named ALH84001. This meteorite was originally a piece of Martian crust, which was then thrown into space as a result of an explosion when a huge asteroid collided with the surface of Mars, which occurred about 16 million years ago. And 13 thousand years ago, after a long journey within solar system This fragment of Martian rock in the form of a meteorite landed in Antarctica, where it was recently discovered. A detailed study of the meteorite revealed rod-shaped structures resembling fossilized bacteria inside it, which gave rise to heated scientific debate about the possibility of life deep in the Martian crust. These disputes will not be resolved until 2005, when the National Aeronautics Administration space research The United States will implement a program to fly an interplanetary spacecraft to Mars to take samples of the Martian crust and deliver samples to Earth. And if scientists manage to prove that microorganisms once inhabited Mars, then we can speak with a greater degree of confidence about the extraterrestrial origin of life and the possibility of life being brought from outer space (Fig. 5).
Rice. 5. Our origin is from microbes.
What have we inherited from ancient life forms? The comparison below of single-celled organisms with human cells reveals many similarities.
 1. Sexual reproduction |
 2. Eyelashes |
 3. Capture other cells |
 4. Mitochondria |
 5. Flagella |
Bacteria and simple eukaryotes also have flagella with a similar internal structure. It consists of a pair of microtubules surrounded by nine others.
The evolution of life on Earth: from simple to complex
The second branch is bacteria - prokaryotic (prenuclear) single-celled organisms that do not have a pronounced nucleus and organelles. And finally, the third branch is single-celled organisms called archaea, or archaebacteria, whose cells have the same structure as prokaryotes, but a completely different chemical structure of lipids.
Many archaebacteria are able to survive in extremely unfavorable environmental conditions. Some of them are thermophiles and live only in hot springs with temperatures of 90 ° C or even higher, where other organisms would simply die. Feeling great in such conditions, these single-celled organisms consume iron and sulfur-containing substances, as well as a number of chemical compounds, toxic to other life forms. According to scientists, the thermophilic archaebacteria found are extremely primitive organisms and, in evolutionary terms, close relatives of the most ancient forms of life on Earth.
It is interesting that modern representatives of all three branches of life, most similar to their ancestors, still live today in places with high temperature. Based on this, some scientists are inclined to believe that, most likely, life arose about 4 billion years ago on the ocean floor near hot springs, erupting streams rich in metals and high-energy substances. Interacting with each other and with the water of the then sterile ocean, entering into a wide variety of chemical reactions, these compounds gave rise to fundamentally new molecules. So, for tens of millions of years, the greatest dish - life - was prepared in this “chemical kitchen”. And about 4.5 billion years ago, single-celled organisms appeared on Earth, whose lonely existence continued throughout the Precambrian period.
The burst of evolution that gave rise to multicellular organisms occurred much later, a little over half a billion years ago. Although microorganisms are so small that a single drop of water can contain billions, the scale of their work is enormous.
It is believed that initially there was no free oxygen in the earth’s atmosphere and the oceans, and under these conditions only anaerobic microorganisms lived and developed. A special step in the evolution of living things was the emergence of photosynthetic bacteria, which, using light energy, converted carbon dioxide into carbohydrate compounds that served as food for other microorganisms. If the first photosynthetics produced methane or hydrogen sulfide, then the mutants that appeared once began to produce oxygen during photosynthesis. As oxygen accumulates in the atmosphere and waters anaerobic bacteria, for which it is destructive, occupied oxygen-free niches.
Ancient fossils found in Australia dating back 3.46 billion years have revealed structures believed to be the remains of cyanobacteria, the first photosynthetic microorganisms. About past dominance anaerobic microorganisms and cyanobacteria are evidenced by stromatolites found in shallow coastal waters of unpolluted salt water bodies. In shape they resemble large boulders and represent an interesting community of microorganisms living in the limestone or dolomite rocks formed as a result of their life activity. To a depth of several centimeters from the surface, stromatolites are saturated with microorganisms: in fact top layer photosynthetic cyanobacteria that produce oxygen live; deeper bacteria are found that are to a certain extent tolerant of oxygen and do not require light; in the lower layer there are bacteria that can only live in the absence of oxygen. Located in different layers, these microorganisms form a system united by complex relationships between them, including food relationships. Behind the microbial film is a rock formed as a result of the interaction of the remains of dead microorganisms with calcium carbonate dissolved in water. Scientists believe that when there were no continents on the primitive Earth and only archipelagos of volcanoes rose above the surface of the ocean, the shallow waters were replete with stromatolites.
As a result of the activity of photosynthetic cyanobacteria, oxygen appeared in the ocean, and approximately 1 billion years after that, it began to accumulate in the atmosphere. First, the resulting oxygen interacted with iron dissolved in water, which led to the appearance of iron oxides, which gradually precipitated at the bottom. Thus, over millions of years, with the participation of microorganisms, huge deposits of iron ore arose, from which steel is smelted today.
Then, when the bulk of the iron in the oceans was oxidized and could no longer bind oxygen, it escaped into the atmosphere in gaseous form.
After photosynthetic cyanobacteria created a certain supply of energy-rich organic matter from carbon dioxide and enriched earth's atmosphere oxygen, new bacteria arose - aerobes, which can only exist in the presence of oxygen. They need oxygen for the oxidation (combustion) of organic compounds, and a significant part of the resulting energy is converted into a biologically available form - adenosine triphosphate (ATP). This process is energetically very favorable: anaerobic bacteria, when decomposing one glucose molecule, receive only 2 ATP molecules, and aerobic bacteria that use oxygen have 36 ATP molecules.
With the advent of oxygen sufficient for an aerobic lifestyle, eukaryotic cells also made their debut, which, unlike bacteria, have a nucleus and organelles such as mitochondria, lysosomes, and in algae and higher plants - chloroplasts, where photosynthetic reactions take place. There is an interesting and well-founded hypothesis regarding the emergence and development of eukaryotes, expressed almost 30 years ago by the American researcher L. Margulis. According to this hypothesis, mitochondria, which function as energy factories in a eukaryotic cell, are aerobic bacteria, and chloroplasts plant cells, in which photosynthesis occurs, are cyanobacteria, probably absorbed about 2 billion years ago by primitive amoebae. As a result of mutually beneficial interactions, the absorbed bacteria became internal symbionts and formed a stable system with the cell that absorbed them - a eukaryotic cell.
Studies of fossil remains of organisms in rocks of different geological ages have shown that for hundreds of millions of years after their origin, eukaryotic life forms were represented by microscopic spherical single-celled organisms such as yeast, and their evolutionary development proceeded at a very slow pace. But a little over 1 billion years ago, many new species of eukaryotes emerged, marking a dramatic leap in the evolution of life.
First of all, this was due to the emergence of sexual reproduction. And if bacteria and single-celled eukaryotes reproduced by producing genetically identical copies of themselves and without the need for a sexual partner, then sexual reproduction in more highly organized eukaryotic organisms it occurs as follows. Two haploid sex cells of the parents, having a single set of chromosomes, fuse to form a zygote that has a double set of chromosomes with the genes of both partners, which creates opportunities for new gene combinations. The emergence of sexual reproduction led to the emergence of new organisms, which entered the arena of evolution.
Three quarters of the entire existence of life on Earth was represented exclusively by microorganisms, until a qualitative leap in evolution occurred, leading to the emergence of highly organized organisms, including humans. Let's trace the main milestones in the history of life on Earth in a descending line.
1.2 billion years ago there was an explosion of evolution, caused by the advent of sexual reproduction and marked by the appearance of highly organized life forms - plants and animals.
The formation of new variations in the mixed genotype that arises during sexual reproduction manifested itself in the form of biodiversity of new life forms.
2 billion years ago, complex eukaryotic cells appeared when single-celled organisms complicated their structure by absorbing other prokaryotic cells. Some of them - aerobic bacteria - turned into mitochondria - energy stations for oxygen respiration. Others - photosynthetic bacteria - began to carry out photosynthesis inside the host cell and became chloroplasts in algae and plant cells. Eukaryotic cells, which have these organelles and a clearly distinct nucleus containing genetic material, make up all modern complex life forms - from molds to humans.
3.9 billion years ago, single-celled organisms appeared that probably looked like modern bacteria and archaebacteria. Both ancient and modern prokaryotic cells have a relatively simple structure: they do not have a formed nucleus and specialized organelles, their jelly-like cytoplasm contains DNA macromolecules - carriers of genetic information, and ribosomes on which protein synthesis occurs, and energy is produced on the cytoplasmic membrane surrounding cell.
4 billion years ago, RNA mysteriously emerged. It is possible that it was formed from simpler organic molecules that appeared on the primitive earth. It is believed that ancient RNA molecules had the functions of carriers of genetic information and protein catalysts, they were capable of replication (self-duplication), mutated and were subject to natural selection. In modern cells, RNA does not have or does not exhibit these properties, but plays a very important role as an intermediary in the transfer of genetic information from DNA to ribosomes, in which protein synthesis occurs.
A.L. Prokhorov
Based on an article by Richard Monasterski
in National Geographic magazine, 1998 No. 3
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