Chemical elements of space. Cosmochemistry: what is it? Black holes in the universe
Nature has generously scattered its material resources around our planet. But it is not difficult to notice the dependence: most often a person uses those substances, the reserves of raw materials of which are limited, and vice versa, he extremely weakly uses such chemical elements and their compounds, the raw materials of which are almost unlimited. In fact, 98.6% of the mass of the physically accessible layer of the Earth consists of only eight chemical elements: iron (4.6%), oxygen (47%), silicon (27.5%), magnesium (2.1%), aluminum (8.8%), calcium (3.6%), sodium (2.6%), potassium (2.5%), nickel. More than 95% of all metal products, designs of a wide variety of machines and mechanisms, transport routes are made from iron ore. It is clear that such a practice is wasteful in terms of both the depletion of iron resources and the energy costs for the primary processing of iron ore raw materials.
Looking at the data presented here on the prevalence of the eight named chemical elements, we can safely say that there are great opportunities in the use of aluminum, and then magnesium and, perhaps, calcium in the creation of metal materials in the near future, but for this, energy-efficient methods of producing aluminum should be developed in order to obtaining aluminum chloride and reducing the latter to metal. This method has already been tested in a number of countries and provided the basis for the design of high-capacity aluminum smelters. But aluminum smelting on a scale comparable to the production of cast iron, steel and ferroalloys cannot yet be implemented in the very near future, because this task must be solved in parallel with the development of appropriate aluminum alloys that can compete with cast iron, steel and other materials from iron ore raw materials. .
The widespread use of silicon serves as a constant reproach to mankind in terms of the extremely low degree of use of this chemical element in the production of materials. Silicates make up 97% of the total mass earth's crust. And this gives grounds to assert that they should be the main raw material for the production of almost all building materials and semi-finished products in the manufacture of ceramics that can compete with metals. In addition, it is necessary to take into account also huge accumulations of industrial waste of a silicate nature, such as "waste rock" during coal mining, "tailings" during the extraction of metals from ores, ash and slag from energy and metallurgical production. And just these silicates must first be converted into raw materials for building materials. On the one hand, this promises great benefits, since raw materials do not need to be mined, they are waiting for their consumers in finished form. On the other hand, its disposal is a measure to combat environmental pollution.
In space, only two elements, hydrogen and helium, are most widely distributed, all other elements can only be considered as an addition to them.
Question 54. Development of ideas about the chemical structure of matter. Chemical compounds.
Chemistry called the science of chemical elements and their compounds.
The history of the development of chemical concepts begins from ancient times. Democritus, Epicurus expressed brilliant ideas that all bodies are composed of atoms of various sizes and different shapes, which determines their qualitative difference. Aristotle and Empedocles believed that bodies combine
The first truly effective method for determining the properties of a substance was proposed in the second half of the 17th century. English scientist R. Boyle (1627-1691). The results of R. Boyle's experimental studies showed that the qualities and properties of bodies depend on what material elements they consist of .
In 1860, the outstanding Russian chemist A.M. Butlerov (1828-1886) created a theory of the chemical structure of matter - a higher level of development of chemical knowledge arose - structural chemistry.
During this period, the technology of organic substances was born.
Under the influence of new production requirements, the doctrine of chemical processes arose , which took into account the change in the properties of a substance under the influence of temperature, pressure, solvents and other factors that replace wood and metal in construction work, food raw materials in the production of drying oil, varnishes, detergents and lubricants.
In 1960-1970. the next, higher level of chemical knowledge appeared - evolutionary chemistry . It is based on the principle of self-organization of chemical systems, that is, the principle of applying the chemical experience of highly organized living nature.
Until recently, chemists considered it clear what should be attributed to chemical compounds, and what to mixtures. Back in 1800-1808. the French scientist J. Proust (1754-1826) established the law of composition constancy: any individual chemical compound has a strictly defined, unchanged composition, a strong attraction of its constituent parts (atoms) and thus differs from mixtures
From the end of the 19th century studies were resumed that questioned the absolutization of the law of constancy of composition. The outstanding Russian chemist N.S. Kurnakov (1860-1941), as a result of studies of intermetallic compounds, i.e. compounds consisting of two metals, established the formation of real individual compounds of variable composition and found the boundaries of their homogeneity on the "composition-property" diagram, separating from them the areas of existence of stoichiometric compounds composition. Chemical compounds of variable composition he called berthollids, and left the name behind the compounds of permanent composition daltonids.
As the results of physical research have shown, the essence of the problem of chemical compounds lies not so much in the constancy or inconstancy of the chemical composition, but in the physical nature of chemical bonds that unite atoms into a single quantum mechanical system - a molecule.
The number of chemical compounds is enormous. They differ in both composition and chemical and physical properties. But still chemical compound - a qualitatively defined substance consisting of one or more chemical elements.
What is the most abundant substance in the universe? Let's approach this question logically. It seems to be known, it is hydrogen. Hydrogen H makes up 74% of the mass of matter in the universe.
Let's not climb into the wilds of the unknown here, let's not count Dark Matter and Dark Energy, let's talk only about ordinary matter, about familiar chemical elements located in (at the moment) 118 cells of the periodic table.
Hydrogen as it is
Atomic hydrogen H 1 is what all stars in galaxies consist of, it is the bulk of our familiar matter, which scientists call baryonic. baryonic matter consists of ordinary protons, neutrons and electrons and is synonymous with the word substance.
But monatomic hydrogen is not exactly a chemical substance in our native, earthly understanding. This is a chemical element. And by substance, we usually mean some kind of chemical compound, i.e. combination of chemical elements. It is clear that the simplest chemical substance is the combination of hydrogen with hydrogen, i.e. ordinary gaseous hydrogen H 2 , which we know, love, and with which we fill zeppelin airships, from which they then explode beautifully.
Two-volume hydrogen H 2 fills most of the gas clouds and nebulae of space. When, under the influence of their own gravity, they gather into stars, the rising temperature breaks the chemical bond, turning it into atomic hydrogen H 1, and the ever-increasing temperature detaches an electron e- from a hydrogen atom, turning into a hydrogen ion or just a proton p+ . In stars, all matter is in the form of such ions, which form the fourth state of matter - plasma.
Again, the chemical hydrogen is not very interesting thing, it's too simple, let's look for something more complex. Compounds made up of different chemical elements.
The next most abundant chemical element in the universe is helium. He, its in the universe 24% of the total mass. In theory, the most common complex chemical there must be a combination of hydrogen and helium, only the trouble is, helium - inert gas. Under ordinary and even not very ordinary conditions, helium will not combine with other substances and with itself. By clever tricks, it can be made to enter into chemical reactions, but such compounds are rare and usually do not last long.
So you need to look for hydrogen compounds with the next most common chemical elements.
Only 2% of the mass of the Universe remains on their share, when 98% are the mentioned hydrogen and helium.
The third most common is not lithium Li, as it might seem, looking at the periodic table. The next most abundant element in the universe is oxygen. O, which we all know, love and breathe in the form of a colorless and odorless diatomic gas O 2 . The amount of oxygen in space far outstrips all other elements from those 2% that remained after the deduction of hydrogen and helium, in fact, half of the remainder, i.e. approximately 1%.
This means that the most common substance in the Universe turns out to be (we deduced this postulate logically, but this is also confirmed by experimental observations) the most ordinary water H2O.
There is more water (mostly frozen in the form of ice) in the universe than anything else. Minus hydrogen and helium, of course.
Everything, literally everything, is made of water. Our solar system is also made up of water. Well, in the sense of the Sun, of course, it consists mainly of hydrogen and helium, and gas giant planets like Jupiter and Saturn are also assembled from them. But the rest of the matter of the Solar System is concentrated not in stone-like planets with a metal core like Earth or Mars, and not in the stone belt of asteroids. The main mass of the Solar System in the icy debris left from its formation, comets, most of the asteroids of the second belt (Kuiper belt) and the Oort cloud, which is even further away, are made of ice.
For example, the well-known former planet Pluto (now dwarf planet Pluto) is 4/5 parts ice.
It is clear that if the water is far from the Sun or any star, it freezes and turns into ice. And if too close, it evaporates, becomes water vapor, which is carried away by the solar wind (a stream of charged particles emitted by the Sun) to distant regions of the star system, where it freezes and again turns into ice.
But around any star (I repeat, around any star!) there is a zone where this water (which, again, I repeat, is the most common substance in the Universe) is in the liquid phase of water itself.
Habitable zone around a star, surrounded by zones where it is too hot and too cold
Liquid water in the universe to hell. Around any of the 100 billion stars in our galaxy Milky Way there are areas called Habitable Zone, in which there is liquid water if there are planets there, and they should be there, even if not for every star, then for every third, or even for every tenth.
I'll say more. Ice can melt not only from the light of a star. In our solar system, there are many satellite moons orbiting gas giants, where it is too cold from lack of sunlight, but on which powerful tidal forces of the corresponding planets act. Liquid water has been proven to exist on Saturn's moon Enceladus, it is assumed to exist on Jupiter's moons Europa and Ganymede, and probably many other places.
Water geysers on Enceladus captured by the Cassini spacecraft
Even on Mars, scientists suggest that there may be liquid water in underground lakes and caverns.
Do you think I will now start talking about the fact that since water is the most common substance in the universe, then hello other life forms, hello aliens? No, just the opposite. I find it funny when I hear the claims of some overzealous astrophysicists - "search for water, you will find life." Or - "there is water on Enceladus / Europa / Ganymede, which means that there must certainly be life there." Or - in the Gliese 581 system, an exoplanet located in the habitable zone was discovered. There is water there, we urgently equip an expedition in search of life!"
There is a lot of water in the universe. But with life, according to modern scientific data, it’s somehow not very good.
The book sets out actual problem modern natural science- the origin of life. It is written on the basis of the most modern data of geology, paleontology, geochemistry and cosmochemistry, which refute many traditional, but outdated ideas about the origin and development of life on our planet. The deep antiquity of life and the biosphere, commensurate with the age of the planet itself, allows the author to conclude that the origin of the Earth and life is a single interconnected process.
For readers interested in earth sciences.
Book:
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I am only surprised that this incredibly complex mechanism is still working at all. When you think about Life, it becomes clear how pitiful and primitive our science is. It is obvious that the properties of a living being are predetermined by a fertilized cell, just as life is predetermined by the existence of an atom, and the mystery of all that exists lies in the lowest level,
A. EinsteinThe relationship between the germs of life and its predecessors - complex carbon compounds - is a paramount scientific problem. The first experiments of L. Pasteur, staged in the second half of the 19th century, showed the impossibility of modern conditions Earth origin of life - the simplest living organisms. This to some extent led to the emergence of the ideas of panspermia, according to which life on Earth never originated at all, but was brought from outer space, where it existed in the form of embryos. The most characteristic supporters of these ideas were G. Helmholtz and S. Arrhenius, although earlier such ideas were expressed by J. Liebig. According to S. Arrhenius, particles of living matter are spores or bacteria that have settled on microparticles space dust, are transferred from one planet to another by the force of light pressure, maintaining their viability. When spores land on a planet with suitable conditions for life, they germinate and give rise to biological evolution.
In somewhat different forms, these ideas are being revived in our time. For example, F. Hoyle put forward the idea of the possibility of the existence of microorganisms in interstellar space. According to his ideas, clouds of cosmic dust are composed mainly of bacteria and spores. It is assumed that in the time interval of 4.6-3.8 billion years ago, two events were possible on Earth - either the origin of life on the planet itself, or it brought microorganisms from outer space. F. Hoyle and S. Wickramasing in 1981 admitted that the latter is more likely. According to their calculations, 10 18 cosmic spores enter the Earth's upper atmosphere every year as a remnant of solid material dispersed in the solar system. Thus, comets are carriers of the germs of life, which were formed earlier in interstellar space and only then fell into the Oort cloud.
It should be noted that the presented ideas are extremely fantastical and do not agree with the known experimental data. However, it is undoubted that life is connected with space according to atomic composition and in terms of energy. This can be seen from Table. 6, which gives the values of the relative distribution of elements in space, in the volatile fraction of comets, in bacteria and mammals. Attention is drawn to the great proximity, and in some cases, the identity of cosmic matter and the living matter of the Earth. The main elements of living matter are the widespread elements of the cosmos. At the same time, H, C, N, O - typical biophilic elements - are the most widely distributed in nature.
It is easy to conclude that living organisms primarily use the most accessible atoms, which, in addition, are capable of forming stable and multiple chemical bonds. It is known that carbon can form long chains, resulting in countless polymers. Sulfur and phosphorus can also form multiple bonds. Sulfur is part of proteins, and phosphorus is part of nucleic acids.
Under the right conditions, the most common atoms combine with each other to form molecules, which are found in cosmic clouds by the methods of modern radio astronomy. Most of the known cosmic molecules are organic, including the most complex 8- and 11-atomic ones. Thus, with regard to composition, the cosmochemistry of the Universe creates extensive possibilities for various combinations of carbon with other elements according to the laws of chemical bonding.
However, the problem of the formation of molecules in cosmic conditions is one of the most difficult problems of cosmochemistry. Actually, in the interstellar medium, even in its densest regions, the elements are in conditions far from thermodynamic equilibrium. Due to the low concentration of matter, chemical reactions in interstellar space are extremely unlikely. Therefore, it was suggested that particles of cosmic dust take part in the construction of interstellar molecules. In the simplest case, hydrogen molecules can appear when its atoms come into contact with solid particles. The most common space molecules, CO, are probably capable of being generated in stellar atmospheres at a sufficient density of matter and then ejected into outer space.
At present, the role of the solid phase in the formation of molecules of organic substances in outer space is becoming more and more clear. The most probable models of this process were developed by J. Greenberg. According to the scientist, cosmic dust particles have a complex structure and consist of a core of predominantly silicate composition, surrounded by a shell of organic substances. Apparently, various chemical processes take place in the shell, leading to the complication of the structure of the original substance. The structure of such dust particles after the first stage of accretion is confirmed by experimental modeling on a mixture of water, methane, ammonia and other simple molecules irradiated with ultraviolet radiation at a temperature of about 10 K. Each dust grain originates from a silicate core that arose in the atmosphere of a cold giant star. An ice shell forms around the core. Under the action of ultraviolet radiation, some shell molecules (H 2 O CH 4, NH 3) dissociate with the formation of radicals - reactive fragments of molecules. These radicals can recombine to form other molecules. As a result of prolonged irradiation, a more complex mixture of molecules and radicals (HN 2 HCO, HOCO, CH 3 OH, CH 3 C, etc.) may appear. When dust grains are destroyed under the influence of cosmic factors, the compounds that have arisen on their surface form molecular clouds.
Judging by the huge masses of molecular clouds, they are the main reservoirs of organic matter in space. However, found in them organic compounds turn out to be relatively simple and still far from those molecular systems that could provide the beginning of life on any favorable planetary body.
The presence of organic substances in meteorites deserves special attention. This is very important for understanding the processes of the origin of high-molecular systems as the precursors of life. It should be noted that meteorites, together with their parent bodies - asteroids, belong to the solar system. Further, the age of meteorites, according to nuclear geochronology, is 4.6-4.5 billion years, which basically coincides with the age of the Earth and the Moon. Consequently, meteorites undoubtedly witness the formation of various chemical compounds, including organic ones, at the earliest stages of the development of the solar system.
Meteorites contain hydrocarbons, carbohydrates, purines, pyrimidines, amino acids, i.e. those chemical compounds that are part of living matter, forming its basis. They are found in carbonaceous chondrites and asteroids of certain structure and composition. Most asteroids move in the belt between Mars and Jupiter. Based on data on the cosmochemistry of comets, it can be assumed that the region of formation of organic compounds covered a vast area within most of the volume of the primary solar nebula. Naturally, in elucidating the general problem of the origin of life, we have no right to ignore data on the composition of meteorites. This circumstance was taken into account to varying degrees by different authors of hypotheses about the origin of life. Thus, we are now entitled to consider the known meteorites as historical documents - authentic witnesses of the early history of the solar system, which also covers the processes of formation of organic substances.
Any meteorite is a solid body consisting of a number of mineral phases. The main ones are silicate (stone), metallic (iron-nickel) and sulfide (troilite). There are also other phases, but they are of secondary importance in their distribution. Various minerals are found in meteorites, the number of which exceeds 100, but only a few are the main rock-forming minerals (olivine, pyroxene, feldspars, nickel iron, troilite, etc.). In addition, 20 minerals were found in meteorites, which are not found in the earth's crust. These include carbides, sulfides, etc., the formation of which is associated with sharply reducing conditions. The most significant concentrations of carbon associated with organic matter are in carbonaceous chondrites.
Fundamentally important information about organic matter in meteorites is presented in the works of G. P. Vdovykin, E. Avders, R. Hayatsu, M. Studir. First organic matter in the composition of meteorites, the famous chemist I. Berzelius identified the carbonaceous chondrite Alais in 1834. The results of his analysis were so impressive that he himself considered this substance of biological origin. During the 19th century, chemical analyzes revealed the presence of solid hydrocarbons, complex organic compounds with sulfur and phosphorus in meteorites. Carbonaceous chondrites, a significant part of the carbon in which is in the form of organic compounds, have been studied most carefully and thoroughly. The total content of carbon and some other volatile substances in carbonaceous chondrites is characterized by the following values (in wt.%):
This shows that the content of carbon (as well as sulfur and water) is maximum in carbonaceous chondrites of the C1 type, and minimum in C3 chondrites. Thus, at present, there is no doubt that in the parent bodies of carbonaceous chondrites, as a result of the very processes of their formation, complex organic compounds arose as a natural result of the chemical evolution of the early solar system.
The elemental chemical composition of carbonaceous chondrites minus volatile substances is very close to that of ordinary chondrites. The main features of the various types of carbonaceous chondrites are as follows.
Type C1 is represented by fragile black stones, crumbling to dust when rubbed with fingers. The fine-grained mass in them is approximately 95%. It is interspersed with chondrules (microchondrules) consisting of olivine and magnetite (1-50 microns in size). The mineral composition of this type of meteorite is shown in fig. 9. Carbonaceous chondrites of type C1 are the richest in organic substances of abiogenic origin.
Type C2 are greyish-black stones, significantly denser than C1. The main fine-grained mass, which makes up 60% of the volume, is interspersed with significantly larger chondrules than in type C1. Intergrowths of primary microchondrules into a single crystal are observed.
Type C3 are hard stones that are dark gray, greenish gray or gray in color. Fine-grained mass occupies 35%. The chondrules are quite large and well defined.
The abundance of many chemical elements in carbonaceous chondrites of the C1 type reveals a number of characteristic relationships that bring them closer to the solar matter. In other words, these carbonaceous chondrites are solidified solar matter, devoid of light gases.
Organic substances found in meteorites are listed in Table. 7. As you can see, their list is quite impressive. Most of these compounds, to one degree or another, correspond to the universal links of metabolism known in living organisms: amino acids, protein-like polymers, mono- and polynucleotides, porphyrins, and other compounds. The proximity to the composition of organic complexes of biological origin turned out to be so great that some authors even began to admit that in the past living organisms were found directly in the meteorites themselves. There was a lively discussion on this issue in the 1960s. However, careful studies of organic compounds from meteorites did not confirm the presence of optical activity, which indicates their abiogenic origin.
A comparison of organic substances of meteorite origin with products of artificial reactions of the Fischer-Tropsch type and fossil organic substances of biological origin shows their great proximity, in particular with regard to the content of certain hydrocarbons. For example, meteorites are dominated by hydrocarbons with 16 atoms per molecule, which is also observed in terrestrial objects and products of laboratory experiments.
Meteorites are fragments of larger bodies - asteroids, most of which is located in the asteroid belt at a distance of 2.3-3.3 AU. e. from the Sun. Over the past 10 years, as a result of astrophysical observations of asteroids in the visible part of the spectrum and infrared waves, data have been obtained that are of paramount importance for establishing the genetic relationship between asteroids and meteorites. By comparing the reflectivity of meteorites and asteroids, it was possible to establish that almost all known classes of meteorites have their analogues among the studied asteroids.
Depending on the reflectivity, asteroids are divided into two main types. large groups- dark, or C-asteroids, and relatively light, or S-asteroids. The former are characterized by low albedo - less than 0.05, the latter - over 0.1. In terms of spectral reflectivity, the group FROM close to carbonaceous chondrites, a S- to stony-iron meteorites and ordinary chondrites. The latest photometric measurements generally confirm the unity of the material of meteorites and asteroids. Therefore, all the mineral, chemical, and structural features of meteorites obtained and studied in terrestrial laboratories can be transferred to asteroids.
As a result of the research, it was possible to establish that the composition of asteroids is different in different regions of the asteroid belt. A fundamentally important cosmochemical regularity has been revealed within the solar system: the composition of asteroids depends on the heliocentric distance. In the inner part of the asteroid belt there are bodies close to ordinary chondrites, but as the distance from the Sun increases, within 2.5-3.3 AU. That is, they become smaller, and the number of asteroids such as carbonaceous chondrites, which occupy a dominant position in the middle and marginal parts of the asteroid belt, increases. In general, according to modern observations, even carbonaceous-chondrite bodies predominate in the asteroid belt.
If indeed most asteroids have the composition of carbonaceous chondrites, then it is quite natural that they contain a lot of organic matter, which determines their dark color and low reflectivity. Thus, the asteroid Bamberg has the lowest reflectivity (albedo 0.03). This is a dark and rather large object in the asteroid belt, with a diameter of about 250 km.
Per recent times Comets are of great interest. It has been suggested that they participated in the emergence of life on Earth, or in any case could make a certain contribution to the composition of its early atmosphere. They could also deliver the first organic molecules to the surface of the nascent planet. The opinion was established that comets best of all reflect the primary conditions in the solar system.
Most comets are located on the very periphery of the solar system, in the so-called Oort cloud. They have extremely elongated orbits and are hundreds and thousands of times farther from the Sun than Pluto. Long-period comets approach the Sun from a distant region. In general, the comet is a lump of dirty snow. "Snow" in a comet is composed of ordinary water ice with an admixture of carbon dioxide and other frozen gases of unknown composition. "Mud" is particles of silicate rocks of various sizes interspersed in cometary ice. It can be assumed that, due to the absence of chemical interactions, comets are untouched samples of the original matter from which the solar system was formed.
As they approach the Sun, the volatile matter of comets evaporates and is thrown off by light pressure, forming a giant tail. All observed cometary phenomena are determined by processes associated with the release of gases and dust. The H + , OH - , O - and H 2 O + ions that make up cometary tails come mainly from water molecules, although other hydrogen compounds are also likely to be present. Atoms, radicals, molecules and ions are presented in the following form: in comets - C, C 2, C 3, CH, CN, CS, CH 3 CN, HCN, NH, NH 2, O, OH, H 2, O 2, Na, S, Si; near the Sun - Ca, CO, Cr, Cu, Fe, V; in the tail - CH + , CO + , CO 2 + , CN + , N 2 + .
Everywhere in comets, biophilic elements are found, mainly C, O, N and H. At present, with a high degree of probability, it has been established that cometary molecules are close to those necessary for pre-biological evolution. They can be represented by molecules of amino acids, purines, pyrimidines. As noted by A. Delsemm, there are several groups of data indicating that cometary dust is of the nature of chondrite meteorites. First, it consists predominantly of silicates and carbon compounds. Secondly, the ratios of metals evaporated from comets during their passage near the Sun correspond to ratios typical of chondrites. Thirdly, dust particles of cosmic origin, probably reflecting the matter of comets, are very close to the composition of the material of carbonaceous chondrites. Indeed, analysis of cosmic dust samples indicates that 80% or more of dust particles smaller than 1 mm are composed of a material similar to carbonaceous chondrites. Some scientists have compared the carbon content in comets and carbonaceous chondrites and have concluded that at least 10% of comet material is organic compounds. The nature of the chemical compounds found in comets indicates a high probability that the molecules that give rise to them are at least comparable in complexity to the molecules of interstellar space.
Thus, all data on the cosmochemistry of meteorites, asteroids, and comets indicate that the formation of organic compounds in the solar system at the early stages of its development was a typical and massive phenomenon. It manifested itself most intensively in the space of the future asteroid ring, but covered in varying degrees and other regions of the protoplanetary solar nebula, including perhaps the region from which the Earth originated. However, the chemical evolution of the substance of the protosolar nebula, having reached a certain stage in the formation of complex organic compounds, turned out to be frozen in most bodies of the solar system, and only on Earth did it continue, reaching incredible complexity in the form of living matter.
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In 1806, at the height of the Napoleonic Wars, an unusual meteorite fell near the French town of Ale. It was only three years after the meteorites were officially "Recognized" by the Paris Academy of Sciences. Prejudices against the "Heavenly Stones" were still very strong, some of the fragments of the Ale meteorite were simply lost, and only one of them after 28 years ended up in the laboratory of the famous Swedish chemist Jens Jakob Berzelius
At first, the scientist thought that there was a mistake - the Ale meteorite was neither stone, nor iron, nor iron-stone. The melting crust (surface layer), however, testified to the cosmic origin of an unusual stone, the ancestor of the rarest and then still unknown type of meteorites - carbonaceous chondrites.
The Ale meteorite contained an organic mass soluble in water. When heated, its particles turned brown and charred - clear sign the presence of organic compounds, carbon compounds. (We recall that such simple carbon-containing compounds as co, co 2, carbonic acid H 2 co 3 and its salts are inorganic compounds.) Although the similarity with terrestrial substances of the same type was obvious, Berzelius reasonably noted that this fact "is not yet Proof of the Presence of Organisms in the Original Source."
Berzelius' work marked the beginning of the study of organic compounds in meteorites. Unfortunately, the material available for research is still very rare. Carbonaceous chondrites are very fragile - they are easy to grind into powder even with your fingers (and at the same time, we repeat, a characteristic smell of oil appears. In general, rare among meteorites, carbonaceous chondrites are also easily destroyed when flying in the earth's atmosphere. Yes, and once on the earth's surface, they , as a rule, disappear without a trace, mixed with terrestrial rocks.It is not surprising, therefore, that only two dozen carbonaceous chondrites have been found and preserved throughout the world.
Four years after the works of Berzelius were published, in 1838 another carbonaceous chondrite fell in South Africa, which was then investigated by the famous German chemist Friedrich Wöhler - the same Wöhler, who a few years earlier managed to obtain a substance of animal origin - urea - from inorganic matter.
Wöhler isolated an oily oily substance “with a Strong Bituminous Smell” from a meteorite and, unlike Berzelius, came to the conclusion that such substances, “based on the current level of knowledge”, can only be synthesized by living organisms. Note that the amount of organic material released from carbonaceous hopdrites is small - about one percent. But even this is quite enough to draw very important conclusions.
In 1864, again in France, near the village of orgueil, a meteorite shower of carbonaceous chondrites fell - an exceptional case in the history of astronomy. The French chemist Klets proved rigorously that the water-insoluble black substance of the Orgueil meteorite is organic compounds, and not at all graphite or amorphous carbon. He was struck by the similarity of these organic compounds with similar substances found in peat or brown coal. In a paper presented to the Paris Academy of Sciences, Klets argued that the organic matter in meteorites "appears to indicate the existence of Organized Matter on Celestial Bodies."
Since then, for almost a century, the study of the organics of meteorites has been carried out episodically, from case to case, without any significant generalizations. Among these few works, mention should be made of the study of the Migei meteorite, carried out in 1889 by Yu. and. simashko. The Russian scientist also discovered bituminous-type organic substances in this carbonaceous chondrite.
Photo carbonaceous chondrite.
One should not think that all organic substances are necessarily associated with life or, moreover, are the property of living beings. Astronomers are aware of numerous simple carbon-containing formations, which certainly have no direct relation to life. Such are, say, the CH and CN radicals observed in interstellar space and the atmospheres of cold stars. Moreover, in outer space, apparently, the synthesis of very complex organic compounds up to and including amino acids is constantly going on. We are convinced of this, in particular, by the curious experiments of the American researcher R. Berger. With the help of an elementary particle accelerator, he bombarded with protons a mixture of methane, ammonia and water, cooled to - 230 s. just a few minutes later, in this ice mixture, the scientist discovered urea, acetamide, acetone. In these experiments, Berger, in fact, simulated the conditions of interplanetary space. The proton flux imitated primary cosmic rays, and the mixture of methane ammonia and ordinary ice- this is, in essence, a typical model of a cometary nucleus.
Another well-known American biochemist, M. Calvin, bombarded a mixture of hydrogen, methane, ammonia, and water vapor with a stream of fast electrons. In these experiments, adenine was obtained - one of the four nitrogenous bases that make up nucleic acids. Didn't such processes take place in the primary atmosphere of the earth and some other planets?
It seems that in space, from inorganic substances and in an inorganic way, protein-like compounds are created - "Semi-finished products" of a possible future life.
Thus, the presence of organic matter in meteorites in itself cannot yet indicate the existence of life on Earth. celestial bodies Oh. These substances could also arise abiogenically, without any direct connection with life. Stronger arguments are needed to prove the contrary.
It is in this regard that the discussion in the modern science of meteorites is being conducted. The dispute is not over yet, but the results obtained are of great interest.
Back in 1951-1952. English biochemist Müller isolated bituminous compounds from carbonaceous chondrint. In essence, he repeated the works of Berzelius, Wöhler, and Kletsz, but on an incomparably higher level. Meteoritic bitumen contains much more sulfur, chlorine and nitrogen than similar terrestrial compounds, this circumstance prompted Muller to conclude that the bitumen in meteorites is of abiogenic origin.
The already mentioned M. Calvin and s. out. Their report, presented in 1960 to an international symposium on the study of outer space, was titled meaningfully: "extraterrestrial life. Some organic constituents of meteorites and their significance for possible biological evolution outside the earth." American researchers isolated volatile substances from carbonaceous chondrite samples, which were then passed through a mass spectrometer. In these experiments, the relative mass of fragments of unknown molecules was determined and, in addition, the infrared and ultraviolet spectra of extracts of carbon-containing meteorite compounds were studied. The results have been stunning.
From the carbonaceous chondrite, it was possible to isolate a substance like two drops of water similar to cytosine - another of the four nitrogenous bases. Found in a meteorite and a mixture of hydrocarbons, similar to oil of terrestrial origin.
The following year, 1961, the work of three American chemists, G. Nagy, D. Hennessey, and W. maintain. From carbonaceous chondrites, they isolated a set of paraffins, very similar to that which is part of the peel of apples or beeswax. In this regard, the disputes around the problem of the origin of oil have intensified.
We still do not know exactly where oil came from - a source of fuel for aircraft, ships and cars, the most valuable raw material for petrochemistry. Was oil formed as a result of the decomposition of once living organisms, or is "Black Gold" a product of some complex abiogenic synthesis? If the first hypothesis is correct, bitumens in meteorites can be considered as traces of extraterrestrial life. Only if the oil is of inorganic origin, then meteorite bitumen has no direct relation to life outside the earth, but, apparently, arose as a result of abiogenic processes.
We have already spoken about experiments simulating the formation of organic compounds in interplanetary space. It is even easier to imagine such an abiogenic synthesis in the bowels of an Earth-like planet. Organic substances in meteorites arose abiogenically - this is the main thesis of those who do not consider meteorites to be carriers of the remains of some extraterrestrial organisms. This position is defended by Anders, Briggs, in our Soviet Union - the researcher of carbonaceous chondrites G. P. Vdovykin. In his opinion, "the study of the spectra of various celestial bodies shows that carbon is one of the most common elements in them: it is found in the form of an element (c 2, c 3) and in the form of compounds (CH 2, CN, co 2, etc. .) In all types of celestial bodies, these components of the atmosphere and starry space could polymerize with the formation of complex organic molecules "(L. Kuznetsova. Thirteen riddles of the sky. M., Soviet Russia, 1967 light.
The most lively discussions are now around the mysterious "Organized Elements". For the first time, these strange inclusions with a diameter of 5 to 50 microns were discovered in 1961 by N. Nagy and D. Klaus while studying samples of four carbonaceous chondrites. Outwardly, they resembled terrestrial fossil microscopic algae. Among them, American researchers identified morphological features five types of objects, and some of the objects turned out to be paired, as if they died in the process of cell division. Almost all of the "Organized Elements" looked like the simplest plants that live only in water, and this circumstance, according to Nagy and Klaus, excluded the possibility of contamination of the meteorite from the soil. Later, F. Staplen and others discovered "Organized Elements" in a number of carbonaceous chondrites, and all researchers noted their similarity with some unicellular algae.
In 1962, the Leningrad geologist b. in. Timofeev isolated strange spore-like formations from the Saratov and Migeya meteorites. There were more than two dozen of them - yellowish-gray, tiny, hollow, almost spherical shells, having a diameter of 10 to 60 microns. The shells turned out to be single-layered, different in thickness, sometimes crumpled into distinctly defined folds. According to the researcher, "the surface of the shells is smooth, less often finely tuberculate. One of the forms shows a round hole - a stomata, characteristic of some unicellular algae. Many of these Finds can be compared with the oldest fossil unicellular algae on earth that lived more than 600 million years ago ago, but they cannot be attributed to any group flora our planet" (light, 1962, number 4, p. 12.
Nucleic acids
Nucleic acids
Deoxyribonucleic and ribonucleic acids are universal components of all living organisms responsible for the storage, transmission and reproduction (realization) of genetic information. All N. to. are divided into two types according to the carbohydrate component of the molecules: deoxyribose in deoxyribonucleic acids (DNA) and ribose in ribonucleic acids (RNA). The biological role of DNA in most organisms is the storage and reproduction of genetic information, and RNA - in the implementation of this information in the structure of protein molecules (Proteins) in the process of their synthesis.
Nucleic acids were discovered in 1868 by the Swiss scientist F. Miescher, who found that these substances are localized in the nuclei of cells, have acid properties and unlike proteins contain phosphorus. Chemically, N. to. are polynucleotides, i.e. biopolymers built from monomer units - mononucleotides, or nucleotides (phosphorus esters of the so-called nucleosides - derivatives of purine and pyrimidine nitrogenous bases, D-ribose or 2-deoxy-D-ribose). The purine bases included in the DNA molecule are adenine (A) and guanine (G), pyrimidine bases are cytosine (C) and thymine (T). In RNA nucleosides, uracil (U) is present instead of thymine. In a polynucleotide chain, nucleotides are connected via a phosphodiester bond (Fig. 1).
The primary structure of N. to. is determined by the order of alternation of nitrogenous bases, and their spatial configuration is determined by non-covalent interactions between sections of the molecule: hydrogen bonds between nitrogenous bases, hydrophobic interactions between base pair planes, electrostatic interactions involving negatively charged phosphate groups and counterions.
Deoxyribonucleic acids isolated from various organisms differ in the ratio of nitrogenous bases included in their composition, i.e. according to the nucleotide composition, which in all DNA obeys the Chargaff rule: 1) the number of adenine molecules in the N. molecule is equal to the number of thymine molecules, i.e. A = T; 2) the number of guanine molecules is equal to the number of cytosine molecules, i.e. G = C; 3) the number of molecules of purine bases is equal to the number of molecules of pyrimidine bases; 4) the number of 6-amino groups is equal to the number of 6-keto groups, which means that the sum of adenine + cytosine is equal to the sum of guanine + thymine, i.e. A + C \u003d G + T. Chargaff's rule is also true for the so-called minor nitrogenous bases (methylated or other derivatives of purine and pyrimidine bases). Thus, the nucleotide composition of each DNA is characterized by a constant value - the molar ratio
(specificity factor) or the percentage of G-C pairs, i.e.
The value of the latter indicator is practically the same for organisms of the same class. In higher plants and vertebrates, it is 0.55-0.93.
A study published in the journal Nature showed that organic compounds, with an unexpectedly high level of complexity, exist throughout the universe. These results suggest that complex organic compounds can be created by stars.
Professor Sun Quoc and Dr. Yong Zhang of the University of Hong Kong have demonstrated that organic substances in the universe are composed of both aromatic (cyclic form) and aliphatic (chain) compounds. These compounds are so complex that their chemical structure resembles coal or oil. Because coal and oil are leftovers ancient life, it was believed that a similar form of organic matter is formed exclusively from living organisms. The team's discovery suggests that complex organic compounds can be synthesized in space even in the absence of any life forms.
Scientists have investigated a mysterious phenomenon: a set of infrared radiation in stars, interstellar space and galaxies. Their spectral signatures are known as "unidentified infrared emissions". For more than two decades, the most widely accepted theory regarding the origin of these signatures has been that they are simple organic molecules made up of carbon and hydrogen atoms called polycyclic aromatic hydrocarbons (PAHs). By observing with the Infrared Space Observatory and the Spitzer Space Telescope, Kuok and Zhang demonstrated that the emission spectrum could not be explained by the presence of PAH molecules. The team put forward the view that substances that generate similar infrared radiation have a much more complex chemical structure.
Stars not only create this complex organic matter, but also push it out into interstellar space. The results are consistent with Kuok's earlier idea that old stars are molecular factories capable of producing organic mixtures. "Our work has demonstrated that stars can easily create complex organic compounds in a near-total vacuum," Kuok said. "Theoretically it's impossible, but we can still see it."
Even more interesting is the fact that the structure of this organic star dust is similar to the complex organic compounds found in meteorites. Since meteorites are remnants of the early solar system, the question arises as to whether stars could have enriched the early solar system. solar system organic compounds. The question of what role these compounds played in the process of the origin and development of life on Earth remains open.
“Carbon occurs in nature both in the free and in the combined state, in very different forms and forms. In the free state, carbon is known in at least three forms: coal, graphite, and diamond. In the state of compounds, carbon is part of the so-called organic substances, that is, many substances that are in the body of every plant and animal. It is found in the form of carbon dioxide in water and air, and in the form of salts of carbon dioxide and organic residues in the soil and the mass of the earth's crust. The variety of substances that make up the body of animals and plants is known to everyone. Wax and oil, turpentine and resin, cotton paper and protein, plant cell tissue and animal muscle tissue, tartaric acid and starch - all these and many other substances included in the tissues and juices of plants and animals are carbon compounds. The field of carbon compounds is so large that it constitutes a special branch of chemistry, i.e., the chemistry of carbon or, better, hydrocarbon compounds.
These words from the Fundamentals of Chemistry by D. I. Mendeleev serve as a detailed epigraph to our story about the vital element - carbon. However, there is one thesis here, with which, from the point of view of modern science about the substance, one can argue, but more on that below.
Probably, the fingers on the hands will be enough to count the chemical elements that at least one scientific book has not been devoted to. But an independent popular science book - not some kind of brochure on 20 incomplete pages with a wrapping paper cover, but a quite solid volume of almost 500 pages - has only one element in the asset - carbon.
In general, the literature on carbon is the richest. These are, firstly, all the books and articles of organic chemists without exception; secondly, almost everything related to polymers; thirdly, countless publications related to fossil fuels; fourthly, a significant part of the biomedical literature ...
Therefore, we will not try to embrace the immensity (it is not by chance that the authors of the popular book on element No. 6 called it “Inexhaustible”!), but we will focus only on the main thing from the main point - we will try to see carbon from three points of view.
Carbon is one of the few "no family, no tribe" elements. The history of human contact with this substance goes back to prehistoric times. The name of the discoverer of carbon is unknown, and it is also unknown which of the forms of elemental carbon - diamond or graphite - was discovered earlier. Both happened way too long ago. Only one thing can be definitely stated: before diamond and before graphite, a substance was discovered, which a few decades ago was considered the third, amorphous form of elemental carbon - coal. But in reality, charcoal, even charcoal, is not pure carbon. It contains hydrogen, oxygen, and traces of other elements. True, they can be removed, but even then the coal carbon will not become an independent modification of elemental carbon. This was established only in the second quarter of our century. Structural analysis showed that amorphous carbon is essentially the same graphite. This means that it is not amorphous, but crystalline; only its crystals are very small and there are more defects in them. After that, they began to believe that carbon on Earth exists only in two elementary forms - in the form of graphite and diamond.
Video Organic compounds in space
Alkanes. Structure and nomenclature
By definition, alkanes are saturated or saturated hydrocarbons that have a linear or branched structure. Also called paraffins. Alkanes contain only single covalent bonds between carbon atoms. The general formula is
To name a substance, you must follow the rules. According to the international nomenclature, names are formed using the suffix -an. The names of the first four alkanes have developed historically. Starting from the fifth representative, the names are made up of a prefix indicating the number of carbon atoms, and the suffix -an. For example, octa (eight) makes octane.
For branched chains, the names add up:
- from the numbers indicating the numbers of carbon atoms around which the radicals stand;
- from the name of the radicals;
- from the name of the main chain.
Example: 4-methylpropane - the fourth carbon atom in the propane chain has a radical (methyl).
Rice. 1. Structural formulas with the names of alkanes.
Every tenth alkane names the next nine alkanes. After decane come undecane, dodecane, and so on; after eicosan, geneicosan, docosan, tricosan, etc.
organic and inorganic substances. organic matter
Organic compounds differ from inorganic compounds primarily in their composition. If inorganic substances can be formed by any elements Periodic system, then the organic composition must certainly include C and H atoms. Such compounds are called hydrocarbons (CH4 - methane, C6H6 - benzene). Hydrocarbon raw materials (oil and gas) are of great benefit to mankind. However, the strife causes serious.
Hydrocarbon derivatives also contain O and N atoms. Representatives of oxygen-containing organic compounds are alcohols and isomeric ethers (C2H5OH and CH3-O-CH3), aldehydes and their isomers - ketones (CH3CH2CHO and CH3COCH3), carboxylic acids and complex ethers (CH3-COOH and HCOOCH3). The latter also include fats and waxes. Carbohydrates are also oxygen-containing compounds.
Why did scientists combine plant and animal substances into one group - organic compounds, and how do they differ from inorganic ones? There is no single clear criterion for separating organic and inorganic substances. Consider a number of features that combine organic compounds.
- Composition (constructed from atoms C, H, O, N, less often P and S).
- Structure (C-H and C-C bonds are mandatory, they form chains and cycles of different lengths);
- Properties (all organic compounds are combustible, form CO2 and H2O during combustion).
Among organic substances, there are many polymers of natural (proteins, polysaccharides, natural rubber, etc.), artificial (viscose) and synthetic (plastics, synthetic rubbers, polyester, and others) origin. They have great molecular weight and more complex, in comparison with inorganic substances, structure.
Finally, there are more than 25 million organic substances.
This is just a superficial look at organic and inorganic substances. More than a dozen have been written about each of these groups. scientific papers, articles and textbooks.
As we have already indicated above, the entire set of organisms belonging to all the kingdoms of nature is considered to be the living substance of the considered shell of the Earth. Human beings occupy a special position among all. The reasons for this were:
- consumer position, not production;
- development of mind and consciousness.
All other representatives are living matter. The functions of living matter were developed and indicated by Vernadsky. He assigned the following role to organisms:
- Redox.
- Destructive.
- Transport.
- Environment-forming.
- Gas.
- Energy.
- Informational.
- concentration.
The most basic functions of the living matter of the biosphere are gas, energy and redox. However, the rest are also important, providing complex processes of interaction between all parts and elements of the living shell of the planet.
Let's consider each of the functions in more detail to understand what exactly is meant and what is the essence.
Infinitely diverse living organisms are composed of a limited set of atoms, the appearance of which we owe to a large extent to the stars. The most powerful event in the life of the universe - Big Bang- filled our world with a substance of very meager chemical composition.
It is believed that the union of nucleons (protons and neutrons) in expanding space did not have time to advance further than helium. Therefore, the pre-galactic Universe was filled almost exclusively with hydrogen nuclei (that is, simply protons) with a small - about a quarter by mass - addition of helium nuclei (alpha particles). There was practically nothing else in it, apart from light electrons. How exactly the primary enrichment of the Universe with nuclei of heavier elements took place, we cannot yet say. To this day, not a single "primordial" star, that is, an object consisting only of hydrogen and helium, has been discovered. There are special programs to search for stars with a low metal content (we recall that astronomers have agreed to call all elements heavier than helium “metals”), and these programs show that stars of “extremely low metallicity” are extremely rare in our Galaxy. They are, in some record specimens the content, for example, of iron is inferior to that of the sun by tens of thousands of times. However, there are only a few such stars, and it may well turn out that “in their person” we are dealing not with “almost primary” objects, but simply with some kind of anomaly. On the whole, even the oldest stars in the Galaxy contain fair amounts of carbon, nitrogen, oxygen, and heavier atoms. This means that even the most ancient galactic luminaries are in fact not the first: before them, the Universe already had some kind of "factories" for the production of chemical elements.
The Herschel European Infrared Space Observatory has detected spectral "fingerprints" of organic molecules in the RTO. In this image, an infrared image of the Orion Nebula taken by NASA's Spitzer Space Telescope is overlaid with its spectrum taken by the Herschel Observatory's HIFI high-resolution spectrograph. It clearly demonstrates its saturation with complex molecules: the lines of water, carbon monoxide and sulfur dioxide, as well as organic compounds - formaldehyde, methanol, dimethyl ether, hydrocyanic acid and their isotopic analogues are easily identified in the spectrum. The unsigned peaks belong to numerous yet unidentified molecules. |
Now it is believed that such factories could be supermassive stars of the so-called population of the third (III) type. The fact is that heavy elements are not just a “seasoning” for hydrogen and helium. These are important participants in the process of star formation, which allow a collapsing protostellar gas clump to release heat released during compression. If you deprive it of such a heat sink, it simply cannot shrink - that is, it cannot become a star ... More precisely, it can, but only on condition that its mass is very large - hundreds and thousands of times more than modern stars. Since a star lives less, the greater its mass, the first giants existed for a very short time. They lived short bright lives and exploded, leaving no trace, except for the atoms of heavy elements that had time to be synthesized in their depths or formed directly during explosions.
In the modern Universe, practically the only supplier of heavy elements is stellar evolution. Most likely, the periodic table is "filled" by stars whose mass exceeds the solar mass by more than an order of magnitude. If on the Sun and other similar luminaries, thermonuclear fusion in the core does not go beyond oxygen, then more massive objects in the process of evolution acquire an “onion” structure: their nuclei are surrounded by layers, and the deeper the layer, the heavier nuclei are synthesized in it. Here the chain of thermonuclear transformations ends not with oxygen, but with iron, with the formation of intermediate nuclei - neon, magnesium, silicon, sulfur and others.
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The Great Nebula of Orion (LTO) is one of the closest star forming regions containing large amounts of gas, dust and newborn stars. At the same time, this nebula is one of the largest "chemical factories" in our Galaxy, and its true "power", as well as the ways of synthesis of molecules of interstellar matter in it, are not yet entirely clear to astronomers. This image was taken with the Wide Field Imager Camera on the 2.2-meter MPG/ES0 telescope at the La Silla Observatory in Chile. |
ORGANIC MOLECULES IN SPACE |
To enrich the Universe with this mixture, it is not enough to synthesize atoms - you also need to throw them into interstellar space. This happens during a supernova explosion: when an iron core forms at a star, it loses stability and explodes, scattering some of the products around it thermonuclear fusion. Along the way, in the expanding shell, reactions occur that generate nuclei heavier than iron. Another type of supernova explosions lead to a similar result - thermonuclear explosions on white dwarfs, the mass of which, due to the flow of matter from a satellite star or due to a merger with another white dwarf, becomes greater than the Chandrasekhar limit (1.4 solar masses).
In the enrichment of the Universe with a number of elements - including carbon and nitrogen necessary for the synthesis of organic molecules - a significant contribution is also made by less massive stars, which end their lives with the formation of a white dwarf and an expanding planetary nebula. At the final stage of evolution, nuclear reactions also begin to occur in their shells, complicating the elemental composition of matter later ejected into outer space.
As a result, the interstellar matter of the Galaxy, to this day consisting mainly of hydrogen and helium, turns out to be polluted (or enriched - that's how you look at it) with atoms of heavier elements.
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Buckminsterfullerenes (abbreviated as "fullerenes" or "buckyballs") - tiny spherical structures consisting of an even number (but not less than 60) carbon atoms connected in a similar pattern to a soccer ball - were first detected in the spectra of a planetary nebula in the Small Magellanic Cloud (MMO) , one of the closest star systems to our galaxy. The discovery was made in July 2010. working group the Spitzer Space Telescope (NASA), which conducts observations in the infrared range. The total mass of fullerenes contained in the nebula is only five ra? less than the mass of the earth. Against the background of the MMO image taken by the Spitzer telescope, an enlarged image of the planetary nebula (smaller inset) and the fullerene molecules found in it (large inset), consisting of 60 carbon atoms, is shown. To date, reports have already been received on the registration of characteristic lines of such molecules in the spectra of objects located within the Milky Way. |
ORGANIC MOLECULES IN SPACE |
These atoms are transported by the general "currents" of galactic gas, together with it they condense into molecular clouds, get into protostellar clumps and protoplanetary disks ... to eventually become part of planetary systems and the beings that inhabit them. At least one example of such a habitable planet is known to us quite reliably.
Organic from inorganic
Terrestrial life - in any case, with scientific point vision - is based on chemistry and is a chain of interconversions of molecules. True, not any, but very complex, but still molecules - combinations of carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur atoms (and a couple of dozen less common elements) in various proportions. The complexity of even the most primitive "living" molecules for a long time prevented us from recognizing ordinary chemical compounds in them. There was an idea that the substances that make up living organisms are endowed with special quality - « life force”, therefore, a special branch of science - organic chemistry - should be engaged in their study.
One of turning points in the history of chemistry, the experiments of Friedrich Wohler are considered, who in 1828 for the first time synthesized urea - an organic substance - from an inorganic one (ammonium cyanate). These experiments were the first step towards the most important concept - the recognition of the possibility of the origin of life from "non-living" ingredients. It was first formulated in specific chemical terms in the early 1920s by the Soviet biologist Alexander Oparin. In his opinion, a mixture of simple molecules (ammonia, water, methane, etc.), now known as the "primordial soup", became the environment for the emergence of life on Earth. In it, under the influence of external “injections” of energy (for example, lightning), the simplest organic molecules were synthesized in a non-biological way, which then “gathered” into highly organized living beings over a very long period of time.
Experimental proof of the possibility of organic synthesis in the "primordial soup" in the early 1950s was the famous experiments of Harold Urey and Stanley Miller, which consisted in passing electrical discharges through a mixture of the above molecules. After a couple of weeks of the experiment, a rich assortment of organics was found in this mixture, including the simplest amino acids and sugars. This clear demonstration of the simplicity of abiogenesis was related not only to the problem of the origin of terrestrial life, but also to the larger problem of life in the Universe: since no exotic conditions were required for the synthesis of organic matter on the young Earth, it would be logical to assume that such processes took place (or will take place) on other planets.
Looking for signs of life
If, until the middle of the 20th century, only Mars was actually considered as the most likely habitat for "brothers in mind", then after the end of World War II, establishing contacts at interstellar distances began to seem like a matter of the near future. It was at that time that the foundations of a new science, located at the intersection of astronomy and biology, were born. It is called in many ways - exobiology, xenobiology, bioastronomy - but the name "astrobiology" is most often used. And one of the most unexpected astrobiological discoveries in recent decades has been the realization of the fact that the simplest "building blocks" of life did not need to be synthesized on Earth from inanimate matter, in the "primordial soup". They could have reached our planet already in a ready state, because organic molecules, as it turned out, are abundant not only on planets, but also - which was not even suspected at first - in interstellar gas.
The most powerful tool to study extraterrestrial matter is spectral analysis. It is based on the fact that electrons in an atom are in states - or, as they say, occupy levels - with strictly defined energies, and move from level to level, emitting or absorbing a photon whose energy is equal to the difference between the energies of the initial and final levels. If an atom is located between the observer and some source of light (for example, the photosphere of the Sun), it will “eat out” from the spectrum of this source only photons of certain frequencies that can cause electron transitions between the energy levels of this atom. Dark dips appear in the spectrum at these frequencies - absorption lines. Since the set of levels is individual not only for each atom, but also for each ion (an atom deprived of one or more electrons), it is possible to reliably establish from the set of spectral lines which atoms gave rise to them. For example, from the lines in the spectrum of the Sun and other stars, you can find out what their atmospheres are made of.
In 1904, Johannes Hartmann was the first to install important fact: not all lines in the spectra of stars arise in stellar atmospheres. Some of them are generated by atoms that are much closer to the observer - not near the star, but in interstellar space. Thus, for the first time, signs of the existence of interstellar gas (more precisely, only one of its components - ionized calcium) were discovered.
Needless to say, this was a shocking discovery. After all, why shouldn't there be ionized calcium in the interstellar medium (ISM)? But the idea that it can contain not only ionized and neutral atoms of various elements, but also molecules, seemed fantastic for a long time. The ISM at that time was considered a place unsuitable for the synthesis of at least some complex compounds: extremely low densities and temperatures should slow down the rates of chemical reactions in it to almost zero. And if suddenly some molecules do appear there, they will immediately disintegrate again into atoms under the influence of starlight.
Therefore, more than 30 years elapsed between the discovery of interstellar gas and the recognition of the existence of interstellar molecules. In the late 1930s, ISM absorption lines were found in the ultraviolet region of the spectrum, which at first could not be attributed to any chemical element. The explanation turned out to be simple and unexpected: these lines do not belong to individual atoms, but to molecules - the simplest diatomic carbon compounds (CH, CN, CH+). Further spectral observations in the optical and ultraviolet ranges made it possible to detect absorption lines from more than a dozen interstellar molecules.
"Hint" of radio astronomy
The real flourishing of research into the interstellar "chemical assortment" began after the advent of radio telescopes. The fact is that the energy levels in an atom - if you do not go into details - are associated only with the movement of electrons around the nucleus, but the molecules that unite several atoms have additional "movements" that are reflected in the spectrum: the molecule can rotate, vibrate, twist. .. And each of these movements is associated with energy, which, like the energy of an electron, can only have a fixed set of values. The various states of molecular rotation or vibration are also called "levels". When moving from level to level, the molecule also emits or absorbs a photon. An important difference is that the energies of the rotational and vibrational levels are relatively close. Therefore, their difference is small, and the photons absorbed or emitted by the molecule during the transition from level to level do not fall into the ultraviolet or even into visible range, and in the infrared (oscillatory transitions) and in the radio range (rotational transitions).
The Soviet astrophysicist Iosif Shklovsky was the first to draw attention to the fact that the spectral emission lines of molecules must be sought in the radio range. Specifically, he wrote about a molecule (more precisely, a free radical) of OH hydroxyl, which under certain conditions becomes a source of radio emission at a wavelength of 18 cm, which is very convenient for observations from the Earth. It was hydroxyl that became the first molecule in the ISM, discovered in 1963 during radio observations and supplementing the list of already known diatomic interstellar molecules.
But then it got more interesting. In 1968, the results of observations of three- and four-atomic molecules - water and ammonia (H 2 0, NH 3) were published. A year later, a message appeared about the discovery at the ISM of the first organic molecule - formaldehyde (H 2 CO). Since then, astronomers have been discovering several new interstellar molecules every year, so that the total number now exceeds two hundred. Certainly dominate this list simple connections, including from two to four atoms, but a significant part (more than a third) are polyatomic molecules.
A good half of the polyatomic interstellar compounds under terrestrial conditions we would unambiguously attribute to organic matter: formaldehyde, dimethyl ether, methyl and ethyl alcohol, ethylene glycol, methyl formate, acetic acid... The longest molecule discovered in the ISM was found in 1997. in one of the dense clumps of the TMS-1 molecular cloud in the constellation Taurus. For the Earth, this is not a very common compound from the cyanopolyin family, which is a chain of 11 carbon atoms, to one end of which a hydrogen atom is "attached", to the other - a nitrogen atom. Other organic molecules were found in the same clot, but for some reason it is especially rich in cyanopolyin molecules with carbon chains of various lengths (3, 5, 7, 9, 11 atoms), for which it was called the "cyanopolyin peak".
Another well-known object with a rich "organic content" is the molecular cloud Sgr B2(N), located near the center of our Galaxy in the direction of the constellation Sagittarius. It contains a particularly large number of complex molecules. However, it does not have any exclusivity in this respect - rather, the effect of “search under the lantern” is triggered here. Finding new molecules, especially organic ones, is a very difficult task, and observers often prefer to point their telescopes at areas of the sky that are more likely to succeed. Therefore, we know a lot about the concentration of organics in the molecular clouds of Taurus, Orion, Sagittarius, and almost do not have information about the content of complex molecules in many other similar clouds. But this does not mean at all that organics are not there - it's just that "antennas have not yet reached" these objects.
Difficulties in deciphering
Here it is necessary to clarify what "complexity" means in this case. Even an elementary analysis of stellar spectra is a very difficult task. Yes, the set of lines of each atom and ion is strictly individual, but in the spectrum of a star, lines of many dozens of elements overlap each other, and it can be very difficult to “sort” them. In the case of the spectra of organic molecules, the situation becomes more complicated in several directions at once. Most of the numerous emission (absorption) lines of atoms and ions fall within a narrow spectral range accessible for observations from the Earth. Complex molecules also have thousands of lines, but these lines are "scattered" much wider - from the near infrared range (units and tens of micrometers) to the radio range (tens of centimeters).
Let's say we want to prove that there is an acrylonitrile (CH 2 CHCN) molecule in the molecular cloud. For this, it is necessary, first, to know in which lines this molecule radiates. But for many compounds such data are not available! Theoretical methods do not always make it possible to calculate the position of the lines, and in the laboratory the spectrum of a molecule often cannot be measured, for example, because it is difficult to isolate it in its pure form. Second, it is necessary to calculate the relative intensities of these lines. Their brightness depends on the properties of the molecule and on the parameters of the medium (temperature, density, etc.) in which it is located. The theory will make it possible to predict that in the investigated molecular cloud the line at one wavelength should be three times brighter than the line of the same molecule at another wavelength. If lines are found at the required wavelengths, but with the wrong ratio of intensities, this is a weighty reason to doubt the correctness of their identification. Of course, to reliably detect a molecule, it is necessary to observe the cloud in the widest possible spectral range. But a significant part of the electromagnetic radiation from space does not reach the surface of the Earth! This means that one has to either observe the spectrum of the molecule fragmentarily in the "transparency windows" of the earth's atmosphere, which, of course, does not add reliability to the results obtained, or use a space telescope, which is extremely rare. Finally, do not forget that the lines of the desired molecule will have to be distinguished from other molecules, of which there are dozens of varieties, and each has thousands of lines ...
It is not surprising, therefore, that astronomers have been going for years to identify some "representatives" of cosmic organics. Indicative in this respect is the history of the discovery of glycine, the simplest amino acid, in the ISM. Although reports of registration in the spectra of molecular clouds characteristic features This molecule has repeatedly appeared, the fact of its presence is still not generally recognized: although many lines, as if belonging to glycine, are actually observed, its other expected lines are absent in the spectra, which casts doubt on the identification.
Interstellar Fusion Laboratories
But all this is the complexity of observations. In theory, over the past decades, the situation with interstellar organic synthesis has become much clearer, and now we clearly understand that the initial ideas about the chemical inertness of the ISM were wrong. To do this, of course, we had to learn a lot about its composition and physical properties beforehand. A significant proportion of the volume of interstellar space is indeed "sterile". It is filled with very hot and rarefied gas with temperatures ranging from thousands to millions of kelvins and is permeated with hard, high-energy radiation. But there are also individual condensations of interstellar matter in the Galaxy, where the temperature is low (from a few to tens of kelvins), and the density is noticeably higher than the average (hundreds or more particles per cubic centimeter). The gas in these condensations is mixed with dust, which effectively absorbs hard radiation, as a result of which their interior - cold, dense, dark - turns out to be a convenient place for chemical reactions to occur and the accumulation of molecules. Basically, such "space laboratories" are found in the already mentioned molecular clouds. Together they occupy less than a percent of the total volume of the galactic disk, but they contain about half the mass of interstellar matter in the Milky Way.
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Polycylic aromatic hydrocarbons (PAHs) are the most complex compounds found in interstellar space. This infrared image of a star-forming region in the constellation Cassiopeia shows the molecular structures of some of them (hydrogen atoms are white, carbon atoms are grey, oxygen atoms are red), as well as several of their characteristic spectral lines. Scientists believe that in the near future the spectra of PAHs will be of particular value for deciphering chemical composition interstellar medium by methods of infrared spectroscopy. |
ORGANIC MOLECULES IN SPACE |
The elemental composition of molecular clouds resembles the composition of the Sun. Basically, they consist of hydrogen - more precisely, hydrogen molecules H 2 with a small "additive" of helium. The remaining elements are present at the level of minor impurities with a relative content of about 0.1% (for oxygen) and below. Accordingly, the number of molecules containing these impurity atoms is also very small compared to the most common H 2 molecule. But why are these molecules formed at all? On Earth, special facilities are used for chemical synthesis, providing sufficiently high densities and temperatures. How does an interstellar "chemical reactor" work - cold and rarefied?
It must be remembered here that astronomy deals with other time scales. On Earth, we need to get results fast. Nature is in no hurry. Synthesis of interstellar organics takes hundreds of thousands and millions of years. But even these slow reactions require a catalyst. In molecular clouds, its role is played by particles of cosmic rays. The first step towards the synthesis of complex organic molecules can be considered the formation S-N connections. But if you just take a mixture of hydrogen molecules and carbon atoms, this bond will not form by itself. Another thing is if some of the atoms and molecules are somehow turned into ions. Chemical reactions involving ions proceed much faster. It is this initial ionization that is provided by cosmic rays, initiating a chain of interactions, during which atoms of heavy elements (carbon, nitrogen, oxygen) begin to "attach" hydrogen atoms to themselves, forming simple molecules, including those discovered in the ISM in the first place ( CH and CH+).
Further synthesis is even easier. Diatomic molecules attach new hydrogen atoms to themselves, turning into three- and four-atomic (CH 2 +, CH 3 +), polyatomic molecules begin to react with each other, transforming into more complex compounds - acetylene, hydrocyanic acid (HCN), ammonia, formaldehyde, which , in turn, become "building blocks" for the synthesis of complex organics.
After the cosmic rays gave the primary impetus chemical reactions, cosmic dust particles become an important catalyst for interstellar organic synthesis. They not only protect the inner regions of molecular clouds from destructive radiation, but also provide their surface for the efficient "production" of many inorganic and organic molecules. In the totality of reactions, it is not difficult to imagine the formation of not only glycine, but also more complex compounds. In this sense, we can say that the task of discovering the simplest amino acid has more of a sporting meaning: who will be the first to confidently find it in space. Scientists have no doubt that glycine is present in molecular clouds.
How to survive the "molecules of life"
In general, at the moment it can be considered proven that a “primary broth” is not necessary for the synthesis of organic matter. Nature perfectly copes with this task in outer space. But does interstellar organic matter have anything to do with the emergence of life? Indeed, stars and planetary systems are formed in molecular clouds and, naturally, "absorb" their matter. However, before becoming a planet, this substance passes through rather harsh conditions of the protoplanetary disk and no less harsh conditions of the young Earth. Unfortunately, our ability to study the evolution of organic compounds in protoplanetary disks is very limited. They are very small in size, and it is even more difficult to search for organic molecules in them than in molecular clouds. So far, about a dozen molecules have been found in the forming planetary systems of other stars. Of course, they also include simple organic compounds (in particular, formaldehyde), but we cannot yet describe in more detail the evolution of organics under these conditions.
The research of our own planetary system comes to the rescue. True, it is already more than four and a half billion years old, but part of its primary protoplanetary matter has been preserved to this day in some meteorites. It was in them that the abundance of organic matter turned out to be quite impressive - especially in the so-called carbonaceous chondrites, which make up a few percent of total number"heavenly stones" that fell to Earth. They have a loose clay structure, are rich in bound water, but most importantly, a significant part of their substance is “occupied” by carbon, which is part of many organic compounds. Meteoritic organic matter consists of relatively simple molecules, among which there are amino acids, and nitrogenous bases, and (carboxylic acids, and "insoluble organic matter", which is a product of polymerization (tarring) of simpler compounds. Of course, we cannot now confidently say that this organic matter was “inherited” from the substance of a protosolar molecular bunch, but indirect evidence indicates this - in particular, a clear excess of isotopomers of a number of molecules was found in meteorites.
Acetaldehyde (left) and its isomers, vinyl alcohol and ethylene oxide, have also been detected in interstellar space. |
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10 eight-atom |
In 1997, radio observations confirmed the presence of acetic acid in space. |
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9 nine-atom molecules and 17 molecules containing from 10 to 70 atoms |
Some of the heaviest (and longest) molecules found in outer space belong to the class of polyins - they contain several triple bonds connected in series "in a chain" by single bonds. They do not occur on earth. |
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MOLECULES CURRENTLY DISCOVERED IN INTERSTELLAR SPACE |
Isotopomers or isotopologues are molecules in which one or more atoms are replaced by a minor (not the most common) isotope of a chemical element. For example, the isotopomer is heavy water, in which the light hydrogen isotope protium is replaced by deuterium. A feature of the chemistry of molecular clouds is that isotopomers are formed in them somewhat more efficiently than "ordinary" molecules. For example, the content of deuterated formaldehyde (HDCO) can be tens of percent of the content of conventional formaldehyde - despite the fact that, in general, deuterium (D) atoms in space are a hundred thousand times less than protium (H) atoms. Interstellar molecules give the same "preference" to the nitrogen isotope 15N over the usual 14N. And the same relative overenrichment is observed in meteorite organic matter.
So far, three important conclusions can be drawn from the available data. First, organic compounds of a very high degree of complexity are very efficiently synthesized in the interstellar medium of our and other galaxies. Secondly, these compounds can be preserved in protoplanetary disks and be part of planetesimals - the "embryos" of planets. And finally, even if the organic matter "did not survive" the very process of the formation of the Earth or another planet, it could well get there later with meteorites (as it happens today).
Naturally, the question arises of how far organic synthesis could go at the pre-planetary stage. But what if not the "building blocks" for the origin of life, but life itself, came to Earth with meteorites? After all, at the beginning of the 20th century it seemed impossible for even simple diatomic molecules to appear in the ISM. Now we are massively finding in molecular clouds substances whose names are difficult to pronounce the first time. The detection of amino acids in the ISM is most likely only a matter of time. What prevents us from taking the next step and assuming that meteorites brought life to Earth "in finished form"?
Indeed, several times in the literature there have been reports that the remains of the simplest extraterrestrial organisms were found in meteorites ... However, so far this information is too unreliable and scattered to be confidently included in the general picture of the origin of life.