The main gases in the composition of the primary atmosphere were. The original atmosphere of the earth. Ecological and geological role of atmospheric processes

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The formation of the Earth's atmosphere began in ancient times - in the protoplanetary stage of the Earth's development, during the period of active volcanic eruptions with the release of a huge amount of gases. Later, when the oceans and the biosphere appeared on Earth, the formation of the atmosphere continued due to gas exchange between water, plants, animals and their decomposition products.

Throughout geological history, the Earth's atmosphere has undergone a series of profound transformations.

Primary atmosphere of the Earth. Recovery.

Part the primary atmosphere of the earth at the protoplanetary stage of the Earth's development (more than 4.2 billion years ago), methane, ammonia and carbon dioxide were predominantly included. Then, as a result of degassing of the Earth's mantle and continuous weathering processes on the earth's surface, the composition of the Earth's primary atmosphere was enriched with water vapor, carbon compounds (CO 2, CO) and sulfur, as well as strong halogen acids (HCl, HF, HI) and boric acid. The primary atmosphere was very subtle.

Secondary atmosphere of the Earth. Oxidizing.

Subsequently, the primary atmosphere began to transform into a secondary one. This happened as a result of the same weathering processes that took place on the earth's surface, volcanic and solar activity, as well as due to the vital activity of cyanobacteria and blue-green algae.

The transformation resulted in the decomposition of methane into hydrogen and carbon dioxide, ammonia into nitrogen and hydrogen. Carbon dioxide and nitrogen began to accumulate in the Earth's atmosphere.

Blue-green algae, through photosynthesis, began to produce oxygen, which was practically all spent on the oxidation of other gases and rocks. As a result, ammonia was oxidized to molecular nitrogen, methane and carbon monoxide - to carbon dioxide, sulfur and hydrogen sulfide - to SO 2 and SO 3.

Thus, the atmosphere gradually changed from reducing to oxidizing.

Formation and evolution of carbon dioxide in the primary and secondary atmosphere.

Sources of carbon dioxide in the early stages of the formation of the Earth's atmosphere:

• Oxidation of methane,
• Degassing of the Earth's mantle,
• Weathering of rocks.

At the turn of the Proterozoic and Paleozoic (about 600 million years ago), the content of carbon dioxide in the atmosphere decreased and amounted to only tenths of a percent of the total volume of gases in the atmosphere.

Carbon dioxide reached the current level of content in the atmosphere only 10-20 million years ago.

Formation and evolution of oxygen in the primary and secondary atmosphere of the Earth.

Oxygen sources in the early stages of the formation of the atmosphere Lands:

• Degassing of the Earth's mantle - almost all oxygen was spent on oxidative processes.
• Photodissociation of water (decomposition into hydrogen and oxygen molecules) in the atmosphere under the influence of ultraviolet radiation - as a result, free oxygen molecules appeared in the atmosphere.
• Conversion of carbon dioxide into oxygen by eukaryotes. The appearance of free oxygen in the atmosphere led to the death of prokaryotes (adapted to life in reducing conditions) and the emergence of eukaryotes (adapted to live in an oxidizing environment).

Change in oxygen concentration in the Earth's atmosphere.

Archean - first half of the Proterozoic - oxygen concentration 0.01% of the current level (Yuri point). Almost all of the oxygen generated was spent on the oxidation of iron and sulfur. This continued until all the ferrous iron on the surface of the earth was oxidized. From that moment on, oxygen began to accumulate in the atmosphere.

Second half of the Proterozoic - end of the Early Vendian - the oxygen concentration in the atmosphere is 0.1% of the current level (Pasteur's point).

Late Vendian - Silurian period. Free oxygen stimulated the development of life - the anaerobic fermentation process was replaced by an energetically more promising and progressive oxygen metabolism. From that moment on, the accumulation of oxygen in the atmosphere proceeded rather quickly. The emergence of plants from the sea to land (450 million years ago) led to the stabilization of the oxygen level in the atmosphere.

Mid Cretaceous ... The final stabilization of the oxygen concentration in the atmosphere is associated with the appearance of flowering plants (100 million years ago).

Formation and evolution of nitrogen in the primary and secondary atmosphere of the Earth.

Nitrogen formed on early stages development of the Earth due to the decomposition of ammonia. The binding of atmospheric nitrogen and its burial in marine sediments began with the appearance of organisms. After the emergence of living organisms on land, nitrogen began to be buried in continental sediments. The nitrogen fixation process was especially enhanced with the advent of terrestrial plants.

Thus, the composition of the Earth's atmosphere determined the characteristics of the vital activity of organisms, contributed to their evolution, development and dispersal over the earth's surface. But in the history of the Earth there have been occasional disruptions in the distribution of the gas composition. The reason for this was various disasters that occurred more than once during the Cryptozoic and Phanerozoic. These disruptions led to massive extinctions of the organic world.

The composition of the ancient and modern atmosphere of the Earth in percentage terms is shown in Table 1.

Table 1. Composition of the primary and modern atmosphere of the Earth.

It was the article “Formation of the Earth's Atmosphere. Primary and Secondary Atmosphere of the Earth ". Read on: «

G.V. Voitkevich, comparing in 1980 the conditions that existed at the dawn of the history of the Earth and Venus, comes to the conclusion that the original atmosphere of the Earth was practically the same as it is now on Venus. He assumes that the initial version of the composition of the Earth's atmosphere corresponds to the conditions for the absence of photosynthesis and carbonates on Earth.

Thus, the degassing of the substance that composes the Earth and the dissipation of gases determined the composition of the original atmosphere of the Earth. Since the Earth was never completely melted and on its surface there were hardly temperatures above the boiling point of water (meaning the global effect), the composition of its original atmosphere was determined by those elements that are themselves volatile or capable of producing volatile compounds: H, O, N , C, F, S, P, CI, Br and inert gases. In the earth's crust, there is a deficiency of almost all of these volatile elements in comparison with their cosmic abundance. This is especially true of He, Ne, H, N, C. Apparently, these elements were lost by the Earth during its accretion. Other light volatile elements such as P, S, C1, firstly, are somewhat heavier, and secondly, they form highly reactive volatile compounds that react with the rocks of the earth's crust, in particular with sedimentary rocks.

It can be assumed that the composition of volatile elements released into the atmosphere at the final stages of the Earth's accretion and supplied during modern phenomena of volcanism or fumarolic activity remains approximately the same. EK Markhinin in 1967 cites data on the composition of volcanic gases and fumarolic emissions, from which it can be seen that carbon-containing gases are in second place after water in terms of the abundance of emissions.

If we accept that the original atmosphere of the Earth consisted of such a set of gases (with the exception of such chemically active gases as HC1, HF and some others), then, apparently, G.V. Voitkevich quite rightly equates the composition of the original atmosphere of the Earth with the modern Venusian and apparently Martian. The judgments of H. Holland, C. Sagan, M. Shidlovsky and others about the sharply reducing initial atmosphere of the Earth (CH 4, Hg, NH 3) find no confirmation either from cosmochemical positions or from theoretical calculations concerning the lifetimes of H 2 , CH 4, NH 3 in the atmosphere, which not only readily dissipate by themselves, but also decompose very quickly due to photochemical processes. J. Walker in 1975-1976 compared models of instantaneous and gradual degassing of matter from Venus and the Earth, and none of them led to a reducing atmosphere.

Formation of the Earth's atmosphere. Evolution of the atmosphere

Of all the known planets, only on Earth has a unique atmosphere favorable for the development of life. In the process of evolution, the Earth's atmosphere was in 3 sharply different compositions.

The primary atmosphere of the Earth was captured by the gravitational field of our planet directly from the protoplanetary cloud during the accretion of planets. Such an atmosphere consisted of hydrogen and helium. According to H. Holland, the primary atmosphere mainly consisted of methane and hydrogen.

It is assumed that in the case of a hydrogen-helium composition, the mass of the primary earth's atmosphere could reach 10 25 -10 26 g, and the pressure at the surface was much higher than 10 4 atm. At the same time, the atmosphere became completely opaque and, therefore, only due to the greenhouse effect and adiabatic compression, the temperature at its base could rise to tens of thousands of degrees. However, it should be noted that there are no geological traces of the existence of such an exotic atmosphere on the Earth, and they should have been preserved in its annals. In addition, any assumptions about the existence of a dense atmosphere in the young Earth is extremely difficult to explain by the mechanisms of its dissipation and the transition from such extreme conditions to modern normal and comfortable for life.

The secondary Earth's atmosphere was formed by degassing volatile compounds from the mantle as a result of volcanic eruptions. This process could begin only after the appearance in the Earth's interior of processes of differentiation of the terrestrial matter, the appearance of the first signs of endogenous tectonic activity on the earth's surface 4-3.8 billion years ago. It is also natural to assume that the degassing process also depended on chemical composition mantle. Therefore, we will consider the main features of the evolution of its chemical composition.

Removal of iron, its compounds and other siderophilic elements (Fe; FeO; FeS; Ni) from the original terrestrial matter in the separation zone of heavy fractions, as well as the further transition of these elements from the mantle itself to the formed terrestrial core, and easily mobile elements (H 2 O ; K 2 O; Na 2 O; CO 2; N 2, etc.) into the earth's crust, hydrosphere and atmosphere, should be accompanied by corresponding changes in the chemical composition of the convective mantle. As the heavy fraction (“nuclear” matter) was removed from the mantle material, the relative concentration of elements and oxides remaining in the mantle increased.

Thus, in the early Archean, after the removal of all iron from the primary substance in the process of zonal differentiation, the content of the most widespread and low-mobile oxides SiO 2; MgO; A1 2 O 3; CaO begins to increase. At present, their concentration in the mantle is approximately 1.5 times higher than in the primary terrestrial matter. The concentration of such a mobile compound as Na 2 O also slightly increased. Compounds Н 2 О, К 2 О and Rb 2 O were carried out to a greater extent, therefore their content in the mantle decreased approximately two times over time (if we take into account the dissociation of water, then for it such a drop may turn out to be more significant). The concentration of radioactive elements U and Th in the mantle decreased even more (several times). This happened both due to the decay of the radioactive elements themselves, and due to their predominant transition to the continental crust. Starting from the middle of the Archean, the FeO concentration began to decrease with time.

In the Proterozoic and Phanerozoic, i.e. After the beginning of the functioning of the barodiffusion mechanism of differentiation of terrestrial matter, the residual concentration of elements and compounds in the mantle as a result of the transfer of iron and its oxides to the core began to increase. The total concentration of "nuclear" matter (in terms of Fe 2 O) in the mantle has decreased over time since the Proterozoic.

In the same way, the concentration of nickel, platinoids, gold, sulfides of iron, lead, copper and some other siderophilic elements, passing into the earth's core, changed in the post-Archean mantle.

After the beginning of the process of differentiation of terrestrial matter in the Early Archean, the concentration of metallic iron in the convective mantle should have rapidly decreased to approximately the equilibrium concentration in silicate melts. In the Late Archean, in connection with the transition of the process of differentiation of terrestrial matter to the separation of much more fusible eutectic alloys Fe FeO and Fe 2 O, the concentration of metallic iron in the convective mantle began to increase again and by the end of the Archean (2.6 10 9 years ago) reached level 5, five%.

This is due to the fact that at the end of the Archean (after the transition of the differentiation process to the separation of Fe - FeO melts) there was a sharp decrease in the temperature of the convective mantle, as a result of which the melting of metallic iron became impossible, and therefore the process of its zonal separation completely stopped.

Completely metallic iron disappeared from the mantle only about 0.5 billion years ago. It is interesting to note that this time closely coincides with the time of the emergence of the animal kingdom and multicellular organisms in the Vendian about 0.6 billion years ago.

Throughout the entire Precambrian history of the development of the Earth in the mantle, and consequently in the rift zones of the Earth, the content of metallic iron, the main chemical reagent that actively absorbed oxygen from the hydrosphere and atmosphere, decreased. Only after the almost complete disappearance of metallic iron from the convective mantle in the earth's atmosphere could the oxygen produced by plants (and photodissociation of water) accumulate in quantities sufficient for the appearance and normal functioning of animal life forms on Earth.

Direct filtration of volatile and mobile elements and compounds through the dense material of the mantle, characterized by a viscosity of the order of ~ 10 20 - 10 23 P, without its melting is almost completely excluded due to the extremely small diffusion coefficients in such a substance: D = 10 -21 - 10 -25 cm 2 / s. Consequently, from the mantle to the outer geospheres (continental crust, hydrosphere, and atmosphere), lithophilic and volatile components can only pass through open deep faults and only together with outpourings of basaltic magmas of mantle origin.

It is important to note that the very processes of differentiation of lithophilic and degassing of volatile compounds become possible only due to the existence of convective mass transfer in the mantle, constantly delivering new volumes of mantle matter to the Earth's surface to the zones of development of draining faults, which have not yet lost volatile and mobile components and therefore are capable of segregation. ... Consequently, the speed of movement of mobile components from the mantle should be proportional to the rate of convective mass transfer in it.

Apparently, the secondary atmosphere consisted of water vapor, CO 2, and other gas fractions (H 2 S, CO, H 2, N 2, CH 4, NH 3, HF, HCl, Ar), i.e. formed due to the flow of gases from the inner regions of the Earth and was significantly reducing. Part of the gases released under the influence of solar radiation decayed: water vapor into hydrogen and oxygen, while the latter entered into a chemical reaction with carbon monoxide and formed carbon dioxide; ammonia, on the other hand, decomposed into nitrogen and hydrogen, while hydrogen in the process of diffusion escaped into outer space and its content in the atmosphere was low. Irreversible degassing could begin only after convective motions appeared in the mantle and its overheating, accompanied by the release of the asthenosphere.

The fact that the Archean and Early Proterozoic atmosphere was sharply reducing is indicated by the widespread in many deposits of that age (for example, in the Witwatersrand Formation in southern Africa, which formed for a long time from 3 to 2.2 billion years ago) such "oxygen-phobic" minerals, as detrital pyrite and uraninite, and the first indisputable indicators of the presence of oxygen in the atmosphere - red-colored weathering crusts - appeared only in the middle Proterozoic about 1.9-1.8 billion years ago. It should not be forgotten that the abundant deposits of oxide-iron ores so characteristic of the Early Precambrian also testify to the oxygen-free atmosphere of that time, since a noticeable transfer of iron by water could only take place in its soluble bivalent form, and the oxidation of iron to the trivalent state took place in water, practically without the participation of atmospheric oxygen.

The secondary atmosphere was very similar to the modern atmosphere of Venus: practically the same air composition with a significant predominance of carbon dioxide and a significant Greenhouse effect... The content of the lightest gases hydrogen and helium has significantly decreased as a result of their escape into space.

The formation of the first surface water bodies also belongs to this stage in the development of the atmosphere. Judging by the first sedimentary rocks discovered by the English geologists S. Murbat, R.K. About Nyon and RJ Pankhurst in southwestern Greenland, it can be assumed that the oceans on Earth already existed 3.8 billion years ago. Despite the fact that the temperature on the planet's surface in those distant times was much higher than today , the pressure at its surface was also very high, and as you know from the course of physics: with increasing pressure, the boiling point of water rises.

Evolution towards the modern oxygen atmosphere did not take place until life began to develop.

It is not known what random events caused the synthesis of organic molecules or the assembly of metabolizable self-replicating structures that we call organisms, but one can guess about some necessary conditions and restrictions.

In the 1950s, there was great optimism that the discovery of deoxyribonucleic acid (DNA) and the laboratory synthesis of such primitive biomolecules from an experimental atmosphere rich in methane (CH 4) and ammonia (NH 3) would provide a clear picture of the origin of life.

However, it now seems more likely that the synthesis of biologically important biomolecules took place in limited, specific environments, such as the surfaces of clay minerals, or in underwater volcanic outcrops.

The most likely assumptions lead to the fact that life began in the oceans about 4.2-3.8 billion years ago, but there is no data on fossils. The oldest known fossils are bacteria from rocks about 3.5 billion years old. In rocks of this age, there is evidence of a fairly advanced metabolism, in which solar energy was used to synthesize organic matter. The earliest of these reactions were probably based on sulfur (S) coming from volcanic outcrops:

CO 2 (r) + 2H 2 S (r)> CH 2 O (TB) + 2S (TB) + H 2 O (L) (organic matter)

Eventually, the photochemical decomposition of water, or photosynthesis, was achieved:

H 2 O (L) + CO 2 (r)> CH 2 O (TB) + O 2 (r)

The production of oxygen during photosynthesis has important implications. At first, oxygen (O 2) was quickly consumed during the oxidation of reduced substances and minerals. However, the moment came when the rate of intake exceeded consumption and O 2 began to gradually accumulate in the atmosphere. The primary biosphere, under the mortal threat of its own toxic by-product (O 2), was forced to adapt to such changes. She accomplished this through the development of new types of biogeochemical metabolism that support the diversity of life on modern Earth. Gradually, the atmosphere of a modern line-up emerged. In addition, oxygen in the stratosphere underwent photochemical reactions that led to the formation of ozone (O 3), which protects the Earth from ultraviolet radiation. For this, an amount of oxygen was enough 25 thousand times less than at the moment and the formation of a layer of ozone with only half the concentration of now. This is already enough to provide very significant protection for organisms from the destructive effects of ultraviolet rays and allow them to begin colonizing land.

Simultaneously with the process of accumulation of the amount of oxygen in the atmosphere, the proportion of nitrogen formed as a result of the oxidation of the ammonia-hydrogen atmosphere by oxygen increased at a low rate. The amount of carbon dioxide decreased with the evolution of the plant world and the increase in the number and volume of reservoirs in the hydrosphere.

And in conclusion, it should be noted that all the above considered biogeochemical transformations of the composition of the atmosphere could be carried out only in a narrow temperature range of the existence of the liquid state of water (0< Т < 100°С) и в условиях, при которых согревающее нас Солнце является спокойной и небольшой звездой, а Земля расположена от него ровно на таком расстоянии, что average temperature the earth's surface does not exceed 15 ° C. If the luminosity of the Sun were at least 1.5-2 times greater, then the Earth would inevitably turn into Venus with a dense atmosphere (which was observed at one of the stages of the development of the atmosphere), and if the luminosity of the Sun were less, it would freeze, like Mars ...

The atmosphere began to form with the formation of the Earth. In the course of the evolution of the planet and as its parameters approached modern values, fundamentally qualitative changes in its chemical composition and physical properties took place. According to the evolutionary model, at an early stage the Earth was in a molten state and about 4.5 billion years ago it was formed as a solid body. This boundary is taken as the beginning of the geological chronology. From that time on, a slow evolution of the atmosphere began. Some geological processes (for example, the outpouring of lava during volcanic eruptions) were accompanied by the release of gases from the bowels of the Earth. They included nitrogen, ammonia, methane, water vapor, CO oxide and carbon dioxide CO2. Under the influence of solar ultraviolet radiation, water vapor decomposed into hydrogen and oxygen, but the liberated oxygen reacted with carbon monoxide to form carbon dioxide. Ammonia decomposed into nitrogen and hydrogen. In the process of diffusion, hydrogen rose up and left the atmosphere, and the heavier nitrogen could not escape and gradually accumulated, becoming the main component, although some of it was bound into molecules as a result of chemical reactions (see ATMOSPHERE CHEMISTRY). Under the influence of ultraviolet rays and electrical discharges, a mixture of gases present in the original atmosphere of the Earth entered into chemical reactions, as a result of which organic substances, in particular amino acids, were formed. With the advent of primitive plants, the process of photosynthesis began, accompanied by the release of oxygen. This gas, especially after diffusion into the upper layers of the atmosphere, began to protect its lower layers and the surface of the Earth from life-threatening ultraviolet and X-rays. According to theoretical estimates, the oxygen content, 25,000 times less than now, could already lead to the formation of an ozone layer with only half the concentration of today. However, this is already enough to provide very significant protection of organisms from the destructive effects of ultraviolet rays.

It is likely that the primary atmosphere contained a lot of carbon dioxide. It was consumed in the course of photosynthesis, and its concentration should have decreased with the evolution of the plant world, as well as due to absorption in the course of some geological processes. Since the greenhouse effect is associated with the presence of carbon dioxide in the atmosphere, fluctuations in its concentration are one of the important reasons for such large-scale climatic changes in the history of the Earth, such as ice ages.

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Ministry of Higher and Secondary Education of the Russian Federation MBOU SOSH 43 Krasnodar PRIMARY ATMOSPHERE OF THE EARTH

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It has not yet been possible to reliably establish the history of the formation of the atmosphere. But it has already been possible to identify some likely changes in its composition. The atmosphere began to emerge immediately after the formation of the Earth. In the process of evolution, it has almost completely lost its original atmosphere. At an early stage, our planet was in a molten state. Solid began to form about four and a half billion years ago. This time will be the beginning of the geological chronology.

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It is precisely during this period that the slow evolution of the atmosphere begins. Processes such as the release of lava during volcanic eruptions are accompanied by the inevitable release of gases such as nitrogen, methane, water vapor and others.

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When exposed to radiation from the sun, water vapor decomposes into oxygen and hydrogen. The liberated oxygen reacts with carbon monoxide to form carbon dioxide. Ammonia decomposes into nitrogen and hydrogen. In the process of diffusion, hydrogen rises upward and leaves the atmosphere. Nitrogen, which is much heavier, cannot escape and gradually build up. Thus, nitrogen becomes the main component

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The primary atmosphere of the Earth contained carbon dioxide and hydrogen, and between them a reaction is possible, leading to the formation of bog gas (methane) and water vapor. But the bulk of the water, according to modern concepts, was degassed from magma during the first hundreds of millions of years after the formation of the atmosphere. Water immediately greatly complicated the nature of the interaction between the components and the very structure of the biogenosphere.

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Saturation of the primary atmosphere with water vapor, the ability of water to accumulate ("slowly cool") solar energy markedly changed the thermodynamic conditions inside the biogenosphere and even beyond. There are two points to keep in mind; First, with the appearance of water, the processes of weathering began to proceed much more vigorously, as a result of which geochemical accumulators are "charged" with solar energy.

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Secondly, the weathering products (clays, for example) entered into compounds with a large amount of water, and this increased their energy barrier, that is, the minerals were removed from the moment at which they could give up the accumulated solar energy. To release this energy, they had to "dry up" first.

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Sedimentary rocks were dehydrated, sinking into the depths of the earth's crust as a result of the transformation of clays into mica. If earlier they were discharged somewhere near the surface, then after the appearance of water on the Earth, geochemical accumulators were able to carry solar energy to the lower boundary of the earth's crust due to moisture. There they gave off the accumulated energy and thereby provided the temperature gradient of the earth's crust.

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When sediment sinks, the dewatering process is counteracted by an increase in pressure, which prevents the release of energy. Magma chambers - the result of a violent release of energy - arose during tectonic ruptures, when the pressure weakened. If we take into account that at that time the shape of the Earth was less stable than it is now, then in the interaction of these factors with geochemical accumulation, one can see the reason for the alleged violent volcanic activity at the dawn of the geological history of our planet.

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When exposed to ultraviolet rays, as well as electrical discharges. A mixture of gases entered into a chemical reaction, after which organic substances - amino acids - were formed. Thus, life could have originated in an atmosphere that is different from today's atmosphere.

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When primitive plants appeared on Earth, the process of photosynthesis began to take place. Which, as you know, is accompanied by the release of free oxygen. After diffusion into the upper layers of the atmosphere, this gas began to protect the lower layers and the surface of the Earth itself from dangerous X-ray and ultraviolet radiation.

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It can be assumed that there was a lot of carbon dioxide in the primary atmosphere, which was consumed in the process of photosynthesis, as the flora evolved. Scientists also believe that fluctuations in its concentration influenced climate change during the development of the Earth.