Science still cannot say even approximately, even with an error of millions of years. It is only indisputable that living matter has changed over hundreds of millions of years of the life of the Earth, depending on environmental conditions, the conditions for the existence of organisms.
Development of plant and animal organisms
Comparing plant and animal organisms, profound differences can be found in them. If, however, we move from higher forms to lower ones, from more highly organized to less organized ones, these differences are gradually smoothed out. The simplest representatives of animals and plants are so close to each other that their division is conditional and it is not possible to establish a sharp boundary here. This speaks volumes about unity of life.
Life gradually developed and improved. As a result of continuous changes, new plant and animal organisms have appeared that are better adapted to the new environment.
The plant and animal world familiar to us is only one of the stages of that grandiose in time process of the development of life, which began a very long time ago.
The history of the origin of life on Earth in the layers of the earth's crust
These layers are like the pages of a special book, a fascinating book about the life of the Earth. You just need to be able to read its dilapidated, sometimes too scattered pages.
In a deep ravine or on the bank of a river, you can find shells that are unusual in appearance and shape, prints of plants and animals on stone, stones that look like honeycombs or small ram's horns, as well as stone tubes pointed on one side, different in size and thickness. . They somewhat resemble fragments of stone fingers. For this similarity, they are colloquially called “damn fingers”.
Fucking finger You may also be lucky enough to find teeth of an unusual shape, bones and even whole skeletons, prints, sometimes huge, of animals never seen before.
The rocks that make up the strata of the earth's crust are no less remarkable than those fossil remains of organisms that are found in them. In some places, blue, red and black clays attract our attention, in others - black, red and green sandstones, white and green sands, limestones, sometimes overflowing with the remains of various organisms.
Researchers of nature have long noted that in different layers there are remains of various organisms.
In some layers, for example, near St. Petersburg, an abundance of small flat shells is striking - “obolus”, approximately the size of a two-kopeck coin (“obolos” in Greek is a small bargaining chip - obol), in other layers, for example, near Moscow, there is an abundance of “damn fingers ".
The abundance of "damn fingers" in the layers Hence, the conclusion was drawn that these layers were formed at different geological times, when these organisms received significant distribution in marine reservoirs.
Obolus inhabited the ancient Silurian Sea, which emerged, as geologists determine, approximately 360 million years ago and existed for 40 million years. This sea occupied a huge area from the eastern borders of Western Europe to the Aral Sea in the east and approximately from the latitude of the city of Tula in the north to the Caucasus Mountains in the south.
Modern seas, such as the Black Sea, also throw out huge masses of all kinds of shells. On the Evpatoria "golden" beach, you will be amazed by the abundance of shells. Local craftsmen skillfully decorate their unpretentious souvenirs with it - boxes, photo frames and various knick-knacks. Along with the artistic purpose, the shell is well used instead of ballast sand for the railway track.
The strata of the Black Sea shell served as the starting material for the formation of layers of shell rock - an excellent building material that lends itself well to processing.
Shell rock is an excellent building material The "devil's finger" has an equally interesting story. The devil is remembered here only out of ignorance: this is nothing more than fragments of the inner shell of an ancient belemnite cephalopod mollusk that lived in the distant Mesozoic era, approximately 185 million years ago. The name of the animal comes from the ancient Greek word "belemnon" - an arrow, the tip of which, in general, looked like a "devil's finger".
Descendants of the Belemnites
A few descendants of belemnites - cuttlefish and giant monsters - octopuses, or octopuses, are found in modern seas, both cold and warm, both near the coast and at great depths (up to 3500 meters). Most cephalopods are predators; sometimes they reach 17 meters, of which 6 meters fall on the body of the animal, the rest - on the tentacles - "legs", up to ten in number.
Cephalopods swim in a special way: by strong contraction of the muscles of their body, they throw out a stream of water from the mouth opening. From this push, the animal rushes swiftly, like a torpedo. You might think that it floats backwards. In case of danger, some cephalopods release the contents of a special ink bag and become invisible to the enemy behind a muddy veil.
The famous Chinese ink and brown sepia paint are made from the contents of the ink bag. Many cephalopods, especially cuttlefish, are eaten (in China) both fresh and dried.
The very "devil's finger" was in the tail of the animal and provided the predator with speed of movement.
ancient seas
Ancient cephalopods were found in abundance in Cretaceous Sea, which in the first half of the Cretaceous period flooded a wide strip along the Ural Range, going into a deep bay to the west to the Tver-Kaluga meridian, and in the second half it occupied almost the entire southern half of the European part of Russia to the southern borders with Turkey and Iran. In this southern region of the Cretaceous Sea, the Main Caucasian Range has already been identified as a rocky island.
Study of the formation of the Earth's layers
If in layers of the earth remote from each other areas, for example, near Moscow and near Ulyanovsk, are found in abundance "devil's fingers" or any other identical organic remains - this convincingly suggests that these layers were formed at the same geological time, otherwise - in the same geological period, epoch, century, etc.
The study of the layers of the earth's crust in the Quaternary period
Interesting material can give us the study of the layers of the earth's crust, formed over the nearest million years to us. This geological period, which continues to the present, is called the Quaternary period.
In the uppermost layers of the Lower and Middle Volga regions, for example, in the Astrakhan, Volgograd, Saratov and Kuibyshev regions, especially in the Trans-Volga region, shells are found similar to those that still live in the Caspian Sea.
Based on the finds of these shells, it was possible to establish the boundaries of the once-existing huge Aral-Caspian Sea. Volgograd and Saratov are now located on its root bank. Researchers can even accurately establish that the northern narrow bay of the sea ran along the high right bank of the Kama far to the northeast.
This sea was like this about 100 thousand years ago, when most of the European territory of Russia was under the cover of the great glaciation and the ice thickness reached, as geologists believe, up to two kilometers.
In deeper layers, in the Volga region, bones of bison bulls, wild horses, huge camels, a mammoth, a gigantic deer, a hairy rhinoceros, a cave lion and other now disappeared animals are found.
The deeper we penetrate into the layers, the more often we will meet the bones of animals, more and more different from the modern representatives of the animal world.
Fossilized remains of animals Studying the petrified remnants of life of past eras, geologists seem to turn over the stone pages of the great book of nature. However, it often does not give an exhaustive answer: many pages are missing, since not all organisms that existed in past epochs of the life of our planet imprinted their mark on the stone.
The imprint of a petrified worm From the long chain of life, starting from the emergence of living matter to the most perfect form - man, only separate fragments have been preserved, many links of this chain are missing.
The most ancient layers of the earth's crust, greatly altered in the process of its formation, contain almost no signs of organic life.
Formation of fossil organisms
More distinct traces of organisms begin to appear in those rocks that were formed from the sediments of ancient reservoirs.
The organisms and their skeletons buried in these sediments gradually turned into stone under favorable conditions, in other words, they became mineralized.
Mineralized finds Their organic matter was replaced from solutions with mineral matter, such as lime carbonate, silica, and other substances. This is how various fossilized shells, bones, pieces of wood and even whole tree trunks were formed.
If we grind a thin transparent plate (thinner than a sheet of paper), the so-called thin section, from a piece of petrified wood, then under a microscope we will clearly see the internal structure of ancient wood.
Sometimes not the shells themselves, parts of the plant, etc., are preserved, but only their imprints, for example, imprints of plant leaves.
There are also casts formed from the material that filled the shell and subsequently hardened.
This is how the “inner cores,” as geologists call them, are obtained. They resemble metal castings in a certain shape. When the shell itself dissolves, a cast of its outer form, or "outer core", is obtained.
The environment in which the remains of animals were preserved determined their safety: in coarse-grained sands, the remains of animals were dissolved by circulating waters, in clays they were crushed, and in metamorphic rocks they completely disappeared.
Only fine-grained silty sediments, peat, natural asphalt, and especially the resin of coniferous trees determined the exceptional preservation of organic remains. Insects, for example, and flowers that got into liquid tree resin millions of years ago, were preserved entirely without the slightest change, as if they were alive. How can this be explained?
The fact is that the resin gradually hardened, petrified, turning into amber - a semi-precious golden stone, often completely transparent. Beads, mouthpieces, brooches, etc. are made from amber. Various insects, especially ants, are often found in amber.
Here is what Lomonosov wrote about these curiosities about 260 years ago:
Walking in the poplar shade, an ant
In sticky pitch he got stuck with his foot.
Although he was despicable among people in his life:
Upon death, they became precious in amber.
Not always, especially in the old days, geological finds received the correct definition and purpose. There were also unforgettable curiosities. In one, for example, Spanish cathedral in the 17th century, the molar tooth of a mammoth was revered as an undoubted tooth of a saint.
Those suffering from toothache applied themselves to Mammoth's tooth and generally gave a good income to the "holy fathers". Note that the approximate dimensions of a mammoth tooth are: the length of the root is 12 centimeters, the length of the chewing surface is 14 centimeters, and its width is 7 centimeters. Each person is supposed to have thirty-two teeth (with a full set of them). What size was the mouth of the saint, judging by the indisputable data of the shrine itself.
It should be noted that legends about giants, who were twenty times taller than a man, were also found in ancient, “scientific” treatises of that time.
There were even more severe cases with geological finds. The imprint of the skeleton of an ancient lizard was recognized, for example, with the blessing of the "learned men" of the first quarter of the 18th century, for the skeleton of a man who drowned during the "Flood".
The question of the origin of life on Earth is one of the most difficult questions of modern natural science, to which there is no unambiguous answer so far.
There are several theories about the origin of life on Earth, the most famous of which are:
- theory of spontaneous (spontaneous) generation;
- the theory of creationism (or creation);
- steady state theory;
- theory of panspermia;
- theory of biochemical evolution (the theory of A.I. Oparin).
Consider the main provisions of these theories.
Theory of spontaneous (spontaneous) generation
The theory of spontaneous generation of life was widespread in the ancient world - Babylon, China, Ancient Egypt and Ancient Greece (Aristotle, in particular, adhered to this theory).
Scientists of the ancient world and medieval Europe believed that living beings constantly arise from inanimate matter: worms from mud, frogs from mud, fireflies from morning dew, etc. So, the famous Dutch scientist of the 17th century. Van Helmont quite seriously described in his scientific treatise an experience in which he got mice in a locked dark closet directly from a dirty shirt and a handful of wheat in 3 weeks. For the first time, the Italian scientist Francesco Redi (1688) decided to subject a widely accepted theory to experimental verification. He placed several pieces of meat in vessels and covered some of them with muslin. In open vessels, white worms appeared on the surface of rotting meat - fly larvae. There were no fly larvae in the vessels covered with muslin. Thus, F. Redi managed to prove that fly larvae do not appear from rotting meat, but from eggs laid by flies on its surface.
In 1765, the famous Italian scientist and physician Lazzaro Spalanzani boiled meat and vegetable broths in sealed glass flasks. Broths in sealed flasks did not deteriorate. He concluded that under the influence of high temperature all living creatures capable of causing spoilage of the broth died. However, the experiments of F. Redi and L. Spalanzani did not convince everyone. Vitalist scientists (from lat. vita- life) believed that spontaneous generation of living beings does not occur in a boiled broth, since a special “life force” is destroyed in it, which cannot penetrate into a sealed vessel, since it is carried through the air.
Disputes about the possibility of spontaneous generation of life intensified in connection with the discovery of microorganisms. If complex living beings can't reproduce spontaneously, perhaps microorganisms can?
In this regard, in 1859, the French Academy announced the award of a prize to the one who finally decides the question of the possibility or impossibility of spontaneous generation of life. This award was received in 1862 by the famous French chemist and microbiologist Louis Pasteur. Just like Spalanzani, he boiled nutrient broth in a glass flask, but the flask was not ordinary, but with a neck in the form of a 5-shaped tube. Air, and hence the "life force", could penetrate into the flask, but the dust, and with it the microorganisms present in the air, settled in the lower elbow of the 5-shaped tube, and the broth in the flask remained sterile (Fig. 1). However, it was worth breaking the neck of the flask or rinsing the lower knee of the 5-shaped tube with sterile broth, as the broth began to quickly become cloudy - microorganisms appeared in it.
Thus, thanks to the work of Louis Pasteur, the theory of spontaneous generation was recognized as untenable and the theory of biogenesis was established in the scientific world, a brief formulation of which is - "everything living is from living things."
Rice. 1. Pasteur flask
However, if all living organisms in the historically foreseeable period of human development originate only from other living organisms, the question naturally arises: when and how did the first living organisms appear on Earth?
Creation theory
Creation theory assumes that all living organisms (or only their simplest forms) were created (“designed”) in a certain period of time by some supernatural being (deity, absolute idea, supermind, supercivilization, etc.). It is obvious that the followers of most of the leading religions of the world, in particular the Christian religion, adhered to this point of view from ancient times.
The theory of creationism is still quite widespread, not only in religious, but also in scientific circles. It is usually used to explain the most complex, unresolved issues of biochemical and biological evolution associated with the emergence of proteins and nucleic acids, the formation of the mechanism of interaction between them, the emergence and formation of individual complex organelles or organs (such as the ribosome, eye or brain). Acts of periodic "creation" also explain the absence of clear transitional links from one type of animal
to another, for example, from worms to arthropods, from monkeys to humans, etc. It must be emphasized that the philosophical dispute about the primacy of consciousness (supermind, absolute idea, deity) or matter is fundamentally unsolvable, however, since an attempt to explain any difficulties of modern biochemistry and evolutionary theory by fundamentally incomprehensible supernatural acts of creation takes these issues beyond the scope of scientific research, the theory of creationism cannot be categorized scientific theories origin of life on earth.
Steady state and panspermia theories
Both of these theories are complementary elements of a single picture of the world, the essence of which is as follows: the universe exists forever and life exists in it forever (stationary state). Life is carried from planet to planet by "seeds of life" traveling in outer space, which can be part of comets and meteorites (panspermia). Similar views on the origin of life were held, in particular, by Academician V.I. Vernadsky.
However, the theory of the stationary state, which assumes an infinitely long existence of the universe, is not consistent with the data of modern astrophysics, according to which the universe arose relatively recently (about 16 billion years ago) by means of a primary explosion.
It is obvious that both theories (panspermia and stationary state) do not offer an explanation of the mechanism of the primary origin of life at all, transferring it to other planets (panspermia) or moving it to infinity in time (the theory of a stationary state).
Theory of biochemical evolution (theory of A.I. Oparin)
Of all theories of the origin of life, the most common and recognized in the scientific world is the theory of biochemical evolution, proposed in 1924 by the Soviet biochemist Academician A.I. Oparin (in 1936 he described it in detail in his book The Emergence of Life).
The essence of this theory is that biological evolution - i.e. The appearance, development and complication of various forms of living organisms was preceded by chemical evolution - a long period in the history of the Earth, associated with the emergence, complication and improvement of the interaction between elementary units, "bricks" that make up all living things - organic molecules.
Prebiological (chemical) evolution
According to most scientists (primarily astronomers and geologists), the Earth was formed as a celestial body about 5 billion years ago. by condensation of particles of a gas and dust cloud rotating around the Sun.
Under the influence of compressive forces, the particles from which the Earth is formed release a huge amount of heat. Thermonuclear reactions begin in the bowels of the Earth. As a result, the Earth gets very hot. Thus, 5 billion years ago The earth was a hot ball rushing through outer space, the surface temperature of which reached 4000-8000°C (laugh. 2).
Gradually, due to the radiation of thermal energy into outer space, the Earth begins to cool. About 4 billion years ago The earth cools so much that a hard crust forms on its surface; at the same time, light, gaseous substances escape from its bowels, rising up and forming the primary atmosphere. The composition of the primary atmosphere was significantly different from the modern one. Apparently, there was no free oxygen in the atmosphere of the ancient Earth, and its composition included substances in a reduced state, such as hydrogen (H 2), methane (CH 4), ammonia (NH 3), water vapor (H 2 O ), and possibly also nitrogen (N 2), carbon monoxide and carbon dioxide (CO and CO 2).
The reducing nature of the Earth's primary atmosphere is extremely important for the origin of life, since substances in a reduced state are highly reactive and, under certain conditions, are able to interact with each other, forming organic molecules. The absence of free oxygen in the atmosphere of the primary Earth (practically all of the Earth's oxygen was bound in the form of oxides) is also an important prerequisite for the emergence of life, since oxygen easily oxidizes and thereby destroys organic compounds. Therefore, in the presence of free oxygen in the atmosphere, the accumulation of a significant amount of organic matter on the ancient Earth would have been impossible.
About 5 billion years ago- the emergence of the Earth as a celestial body; surface temperature — 4000-8000°C
About 4 billion years ago - formation of the earth's crust and primary atmosphere
At 1000°C- in the primary atmosphere, the synthesis of simple organic molecules begins
The energy for synthesis is given by:
The temperature of the primary atmosphere is below 100 ° C - the formation of the primary ocean -
Synthesis of complex organic molecules - biopolymers from simple organic molecules:
- simple organic molecules - monomers
- complex organic molecules - biopolymers
Scheme. 2. Main stages of chemical evolution
When the temperature of the primary atmosphere reaches 1000°C, the synthesis of simple organic molecules begins in it, such as amino acids, nucleotides, fatty acids, simple sugars, polyhydric alcohols, organic acids, etc. The energy for synthesis is supplied by lightning discharges, volcanic activity, hard space radiation and, finally, the ultraviolet radiation of the Sun, from which the Earth is not yet protected by the ozone screen, and it is ultraviolet radiation that scientists consider the main source of energy for abiogenic (that is, passing without the participation of living organisms) synthesis of organic substances.
The recognition and wide dissemination of the theory of A.I. Oparin was greatly facilitated by the fact that the processes of abiogenic synthesis of organic molecules are easily reproduced in model experiments.
The possibility of synthesizing organic substances from inorganic substances has been known since the beginning of the 19th century. Already in 1828, the outstanding German chemist F. Wöhler synthesized an organic substance - urea from inorganic - ammonium cyanate. However, the possibility of abiogenic synthesis of organic substances under conditions close to those of the ancient Earth was first shown in the experiment of S. Miller.
In 1953, a young American researcher, a graduate student at the University of Chicago, Stanley Miller, reproduced in a glass flask with electrodes soldered into it the primary atmosphere of the Earth, which, according to scientists of that time, consisted of hydrogen, methane CH 4, ammonia NH, and water vapor H 2 0 (Fig. 3). Through this gas mixture, S. Miller passed electric discharges simulating thunderstorms for a week. At the end of the experiment, α-amino acids (glycine, alanine, asparagine, glutamine), organic acids (succinic, lactic, acetic, glycocolic), γ-hydroxybutyric acid and urea were found in the flask. When repeating the experiment, S. Miller managed to obtain individual nucleotides and short polynucleotide chains of five to six links.
Rice. 3. Installation by S. Miller
In further experiments on abiogenic synthesis conducted by various researchers, not only electrical discharges were used, but also other types of energy characteristic of the ancient Earth, such as cosmic, ultraviolet and radioactive radiation, high temperatures inherent in volcanic activity, as well as various options for gas mixtures, imitating the original atmosphere. As a result, almost the entire spectrum of organic molecules characteristic of living things was obtained: amino acids, nucleotides, fat-like substances, simple sugars, organic acids.
Moreover, abiogenic synthesis of organic molecules can also occur on Earth at the present time (for example, in the course of volcanic activity). At the same time, not only hydrocyanic acid HCN, which is a precursor of amino acids and nucleotides, but also individual amino acids, nucleotides, and even such complex organic substances as porphyrins can be found in volcanic emissions. Abiogenic synthesis of organic substances is possible not only on Earth, but also in outer space. The simplest amino acids are found in meteorites and comets.
When the temperature of the primary atmosphere dropped below 100 ° C, hot rains fell on the Earth and the primary ocean appeared. With streams of rain, abiogenically synthesized organic substances entered the primary ocean, which turned it, but in the figurative expression of the English biochemist John Haldane, into a dilute "primary soup". Apparently, it is in the primordial ocean that the processes of formation of simple organic molecules—monomers of complex organic molecules—biopolymers begin (see Fig. 2).
However, the processes of polymerization of individual nucleoside, amino acids and sugars are condensation reactions, they proceed with the elimination of water, therefore, the aqueous medium does not contribute to polymerization, but, on the contrary, to the hydrolysis of biopolymers (i.e., their destruction with the addition of water).
The formation of biopolymers (in particular, proteins from amino acids) could take place in the atmosphere at a temperature of about 180°C, from where they were washed into the primary ocean with atmospheric precipitation. In addition, it is possible that on the ancient Earth, amino acids were concentrated in drying up reservoirs and polymerized in a dry form under the influence of ultraviolet light and the heat of lava flows.
Despite the fact that water promotes the hydrolysis of biopolymers, the synthesis of biopolymers in a living cell occurs precisely in an aqueous medium. This process is catalyzed by special catalytic proteins - enzymes, and the energy necessary for synthesis is released during the breakdown of adenosine triphosphate - ATP. It is possible that the synthesis of biopolymers in the aquatic environment of the primary ocean was catalyzed by the surface of certain minerals. It has been experimentally shown that a solution of the amino acid alanine can polymerize in an aqueous medium in the presence of a special type of alumina. In this case, the peptide polyalanine is formed. The polymerization reaction of alanine is accompanied by the breakdown of ATP.
The polymerization of nucleotides is easier than the polymerization of amino acids. It has been shown that in solutions with a high salt concentration, individual nucleotides spontaneously polymerize, turning into nucleic acids.
The life of all modern living beings is a process of continuous interaction between the most important biopolymers of a living cell - proteins and nucleic acids.
Proteins are the "working molecules", "engineer molecules" of a living cell. Describing their role in metabolism, biochemists often use such figurative expressions as "the protein works", "the enzyme leads the reaction." The most important function of proteins is catalytic. As you know, catalysts are substances that speed up chemical reactions, but they themselves are not included in the final products of the reaction. Tanks-catalysts are called enzymes. Enzymes in bend and thousands of times accelerate metabolic reactions. Metabolism, and hence life without them, is impossible.
Nucleic acids- these are "molecules-computers", molecules are the keepers of hereditary information. Nucleic acids do not store information about all the substances of a living cell, but only about proteins. It is enough to reproduce in the daughter cell the proteins characteristic of the mother cell so that they accurately recreate all the chemical and structural features of the mother cell, as well as the nature and rate of metabolism inherent in it. Nucleic acids themselves are also reproduced due to the catalytic activity of proteins.
Thus, the mystery of the origin of life is the mystery of the emergence of the mechanism of interaction between proteins and nucleic acids. What information does modern science have about this process? What molecules were the primary basis of life - proteins or nucleic acids?
Scientists believe that despite the key role of proteins in the metabolism of modern living organisms, the first "living" molecules were not proteins, but nucleic acids, namely ribonucleic acids (RNA).
In 1982, American biochemist Thomas Check discovered the autocatalytic properties of RNA. He experimentally showed that in a medium containing a high concentration of mineral salts, ribonucleotides spontaneously (spontaneously) polymerize, forming polynucleotides - RNA molecules. On the original polynucleotide chains of RNA, as on a matrix, RNA copies are formed by pairing of complementary nitrogenous bases. The RNA template copying reaction is catalyzed by the original RNA molecule and does not require the participation of enzymes or other proteins.
What happened next is fairly well explained by what might be called "natural selection" at the molecular level. During self-copying (self-assembly) of RNA molecules, inaccuracies and errors inevitably arise. The erroneous RNA copies are copied again. When copying again, errors may occur again. As a result, the population of RNA molecules in a certain part of the primary ocean will be heterogeneous.
Since RNA decay processes are also taking place in parallel with the synthesis processes, molecules with either greater stability or better autocatalytic properties will accumulate in the reaction medium (i.e., molecules that copy themselves faster, “multiply” faster).
On some RNA molecules, as on a matrix, self-assembly of small protein fragments - peptides can occur. A protein "sheath" is formed around the RNA molecule.
Along with autocatalytic functions, Thomas Check discovered the phenomenon of self-splicing in RNA molecules. As a result of self-splicing, RNA regions that are not protected by peptides are spontaneously removed from RNA (they are, as it were, “cut out” and “ejected”), and the remaining RNA regions encoding protein fragments “grow together”, i.e. spontaneously combine into a single molecule. This new RNA molecule will already code for a large complex protein (Figure 4).
Apparently, initially protein sheaths performed primarily a protective function, protecting RNA from destruction and thereby increasing its stability in solution (this is the function of protein sheaths in the simplest modern viruses).
Obviously, at a certain stage of biochemical evolution, RNA molecules, which encode not only protective proteins, but also catalytic proteins (enzymes), sharply accelerating the rate of RNA copying, gained an advantage. Apparently, this is how the process of interaction between proteins and nucleic acids, which we now call life, arose.
In the process of further development, thanks to the appearance of a protein with the functions of an enzyme, reverse transcriptase, on single-stranded RNA molecules, molecules of deoxyribonucleic acid (DNA) consisting of two strands began to be synthesized. The absence of an OH group in the 2" position of deoxyribose makes DNA molecules more stable with respect to hydrolytic cleavage in slightly alkaline solutions, namely, the reaction of the medium in primary reservoirs was slightly alkaline (this reaction of the medium was also preserved in the cytoplasm of modern cells).
Where did the development of a complex process of interaction between proteins and nucleic acids take place? According to the theory of A.I. Oparin, the so-called coacervate drops became the birthplace of life.
Rice. 4. Hypothesis of the emergence of interaction between proteins and nucleic acids: a) in the process of self-copying of RNA, errors accumulate (1 - nucleotides corresponding to the original RNA; 2 - nucleotides that do not correspond to the original RNA - errors in copying); b) due to its physicochemical properties, amino acids “stick” to a part of the RNA molecule (3 - RNA molecule; 4 - amino acids), which, interacting with each other, turn into short protein molecules - peptides. As a result of self-splicing inherent in RNA molecules, the parts of the RNA molecule that are not protected by peptides are destroyed, and the remaining ones "grow" into a single molecule encoding a large protein. The result is an RNA molecule covered with a protein sheath (the most primitive modern viruses, for example, the tobacco mosaic virus, have a similar structure)
The phenomenon of coacervation consists in the fact that under certain conditions (for example, in the presence of electrolytes) macromolecular substances are separated from the solution, but not in the form of a precipitate, but in the form of a more concentrated solution - coacervate. When shaken, the coacervate breaks up into separate small droplets. In water, such drops are covered with a hydration shell (a shell of water molecules) that stabilizes them - fig. 5.
Coacervate drops have some semblance of metabolism: under the influence of purely physical and chemical forces, they can selectively absorb certain substances from the solution and release their decay products into the environment. Due to the selective concentration of substances from the environment, they can grow, but when they reach a certain size, they begin to "multiply", budding small droplets, which, in turn, can grow and "bud".
The coacervate droplets resulting from the concentration of protein solutions in the process of mixing under the action of waves and wind can be covered with a lipid shell: a single membrane resembling soap micelles (with a single detachment of a drop from the surface of water covered with a lipid layer), or a double membrane resembling a cell membrane ( when a drop covered with a single-layer lipid membrane falls again onto the lipid film covering the surface of the reservoir - Fig. 5).
The processes of the emergence of coacervate droplets, their growth and "budding", as well as "dressing" them with a membrane from a double lipid layer are easily modeled in the laboratory.
For coacervate droplets, there is also a process of "natural selection" in which the most stable droplets remain in solution.
Despite the outward resemblance of coacervate drops to living cells, coacervate drops lack the main sign of a living thing - the ability to accurately reproduce, self-copy. Obviously, the precursors of living cells were such coacervate drops, which included complexes of replicator molecules (RNA or DNA) and the proteins they encode. It is possible that RNA-protein complexes existed for a long time outside coacervate droplets in the form of the so-called “free-living gene”, or it is possible that their formation took place directly inside some coacervate droplets.
Possible path of transition from coacervate drops to primitive flares:
a) the formation of a coacervate; 6) stabilization of coacervate drops in an aqueous solution; c) - formation of a double lipid layer around the drop, similar to a cell membrane: 1 - coacervate drop; 2 - monomolecular layer of lipid on the surface of the reservoir; 3 — formation of a single lipid layer around the drop; 4 — formation of a double lipid layer around the drop, similar to a cell membrane; d) - a coacervate drop surrounded by a double lipid layer, with a protein-nucleotide complex included in its composition - a prototype of the first living cell
From a historical point of view, the extremely complex process of the origin of life on Earth, which is not fully understood by modern science, passed extremely quickly. For 3.5 billion years, the so-called. chemical evolution ended with the appearance of the first living cells and biological evolution began.
Is life the result of evolution or creation? This dilemma troubles the minds of more than one generation of scientists. Endless disputes on this score give rise to more and more curious theories.
Order versus chaos
The second law of thermodynamics (entropy) states that all elements of the cosmos move from order to chaos. This is pointed out by NASA scientist Robert Destroy, who claims that "the universe stops like a clock." Creationists rely on the law of entropy to prove the inconsistency of the point of view of evolutionists, which assumes the spontaneous development and complication of all elements of the surrounding world.
The 19th-century theologian William Peley drew the following analogy. We know that pocket watches did not come into being by themselves, but were made by man: it follows that such a complex structure as the human body is also the result of creation.
Charles Darwin opposed this point of view with his theory of the power of natural selection, which, based on hereditary variability in the process of long evolution, is capable of forming the most complex organic structures.
“But organic life could not have arisen from inanimate matter,” creationists pointed out the weak spot in Darwin's theory.
It is only relatively recently that the studies of the chemists Stanley Miller and Harold Urey have made it possible to obtain arguments in defense of the theory of evolution.
The experiment of American scientists confirmed the hypothesis that conditions existed on the primitive Earth that contributed to the emergence of biological molecules from inorganic substances. According to their findings, molecules were formed in the atmosphere as a result of ordinary chemical reactions, and then, falling into the ocean with rain, led to the birth of the first cell.
How old is the earth?
In 2010, American biochemist Douglas Theobald tried to prove that all life on Earth has a common ancestor. He mathematically analyzed the sequences of the most common proteins and found that humans, flies, plants, and bacteria have the selected molecules. The probability of a common ancestor, according to the calculations of the scientist, was 102860.
According to the theory of evolution, the process of transition from the simplest to the highest organisms takes billions of years. But creationists claim that this is impossible, since the age of the Earth does not exceed several tens of thousands of years.
All species of animals and plants, in their opinion, appeared almost simultaneously and independently of each other - in the form in which we can observe them now.
Modern science, relying on the data of radioisotope analysis of terrestrial samples and meteoritic matter, determines the age of the Earth as 4.54 billion years. However, as some experiments have shown, such a dating method can have very serious errors.
In 1968, the American Journal of Geographical Research published radioisotope analysis of volcanic rocks formed in Hawaii as a result of a volcanic eruption that occurred in 1800. The age of the rocks was determined in the range from 22 million to 2 billion years.
Radiocarbon analysis also leaves many questions, with the help of which the dating of biological remains is carried out. This method allows for an age limit of 60,000 years for samples with 10 carbon-14 half-lives. But how to explain the fact that carbon-14 is found in samples of "Jurassic wood"? “Only because the age of the Earth has been unreasonably aged,” the creationists insist.
Paleontologist Harold Coffin notes that the formation of sedimentary rocks occurred unevenly and it is difficult to determine the true age of our planet from them. For example, fossil tree fossils near Joggins, Canada, vertically penetrating a layer of earth for 3 meters or more, indicate that plants were buried under the rock layer in a very short period of time as a result of catastrophic events.
Rapid evolution
Assuming that the Earth is not so ancient, is it possible for evolution to "fit" into a more compressed time frame? In 1988, a team of American biologists led by Richard Lensky decided to conduct a long-term experiment simulating the evolutionary process in the laboratory using the example of E. coli bacteria.
12 colonies of bacteria were placed in an identical medium, where only glucose was present as a nutrition source, as well as citrate, which, in the presence of oxygen, could not be absorbed by bacteria.
Scientists have observed E. coli for 20 years, during which time more than 44 thousand generations of bacteria have changed. In addition to the changes in bacterial size that are typical of all colonies, scientists discovered an interesting feature inherent in only one colony: in it, bacteria somewhere between the 31st and 32nd thousand generations showed the ability to absorb citrate.
In 1971, Italian scientists brought 5 individuals of wall lizards to the island of Pod Markara, located in the Adriatic Sea. Unlike the previous habitat, the island had few insects that lizards fed on, but a lot of grass. Scientists checked the results of their experiment only in 2004. What did they see?
Lizards have adapted to an unusual environment: their population has reached 5,000 individuals, but most importantly, the appearance and structure of internal organs have changed in reptiles. In particular, the head and bite force increased to cope with large leaves, and a new section in the digestive tract appeared - the fermentation chamber, which allowed the lizards' intestines to digest tough cellulose. So, in just 33 years, wall lizards turned from predators into herbivores!
Weak link
If science is able to confirm intraspecific changes experimentally, then the possibility of the appearance of a new species in the course of evolution still remains exclusively in theory. Proponents of creationism not only point out to evolutionists the absence of intermediate forms of living organisms, but also try to scientifically confirm the failure of the evolutionary theory of the origin of species.
Spanish geneticist Svante Paabo managed to extract DNA from a fragment of a Neanderthal vertebra that supposedly lived about 50,000 years ago. A comparative analysis of the DNA of modern humans and Neanderthals showed that the latter is not our ancestor.
US geneticist Alan Wilson, using the mitochondrial DNA method, was able to presumably tell when "Eve" appeared on Earth. His research gave an age of 150-200 thousand years. Japanese scientist Satoshi Horai gives similar data. In his opinion, modern man appeared in Africa about 200 thousand years ago, and from there moved to Eurasia, where he rather quickly replaced the Neanderthal.
Drawing on data from the fossil record, biologist Jonathan Wells observes: “It is quite clear that, at the level of kingdoms, phyla, and classes, descent from common ancestors through modification cannot be considered an indisputable fact.”
The Russian mathematician and philosopher Julius Schroeder notes that we do not know how to measure the duration of the six days in which God created the world on a scale known to us, because time itself was created in the same days. “The order of creation is consistent with the ideas of modern cosmology,” the scientist notes.
Doctor of Biological Sciences Yuri Simakov considers a person to be a product of genetic engineering. He suggests that the experiment was carried out at the junction of two species - Neanderthal and Homo sapiens. According to the biologist, there is "a complex and deliberate intervention of the mind, which should be an order of magnitude superior to ours."
The staff at the Evolution Hall at the St. Louis Zoo decided to jokingly reconcile the two theories. At the entrance, they put up a sign that read: "This is not at all asserted that the world of life could not be created immediately - it just looks like it appeared as a result of a long evolution."
Doctor of Geological and Mineralogical Sciences I. A. REZANOV
In the language of literature, life was born "when the Earth screamed." But for the Earth to scream, it was not enough experience of Professor Challenger and little imagination of Conan Doyle, who forced his hero to drill a well. Speaking scientifically, I believe that we owe our lives to two catastrophes on a cosmic scale. In my opinion, only one source of information is able to reliably tell what events led to the emergence of life - this is the "stone chronicle" of the planet.
It is difficult for a non-specialist to believe that radioactive analysis makes it possible not only to accurately date the episodes of the geological scenario, even of such unimaginable antiquity, but also to recreate pictures of the physical processes of that time. How did life arise from dead matter?
According to the latest geological data, in the first 600 million years of the existence of the Earth (4.0-3.9 billion years ago), such extreme conditions reigned on the planet that life was impossible. The dense atmosphere consisted mainly of hydrogen with an admixture of helium. The vents of numerous volcanoes spewed carbon dioxide, methane, ammonia, hydrogen sulfide and other gases. An analysis of the patriarchal stones showed that the pressure reached six thousand atmospheres, the surface of the planet heated up to 600 ° C, that is, it was hotter in this hellish hell than it is now on Venus, where life has not been found.
But younger rocks, born 3.8 billion years ago and later, were already formed in conditions close to modern ones. These pages of the stone chronicle testify that by that time the dense and highly heated hydrogen atmosphere had left the planet. It was possible to understand what provoked this only after waiting for the return of spacecraft from the Moon. Studying samples of lunar soil, selenologists in this space supplement to the Earth's stone record read that 3.9 billion years ago a giant catastrophe occurred in the solar system. The lunar seas - crater-shaped funnels with a diameter of up to 1200 kilometers - were knocked out at that time during the bombardment by giant asteroids. Cosmic bodies, bombing the Moon, gave her a powerful impulse of heat, which heated her bowels to melting. Since then, two types of relief have been distinguished on the surface of the Moon: light "continents" and dark "seas" filled with molten basalts.
Academician V. G. Fesenkov and many other astronomers believed that the most probable cause of the catastrophe was the explosion of a planet whose orbit coincided with the asteroid belt located between the orbits of Mars and Jupiter.
If measured by the scale of the solar system, then the Moon is not far from the Earth. Consequently, a flurry of asteroids and meteorites also hit the Earth. Everyone knows that sound is transmitted due to vibrations of molecules. If there was no atmosphere on the Moon even then, then all these cataclysms took place in terrible silence (for a person, of course, if he could be present there). But what kind of cyclopean symphony would a witness over our planet hear? It is perhaps weak to say, following Conan Doyle, that "the Earth cried out." She roared. Falling, fragments-asteroids caused powerful air currents, and it became 100 degrees hotter in hell. The extra heat was enough to rip off the Earth's hydrogen blanket. And only after that, suitable conditions appeared on Earth for the emergence of life. As they say, there would be no happiness, but misfortune helped.
It turns out that the disaster has become necessary condition the birth of life, but was that enough? No, because neither the atmosphere nor the hydrosphere remained on the surface of the Earth, and the crust and mantle melted. The planet was enveloped in molten, viscous granite crust, which did not allow gases to pass through. Gases accumulated in a less viscous mantle. Only at a pressure of at least ten thousand atmospheres and a temperature of at least 1000°C, the gases CO, CO2, H2, CH4, and NH3, poorly soluble in magma, broke through the crust in the form of giant jets.
It is known that complex organic compounds (amino acids, sugars, porphyrins) are formed during a volcanic eruption. Thus, only during one eruption of the Tyatya volcano on the Kuril Islands in 1973, 200 tons of complex organic matter accumulated in the ashes. How much of it was formed on the planet after the breakdown of the primary hydrogen atmosphere from the Earth, when giant gas jets constantly gushed out with an intensity thousands of times greater than the strength of current volcanic eruptions? At that time, millions of tons of organic compounds were synthesized annually in the vents of gas volcanoes. For geologically a short time(the first millions of years) on the surface of the planet, a layer cake several tens of meters thick was baked from alternating layers of ash and organic compounds.
The abundance of organics was the second necessary reason for the birth of life on Earth. But even this was not enough. What else?
More than a hundred years ago, the famous French naturalist Louis Pasteur discovered that organic compounds in plants and animals are optically asymmetric - they rotate the plane of polarization of the light falling on them. All amino acids that make up animals and plants rotate the plane of polarization to the left, and all sugars to the right. If we synthesize compounds of the same chemical composition, then each of them will have an equal number of left- and right-handed molecules.
Now imagine that the environment with left and right molecules has passed into a state with only left or only right molecules. Experts call such an environment chirally (from the Greek word "heira" - hand) ordered. The self-reproduction of the living (biopoiesis, as defined by D. Bernal) could arise and be maintained only in such an environment.
The Soviet scientist L. L. Morozov proved that the transition to chiral ordering could not occur evolutionarily, but only with a sharp phase change. Academician V. I. Gol'danskii called this transition a chiral catastrophe. Still, scientists differ from other people not only in knowledge. Everyone used to think that a catastrophe is something terrifying, and physicists called a catastrophe the phenomenon due to which life was born and, ultimately, they themselves.
How did the conditions for the phase catastrophe that caused the chiral transition arise?
The most important thing was that the lower layers of the growing ash-organic cake were fried on the earth's crust heated to 600, and the upper ones cooled to the temperature of space, that is, absolute zero. The temperature difference reached 1000°. It is clear that the bottom of the pie burned, that is, the organic molecules melted under the influence of high temperature and even completely destroyed, and the top of the pie remained unbaked for the time being, as the organic molecules were frozen. Of course, the gases and, possibly, water vapor that leaked from the earth's crust changed the chemical composition of organic compounds. The gases carried heat with them, causing the melting boundary of the organic layer to move up and down.
At very low pressures of the atmosphere, water was on the earth's surface only in the form of steam and ice. When the pressure reached the so-called triple point of water (0.006 atmospheres), water for the first time could be in the form of a liquid.
Of course, it is only experimentally possible to prove what exactly caused the chiral transition: terrestrial or cosmic causes. But one way or another, at some point, chirally ordered molecules (namely, left-handed amino acids and right-handed sugars) turned out to be more stable and an unstoppable increase in their number began - a chiral transition.
The stone chronicle also tells that at that time there were neither mountains nor depressions on Earth. The semi-molten granite crust was a surface as flat as the level of the modern ocean. However, within this plain there were still depressions due to the uneven distribution of masses inside. These lowerings have played an extremely important role. The fact is that flat-bottomed depressions with a diameter of hundreds and even thousands of kilometers and a depth of no more than a hundred meters, probably became the cradle of life. After all, the water that collected on the surface of the planet flowed into them. The water diluted the chiral organic compounds in the ash layer. The chemical composition of the compound gradually changed, and the temperature stabilized. The transition from the inanimate to the living, which began in anhydrous conditions, continued already in the aquatic environment.
Is that the plot the origin of life? Most likely yes. In the Isua geological section (West Greenland), which is 3.8 billion years old, gasoline- and oil-like compounds were found with the C12/C13 isotopic ratio characteristic of photosynthetic carbon. If the biological nature of carbon compounds from the Isua section is confirmed, then it will turn out that the whole plot - from the emergence of chiral organic matter to the appearance of a cell capable of photosynthesis and reproduction - was played out in only a hundred million years.
A phenomenon of cosmic proportions, predicted at the tip of a pen by Soviet scientists, is waiting for its experimental confirmation in order to move from the category of daring hypotheses to the honorable category of theories.