The problem of the origin of water and the formation of the hydrosphere, despite the rather high modern level development of geosciences, is still the least developed. There are many hypotheses of the origin of water and the development of the hydrosphere, but none of them has gone beyond the stage of a working hypothesis, accumulation, preliminary systematization and generalization of materials.

All hypotheses can be conditionally combined into two large groups:

1) telluric origin;

2) cosmic origin water.

The most convincing hypotheses first group, according to which the lithosphere, atmosphere and hydrosphere were formed in a single process, as a result of the melting and degassing of the mantle substance. According to A.P. Vinogradov, at the time of the formation of the Earth from a protoplanetary cloud, all elements of its future atmosphere and hydrosphere were in a bound form in the composition solids: water - in hydroxides, nitrogen - in nitrites and nitrates, oxygen - in metal oxides, carbon - in graphites, carbides and carbonates. Having reached approximately the modern mass, the Earth began to warm up as a result of the gravitational compression of its bowels and due to the decay of radioactive isotopes, and melting and differentiation of matter into volatile, low-melting and refractory substances began in the mantle. Refractory substances remained in the bowels of the Earth, low-melting substances in the form of basalt formed the earth's crust. Volatile substances - water vapor of volcanic gases, carbon compounds, sulfur, ammonia, halogen acids, hydrogen, argon and some other gases - rose to the surface and formed the atmosphere and hydrosphere. Moreover, almost all of the water vapor condensed (the temperature above the Earth's surface did not exceed +15 °C), turned into liquid water, and thus formed "praeoceans". Other components of volcanic gases also passed into the primary ocean, dissolving in water - a large proportion of carbon dioxide, acids, sulfur compounds and part of ammonia. Acids, especially in water, reacted with rock silicates, extracting alkaline, alkaline earth and other elements from them. As a result, the water ceased to be acidic, and the soluble salts of the elements extracted from silicates passed into the ocean, so the water in it immediately became salty. The primary ocean was probably shallow, but covered almost the entire Earth. With an increase in the mass of the hydrosphere, the volume of the ocean also increased, and its outlines changed, which was associated with the formation of continental and oceanic crust. Water (fresh) evaporated from the surface of the ocean, which, returning in the form of rains to the earth's surface, formed land waters. The waters of the ocean, land and atmosphere made up a single earthly shell - the hydrosphere. This determined one of the specific features of the Earth, which distinguishes it from other planets of the solar system - the constant presence of a hydrosphere on it.

2.2 Water resources of the planet

The concept of "hydrosphere" is constantly transformed. Currently hydrosphere It is customary to call the water shell of the Earth, including all unbound water, regardless of its state: liquid, solid, gaseous.

Bottom line the hydrosphere is taken at the level of the mantle surface (Mohorovicic surface), and the upper one passes in the upper layers of the atmosphere. The hydrosphere includes the World Ocean, land waters (rivers, lakes, swamps, glaciers), atmospheric moisture, as well as groundwater occurring everywhere on the continents, at the bottom of lake and sea depressions and under the thickness of eternal ice.

Thus, being part of the geographic shell, the hydrosphere covers the entire complex of earthly shells. The hydrosphere is continuous, as the litho- and atmosphere are continuous, and is one. Its unity lies in the common origin of all natural waters from the Earth's mantle, in the unity of their evolution, the interconnection of all types of waters and the ability to transfer one type of water to another, in the unity of their functions in nature (substance and energy exchange).

The world's water reserves on Earth are colossal. The total volume of the hydrosphere according to the latest data (table 2.1) is about 1390 million km 3. If all the waters of the hydrosphere are evenly distributed over the surface of the Earth, its layer will have a thickness of about 2.5 km.

It is assumed that this amount of water remains practically unchanged during geological time, despite the continuing

Table 2.1 - World water reserves

Parts of the hydrosphere	Distribution area, million km 2	Volume of water, thousand km 3	Water layer, m	Share in world reserves, %
From the total water supply	From fresh water
World Ocean	361,26	1340,74		96,49	–
Groundwater (gravitational and capillary)	134,73	23,40		1,68	–
Mostly fresh groundwater	134,73	10,53		0,76	29,39
soil moisture	82,00	0,02	0,24	0,001	0,06
Glaciers and permanent snow cover Including:	16,23	24,87		1,79	69,41
In Antarctica	13,98	22,41		1,61	62,55
In Greenland	1,80	2,34		0,17	6,53
On the arctic islands(Canadian Arctic Archipelago, new earth, Northern land, Franz Josef Land, Svalbard, small islands)	0,23	0,08		0,006	0,22
AT mountainous areas outside the Arctic and Antarctic	0,22	0,04		0,003	0,11
Ground ice in the permafrost zone	21,00	0,30		0,022	0,84
Water reserves in lakes Including:	2,06	0,18		0,013	–
In fresh	1,24	0,09		0,0065	0,25
in salty	0,82	0,09		0,0065	–
swamp waters	2,68	0,01	3,73	0,0007	0,03
Waters in riverbeds	148,84	0,002	0,013	0,0001	0,006
biological water(water contained in living organisms and plants)	510,10	0,001	0,002	0,0001	0,003
Water in the atmosphere	510,10	0,01	0,02	0,0007	0,03
Total water supply	510,10	1389,53			–
fresh water	148,84	35,83		2,58

Note. The calculation of groundwater reserves was carried out according to separate continents excluding groundwater reserves in Antarctica, tentatively estimated at 2 million km 3, including mostly fresh water - about 1 million. km 3.

Figure 2.1 - Water resources of the Earth (· 10 6 km 3), according to

the inflow of water from the mantle and from the Cosmos (ice nuclei of comets, meteoric matter, dust...) and its loss due to the decomposition of water by photosynthesis and the dissipation of light gases in the Cosmos. However, the ratio of its individual species listed in Table 2.1 cannot be considered constant and absolutely accurate. It changed in different periods of the life of the Earth. The data available in the literature on the ratio of parts of the hydrosphere are somewhat different (Figure 2.1).

In the modern era, the main water reserves are concentrated in the World Ocean (96.5%). Fresh water in the hydrosphere is only 2.58% of the total water reserves. Most fresh water is contained in the glaciers and snow cover of Antarctica, the Arctic and mountainous countries (1.78% of the volume of the hydrosphere or 69.3% of the fresh water reserves on Earth). If all the ice is evenly distributed over the surface the globe, he will cover it with a layer of 53 m, and if these masses of ice are melted, then the level of ice is evenly distributed over the surface of the globe, he will cover it with a layer of 53 m, and if these masses of ice are melted, then the ocean level will rise by 64 m. Glaciers occupy special place in the water cycle on Earth, because they retain moisture in a solid state for many years. On average, a snowflake that falls on a glacier rests there for more than 8,000 years before it turns back into water and falls into active circulation water.

Huge reserves of water are accumulated in the lithosphere. The share of fresh groundwater in the total supply of fresh water on Earth is 29.4%. Rivers account for 0.006%, fresh lakes - 0.25%, water contained in the atmosphere - 0.03% total fresh water. The share of fresh water suitable for water supply accounts for 4.2 million km 3, or only 0.3% of the volume of the hydrosphere.

An interesting fact is that the largest storage of surface fresh water is Lake Baikal, which contains 1/5 of the world's total surface fresh water reserves. This can be supported by another example. If we assume that the water reserves will be withdrawn from the lake, then the filling of the vacated volume of the lake with all the flowing rivers would occur only in 250-300 years, provided that the water from the lake would not be spent on runoff and evaporation.

The most important properties of water

Water - one of the most amazing compounds on Earth - has long amazed researchers with the unusualness of many of its physical properties:

1) Inexhaustibility as a substance and natural resource; if all other resources of the earth are destroyed or dissipated, then water, as it were, escapes from this, taking on various forms or states: in addition to liquid, solid and gaseous. It is the only substance and resource of this type. This property ensures the omnipresence of water, it permeates the entire geographic envelope of the Earth and performs a variety of work in it.

2) The expansion inherent only to it during solidification (freezing) and a decrease in volume during melting (transition to a liquid state).

3) Maximum Density at a temperature of +4 °C and associated with this very important properties for natural and biological processes, for example, the exclusion of deep freezing of water bodies. Typically the maximum density physical bodies observed at the freezing point. The maximum density of distilled water is observed under abnormal conditions - at a temperature of 3.98-4 ° C (or rounded +4 ° C), i.e. at a temperature above the solidification (freezing) point. When the water temperature deviates from 4 °C in both directions, the density of water decreases.

4) When melting (melting), ice floats on the surface of water (unlike other liquids).

5) An anomalous change in the density of water entails the same anomalous change in the volume of water when heated: with an increase in temperature from 0 to 4 ° C, the volume of heated water decreases and only with a further increase begins to increase. If, with a decrease in temperature and during the transition from a liquid state to a solid state, the density and volume of water changed in the same way as it happens with the vast majority of substances, then when winter approaches, the surface layers of natural waters would cool to 0 ° C and sink to the bottom, freeing up space. warmer layers, and so it would continue until the entire mass of the reservoir would have acquired a temperature of 0 ° C. Further, the water would begin to freeze, the resulting ice floes would sink to the bottom, and the reservoir would freeze to its entire depth. At the same time, many forms of life in water would be impossible. But since water reaches its highest density at 4 °C, the movement of its layers caused by cooling ends when this temperature is reached. With a further decrease in temperature, the cooled layer, which has a lower density, remains on the surface, freezes and thereby protects the underlying layers from further cooling and freezing.

6) The transition of water from one state to another is accompanied by costs (evaporation, melting) or release (condensation, freezing) of the corresponding amount of heat. It takes 677 cal to melt 1 g of ice, and 80 cal less to evaporate 1 g of water. The high latent heat of ice melting ensures slow melting of snow and ice.

7) The ability to relatively easily pass into a gaseous state (evaporate) not only at positive, but also at negative temperatures. In the latter case, evaporation occurs bypassing liquid phase- from solid (ice, snow) immediately into vapor. This phenomenon is called sublimation.

8) If we compare the boiling and freezing points of hydrides, formed by elements the sixth group of the periodic table (selenium H 2 Se, tellurium H 2 Te) and water (H 2 O), then, by analogy with them, the boiling point of water should be about 60 ° C, and the freezing point should be below 100 ° C. But here too anomalous properties of water appear - at a normal pressure of 1 atm. Water boils at +100°C and freezes at 0°C.

9) Of great importance in the life of nature is the fact that water has an anomalously high heat capacity, 3,000 times greater than air. This means that when 1 m 3 of water is cooled by 1 0 C, 3000 m 3 of air is heated by the same amount. Therefore, by accumulating heat, the Ocean has a softening effect on the climate of coastal areas.

10) Water absorbs heat during evaporation and melting, releasing it during condensation from steam and freezing.

11) Water's ability to dispersed media, for example, in finely porous soils or biological structures, go into a bound or dispersed state. In these cases, the properties of water (its mobility, density, freezing point, surface tension, and other parameters), which are extremely important for the processes in natural and biological systems, change very much.

12) Water is a universal solvent, therefore, not only in nature, but also under laboratory conditions, there is no ideally pure water for the reason that it is capable of dissolving any vessel in which it is enclosed. There is an assumption that the surface tension of ideally pure water would be such that it would be possible to skate on it. The ability of water to dissolve ensures the transfer of substances into geographical envelope, underlies the exchange of substances between organisms and the environment, at the heart of nutrition.

13) Of all liquids (except mercury), water has the highest surface pressure and surface tension: \u003d 75 10 -7 J / cm 2 (glycerin - 65, ammonia - 42, and all the rest - below 30 10 -7 J / cm 2). Because of this, a drop of water tends to take the form of a ball, and when it comes into contact with solids, it wets the surface of most of them. That is why it can rise up the capillaries of rocks and plants, providing soil formation and plant nutrition.

14) Water has a high thermal stability. Water vapor begins to decompose into hydrogen and oxygen only at temperatures above 1000 °C.

15) Chemically pure water is a very poor conductor of electricity. Due to the low compressibility, sound and ultrasonic waves propagate well in water.

16) The properties of water change greatly under the influence of pressure and temperature. So, with an increase in pressure, the boiling point of water rises, and the freezing point, on the contrary, decreases. With an increase in temperature, the surface tension, density and viscosity of water decrease and the electrical conductivity and speed of sound in water increase.

The anomalous properties of water taken together, indicating its extremely high resistance to exposure external factors, are caused by the presence of additional forces between molecules, called hydrogen bonds. The essence of a hydrogen bond is that a hydrogen ion bound to some ion of another element is able to electrostatically attract an ion of the same element from another molecule. The water molecule has an angular structure: its constituent nuclei form isosceles triangle, at the base of which there are two protons, and at the top - the nucleus of the oxygen atom (Figure 2.2).

Figure 2.2 - The structure of the water molecule

Of the 10 electrons (5 pairs) present in the molecule, one pair (internal electrons) is located near the oxygen nucleus, and of the remaining 4 pairs of electrons (external), one pair is socialized between each of the protons and the oxygen nucleus, while 2 pairs remain undefined and are directed to the opposite vertices of the tetrahedron from the protons. Thus, in a water molecule there are 4 poles of charges located at the vertices of the tetrahedron: 2 negative, created by an excess of electron density at the locations of lone pairs of electrons, and 2 positive, created by its deficiency at the locations of protons.

As a result, the water molecule turns out to be an electric dipole. The positive pole of one water molecule attracts the negative pole of another water molecule. The result is aggregates (or associations of molecules) of two, three or more molecules (Figure 2.3).

Figure 2.3 - Formation of associated molecules by water dipoles:

1 - monohydrol H 2 O; 2 - dihydrol (H 2 O) 2; 3 - trihydrol (H 2 O) 3

Therefore, single, double and triple molecules are simultaneously present in water. Their content varies with temperature. Ice contains mainly trihydrols, the volume of which is greater than monohydrols and dihydrols. With an increase in temperature, the speed of movement of molecules increases, the forces of attraction between molecules weaken, and in the liquid state, water is a mixture of tri-, di- and monohydrols. With a further increase in temperature, trihydrol and dihydrol molecules decompose; at a temperature of 100 ° C, water consists of monohydrols (steam).

The existence of the undivided electron pairs determines the possibility of the formation of two hydrogen bonds. Two more bonds arise due to two hydrogen atoms. As a result, each water molecule is able to form four hydrogen bonds (Figure 2.4).

Figure 2.4 - Hydrogen bonds in water molecules:

– hydrogen bond designation

Due to the presence of hydrogen bonds in water, a high degree of order is noted in the arrangement of its molecules, which brings it closer to a solid body, and numerous voids appear in the structure, making it very loose. The structure of ice belongs to the least dense structures. There are voids in it, the dimensions of which somewhat exceed the dimensions of the H 2 O molecule. When ice melts, its structure is destroyed. But even in liquid water, hydrogen bonds between molecules are preserved: associates appear - the embryos of crystalline formations. In this sense, water is, as it were, in an intermediate position between the crystalline and liquid states and is more similar to a solid than to ideal fluid. However, unlike ice, each associate exists for a very long time. a short time: constantly there is a destruction of some and the formation of other aggregates. In the voids of such "ice" aggregates, single water molecules can be placed, while the packing of water molecules becomes denser. That is why when ice melts, the volume occupied by water decreases, its density increases. At + 4 °C, water has the densest packing.

When water is heated, part of the heat is spent on breaking hydrogen bonds. This explains the high heat capacity of water. Hydrogen bonds between water molecules are completely destroyed when water passes into steam.

The complexity of the structure of water is due not only to the properties of its molecule, but also to the fact that, due to the existence of oxygen and hydrogen isotopes, water contains molecules with different molecular weights (from 18 to 22). The most common is the "regular" molecule with a molecular weight of 18. The content of molecules with a large molecular weight is small. Thus, "heavy water" (molecular weight 20) is less than 0.02% of all water reserves. It is not found in the atmosphere, in a ton river water it is not more than 150 g, sea -160-170 g. However, its presence gives "ordinary" water a greater density, affects its other properties.

Amazing Properties water allowed the emergence and development of life on Earth. Thanks to them, water can play an indispensable role in all processes occurring in the geographic envelope.

Introduction

In this paper, the topic "Hydrosphere and Earth's atmosphere" is considered.

The liquid shell of the Earth, which covers 70.8% of its surface, is called the hydrosphere. The oceans are the main reservoirs of water. They contain 97% of the world's water reserves. The currents in the oceans carry heat from the equatorial regions to the polar regions and thereby regulate the Earth's climate to a certain extent. So, the Gulf Stream, starting from the coast of Mexico and carrying warm waters to the coast of Svalbard, leads to the fact that the average temperature northwestern Europe well above the temperature of northeastern Canada.

According to modern concepts, the presence of large bodies of water on Earth played a decisive role in the emergence of life on our planet. Part of the water on Earth, with a total volume of about 24 million km 3, is in a solid state, in the form of ice and snow. Ice covers about 3% earth's surface. If this water were turned into a liquid state, then the level of the world ocean would rise by 62 meters. Every year, about 14% of the earth's surface is covered with snow. Snow and ice reflect from 45 to 95% of the energy of the sun's rays, which ultimately leads to a significant cooling of large areas of the Earth's surface. It has been calculated that if the whole Earth were covered with snow, then the average temperature on its surface would drop from the current +15 C to 88 C.

The average temperature of the Earth's surface is 40 C higher than the temperature that the Earth should have, illuminated by the sun's rays. This is again connected with water, more precisely, with water vapor. The fact is that Sun rays, reflected from the surface of the Earth, are absorbed by water vapor and reflected back to the Earth. This is called the greenhouse effect.

The air shell of the Earth, the atmosphere, has already been studied in sufficient detail. The density of the atmosphere near the Earth's surface is 1.22 10 -3 g/cm 3 . If we talk about the chemical composition of the atmosphere, then the main component here is nitrogen; its percentage by weight is 75.53%. Oxygen in the Earth's atmosphere is 23.14%, of other gases, the most representative is argon - 1.28%, carbon dioxide in the atmosphere is only 0.045%. This composition of the atmosphere is preserved up to an altitude of 100-150 km. On the high altitudes nitrogen and oxygen are in the atomic state. From a height of 800 km, helium predominates, and from 1600 km, hydrogen, which forms a hydrogen geocorona extending to a distance of several Earth radii.

The atmosphere protects everything living on Earth from the harmful effects of ultraviolet radiation from the Sun and cosmic rays - high-energy particles moving towards it from all sides at almost light speeds.

Let's take a closer look at the Earth's hydrosphere and atmosphere.

1. Hydrosphere

Hydrosphere(from hydro ... and sphere) - an intermittent water shell of the Earth, located between the atmosphere and the solid earth's crust (lithosphere) and representing a combination of oceans, seas and surface waters of land. In more broad sense The hydrosphere also includes groundwater, ice and snow in the Arctic and Antarctic, as well as atmospheric water and water contained in living organisms. The bulk of the water in the hydrosphere is concentrated in the seas and oceans, the second place in terms of the volume of water masses is occupied by groundwater, the third is the ice and snow of the Arctic and Antarctic regions. Surface waters of land, atmospheric and biologically bound waters make up fractions of a percent of the total volume of water in the hydrosphere (Fig. 1). Chemical composition hydrosphere approaches the average composition sea ​​water.

Surface waters, occupying a relatively small share in the total mass of the hydrosphere, nevertheless play an important role in the life of our planet, being the main source of water supply, irrigation and watering. The waters of the hydrosphere are in constant interaction with the atmosphere, the earth's crust and the biosphere. The interaction of these waters and mutual transitions from one type of water to another constitute a complex water cycle on the globe. The hydrosphere was the first place where life originated on Earth. Only at the beginning of the Paleozoic era began the gradual migration of animals and plant organisms on land.

Water types	Name	Volume, million km 3	Quantity in relation to the total volume of the hydrosphere,%
sea ​​waters
Ground (excluding soil) water	unpaved
Ice and snow (Arctic, Antarctica, Greenland, mountain ice regions)
Surface waters of land: lakes, reservoirs, rivers, swamps, soil waters
Atmospheric waters	atmospheric
	biological

Rice. 1. Types of waters of the hydrosphere

2. Atmosphere

Atmosphere Earth (from Greek atmos - steam and sphaira - ball) - gaseous shell, surrounding the earth. The atmosphere is considered to be that area around the Earth in which the gaseous medium rotates together with the Earth as a whole. The mass of the atmosphere is about 5.15-10 15 tons. The atmosphere provides the possibility of life on Earth and has big influence on different aspects of human life.

Origin and role of the atmosphere

The modern Earth's atmosphere is apparently of secondary origin and was formed from gases released by the solid shell of the Earth (the lithosphere) after the formation of the planet. During the geological history of the Earth, the atmosphere has undergone a significant evolution under the influence of a number of factors: dissipation (volatilization) atmospheric gases in space; release of gases from the lithosphere as a result of volcanic activity; dissociation (splitting) of molecules under the influence of solar ultraviolet radiation; chemical reactions between the components of the atmosphere and the rocks that make up the earth's crust; accretion (capture) of the interplanetary medium (for example, meteoric matter). The development of the atmosphere was closely connected with geological and geochemical processes, as well as with the activities of living organisms. Atmospheric gases, in turn, had a great influence on the evolution of the lithosphere. For example, a huge amount of carbon dioxide that entered the atmosphere from the lithosphere was then accumulated in carbonate rocks. Atmospheric oxygen and water coming from the atmosphere were the most important factors that affect the rocks. Throughout Earth's history, the atmosphere has played big role during the weathering process. This process involved atmospheric precipitation, which formed rivers that changed the earth's surface. No less important was the activity of the wind, which carried fine fractions of rocks over long distances. Significantly influenced the destruction of rocks temperature fluctuations and other atmospheric factors. Along with this, the atmosphere protects the Earth's surface from the destructive action of falling meteorites, most of which burns up when entering the dense layers of the atmosphere.

The activities of living organisms that strong influence on the development of the atmosphere itself in a very to a large extent depends on atmospheric conditions. The atmosphere traps most of the sun's ultraviolet radiation, which has a detrimental effect on many organisms. Atmospheric oxygen is used in the process of respiration by animals and plants, atmospheric carbon dioxide - in the process of plant nutrition. Climatic factors, in particular the thermal regime and the regime of moisture, affect the state of health and human activity. Particularly dependent on climatic conditions. Agriculture. In turn, human activity has an ever-increasing impact on the composition of the atmosphere and on the climate regime.

The structure of the atmosphere

Numerous observations show that the atmosphere has a clearly defined layered structure (Fig. 2). The main features of the layered structure of the atmosphere are determined primarily by the features of the vertical temperature distribution. In the lowest part of the atmosphere - the troposphere, where intense turbulent mixing is observed, the temperature decreases with increasing altitude, and the decrease in temperature along the vertical is on average 6 ° per 1 km. The height of the troposphere varies from 8-10 km in polar latitudes to 16-18 km near the equator. Due to the fact that air density decreases rapidly with height, about 80% of the total mass of the atmosphere is concentrated in the troposphere. Above the troposphere there is a transitional layer - the tropopause with a temperature of 190-220 K, above which the stratosphere begins. In the lower part of the stratosphere, the decrease in temperature with height stops, and the temperature remains approximately constant up to an altitude of 25 km - the so-called. isothermal region (lower stratosphere); higher temperature begins to increase - inversion region (upper stratosphere). The temperature reaches a maximum of ~270 K at the level of the stratopause located at an altitude of about 55 km. The layer of the atmosphere, located at altitudes from 55 to 80 km, where the temperature again decreases with height, is called the mesosphere. Above it is a transition layer - the mesopause, above which the thermosphere is located, where the temperature, increasing with height, reaches very large values(over 1000 K). Even higher (at altitudes of ~ 1000 km or more) is the exosphere, from where atmospheric gases are dispersed into world space due to dissipation and where there is a gradual transition from the atmosphere to interplanetary space. Usually, all layers of the atmosphere above the troposphere are called the upper, although sometimes the stratosphere or its lower part is also referred to the lower layers of the atmosphere.

All structural parameters of the atmosphere (temperature, pressure, density) have significant spatial and temporal variability (latitudinal, annual, seasonal, daily, etc.). Therefore, the data in Fig. 2 reflect only the average state of the atmosphere.

The layered structure of the atmosphere has many other diverse manifestations. The chemical composition of the atmosphere is heterogeneous in height. If at altitudes up to 90 km, where there is intense mixing of the atmosphere, the relative composition of the constant components of the atmosphere remains practically unchanged (the entire thickness of the atmosphere is called the homosphere), then above 90 km - in the heterosphere - under the influence of the dissociation of atmospheric gas molecules by the ultraviolet radiation of the Sun, strong change chemical composition of the atmosphere with height. Typical Features this part of the atmosphere - layers of ozone and the own glow of the atmosphere. A complex layered structure is characteristic of atmospheric aerosol - suspended in the atmosphere particulate matter terrestrial and cosmic origin. The most common aerosol layers are below the tropopause and at an altitude of about 20 km. Layered is the vertical distribution of electrons and ions in the atmosphere, which is expressed in the existence of D-, E- and F-layers of the ionosphere.

Composition of the atmosphere

Unlike the atmospheres of Jupiter, Saturn, which consist mainly of hydrogen and helium, and the atmospheres of Mars and Venus, the main component of which is carbon dioxide The earth's atmosphere is composed primarily of nitrogen and oxygen. The Earth's atmosphere also contains argon, carbon dioxide, neon and other constant to variable components. The relative volume concentration of permanent gases, as well as information on the average concentrations of a number of variable components (carbon dioxide, methane, nitrous oxide, and some others) related only to the lower layers of the atmosphere, are given in Table 1.

The most important variable constituent of the atmosphere is water vapour. The spatial and temporal variability of its concentration varies widely - at the earth's surface from 3% in the tropics to 2 10 -5% in Antarctica. The bulk of water vapor is concentrated in the troposphere, since its concentration decreases rapidly with height. The average content of water vapor in the vertical column of the atmosphere in temperate latitudes is about 1.6-1.7 cm of the "precipitated water layer" (the layer of condensed water vapor will have such a thickness). Data on the content of water vapor in the stratosphere are contradictory. It was assumed, for example, that in the altitude range from 20 to 30 km, the specific humidity strongly increases with height. However, subsequent measurements indicate a greater dryness of the stratosphere. Apparently, the specific humidity in the stratosphere depends little on height and amounts to 2–4 mg/kg.

Table 1. Chemical composition of dry atmospheric air near the earth's surface

The variability of water vapor content in the troposphere is determined by the interaction of evaporation, condensation, and horizontal transport. As a result of the condensation of water vapor, clouds form and atmospheric precipitation occurs in the form of rain, hail and snow. Processes of phase transitions of water proceed mainly in the troposphere. That is why clouds in the stratosphere (at altitudes of 20-30 km) and mesosphere (near the mesopause), called mother-of-pearl and silver, are observed relatively rarely, while tropospheric clouds usually cover about 50% of the entire earth's surface.

Ozone has an impact on atmospheric processes, especially on the thermal regime of the stratosphere. It is mainly concentrated in the stratosphere, where it causes the absorption of ultraviolet solar radiation, which is the main factor in heating the air in the stratosphere. Average monthly values general content ozone change depending on latitude and season within 0.23-0.52 cm (this is the thickness of the ozone layer at ground pressure and temperature). There is an increase in the ozone content from the equator to the pole and an annual variation with a minimum in autumn and a maximum in spring.

An essential variable component of the atmosphere is carbon dioxide, the variability of the content of which is associated with the vital activity of plants (photosynthesis processes), industrial pollution and solubility in sea water (gas exchange between the ocean and the atmosphere). Typically, changes in carbon dioxide content are small, but sometimes they can reach noticeable values. Recent decades there has been an increase in carbon dioxide content due to industrial pollution, which may have an impact on the climate due to the carbon dioxide created greenhouse effect. It is assumed that, on average, the concentration of carbon dioxide remains unchanged throughout the thickness of the homosphere. Above 100 km, its dissociation begins under the influence of ultraviolet solar radiation with wavelengths shorter than 1690 A.

One of the most optically active components - atmospheric aerosol - particles suspended in the air ranging in size from several nm to several tens of microns, formed during the condensation of water vapor and entering the atmosphere from the earth's surface as a result of industrial pollution, volcanic eruptions, as well as from space. Aerosol is observed both in the troposphere and in the upper atmosphere. The aerosol concentration decreases rapidly with height, but this trend is superimposed by numerous secondary maxima associated with the existence of aerosol layers.

Conclusion

hydrosphere atmosphere earth shell

Each of us from the course of natural history and geography knows that we live at the bottom air ocean- atmosphere.

Most upper shells Earth - hydrosphere and atmosphere - differ markedly from other shells that form the solid body of the planet. By mass, this is a very small part of the globe, no more than 0.025% of its total mass. But the significance of these shells in the life of the planet is enormous. The hydrosphere and atmosphere arose at an early stage in the formation of the planet. The hydrosphere and atmosphere are the main shells of the biosphere.

The biosphere occupies a special place among the community of the Earth's shells. It captures the upper layer of the lithosphere, almost the entire hydrosphere and the lower layers of the atmosphere. The biosphere was understood as the totality of the living matter inhabiting the surface of the planet, together with the habitat. The significance of this system goes beyond the purely earthly world, it represents a link of the cosmic scale.

The atmosphere of the Earth is fundamentally different from the atmospheres of other planets: it has a low content of carbon dioxide, a high content of molecular oxygen and a relatively high content of water vapor. There are two reasons why the Earth's atmosphere is distinguished: the water of the oceans and seas absorbs carbon dioxide well, and the biosphere saturates the atmosphere with molecular oxygen formed in the process of plant photosynthesis. Calculations show that if we release all the carbon dioxide absorbed and bound in the oceans, simultaneously removing from the atmosphere all the oxygen accumulated as a result of the vital activity of plants, then the composition of the earth's atmosphere in its main features would become similar to the composition of the atmospheres of Venus and Mars.

The atmosphere is made up of several layers. The bottom layer is the troposphere. Over different latitudes of the earth, its thickness is different. Above the troposphere is the tropopause with a constant low temperature. Above it is the stratosphere up to a height of 50 kilometers. Mesosphere 55-80 kilometers. Thermosphere 80-1000 kilometers. Exosphere 1000-2000 kilometers. Traces of gases were found at an altitude of 20,000 kilometers. Above 600 kilometers, helium predominates, and above 1600 kilometers, hydrogen.

In the Earth's atmosphere, saturated water vapor creates a cloud layer covering a significant part of the planet. The clouds of the earth enter essential element in the water cycle occurring on our planet in the hydrosphere - atmosphere - land system.

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Hydrosphere

Water is almost ubiquitous on Earth. It forms its own shell. Which is called the hydrosphere. This shell penetrates into all other spheres of the Earth, since it, like water, is "everywhere". Here a broad interpretation of the hydrosphere is given, which includes all types of natural waters. The hydrosphere covers the waters of the oceans surface water, atmospheric waters, ground and underground ice, all types of water of the earth's interior and biogenic waters, that is, it is possible to distinguish aboveground, ground and underground hydrosphere.

The subject of study of hydrogeology is underground hydrosphere is the most complex water earthly shell. Its complexity is explained by several circumstances: 1) a very thin layer of the underground hydrosphere accessible for study (up to 5-12 km); 2) the presence in the underground hydrosphere, in addition to the liquid, solid and vapor phases, of several specific types of water (physically bound, chemically bound, etc.); 3) specific and diverse conditions and processes of interaction of water with the water-containing medium (rocks, gases, living organisms). With all this, it should be remembered that the underground hydrosphere is primary in relation to the terrestrial and aboveground water shells. First, underground waters were formed, which, in the process of the evolution of the Earth, passed into the ground and above-ground state. Gradually, the nature of water exchange between the shells acquired a modern look.

The separation of the Earth's shells occurred about 4 billion years ago. According to the hypothesis of American scientists, 4.25 billion years ago, the Earth collided with space object the size of Mars. From the collision, the surface layer of the Earth 1000 km thick melted, the Earth received an impulse and spun around its axis with an ecliptic of 23 0, which stabilized earth day(24 hours). 90% substance cosmic body was absorbed by the Earth, and 10% formed a “ring” similar to Saturn, which then gathered and formed the Moon. At first, it was 15 times closer to Earth. All this led to the separation of the shells of the Earth. Due to the heating of the mantle substance, according to Academician A.P. Vinogradov, it was divided into two phases: refractory (dunites) and fusible (basalts).

During this process, the most volatile components of basaltic magma, water vapor and gases, rushed to the Earth's surface. The mechanism of this grandiose process of melting and degassing of the mantle A.P. Vinogradov was reproduced experimentally (zone melting). The mantle contains approximately 20·10 8 tons of water, and 7.5 - 24% of this amount migrated to the earth's crust and the World Ocean, i.e. participated in the creation of the hydrosphere. 1·10 4 tons could come from space with meteorites, i.е. 4 orders of magnitude smaller. The upper layers of the atmosphere could provide even less water ( noctilucent clouds discovered by Vernadsky).

Thus, the mantle is the only source of water on Earth.

1. Evolution of the hydrosphere began at the turn of the Archean - Proterozoic, when a dynamic balance was established between water and gases. At the same time, a granite layer formed, geosynclines and platforms separated, and continental seas arose. All this marked the beginning of the atmosphere and the regular hydrological cycle of water.

According to A.P. Vinogradov, volatile substances became a source of anions of the salt mass of ocean water, and all the main cations were formed during the destruction of rocks.

At an early stage, there was almost no oxygen in the atmosphere, but there were CO 2, NH 3, NH 4, H 2 S, Hcl, etc.

2. Approximately 2.0 - 2.7 billion years ago there was a change in reducing conditions in the atmosphere and on the surface to oxidizing ones, and the source of O 2 was photochemical reactions with H 2 O and CO 2 in the upper layers of the atmosphere.

3. The emergence of life. In connection with intense cosmic and ultraviolet radiation, complex organic compounds from CH 4, NH 3, H 2, H 2 S, CO 2, H 2 O, etc., and on their basis, at a certain depth in the ocean (under the screen of the water layer), the simplest organisms developed, but they did not exist on land ( since the ozone screen did not yet exist. Its formation caused the first deep biological revolution, since the reduction of H 2 O in the process of life led to the release of free oxygen, which was the beginning of the formation of the modern oxygen-nitrogen atmosphere and the ozone screen, and life could develop on land As a result of the formation of the atmosphere, the radiogenic and photogenic synthesis of complex organic molecules ceased.

4. In the early Paleozoic, aНСО 3 – СОˉ 3 equilibrium, which ensured the stability of the composition of ocean waters. With the advent of life on Earth, the processes of weathering changed in the direction of intensification under the influence of CO 2 . As a result of photosynthesis, oxygen in the atmosphere is currently renewed in 2–3 thousand years, and carbon dioxide in 350–500 years (excluding the modern greenhouse effect), and all the water of the World Ocean passes through photosynthetic plants in several million years.

5. Formation of fresh water on Earth.

The main factors in the appearance of fresh water on Earth are the emergence of life, the formation modern atmosphere, dismemberment of the earth's crust into platforms and geosynclines. All this has an age of 2.5 - 3.0 billion years. It was the emergence of a large hydrological water cycle that led to the formation fresh groundwater from atmospheric precipitation.

Concerning the composition of the waters of the World Ocean, there are ambiguous opinions. Some believe that it was formed in the early Paleozoic. Others are in favor of significant changes in composition even over the last 0.5-0.6 billion years. For example, Yu.P. Kazansky established 5 hydrogeological types ocean waters during the evolution of the hydrosphere from the Archean to the Cenozoic, and the modern sulfate-chloride sodium-calcium composition appeared, according to his data, in Perm. Along with water exchange between the oceans and underground hydrosphere happened and is happening salt exchange. The composition of the World Ocean reflects the conditions of previous eras, and due to the huge water masses, it reacts poorly to outside influences. The isotopic ratio of H 2 /H 1 and O 18 / O 16 does not change over 300 - 500 million years. This consistency is used as the Standard middle ocean water (SMOW) standard.

We will have to start the story about the origin of the Earth and the solar system from afar. In 1687, I. Newton deduced law gravity : every body in the universe attracts the rest with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Theoretically, the law of universal gravitation makes it possible to calculate the movements of any body in the Universe under the influence of the gravitation of other bodies. But - alas! - theoretically only: the equations needed to describe the motion of everything three isolated bodies under the influence of each other's attraction are so complex that their solution could not be obtained for almost three centuries, until the 60s of the XX century. It is clear that about complete solution for such a system of bodies as the solar system, there is no need to speak. As for the approximate calculations that many eminent mathematicians and astronomers (J. Lagrange, P. Laplace and others) were engaged in, they show that perturbations in the orbits of the planets are of a periodic nature: the parameters of the orbit change in one direction, then in the opposite direction, and so to infinity. There seems to be nothing in the structure of the solar system itself, determined by gravity, that would prevent it from existing forever; No wonder Newton himself asked about origin The solar system did not set at all.

Let's think, however: if gravity alone were the cause of the motion of the planets, then what would happen to them? That's right, they would "fall" into the Sun. But the planets safely move along their orbits perpendicular to the force of gravity acting on them and at the same time still rotate around their own axis. This movement could not arise - and did not arise! under the influence of the sun's gravity. Where did it come from? The fact is that every rotating body has a certain quality, which is called angular momentum(MKD). The magnitude of the MKD depends on three parameters: the mass of the body, its circular velocity, and the distance to the center of rotation. To XVIII century it was found that the MKD does not arise from nothing and does not disappear without a trace, but can only be transmitted from body to body. This is law of conservation of angular momentum, which belongs to a number of conservation laws (such as the laws of conservation of matter, energy, etc.). And if so, then any theory of the origin of the Universe (or the Solar System) should at least not contradict it.

So, all the bodies that make up the solar system have their own MCD. It is impossible to create an MKD - where did it come from? Consider the following way out of this impasse. MKD can differ depending on the direction of rotation: on and against clockwise - positive and negative MCD. If the body (or system of bodies) is informed of two MCDs ( equal size, but of different signs), then both moments cancel each other out, and a system devoid of MCD appears. But in this case, the opposite is also true: a system that initially did not have an MQD can be divided into two: one with a positive, the other with an equal negative MQD. Thus, the MKD seems to appear and disappear without violating the conservation law. Proceeding from this, it can be assumed that the Universe at first did not have an MCD, but then some of its parts received positive moment, and others - at the same time - negative.

So, if you look at the solar system "from above" - ​​from a certain point above north pole Earth (and, accordingly, above the plane of its orbit), it turns out that the Earth, the Sun and most other bodies rotate around their axis counterclockwise; planets around the sun and satellites around the planets - too. This means that the positive and negative MCDs of all the bodies that make up the Solar System are by no means balanced with each other; the total MCD of this system is very large, and it is necessary to elucidate its origin.

In 1796, P. Laplace formulated nebular theory, according to which the sequence of events during the formation of the solar system is as follows. There is a primary gas and dust cloud (nebula - in Latin "nebula"), which arose as a result of the concentration of scattered interstellar matter under the influence of the mutual attraction of its particles (in accordance with the law of universal gravitation). The nebula is not a perfect ball, and its edges - just according to the theory of probability - are at an unequal distance from the nearest nebula (or star), and therefore are attracted by that one with an unequal force (which, as we remember, is inversely proportional to the square of the distance). This disequilibrium is enough for our nebula to receive a primary push, which will give it rotary motion, albeit extremely weak.

As soon as the nebula begins to rotate around its axis, gravity arises in it (as in a spaceship, which is specially “spun” to counteract weightlessness). Under the influence of gravity, the nebula should begin to shrink, i.e. its radius decreases. And we remember that the MCD (which is a constant value) depends on three parameters: masses body, radius and speed its rotation; mass is also a constant value, therefore, a decrease in radius can only be compensated by an increase in rotation speed. As a result, a huge ball of gas will rotate faster and faster, working like a centrifuge: under the action of centrifugal force, its equator swells, giving the ball the shape of an increasingly flattened ellipsoid. There comes a time when ever-increasing centrifugal force at the equator, it balances the force of attraction and a ring begins to peel off from it (the equator), and then, as the nebula further contracts, again and again. The substance of these rotating rings begins to condense into planets under the influence of the mutual attraction of its particles, from which, in turn, their satellites are torn off.

Laplace's theory, according to which the Earth was initially cold, remained popular for almost a century, although some astronomical data contradicted it (for example, the rotation of Venus and Uranus in the opposite direction to all other planets and the Sun). However, closer to late XIX century, when it was firmly established that the temperature in the bowels of our planet is extremely high (according to modern data, over 1000 ° C), most scientists began to share the opinion about initially hot Earth - a fireball, gradually cooling from the surface. The search for the source of this hot substance was quite natural to begin with the Sun. At the beginning of the twentieth century, astronomers T. Chamberlain and F. Multon put forward, and J. Jeans mathematically substantiated planetesimal theory origin of the planets in the solar system. Its essence lies in the fact that once another star passed close to the Sun ("nearby" - this is on a cosmic scale). At the same time, mutual attraction pulled out of each of them a giant prominence of stellar matter, which, having united, made up an “interstellar bridge”, which then broke up into separate “drops” - planetesimals. The cooling planetesimals gave rise to the planets and their satellites.

However, the second half of the 20th century was the time to return to the concept of the original cold earth. First, there were serious, purely astronomical, objections to the planetesimal theory. G. Ressel, for example, drew attention to the simple circumstance that if a ribbon of stellar matter is stretched between the Sun and a passing star, then its middle part (where the attraction of the two luminaries is mutually balanced) will have to remain in complete immobility. And vice versa, it turned out that some of Laplace's positions that turned out to be erroneous could well be corrected in the framework of the further development of the nebular theory. As an example, we can cite the hypothesis of O. Yu. Schmidt (in which the gas-dust cloud is captured by the Sun that already exists at that time) or the now more popular model of K. von Weizsäcker (in which the rotating nebula is no longer a homogeneous ball, as in Laplace , but a system of multi-velocity vortices, somewhat reminiscent of a ball bearing). It is also believed that gas and dust in a rotating gas-dust nebula behave differently: dust collects in a flat equatorial disk, and gas forms an almost spherical cloud, thickening towards the center of the nebula. Subsequently, the dust of the equatorial disk sticks together into planets, and the gas under its own weight heats up so that it “flares” in the form of the Sun.

Another thing turned out to be more essential for the victory of the "cold" concept: a convincing and at the same time quite simple answer to the question was found - where does the heat come from, which warmed up the bowels of the initially cold Earth to such high temperatures? These sources of heat, as is now believed, are two: the decay energy radioactive elements and gravitational differentiation of subsoil. With radioactivity, everything is quite clear, and the source is secondary - according to modern estimates, it accounts for no more than 15% of the heating energy. The idea of ​​gravitational differentiation of the bowels (its detailed development is associated with the name of O. G. Sorokhtin) is as follows.

Knowing the mass and volume of the Earth (they were calculated back in the 18th century), it is easy to determine averaged density terrestrial matter- 5.5 g/cm 3 . Meanwhile, the density of rocks available to us for direct study half as much: average density the substance of the earth's crust is 2.8 g / cm 3. From this it is clear that the substance deep bowels The earth should have a density much higher than average.

It is known that almost 9/10 of the mass of the Earth falls on the share of only four chemical elements - oxygen (which is part of the oxides), silicon, aluminum and iron. Therefore, it can be stated with sufficient certainty that the "lighter" outer layers of the planet consist mainly of silicon compounds (aluminosilicates), and the "heavy" inner layers consist of iron.

At the time of the formation of the Earth ("hot" or "cold" way - for us now it does not matter), "heavy" and "light" elements and their compounds could not but be completely mixed. However, their gravitational differentiation begins further: under the influence of gravity, "heavy" compounds (iron) "sink" - sink to the center of the planet, and "light" (silicon) - "float" to its surface. Let's now consider this process in a mentally carved vertical column of terrestrial matter, the base of which is the center of the planet, and the top is its surface. "Sinking" iron constantly shifts the center of gravity of this pillar to its base. Wherein potential energy column (proportional to the product of the mass of the body and the height of its rise, which in our case is the distance between the center of the Earth and the center of gravity of the column) is constantly decreasing. The total energy of the Earth, in accordance with the laws of conservation, is unchanged; therefore, the potential energy lost in the process of gravitational differentiation can only be converted into the kinetic energy of molecules, i.e. be released as heat.

Calculations of geophysicists show that this energy is a monstrous amount of 4·10 30 cal (which is equivalent to a trillion total nuclear ammunition of all countries of the world). This is quite enough to - even without resorting to the energy of radioactive decay - to heat up the bowels of the initially cold Earth to a molten state. However, when calculating the heat balance of the Earth throughout its history, geophysicists came to the conclusion that the temperature of its interior could only reach 1600°C in some places, mostly around 1200°C; which means that our planet, contrary to previous ideas, never fully melted. Of course, the planet is constantly losing thermal energy as it cools off the surface, but this loss is largely (if not completely) offset by solar radiation.

So, the Earth throughout its history is a solid body (moreover, in the depths, with high pressures - very rigid body), which, however, paradoxically behaves under very large constant loads as extremely viscous liquid. The very shape of the planet - an ellipsoid with a slightly protruding North Pole and a slightly depressed South Pole - ideally corresponds to the one that should take the liquid in a state of equilibrium. In the thickness of this “liquid”, extremely slow, but unthinkably powerful movements of colossal masses of matter constantly occur, which are associated with volcanism, mountain building, horizontal displacements of continents, etc. We will discuss their regularities in the next chapter. Here it is important to remember that the source of energy for all these processes is ultimately the same gravitational differentiation of matter in the bowels of the planet. Accordingly, when this process is completed completely, our planet will become geologically inactive, "dead" - like the Moon. According to the calculations of geophysicists, by now, 85% of the iron present on Earth has sunk into its core, and it will take another 1.5 billion years to “settle” the remaining 15%.

As a result of gravitational differentiation, the bowels of the planet are divided (like milk in a separator) into three main layers: "heavy", "intermediate" and "light". The inner "heavy" layer (with a substance density of about 8 g / cm 3) - central core, consisting of compounds of iron and other metals; of the 6400 km that make up the radius of the planet, the core accounts for 2900 km. The surface "light" layer (the density of its substance is about 2.5 g / cm 3) is called bark. The average thickness of the crust is only 33 km; it is separated from the underlying layers Mohorovicic surface, upon passing through which the propagation velocity increases abruptly elastic waves. Between the cortex and the nucleus is an "intermediate" layer - mantle; its rocks have a density of about 3.5 g/cm 3 and are in a partially molten state. Upper mantle separated from lower mantle lying 60–250 km from the surface by a molten layer of basalts - asthenosphere; the upper mantle, together with the crust, forms hard shell planets - lithosphere(Fig. 4). In the asthenosphere there are magma chambers that feed volcanoes, the activity of which the Earth owes to its mobile shell - hydrosphere and atmosphere.

Rice. 4. The structure of the bowels of the planet (with a schematic volcano)

According to modern concepts, the atmosphere and hydrosphere arose as a result of the degassing of magma, melted out during volcanic processes from the upper mantle and creating the earth's crust. The atmosphere and hydrosphere consist of light volatile substances (compounds of hydrogen, carbon and nitrogen), the content of which on Earth as a whole is very small - about a million times less than in space. The reason for this deficit is that these volatile substances were “washed out” from the protoplanetary cloud. solar wind(i.e. solar plasma flows) and light pressure. At the time of the formation of the Earth from a protoplanetary cloud, all elements of its future atmosphere and hydrosphere were in a bound form, in the composition of solid substances: water - in hydroxides, nitrogen - in nitrides (and, possibly, nitrates), oxygen - in metal oxides, carbon - in graphite, carbides and carbonates.

Modern volcanic gases are approximately 75% water vapor and 15% carbon dioxide, and the remainder is methane, ammonia, sulfur compounds (H 2 S and SO 2) and "sour fumes" (HCl, HF, HBr, HI), as well as inert gases; free oxygen is completely absent. The study of the content of gas bubbles in the oldest (Katarhean) quartzites of the Aldan shield showed that qualitative composition these gases is fully consistent with what is listed above. Since this primary atmosphere was still very thin, the temperature on the Earth's surface was radiative equilibrium temperature, resulting from the alignment of the solar heat flux absorbed by the surface with the heat flux radiated by it; for a planet with the parameters of the Earth, the temperature of radiative equilibrium is approximately 15°C.

As a result, almost all water vapor from the composition of volcanic gases should have condensed, forming the hydrosphere. In that primary ocean passed, dissolving in water, and other components of volcanic gases - most of the carbon dioxide, "acid smoke", sulfur oxides and part of the ammonia. As a result, the primary atmosphere (containing - in equilibrium with the ocean - water vapor, CO 2 , CO, CH 4 , NH 3 , H 2 S, inert gases and is restorative) remained thin and the temperature on the planet's surface did not deviate in any noticeable way from the point of radiative equilibrium, remaining within the limits of the existence of liquid water. This predetermined one of the main differences of the Earth from other planets of the solar system - the constant presence of a hydrosphere on it.

How did the volume of the hydrosphere change throughout its history? In molten basalt (in the asthenosphere) at a temperature of 1000°C and a pressure of 5–10 thousand atmospheres, up to 7–8% H 2 O is dissolved: this is exactly how much water, as established by volcanologists, is degassed during the outpouring of lavas. Most of this water (thus of mantle origin) replenished the hydrosphere, but part of it was absorbed back into the rocks. oceanic crust(this process is called serpentinization). The calculations of geophysicists show that in the Katarchean and Archean there was little water in the ocean basins and it did not yet cover mid-ocean ridges. Water did not enter the oceanic crust from the oceans, but from below - directly from the mantle. At the beginning of the Proterozoic, the level of the oceans reached the peaks of the mid-ocean ridges, but throughout the entire Early Proterozoic, almost the entire volume of water entering the oceans was absorbed by the rocks of the oceanic crust. By the beginning of the Middle Proterozoic, the processes of serpentinization ended and the oceanic crust acquired its modern composition. Since that time, the volume of the oceans began to increase again. This will continue (with a gradual slowdown) until volcanic processes stop on Earth.

If you ask a person: “Why is the sea salty?”, He will almost certainly answer: “Because of the same reason why drainless lakes are salty (like Lake Elton, which supplies us with table salt): the rivers flowing into the sea carry a certain amount of salt, then the water evaporates, and the salt remains." This answer is incorrect: the salinity of the ocean is of a completely different nature than the salinity of the inland end waters of runoff. The fact is that the water of the primary ocean had various impurities. One source of these impurities was water-soluble atmospheric gases, the other was rocks, from which, as a result of erosion (both on land and on the seabed), various substances. "Acid smokes", dissolving in water, gave halogen acids, which immediately reacted with silicates (the main component of rocks) and extracted from them an equivalent amount of metals (primarily alkaline and alkaline earth metals - Na, Mg, Ca, Sr, K, Li ). At the same time, firstly, the water became practically neutral from acidic, and secondly, the salts of the elements extracted from the silicates passed into solution; thus, ocean water was salty from the beginning. The concentration of cations in sea water coincides with the abundance of these metals in the rocks of the earth's crust, but the content of the main anions (Cl–, Br–, SO 4 –, HCO 3 –) in sea water is much higher than their amount that can be extracted from mountain breeds. Therefore, geochemists believe that all anions of sea water arose from the products of degassing of the mantle, and all cations - from destroyed rocks.

The main factor determining the acidity of sea water is the content of carbon dioxide in it (CO 2 is water-soluble, now 140 trillion tons are dissolved in the oceans - against 2.6 trillion tons contained in the atmosphere). In the oceans, there is a dynamic balance between insoluble calcium carbonate CaCO 3 and soluble bicarbonate Ca (HCO 3) 2: with a lack of CO 2, the “extra” bicarbonate turns into carbonate and precipitates, and with an excess of CO 2, carbonate turns into bicarbonate and goes into solution . Carbonate-bicarbonate buffer originated in the ocean initial stage its existence, and since then it has maintained the acidity of ocean water at a stable level.

As for the atmosphere, its composition began to change in the Proterozoic, when photosynthetic organisms began to produce (as a by-product of their vital activity) free oxygen; It is now considered firmly established that all free oxygen on the planet is of biogenic origin. Oxygen, unlike carbon dioxide, is poorly soluble in water (the ratio between atmospheric and dissolved CO 2, as we have seen, is 1:60, and for O 2 it is 130:1), and therefore almost all of the increase in oxygen is in atmosphere. There it oxidizes CO and CH 4 to CO 2 , H 2 S to S and SO 2 , and NH 3 to N 2 ; native sulfur naturally falls to the surface, carbon dioxide and sulfur dioxide dissolve in the ocean, and as a result, only chemically inert nitrogen (78%) and oxygen (21%) remain in the atmosphere. Atmosphere from reducing becomes modern, oxidizing; however, we will discuss the history of oxygen on Earth in more detail later, where we will talk about the early evolution of living beings (Chapter 5).

In addition to oxygen and nitrogen, the atmosphere contains a small amount of so-called greenhouse gases- carbon dioxide, water vapor and methane. Although they make up an insignificant fraction of the atmosphere (less than 1%), they nevertheless have an important impact on the global climate. It's all about the special properties of these gases: being relatively transparent to short-wave radiation coming from the Sun, they are at the same time opaque to long-wave radiation emitted by the Earth into space. For this reason, variations in the amount of atmospheric CO 2 can cause significant changes in the planet's heat balance: with an increase in the concentration of this gas, the atmosphere in its properties approaches the glass roof of a greenhouse, which provides heating of greenhouse air by "capturing" radiant energy, - the greenhouse effect.

The Earth's crust, hydrosphere and atmosphere were formed mainly as a result of the release of substances from the upper mantle of the young Earth. Currently, the formation of oceanic crust occurs in the mid-ocean ridges and is accompanied by the release of gases and small amounts of water. The formation of the crust on the young Earth was caused by the same processes - due to them, a shell of rock was formed with a thickness of less than 0.0001% of the volume of the entire planet. The composition of this shell, which forms the continental and oceanic crust, evolved over time, primarily due to the sublimation of elements from the mantle as a result of partial melting at a depth of approximately 100 km. The average chemical composition of modern crust shows that oxygen is contained in it in most, combining in different forms with silicon, aluminum and other elements to form silicates.

Based on many data, it can be assumed that volatile elements were released from the mantle as a result of volcanic eruptions that accompanied the formation of the crust. Most likely, initially, the atmosphere consisted of carbon dioxide and nitrogen with some hydrogen and water vapor. Evolution towards a modern oxygen atmosphere did not occur until life began to evolve.

Formation of the hydrosphere

Water in its three states - liquid, ice and water vapor - is widespread on the surface of the Earth and occupies a volume of 1.4 billion km 3. Almost all of this water (> 97 %) is located in the oceans, and most of the rest forms ice polar caps and glaciers (about 2 %). Continental fresh waters represent less than 1 % total volume. The atmosphere contains relatively little water (0.001% in the form of vapors). In general, these reservoirs of water are called hydrosphere.

The sources of water during the formation of the hydrosphere are controversial. In any case, when the surface of the Earth has cooled down to T< 100°С, водяные пары, дегазирующиеся из мантии, сконденсировались.

The oceans were formed about 3.8 · 10 9 years ago, as evidenced by the age of the sedimentary rocks submerged in the ocean.

Very little water vapor penetrates into space from the atmosphere, because at an altitude of about 15 km, low temperatures cause it to condense and fall to lower levels. Very little water is currently being degassed from the mantle. Thus, after the main phase of degassing, the total volume of water on the earth's surface changed little over geological time.

The circulation between reservoirs of water in the hydrosphere is called hydrological cycle.

Although the volume of water vapor contained in the atmosphere is small (about 0.013 10 6 km3), water is constantly moving through this reservoir. It evaporates from the surface of the oceans (0.423 10 6 km 3 / year) and land (0.073 10 6 km 3 year) and is transported with air masses (0.037 10 6 km 3 / year). Despite the short residence time in the atmosphere (typically 10 days), the average water transport distance is about 1000 km. Water vapor then returns either to the oceans (0.386 10 6 km 3 /year) or to the continents (0.110 10 6 km 3 /year) in the form of snow or rain. Most of the rainfall that falls on the continents percolates through sediments and porous or fractured rocks, forming groundwater (9.5 10 6 km 3); the rest of the water flows over the surface in the form of rivers (0.13 10 6 km 3) or re-evaporates into the atmosphere.

The rapid transport of water in the atmosphere is determined by the incoming solar radiation. Almost all of the radiation reaching the crust goes into the evaporation of liquid water and the formation of atmospheric water vapor. Most of the remaining radiation is absorbed by the crust, and the efficiency of this process decreases with increasing latitude, mainly due to the spherical shape of the Earth.