Great geological cycle. Big encyclopedia of oil and gas

Large (geological) and small (biogeochemical) cycles of matter

All substances on our planet are in the process of circulation. Solar energy causes two cycles of matter on Earth:

Large (geological or abiotic);

Small (biotic, biogenic or biological).

The cycles of matter and the flows of cosmic energy create the stability of the biosphere. The cycle of solid matter and water, which occurs as a result of the action of abiotic factors (inanimate nature), is called the great geological cycle. With a large geological cycle (millions of years flow), rocks are destroyed, weathered, substances dissolve and enter the World Ocean; geotectonic changes are taking place, the sinking of the continents, the rise of the seabed. The water cycle time in glaciers is 8,000 years, in rivers - 11 days. It is the large circulation that supplies living organisms with nutrients and largely determines the conditions for their existence.

A large, geological cycle in the biosphere is characterized by two important points: oxygen carbon geological

• a) carried out throughout geological development Earth;
• b) is a modern planetary process that takes a leading part in further development biosphere.

At the present stage of human development, as a result of a large circulation, pollutants are also transported over long distances - oxides of sulfur and nitrogen, dust, radioactive impurities. The territories of temperate latitudes of the Northern Hemisphere were subjected to the greatest pollution.

A small, biogenic or biological circulation of substances occurs in solid, liquid and gaseous phases with the participation of living organisms. The biological cycle, in contrast to the geological cycle, requires less energy. A small cycle is part of a large one, occurs at the level of biogeocenoses (within ecosystems) and lies in the fact that soil nutrients, water, carbon accumulate in plant matter and are spent on building the body. The decay products of organic matter decompose to mineral components. The small cycle is not closed, which is associated with the entry of substances and energy into the ecosystem from the outside and with the release of some of them into the biospheric cycle.

Many chemical elements and their compounds are involved in large and small cycles, but the most important of them are those that determine the current stage of development of the biosphere, associated with human economic activity. These include the cycles of carbon, sulfur and nitrogen (their oxides are the main pollutants of the atmosphere), as well as phosphorus (phosphates are the main pollutant of continental waters). Almost all pollutants act as harmful, and they are classified as xenobiotics. Currently, the cycles of xenobiotics - toxic elements - mercury (a food contaminant) and lead (a component of gasoline) are of great importance. In addition, many substances of anthropogenic origin (DDT, pesticides, radionuclides, etc.) enter the small circulation from the large circulation, which cause harm to biota and human health.

The essence of the biological cycle is the flow of two opposite, but interrelated processes - the creation of organic matter and its destruction by living matter.

In contrast to the large cycle, the small one has a different duration: seasonal, annual, perennial and secular small cycles are distinguished. Circulation of chemicals from the inorganic environment through vegetation and animals back to the inorganic environment using solar energy chemical reactions called the biogeochemical cycle.

The present and future of our planet depends on the participation of living organisms in the functioning of the biosphere. In the circulation of substances, living matter, or biomass, performs biogeochemical functions: gas, concentration, redox and biochemical.

The biological cycle occurs with the participation of living organisms and consists in the reproduction of organic matter from inorganic and the decomposition of this organic to inorganic through the food trophic chain. The intensity of production and destruction processes in the biological cycle depends on the amount of heat and moisture. For example, the low rate of decomposition of organic matter in the polar regions depends on the deficit of heat.

An important indicator of the intensity of the biological cycle is the rate of circulation of chemical elements. The intensity is characterized by an index equal to the ratio of the mass of forest litter to the litter. The higher the index, the lower the intensity of the cycle.

Index in coniferous forests - 10 - 17; broad-leaved 3 - 4; savanna no more than 0.2; humid tropical forests no more than 0.1, i.e. here the biological cycle is the most intense.

The flow of elements (nitrogen, phosphorus, sulfur) through microorganisms is an order of magnitude higher than through plants and animals. The biological cycle is not completely reversible, it is closely related to the biogeochemical cycle. Chemical elements circulate in the biosphere along various paths of the biological cycle:

• - absorbed by living matter and charged with energy;
• - leave living matter, releasing energy into the external environment.

These cycles are of two types: the circulation of gaseous substances; sedimentary cycle (reserve in the earth's crust).

The cycles themselves consist of two parts:

• - reserve fund (this is a part of the substance that is not associated with living organisms);
• - mobile (exchange) fund (a smaller part of the substance associated with direct exchange between organisms and their immediate environment).

Cycles are divided into:

• - gas-type cycles with a reserve fund in the earth's crust (cycles of carbon, oxygen, nitrogen) - capable of rapid self-regulation;
• - sedimentary cycles with a reserve fund in the earth's crust (circulations of phosphorus, calcium, iron, etc.) - are more inert, the bulk of the substance is in a form "inaccessible" to living organisms.

Cycles can also be divided into:

• - closed (circulation of gaseous substances, for example, oxygen, carbon and nitrogen - a reserve in the atmosphere and hydrosphere of the ocean, so the shortage is quickly compensated);
• - open (creating a reserve fund in the earth's crust, for example, phosphorus - therefore, losses are poorly compensated, i.e. a deficit is created).

The energy basis for the existence of biological cycles on Earth and their initial link is the process of photosynthesis. Each new cycle of circulation is not an exact repetition of the previous one. For example, during the evolution of the biosphere, some of the processes were irreversible, resulting in the formation and accumulation of biogenic precipitation, an increase in the amount of oxygen in the atmosphere, a change in the quantitative ratios of isotopes of a number of elements, etc.

The circulation of substances is commonly called biogeochemical cycles. The main biogeochemical (biospheric) cycles of substances: the water cycle, the oxygen cycle, the nitrogen cycle (participation of nitrogen-fixing bacteria), the carbon cycle (participation of aerobic bacteria; annually about 130 tons of carbon is discharged into the geological cycle), the phosphorus cycle (participation of soil bacteria; annually in 14 million tons of phosphorus are washed out of the oceans), the sulfur cycle, the cycle of metal cations.

The water cycle

The water cycle is a closed cycle that can be performed, as mentioned above, even in the absence of life, but living organisms modify it.

The cycle is based on the principle that total evaporation is compensated by precipitation. For the planet as a whole, evaporation and precipitation balance each other out. At the same time, more water evaporates from the ocean than returns with precipitation. On land, on the contrary, more precipitation falls, but the excess flows into lakes and rivers, and from there again into the ocean. The balance of moisture between continents and oceans is maintained by river runoff.

Thus, the global hydrological cycle has four main flows: precipitation, evaporation, moisture transfer, and transpiration.

Water - the most common substance in the biosphere - serves not only as a habitat for many organisms, but also is integral part bodies of all living beings. Despite the enormous importance of water in all life processes occurring in the biosphere, living matter does not play a decisive role in the large water cycle on the globe. The driving force of this cycle is the energy of the sun, which is spent on the evaporation of water from the surface of water basins or land. Evaporated moisture condenses in the atmosphere in the form of wind-blown clouds; As clouds cool, precipitation falls.

The total amount of free unbound water (the proportion of oceans and seas where liquid salt water) accounts for 86 to 98%. The rest of the water (fresh water) is stored in polar caps and glaciers and forms water basins and its groundwater. Precipitation that falls on the surface of land covered with vegetation is partially retained by the leaf surface and subsequently evaporates into the atmosphere. Moisture reaching the soil can join surface runoff or be absorbed by the soil. Completely absorbed by the soil (this depends on the type of soil, features of rocks and vegetation cover), excess sediment can seep deep into the groundwater. If the amount of precipitation exceeds the water capacity upper layers soil, surface runoff begins, the speed of which depends on the condition of the soil, the steepness of the slope, the duration of precipitation and the nature of the vegetation (vegetation can protect the soil from water erosion). Water trapped in the soil can evaporate from its surface or, after absorption by plant roots, be transpired (evaporate) into the atmosphere through the leaves.

The transpiration flow of water (soil - plant roots - leaves - atmosphere) is the main path of water through living matter in its large circulation on our planet.

The carbon cycle

The whole variety of organic substances, biochemical processes and life forms on Earth depends on the properties and characteristics of carbon. The carbon content in most living organisms is about 45% of their dry biomass. All the living matter of the planet is involved in the cycle of organic matter and all carbon of the Earth, which continuously arises, mutates, dies, decomposes, and in this sequence carbon is transferred from one organic substance to the construction of another along the food chain. In addition, all living things breathe, releasing carbon dioxide.

The carbon cycle on land. The carbon cycle is maintained through photosynthesis by land plants and oceanic phytoplankton. By absorbing carbon dioxide (fixing inorganic carbon), plants use the energy of sunlight to convert it into organic compounds - creating their own biomass. At night, plants, like all living things, breathe, releasing carbon dioxide.

Dead plants, corpses and excrement of animals serve as food for numerous heterotrophic organisms (animals, saprophyte plants, fungi, microorganisms). All these organisms live mainly in the soil and in the course of their life activity create their own biomass, which includes organic carbon. They also release carbon dioxide, creating "soil respiration". Often, dead organic matter is not completely decomposed and humus (humus) accumulates in soils, which plays an important role in soil fertility. The degree of mineralization and humification of organic substances depends on many factors: humidity, temperature, physical properties of the soil, composition of organic residues, etc. Under the action of bacteria and fungi, humus can decompose to carbon dioxide and mineral compounds.

The carbon cycle in the oceans. The carbon cycle in the ocean is different from that on land. In the ocean, the weak link of organisms of higher trophic levels, and therefore all links of the carbon cycle. The transit time of carbon through the trophic link of the ocean is short, and the amount of carbon dioxide released is insignificant.

The ocean plays the role of the main regulator of carbon dioxide content in the atmosphere. There is an intensive exchange of carbon dioxide between the ocean and the atmosphere. Ocean waters have a large dissolving power and buffer capacity. The system consisting of carbonic acid and its salts (carbonates) is a kind of depot of carbon dioxide, connected with the atmosphere through the diffusion of CO? from water to atmosphere and vice versa.

Phytoplankton photosynthesis proceeds intensively in the ocean during the day, while free carbon dioxide is intensively consumed, carbonates serve as an additional source of its formation. At night, with an increase in the content of free acid due to the respiration of animals and plants, a significant part of it again enters into the composition of carbonates. The ongoing processes go in the following directions: living matter? CO?? H?CO?? Sa(NSO?)?? CaCO?.

In nature, a certain amount of organic matter does not undergo mineralization as a result of lack of oxygen, high acidity of the environment, specific burial conditions, etc. Part of the carbon leaves the biological cycle in the form of inorganic (limestone, chalk, corals) and organic (shale, oil, coal) deposits.

Human activity is making significant changes to the carbon cycle on our planet. Landscapes, types of vegetation, biocenoses and their food chains are changing, vast areas of the land surface are being drained or irrigated, soil fertility is improving (or worsening), fertilizers and pesticides are being applied, etc. The most dangerous is the release of carbon dioxide into the atmosphere as a result of fuel combustion. This increases the rate of carbon cycle and shortens its cycle.

Oxygen cycle

Oxygen is a prerequisite for the existence of life on Earth. It is included in almost all biological compounds, participates in biochemical reactions of oxidation of organic substances, providing energy for all vital processes of organisms in the biosphere. Oxygen ensures the respiration of animals, plants and microorganisms in the atmosphere, soil, water, participates in chemical oxidation reactions occurring in rocks, soils, silts, aquifers.

The main branches of the oxygen cycle:

• - the formation of free oxygen during photosynthesis and its absorption during the respiration of living organisms (plants, animals, microorganisms in the atmosphere, soil, water);
• - formation of an ozone screen;
• - creation of redox zoning;
• - oxidation of carbon monoxide during volcanic eruptions, accumulation of sulfate sedimentary rocks, oxygen consumption in human activities, etc.; everywhere molecular oxygen is involved in photosynthesis.

nitrogen cycle

Nitrogen is part of the biologically important organic substances of all living organisms: proteins, nucleic acids, lipoproteins, enzymes, chlorophyll, etc. Despite the content of nitrogen (79%) in the air, it is deficient for living organisms.

Nitrogen in the biosphere is in a gaseous form (N2) inaccessible to organisms - it is chemically low active, therefore it cannot be directly used by higher plants (and most lower plants) and the animal world. Plants absorb nitrogen from the soil in the form of ammonium ions or nitrate ions, i.e. so-called fixed nitrogen.

There are atmospheric, industrial and biological nitrogen fixation.

Atmospheric fixation occurs when the atmosphere is ionized by cosmic rays and during strong electrical discharges during thunderstorms, while nitrogen and ammonia oxides are formed from the molecular nitrogen of the air, which, due to atmospheric precipitation, turn into ammonium, nitrite, nitrate nitrogen and enter the soil and water basins.

Industrial fixation occurs as a result of human activities. The atmosphere is polluted with nitrogen compounds by plants producing nitrogen compounds. Hot emissions from thermal power plants, factories, spacecraft, supersonic aircraft oxidize nitrogen in the air. Nitrogen oxides, interacting with air water vapor with precipitation, return to the ground, enter the soil in ionic form.

Biological fixation plays a major role in the nitrogen cycle. It is carried out by soil bacteria:

• - nitrogen-fixing bacteria (and blue-green algae);
• - microorganisms living in symbiosis with higher plants (nodule bacteria);
• - ammonifying;
• - nitrifying;
• - denitrifying.

Freely living in the soil, nitrogen-fixing aerobic (existing in the presence of oxygen) bacteria (Azotobacter) are able to fix atmospheric molecular nitrogen due to the energy obtained from the oxidation of soil organic matter during respiration, ultimately binding it with hydrogen and introducing it in the form of an amino group (- NH2) into the composition of amino acids in your body. Molecular nitrogen is also capable of fixing some anaerobic (living in the absence of oxygen) bacteria that exist in the soil (Clostridium). Dying off, both those and other microorganisms enrich the soil with organic nitrogen.

Blue-green algae, which are especially important for the soils of rice fields, are also capable of biological fixation of molecular nitrogen.

The most effective biological fixation of atmospheric nitrogen occurs in bacteria living in symbiosis in the nodules of leguminous plants (nodule bacteria).

These bacteria (Rizobium) use the energy of the host plant to fix nitrogen while supplying the host's terrestrial organs with available nitrogen compounds.

Assimilated nitrogen compounds from the soil in nitrate and ammonium forms, plants build the necessary nitrogen-containing compounds of their body (nitrate nitrogen in plant cells is preliminarily restored). Producer plants supply nitrogenous substances to the entire animal world and humanity. Dead plants are used, according to the trophic chain, by bioreducers.

Ammonifying microorganisms decompose organic substances containing nitrogen (amino acids, urea) with the formation of ammonia. Part of the organic nitrogen in the soil is not mineralized, but is converted into humic substances, bitumen, and components of sedimentary rocks.

Ammonia (as ammonium ion) can enter the root system of plants, or be used in nitrification processes.

Nitrifying microorganisms are chemosynthetics, they use the energy of ammonia oxidation to nitrates and nitrites to nitrates to ensure all life processes. Due to this energy, nitrifiers restore carbon dioxide and build the organic substances of their body. Oxidation of ammonia during nitrification proceeds according to the following reactions:

NH? + 3O? ? 2HNO? + 2H?O + 600 kJ (148 kcal).

HNO? +O? ? 2HNO? + 198 kJ (48 kcal).

Nitrates formed in the processes of nitrification again enter the biological cycle, are absorbed from the soil by the roots of plants or after entering with water runoff into water basins - phytoplankton and phytobenthos.

Along with organisms that fix atmospheric nitrogen and nitrify it, there are microorganisms in the biosphere that can reduce nitrates or nitrites to molecular nitrogen. Such microorganisms, called denitrifiers, with a lack of free oxygen in water or soil, use the oxygen of nitrates to oxidize organic substances:

C?H??O?(glucose) + 24KNO? ? 24KHCO? + 6CO? + 12N? + 18H?O + energy

The energy released at the same time serves as the basis for all vital activity of denitrifying microorganisms.

Thus, living substances play an exceptional role in all links of the cycle.

At present, the industrial fixation of atmospheric nitrogen by humans plays an increasingly important role in the nitrogen balance of soils and, consequently, in the entire nitrogen cycle in the biosphere.

Phosphorus cycle

The phosphorus cycle is simpler. While the reservoir of nitrogen is air, the reservoir of phosphorus is rocks, from which it is released during erosion.

Carbon, oxygen, hydrogen and nitrogen migrate more easily and faster in the atmosphere, as they are in gaseous form, forming gaseous compounds in biological cycles. For all other elements, except for sulfur, necessary for the existence of living matter, the formation of gaseous compounds in biological cycles is uncharacteristic. These elements migrate mainly in the form of ions and molecules dissolved in water.

Phosphorus, assimilated by plants in the form of orthophosphoric acid ions, plays an important role in the life of all living organisms. It is part of ADP, ATP, DNA, RNA, and other compounds.

The cycle of phosphorus in the biosphere is open. In terrestrial biogeocenoses, phosphorus, after absorption by plants from the soil through the food chain, again enters the soil in the form of phosphates. The main amount of phosphorus is again absorbed by the root system of plants. Partially, phosphorus can be washed out with the runoff of rainwater from the soil into water basins.

In natural biogeocenoses, there is often a lack of phosphorus, and in an alkaline and oxidized environment, it is usually found in the form of insoluble compounds.

A large amount of phosphates contain rocks of the lithosphere. Some of them gradually pass into the soil, some are developed by man for the production of phosphate fertilizers, most of them are leached and washed into the hydrosphere. There they are used by phytoplankton and related organisms at different trophic levels of complex food chains.

In the World Ocean, the loss of phosphates from the biological cycle occurs due to the deposition of plant and animal remains at great depths. Since phosphorus moves mainly from the lithosphere to the hydrosphere with water, it migrates to the lithosphere biologically (eating fish by seabirds, using benthic algae and fishmeal as fertilizer, etc.).

Of all the elements of the mineral nutrition of plants, phosphorus can be considered deficient.

Sulfur cycle

For living organisms, sulfur is of great importance, since it is part of the sulfur-containing amino acids (cystine, cysteine, methionine, etc.). Being in the composition of proteins, sulfur-containing amino acids maintain the necessary three-dimensional structure of protein molecules.

Sulfur is absorbed by plants from the soil only in the oxidized form, in the form of an ion. In plants, sulfur is reduced and is part of amino acids in the form of sulfhydryl (-SH) and disulfide (-S-S-) groups.

Animals assimilate only reduced sulfur, which is part of organic matter. After the death of plant and animal organisms, sulfur returns to the soil, where, as a result of the activity of numerous forms of microorganisms, it undergoes transformations.

Under aerobic conditions, some microorganisms oxidize organic sulfur to sulfates. Sulfate ions, being absorbed by the roots of plants, are again included in the biological cycle. Some sulfates can be included in water migration and removed from the soil. In soils rich in humic substances, a significant amount of sulfur is found in organic compounds, which prevents its leaching.

Under anaerobic conditions, the decomposition of organic sulfur compounds produces hydrogen sulfide. If sulfates and organic substances are in an oxygen-free environment, then the activity of sulfate-reducing bacteria is activated. They use the oxygen of sulfates to oxidize organic matter and thus obtain the energy necessary for their existence.

Sulfate-reducing bacteria are common in groundwater, silt and stagnant sea water. Hydrogen sulfide is a poison for most living organisms, so its accumulation in water-filled soil, lakes, estuaries, etc. significantly reduces or even completely stops vital processes. Such a phenomenon is observed in the Black Sea at a depth below 200 m from its surface.

Thus, to create a favorable environment, it is necessary to oxidize hydrogen sulfide to sulfate ions, which will destroy the harmful effect of hydrogen sulfide, sulfur will turn into a form accessible to plants - in the form of sulfate salts. This role is performed in nature by a special group of sulfur bacteria (colorless, green, purple) and thionic bacteria.

Colorless sulfur bacteria are chemosynthetic: they use the energy obtained from the oxidation of hydrogen sulfide by oxygen to elemental sulfur and its further oxidation to sulfates.

Colored sulfur bacteria are photosynthetic organisms that use hydrogen sulfide as a hydrogen donor to reduce carbon dioxide.

The resulting elemental sulfur in green sulfur bacteria is released from the cells, in purple bacteria it accumulates inside the cells.

The overall reaction of this process is photoreduction:

CO?+ 2H?S light? (CH?O) + H?O +2S.

Thion bacteria oxidize elemental sulfur and its various reduced compounds to sulfates at the expense of free oxygen, returning it back to the mainstream of the biological cycle.

In the processes of the biological cycle, where sulfur is converted, living organisms, especially microorganisms, play a huge role.

The main reservoir of sulfur on our planet is the World Ocean, since sulfate ions continuously enter it from the soil. Part of the sulfur from the ocean returns to land through the atmosphere according to the scheme hydrogen sulfide - oxidizing it to sulfur dioxide - dissolving the latter in rainwater with the formation of sulfuric acid and sulfates - returning sulfur with precipitation to the Earth's soil cover.

Cycle of inorganic cations

In addition to the basic elements that make up living organisms (carbon, oxygen, hydrogen, phosphorus and sulfur), many other macro- and microelements - inorganic cations - are vital. In water basins, plants receive the metal cations they need directly from the environment. On land, the main source of inorganic cations is the soil, which received them in the process of destruction of parent rocks. In plants, the cations absorbed by the root systems move to the leaves and other organs; some of them (magnesium, iron, copper and a number of others) are part of biologically important molecules (chlorophyll, enzymes); others, remaining in a free form, participate in maintaining the necessary colloidal properties of the protoplasm of cells and perform various other functions.

When living organisms die, inorganic cations return to the soil in the process of mineralization of organic substances. The loss of these components from the soil occurs as a result of leaching and removal of metal cations with rainwater, rejection and removal of organic matter by humans during the cultivation of agricultural plants, logging, mowing grass for livestock feed, etc.

The rational use of mineral fertilizers, soil reclamation, the application of organic fertilizers, and proper agricultural technology will help restore and maintain the balance of inorganic cations in the biocenoses of the biosphere.

Anthropogenic cycling: cycling of xenobiotics (mercury, lead, chromium)

Humanity is part of nature and can only exist in constant interaction with it.

There are similarities and contradictions between the natural and anthropogenic circulation of matter and energy occurring in the biosphere.

The natural (biogeochemical) cycle of life has the following features:

• - the use of solar energy as a source of life and all its manifestations based on thermodynamic laws;
• - it is carried out without waste, i.e. all the products of its vital activity are mineralized and re-included in the next cycle of the circulation of substances. At the same time, spent, devalued thermal energy is removed outside the biosphere. During the biogeochemical cycle of substances, waste is generated, i.e. reserves in the form of coal, oil, gas and other mineral resources. In contrast to the waste-free natural cycle, the anthropogenic cycle is accompanied by an increase in waste every year.

There is nothing useless or harmful in nature, even volcanic eruptions have benefits, because the necessary elements (for example, nitrogen) enter the air with volcanic gases.

There is a law of global closure of the biogeochemical circulation in the biosphere, which is valid at all stages of its development, as well as a rule for increasing the closure of the biogeochemical circulation in the course of succession.

Humans play a huge role in the biogeochemical cycle, but in the opposite direction. Man violates the existing cycles of substances, and this manifests his geological force - destructive in relation to the biosphere. As a result of anthropogenic activity, the degree of isolation of biogeochemical cycles decreases.

The anthropogenic cycle is not limited to the energy of sunlight captured by the green plants of the planet. Mankind uses the energy of fuel, hydro and nuclear power plants.

It can be argued that anthropogenic activity at the present stage is a huge destructive force for the biosphere.

The biosphere has a special property - significant resistance to pollutants. This stability is based on the natural ability of the various components natural environment to self-purification and self-healing. But not limitless. The possible global crisis caused the need to build a mathematical model of the biosphere as a whole (the "Gaia" system) in order to obtain information about the possible state of the biosphere.

A xenobiotic is a substance alien to living organisms that appears as a result of anthropogenic activity (pesticides, household chemicals and other pollutants), capable of causing disruption of biotic processes, incl. illness or death. Such pollutants do not undergo biodegradation, but accumulate in trophic chains.

Mercury is a very rare element. It is dispersed in the earth's crust and only in a few minerals, such as cinnabar, is contained in a concentrated form. Mercury is involved in the cycle of matter in the biosphere, migrating in the gaseous state and in aqueous solutions.

It enters the atmosphere from the hydrosphere during evaporation, during release from cinnabar, with volcanic gases and gases from thermal springs. Part of the gaseous mercury in the atmosphere passes into the solid phase and is removed from the air. Fallen mercury is absorbed by soils, especially clay, water and rocks. In combustible minerals - oil and coal - mercury contains up to 1 mg / kg. There are approximately 1.6 billion tons in the water mass of the oceans, 500 billion tons in bottom sediments, and 2 million tons in plankton. About 40 thousand tons are carried out by river waters from land every year, which is 10 times less than what enters the atmosphere during evaporation (400 thousand tons). About 100 thousand tons fall on the land surface annually.

Mercury has turned from a natural component of the natural environment into one of the most hazardous man-made emissions into the biosphere for human health. It is widely used in metallurgy, chemical, electrical, electronic, pulp and paper and pharmaceutical industries and is used for the production of explosives, varnishes and paints, as well as in medicine. Industrial effluents and atmospheric emissions, along with mercury mines, mercury production plants and thermal power plants (CHP and boiler houses) using coal, oil and oil products, are the main sources of biosphere pollution with this toxic component. In addition, mercury is an ingredient in organomercury pesticides used in agriculture to treat seeds and protect crops from pests. It enters the human body with food (eggs, pickled grain, meat of animals and birds, milk, fish).

Mercury in water and bottom sediments of rivers

It has been established that about 80% of mercury entering natural water bodies is in a dissolved form, which ultimately contributes to its spread over long distances along with water flows. The pure element is non-toxic.

Mercury is found in bottom silt water more often in relatively harmless concentrations. Inorganic mercury compounds are converted into toxic organic mercury compounds, such as methylmercury CH?Hg and ethylmercury C?H?Hg, by bacteria living in detritus and sediment, in the bottom silt of lakes and rivers, in the mucus that covers the bodies of fish, and also in fish stomach mucus. These compounds are easily soluble, mobile and highly toxic. The chemical basis of the aggressive action of mercury is its affinity for sulfur, in particular with the hydrogen sulfide group in proteins. These molecules bind to chromosomes and brain cells. Fish and shellfish can accumulate them to dangerous levels for the person who eats them, causing Minamata disease.

Metal mercury and its inorganic compounds act mainly on the liver, kidneys and intestinal tract, however, under normal conditions, they are relatively quickly excreted from the body and the amount dangerous for the human body does not have time to accumulate. Methylmercury and other alkyl mercury compounds are much more dangerous, because cumulation occurs - the toxin enters the body faster than it is excreted from the body, acting on the central nervous system.

Bottom sediments are an important characteristic of aquatic ecosystems. By accumulating heavy metals, radionuclides and highly toxic organic substances, bottom sediments, on the one hand, contribute to the self-purification of aquatic environments, and, on the other hand, are a constant source of secondary pollution of water bodies. Bottom sediments are a promising object of analysis, reflecting a long-term pattern of pollution (especially in slow-flowing water bodies). Moreover, the accumulation of inorganic mercury in bottom sediments is observed especially in river mouths. A tense situation may arise when the adsorption capacity of sediments (silt, precipitation) is exhausted. When the adsorption capacity is reached, heavy metals, incl. mercury will enter the water.

It is known that under marine anaerobic conditions in the sediments of dead algae, mercury attaches hydrogen and passes into volatile compounds.

With the participation of microorganisms, metallic mercury can be methylated in two stages:

CH?Hg+ ? (CH?)?Hg

Methylmercury appears in the environment practically only during the methylation of inorganic mercury.

The biological half-life of mercury is long, it is 70-80 days for most tissues of the human body.

Large fish, such as swordfish and tuna, are known to be contaminated with mercury early in the food chain. At the same time, it is not without interest to note that, to an even greater extent than in fish, mercury accumulates (accumulates) in oysters.

Mercury enters the human body through breathing, with food and through the skin according to the following scheme:

First, there is a transformation of mercury. This element occurs naturally in several forms.

Metallic mercury, used in thermometers, and its inorganic salts (eg chloride) are eliminated from the body relatively quickly.

Much more toxic are alkyl mercury compounds, in particular methyl and ethyl mercury. These compounds are very slowly excreted from the body - only about 1% of the total amount per day. Although most of the mercury that enters natural waters is in the form of inorganic compounds, it always ends up in fish in the form of the much more poisonous methylmercury. Bacteria in the bottom silt of lakes and rivers, in the mucus that covers the bodies of fish, as well as in the mucus of the fish stomach, are able to convert inorganic mercury compounds into methylmercury.

Second, selective accumulation, or biological accumulation (concentration), raises the mercury content in fish and shellfish to levels many times higher than in bay water. Fish and shellfish that live in the river accumulate methylmercury to concentrations that are dangerous for humans who use them for food.

% of the world's fish catch contains mercury in an amount not exceeding 0.5 mg/kg, and 95% - below 0.3 mg/kg. Almost all mercury in fish is in the form of methylmercury.

Given the different toxicity of mercury compounds for humans in food products, it is necessary to determine inorganic (total) and organically bound mercury. We only determine the total mercury content. According to medical and biological requirements, the content of mercury in freshwater predatory fish is allowed 0.6 mg/kg, in marine fish - 0.4 mg/kg, in freshwater non-predatory fish only 0.3 mg/kg, and in tuna up to 0.7 mg/kg. kg. In products baby food the content of mercury should not exceed 0.02 mg/kg in canned meat, 0.15 mg/kg in canned fish, in the rest - 0.01 mg/kg.

Lead is present in almost all components of the natural environment. It contains 0.0016% in the earth's crust. The natural level of lead in the atmosphere is 0.0005 mg/m3. Most of it is deposited with dust, about 40% falls with atmospheric precipitation. Plants get lead from soil, water and atmospheric fallout, while animals get lead from plants and water. Metal enters the human body with food, water and dust.

The main sources of lead pollution in the biosphere are gasoline engines, the exhaust gases of which contain triethyl lead, thermal power plants burning coal, mining, metallurgical and chemical industries. A significant amount of lead is introduced into the soil along with wastewater used as fertilizer. To extinguish the burning reactor of the Chernobyl nuclear power plant, lead was also used, which entered the air pool and dispersed over vast areas. With an increase in environmental pollution with lead, its deposition in the bones, hair, and liver increases.

Chromium. The most dangerous is toxic chromium (6+), which is mobilized in acidic and alkaline soils, in fresh and marine waters. IN sea ​​water chromium is 10 - 20% represented by the Cr (3+) form, 25 - 40% - by Cr (6+), 45 - 65% - by the organic form. In the pH range 5 - 7, Cr (3+) predominates, and at pH > 7 - Cr (6+). It is known that Cr (6+) and organic chromium compounds do not co-precipitate with iron hydroxide in sea water.

Natural cycles of substances are practically closed. In natural ecosystems, matter and energy are spent sparingly, and the waste of some organisms is an important condition for the existence of others. The anthropogenic cycle of substances is accompanied by a huge consumption of natural resources and a large amount of waste that causes environmental pollution. The creation of even the most advanced treatment facilities does not solve the problem, so it is necessary to develop low-waste and waste-free technologies that make it possible to make the anthropogenic cycle as closed as possible. Theoretically, it is possible to create a waste-free technology, but low-waste technologies are real.

Adaptation to natural phenomena

Adaptations are various adaptations to the environment developed by organisms (from the simplest to the highest) in the process of evolution. The ability to adapt is one of the main properties of the living, providing the possibility of their existence.

The main factors that develop the process of adaptation include: heredity, variability, natural (and artificial) selection.

Tolerance can change if the body enters other external conditions. Getting into such conditions, after a while, he gets used to it, as it were, adapts to them (from lat. adaptation - to adapt). The consequence of this is a change in the provisions of the physiological optimum.

The property of organisms to adapt to existence in a particular range environmental factor called ecological plasticity.

The wider the range of the ecological factor within which a given organism can live, the greater its ecological plasticity. According to the degree of plasticity, two types of organisms are distinguished: stenobiont (stenoeks) and eurybiont (euryeks). Thus, stenobionts are ecologically non-plastic (for example, flounder lives only in salt water, and crucian carp only in fresh water), i.e. short-hardy, and eurybionts are ecologically plastic, i.e. are more hardy (for example, the three-spined stickleback can live in both fresh and salt waters).

Adaptations are multidimensional, as an organism must conform to many different environmental factors at the same time.

There are three main ways of adapting organisms to environmental conditions: active; passive; avoidance of adverse effects.

The active path of adaptation is the strengthening of resistance, the development of regulatory processes that make it possible to carry out all the vital functions of the body, despite the deviation of the factor from the optimum. For example, warm-blooded animals maintain a constant body temperature - optimal for the biochemical processes occurring in it.

The passive path of adaptation is the subordination of the vital functions of organisms to changes in environmental factors. For example, under adverse environmental conditions, many organisms go into a state of anabiosis ( hidden life), at which the metabolism in the body practically stops (the state of winter dormancy, the stupor of insects, hibernation, the preservation of spores in the soil in the form of spores and seeds).

Avoidance of adverse effects - the development of adaptations, the behavior of organisms (adaptation), which help to avoid adverse conditions. In this case, adaptations can be: morphological (the structure of the body changes: modification of the leaves of a cactus), physiological (the camel provides itself with moisture due to the oxidation of fat reserves), ethological (changes in behavior: seasonal bird migrations, hibernation in winter).

Living organisms are well adapted to periodic factors. Non-periodic factors can cause disease and even death of the organism (for example, drugs, pesticides). However, with prolonged exposure, adaptation to them may also occur.

Organisms adapted to daily, seasonal, tidal rhythms, rhythms of solar activity, lunar phases and other strictly periodic phenomena. So, seasonal adaptation is distinguished as seasonality in nature and the state of winter dormancy.

Seasonality in nature. The leading value for plants and animals in the adaptation of organisms is the annual temperature variation. The period favorable for life, on average for our country, lasts about six months (spring, summer). Even before the arrival of stable frosts, a period of winter dormancy begins in nature.

Winter dormancy. Winter dormancy is not just a stoppage of development as a result of low temperatures, but a complex physiological adaptation, moreover, occurring only at a certain stage of development. For example, the malarial mosquito and the nettle moth overwinter in the adult insect stage, the cabbage butterfly in the pupal stage, and the gypsy moth in the egg stage.

Biorhythms. Each species in the process of evolution has developed a characteristic annual cycle of intensive growth and development, reproduction, preparation for winter and wintering. This phenomenon is called biological rhythm. The coincidence of each period of the life cycle with the corresponding season is crucial for the existence of the species.

The main factor in the regulation of seasonal cycles in most plants and animals is the change in the length of the day.

Biorhythms are:

exogenous (external) rhythms (arise as a reaction to periodic changes in the environment (change of day and night, seasons, solar activity) endogenous (internal rhythms) are generated by the body itself

In turn, endogenous are divided into:

Physiological rhythms (heartbeat, respiration, endocrine glands, DNA, RNA, protein synthesis, enzymes, cell division, etc.)

Ecological rhythms (daily, annual, tidal, lunar, etc.)

The processes of DNA, RNA, protein synthesis, cell division, heartbeat, respiration, etc. have rhythm. External influences can shift the phases of these rhythms and change their amplitude.

Physiological rhythms vary depending on the state of the body, while environmental rhythms are more stable and correspond to external rhythms. With endogenous rhythms, the body can navigate in time and prepare in advance for the upcoming changes in the environment - this is the biological clock of the body. Many living organisms are characterized by circadian and circanian rhythms.

Circadian rhythms (circadian) - recurring intensities and nature of biological processes and phenomena with a period of 20 to 28 hours. Circadian rhythms are associated with the activity of animals and plants during the day and, as a rule, depend on temperature and light intensity. For example, bats fly at dusk and rest during the day, many planktonic organisms stay at the surface of the water at night and descend into the depths during the day.

Seasonal biological rhythms are associated with the influence of light - the photoperiod. The reaction of organisms to the length of the day is called photoperiodism. Photoperiodism is a common important adaptation that regulates seasonal phenomena in a wide variety of organisms. The study of photoperiodism in plants and animals showed that the reaction of organisms to light is based on the alternation of periods of light and darkness of a certain duration during the day. The reaction of organisms (from unicellular to humans) to the length of day and night shows that they are able to measure time, i.e. have some kind of biological clock. The biological clock, in addition to seasonal cycles, controls many other biological phenomena, determines the correct daily rhythm of both the activity of entire organisms and processes that occur even at the level of cells, in particular, cell divisions.

A universal property of all living things, from viruses and microorganisms to higher plants and animals, is the ability to give mutations - sudden, natural and artificially caused, inherited changes in the genetic material, leading to a change in certain signs of the organism. Mutational variability does not correspond to environmental conditions and, as a rule, disrupts existing adaptations.

Many insects fall into diapause (a long stop in development) at a certain stage of development, which should not be confused with a state of rest under adverse conditions. The reproduction of many marine animals is influenced by lunar rhythms.

Circanian (near-annual) rhythms are recurring changes in the intensity and nature of biological processes and phenomena with a period of 10 to 13 months.

The physical and psychological state of a person also has a rhythmic character.

The disturbed rhythm of work and rest reduces efficiency and has an adverse effect on human health. The human condition in extreme conditions will depend on the degree of his preparedness for these conditions, since there is practically no time for adaptation and recovery.

All substances on the planet are in the process of circulation. Solar energy causes two cycles of matter on Earth: large (geological, biospheric) And small (biological).

The large circulation of substances in the biosphere is characterized by two important points: it is carried out throughout the entire geological development of the Earth and is a modern planetary process that takes a leading part in the further development of the biosphere.

The geological cycle is associated with the formation and destruction of rocks and the subsequent movement of destruction products - detrital material and chemical elements. A significant role in these processes was played and continues to be played by the thermal properties of the surface of land and water: the absorption and reflection of sunlight, thermal conductivity and heat capacity. The unstable hydrothermal regime of the Earth's surface, together with the planetary atmospheric circulation system, determined the geological circulation of substances, which at the initial stage of the Earth's development, along with endogenous processes, was associated with the formation of continents, oceans and modern geospheres. With the formation of the biosphere, the products of vital activity of organisms were included in the great cycle. The geological cycle supplies living organisms with nutrients and largely determines the conditions for their existence.

Main chemical elements lithospheres: oxygen, silicon, aluminum, iron, magnesium, sodium, potassium and others - participate in a large circulation, passing from the deep parts of the upper mantle to the surface of the lithosphere. Igneous rock formed during crystallization

Magma, having entered the surface of the lithosphere from the depths of the Earth, undergoes decomposition and weathering in the biosphere. Weathering products pass into a mobile state, are carried by waters, wind to low relief places, fall into rivers, the ocean and form thick strata of sedimentary rocks, which over time, plunging to a depth in areas with elevated temperature and pressure, undergo metamorphosis, i.e. "remelted". During this remelting, a new metamorphic rock appears, entering the upper horizons of the earth's crust and re-entering the circulation of substances. (Fig. 32).

Rice. 32. Geological (large) circulation of substances

Easily mobile substances - gases and natural waters that make up the atmosphere and hydrosphere of the planet - undergo the most intensive and rapid circulation. The material of the lithosphere cycles much more slowly. In general, each circulation of any chemical element is part of the general large circulation of substances on Earth, and all of them are closely interconnected. The living matter of the biosphere in this circulation performs a huge job of redistributing the chemical elements that continuously circulate in the biosphere, passing from the external environment to organisms and again to the external environment.

Small, or biological, circulation of substances- This

circulation of substances between plants, animals, fungi, microorganisms and soil. The essence of the biological cycle is the flow of two opposite, but interrelated processes - the creation of organic substances and their destruction. The initial stage in the emergence of organic substances is due to the photosynthesis of green plants, i.e., the formation of living matter from carbon dioxide, water, and simple mineral compounds using solar energy. Plants (producers) extract molecules of sulfur, phosphorus, calcium, potassium, magnesium, manganese, silicon, aluminum, zinc, copper and other elements from the soil in a solution. Herbivorous animals (consumers of the first order) absorb compounds of these elements already in the form of food of plant origin. Predators (consumers of the second order) feed on herbivorous animals, consuming food of a more complex composition, including proteins, fats, amino acids and other substances. In the process of destruction by microorganisms (decomposers) of organic matter of dead plants and animal remains, simple mineral compounds enter the soil and aquatic environment, available for assimilation by plants, and the next round of the biological cycle begins. (Fig. 33).

Small (biological) circulation

The mass of living matter in the biosphere is relatively small. If it is distributed over the earth's surface, then a layer of only 1.5 cm will be obtained. Table 4.1 compares some quantitative characteristics of the biosphere and other geospheres of the Earth. The biosphere, accounting for less than 10-6 masses of other shells of the planet, has an incomparably greater diversity and renews its composition a million times faster.

Table 4.1

Comparison of the biosphere with other geospheres of the Earth

*Live substance based on live weight

4.4.1. Functions of the biosphere

Thanks to the biota of the biosphere, the predominant part of the chemical transformations on the planet is carried out. Hence the judgment of V.I. Vernadsky about the huge transformative geological role of living matter. Throughout organic evolution, living organisms have passed through themselves, through their organs, tissues, cells, blood, the entire atmosphere, the entire volume of the World Ocean, most of the mass of soil, a huge mass of mineral substances through themselves, through their organs, tissues, cells, blood, a thousand times (for different cycles from 103 to 105 times). And they not only missed it, but also modified the earthly environment in accordance with their needs.

Thanks to the ability to transform solar energy into the energy of chemical bonds, plants and other organisms perform a number of fundamental biogeochemical functions on a planetary scale.

gas function. Living beings constantly exchange oxygen and carbon dioxide with the environment in the processes of photosynthesis and respiration. Plants played a decisive role in the change from a reducing environment to an oxidizing environment in the geochemical evolution of the planet and in the formation of the gas composition of the modern atmosphere. Plants strictly control the concentrations of O2 and CO2, which are optimal for the totality of all modern living organisms.

concentration function. By passing large volumes of air and natural solutions through their bodies, living organisms carry out biogenic migration (the movement of chemicals) and the concentration of chemical elements and their compounds. This refers to the biosynthesis of organic matter, the formation of coral islands, the construction of shells and skeletons, the appearance of sedimentary limestone strata, deposits of certain metal ores, the accumulation of iron-manganese nodules, on the ocean floor, etc. The early stages of biological evolution took place in aquatic environment. Organisms have learned to extract the substances they need from a dilute aqueous solution, multiplying their concentration in their bodies many times over.

The redox function of living matter is closely related to the biogenic migration of elements and the concentration of substances. Many substances in nature are stable and do not undergo oxidation under normal conditions, for example, molecular nitrogen is one of the most important biogenic elements. But living cells have such powerful catalysts - enzymes that they are able to carry out many redox reactions millions of times faster than it can take place in an abiotic environment.

Information function of the living matter of the biosphere. It was with the advent of the first primitive living beings that active (“live”) information appeared on the planet, which differs from the “dead” information, which is a simple reflection of the structure. Organisms turned out to be able to receive information by connecting the flow of energy with an active molecular structure that plays the role of a program. The ability to perceive, store and process molecular information has undergone an advanced evolution in nature and has become the most important ecological system-forming factor. The total stock of biota genetic information is estimated at 1015 bits. The total power of the flow of molecular information associated with the metabolism and energy in all cells of the global biota reaches 1036 bit/s (Gorshkov et al., 1996).

4.4.2. Components of the biological cycle.

The biological cycle is carried out between all components of the biosphere (ie, between soil, air, water, animals, microorganisms, etc.). It occurs with the obligatory participation of living organisms.

Solar radiation reaching the biosphere carries an energy of about 2.5 * 1024 J per year. Only 0.3% of it is directly converted in the process of photosynthesis into the energy of chemical bonds of organic substances, i.e. involved in the biological cycle. And 0.1 - 0.2% of the solar energy falling on the Earth turns out to be contained in net primary production. Further fate This energy is associated with the transfer of organic matter of food through the cascades of trophic chains.

The biological cycle can be conditionally divided into interrelated components: the cycle of substances and the energy cycle.

4.4.3. Energy cycle. Energy transformation in the biosphere

An ecosystem can be described as a collection of living organisms continuously exchanging energy, matter, and information. Energy can be defined as the ability to do work. The properties of energy, including the movement of energy in ecosystems, are described by the laws of thermodynamics.

The first law of thermodynamics or the law of conservation of energy states that energy does not disappear and is not created anew, it only changes from one form to another.

The second law of thermodynamics states that entropy can only increase in a closed system. With regard to energy in ecosystems, the following formulation is convenient: the processes associated with the transformation of energy can occur spontaneously only if the energy passes from a concentrated form to a diffuse one, that is, it degrades. A measure of the amount of energy that becomes unavailable for use, or otherwise a measure of the change in order that occurs when energy is degraded, is entropy. The higher the order of the system, the lower its entropy.

In other words, living matter receives and transforms the energy of the cosmos, the sun into the energy of terrestrial processes (chemical, mechanical, thermal, electrical). It involves this energy and inorganic matter in the continuous circulation of substances in the biosphere. The flow of energy in the biosphere has one direction - from the Sun through plants (autotrophs) to animals (heterotrophs). Natural untouched ecosystems in a stable state with constant important environmental indicators (homeostasis) are the most ordered systems and are characterized by the lowest entropy.

4.4.4. The cycle of substances in nature

The formation of living matter and its decomposition are two sides of a single process, which is called the biological cycle of chemical elements. Life is the circulation of chemical elements between organisms and the environment.

The reason for the cycle is the limitedness of the elements from which the bodies of organisms are built. Each organism extracts from the environment the substances necessary for life and returns unused. Wherein:

some organisms consume minerals directly from the environment;

others use products processed and isolated first;

the third - the second, etc., until the substances return to the environment in their original state.

In the biosphere, the need for the coexistence of various organisms that can use each other's waste products is obvious. We see practically waste-free biological production.

The cycle of substances in living organisms can be conditionally reduced to four processes:

1. Photosynthesis. As a result of photosynthesis, plants absorb and accumulate solar energy and synthesize organic substances - primary biological products - and oxygen from inorganic substances. Primary biological products are very diverse - they contain carbohydrates (glucose), starch, fiber, proteins, fats.

The scheme of photosynthesis of the simplest carbohydrate (glucose) has the following scheme:

This process takes place only during the day and is accompanied by an increase in the mass of plants.

On Earth, about 100 billion tons of organic matter are formed annually as a result of photosynthesis, about 200 billion tons of carbon dioxide are assimilated, and about 145 billion tons of oxygen are released.

Photosynthesis plays a decisive role in ensuring the existence of life on Earth. Its global significance is explained by the fact that photosynthesis is the only process during which energy in the thermodynamic process, according to the minimalist principle, does not dissipate, but rather accumulates.

By synthesizing the amino acids necessary for building proteins, plants can exist relatively independently of other living organisms. This manifests the autotrophy of plants (self-sufficiency in nutrition). At the same time, the green mass of plants and the oxygen formed in the process of photosynthesis are the basis for maintaining the life of the next group of living organisms - animals, microorganisms. This shows the heterotrophy of this group of organisms.

2. Breathing. The process is the reverse of photosynthesis. Occurs in all living cells. During respiration, organic matter is oxidized by oxygen, resulting in the formation of carbon dioxide, water and energy.

3. Nutritional (trophic) relationships between autotrophic and heterotrophic organisms. In this case, there is a transfer of energy and matter along the links of the food chain, which we discussed in more detail earlier.

4. The process of transpiration. One of the most important processes in the biological cycle.

Schematically, it can be described as follows. Plants absorb soil moisture through their roots. At the same time, mineral substances dissolved in water enter them, which are absorbed, and moisture evaporates more or less intensively, depending on environmental conditions.

4.4.5. Biogeochemical cycles

Geological and biological cycles are connected - they exist as a single process, giving rise to the circulation of substances, the so-called biogeochemical cycles (BGCC). This circulation of elements is due to the synthesis and decay of organic substances in the ecosystem (Fig. 4.1). Not all elements of the biosphere are involved in BHCC, but only biogenic ones. Living organisms consist of them, these elements enter into numerous reactions and participate in the processes occurring in living organisms. In percentage terms, the total mass of the living matter of the biosphere consists of the following main biogenic elements: oxygen - 70%, carbon - 18%, hydrogen - 10.5%, calcium - 0.5%, potassium - 0.3%, nitrogen - 0, 3%, (oxygen, hydrogen, nitrogen, carbon are present in all landscapes and are the basis of living organisms - 98%).

Essence of biogenic migration of chemical elements.

Thus, in the biosphere there is a biogenic cycle of substances (ie, a cycle caused by the vital activity of organisms) and a unidirectional flow of energy. Biogenic migration of chemical elements is determined mainly by two opposite processes:

1. The formation of living matter from the elements of the environment due to solar energy.

2. The destruction of organic substances, accompanied by the release of energy. At the same time, elements of mineral substances repeatedly enter living organisms, thereby entering into the composition of complex organic compounds, forms, and then, when the latter are destroyed, they again acquire a mineral form.

There are elements that are part of living organisms, but not related to biogenic ones. Such elements are classified according to their weight fraction in organisms:

Macronutrients - components of at least 10-2% of the mass;

Trace elements - components from 9 * 10-3 to 1 * 10-3% of the mass;

Ultramicroelements - less than 9 * 10-6% of the mass;

To determine the place of biogenic elements among other chemical elements of the biosphere, let us consider the classification adopted in ecology. According to the activity shown in the processes occurring in the biosphere, all chemical elements are divided into 6 groups:

The noble gases are helium, neon, argon, krypton, xenon. Inert gases are not part of living organisms.

Noble metals - ruthenium, radium, palladium, osmium, iridium, platinum, gold. These metals almost do not create compounds in the earth's crust.

Cyclic or biogenic elements (they are also called migratory). This group of biogenic elements in the earth's crust accounts for 99.7% of the total mass, and the remaining 5 groups - 0.3%. Thus, the bulk of the elements are migrants who carry out circulation in geographical envelope, and the part of inert elements is very small.

Scattered elements, characterized by the predominance of free atoms. They enter into chemical reactions, but their compounds are rarely found in the earth's crust. They are divided into two subgroups. The first - rubidium, cesium, niobium, tantalum - create compounds in the depths of the earth's crust, and on the surface of their minerals are destroyed. The second - iodine, bromine - react only on the surface.

Radioactive elements - polonium, radon, radium, uranium, neptunium, plutonium.

Rare earth elements - yttrium, samarium, europium, thulium, etc.

Year-round biochemical cycles set in motion about 480 billion tons of matter.

IN AND. Vernadsky formulated three biogeochemical principles that explain the essence of biogenic migration of chemical elements:

Biogenic migration of chemical elements in the biosphere always tends to its maximum manifestation.

The evolution of species in the course of geological time, leading to the creation of sustainable forms of life, proceeds in a direction that enhances the biogenic migration of atoms.

Living matter is in continuous chemical exchange with its environment, which is a factor that recreates and maintains the biosphere.

Let us consider how some of these elements move in the biosphere.

The carbon cycle. The main participant in the biotic cycle is carbon as the basis of organic substances. Mostly carbon cycle occurs between living matter and carbon dioxide of the atmosphere in the process of photosynthesis. Herbivores get it with food, predators get it from herbivores. When breathing, rotting, carbon dioxide is partially returned to the atmosphere, the return occurs when organic minerals are burned.

In the absence of carbon return to the atmosphere, it would be used up by green plants in 7-8 years. The rate of biological turnover of carbon through photosynthesis is 300 years. The oceans play an important role in regulating the content of CO2 in the atmosphere. If the CO2 content rises in the atmosphere, some of it dissolves in water, reacting with calcium carbonate.

The oxygen cycle.

Oxygen has a high chemical activity, enters into compounds with almost all elements of the earth's crust. It occurs mainly in the form of compounds. Every fourth atom of living matter is an oxygen atom. Almost all of the molecular oxygen in the atmosphere originated and is maintained at a constant level due to the activity of green plants. Atmospheric oxygen, bound during respiration and released during photosynthesis, passes through all living organisms in 200 years.

The nitrogen cycle. Nitrogen is an integral part of all proteins. The total ratio of bound nitrogen, as an element constituting organic matter, to nitrogen in nature is 1:100,000. The chemical bond energy in the nitrogen molecule is very high. Therefore, the combination of nitrogen with other elements - oxygen, hydrogen (the process of nitrogen fixation) - requires a lot of energy. Industrial nitrogen fixation takes place in the presence of catalysts at a temperature of -500°C and a pressure of -300 atm.

As you know, the atmosphere contains more than 78% of molecular nitrogen, but in this state it is not available to green plants. For their nutrition, plants can use only salts of nitric and nitrous acids. What are the ways of formation of these salts? Here are some of them:

In the biosphere, nitrogen fixation is carried out by several groups of anaerobic bacteria and cyanobacteria at normal temperature and pressure due to the high efficiency of biocatalysis. It is believed that bacteria convert approximately 1 billion tons of nitrogen per year into a bound form (the world volume of industrial fixation is about 90 million tons).

Soil nitrogen-fixing bacteria are able to assimilate molecular nitrogen from the air. They enrich the soil with nitrogenous compounds, so their value is extremely high.

As a result of the decomposition of nitrogen-containing compounds of organic substances of plant and animal origin.

Under the action of bacteria, nitrogen is converted into nitrates, nitrites, ammonium compounds. In plants, nitrogen compounds take part in the synthesis of protein compounds, which are transferred from organism to organism in food chains.

Phosphorus cycle. Another important element, without which protein synthesis is impossible, is phosphorus. The main sources are igneous rocks (apatites) and sedimentary rocks (phosphorites).

Inorganic phosphorus is involved in the cycle as a result of natural leaching processes. Phosphorus is assimilated by living organisms, which, with its participation, synthesize a number of organic compounds and transfer them to various trophic levels.

Having finished their journey along the trophic chains, organic phosphates are decomposed by microbes and turn into mineral phosphates available to green plants.

In the process of biological circulation, which ensures the movement of matter and energy, there is no place for the accumulation of waste. The waste products (i.e. waste products) of each life form are the breeding ground for other organisms.

Theoretically, the biosphere should always maintain a balance between the production of biomass and its decomposition. However, in certain geological periods, the balance of the biological cycle was disturbed when, due to certain natural conditions, cataclysms, not all biological products were assimilated and transformed. In these cases, surpluses of biological products were formed, which were conserved and deposited in the earth's crust, under the water column, sediments, and ended up in the permafrost zone. So deposits of coal, oil, gas, limestone were formed. It should be noted that they do not litter the biosphere. The energy of the Sun, accumulated in the process of photosynthesis, is concentrated in organic minerals. Now, by burning organic fossil fuels, a person releases this energy.

Is an outstanding Russian scientist academician V.I. Vernadsky.

Biosphere- the complex outer shell of the Earth, which contains the totality of living organisms and that part of the planet's substance that is in the process of continuous exchange with these organisms. This is one of the most important geospheres of the Earth, which is the main component of the natural environment surrounding man.

The earth is made up of concentric shells(geospheres) both internal and external. The inner ones are the core and the mantle, and the outer ones are: lithosphere - the stone shell of the Earth, including the earth's crust (Fig. 1) with a thickness of 6 km (under the ocean) to 80 km (mountain systems); hydrosphere - water shell of the Earth; atmosphere- the gaseous envelope of the Earth, consisting of a mixture of various gases, water vapor and dust.

At an altitude of 10 to 50 km there is an ozone layer, with its maximum concentration at an altitude of 20-25 km, protecting the Earth from excessive ultraviolet radiation, which is fatal to the body. The biosphere also belongs here (to the external geospheres).

Biosphere - the outer shell of the Earth, which includes part of the atmosphere up to a height of 25-30 km (to the ozone layer), almost the entire hydrosphere and the upper part of the lithosphere to a depth of about 3 km

Rice. 1. Scheme of the structure of the earth's crust

(Fig. 2). The peculiarity of these parts is that they are inhabited by living organisms that make up the living substance of the planet. Interaction abiotic part of the biosphere- air, water, rocks and organic matter - biota led to the formation of soils and sedimentary rocks.

Rice. 2. The structure of the biosphere and the ratio of surfaces occupied by the main structural units

The cycle of substances in the biosphere and ecosystems

All available to living organisms chemical compounds limited in the biosphere. The exhaustibility of chemical substances suitable for assimilation often hinders the development of certain groups of organisms in local areas of the land or ocean. According to Academician V.R. Williams, the only way to give the finite properties of the infinite is to make it rotate along a closed curve. Consequently, the stability of the biosphere is maintained due to the circulation of substances and energy flows. Available two main cycles of substances: large - geological and small - biogeochemical.

Great geological cycle(Fig. 3). Crystalline rocks (igneous) under the influence of physical, chemical and biological factors are transformed into sedimentary rocks. Sand and clay are typical sediments, products of the transformation of deep rocks. However, the formation of sediments occurs not only due to the destruction of existing rocks, but also through the synthesis of biogenic minerals - the skeletons of microorganisms - from natural resources - ocean waters, seas and lakes. Loose watery sediments, as they are isolated at the bottom of reservoirs by new portions of sedimentary material, immersed to a depth, falling into new thermodynamic conditions (higher temperatures and pressures), lose water, harden, transforming into sedimentary rocks.

In the future, these rocks sink into even deeper horizons, where the processes of their deep transformation to new temperature and pressure conditions take place - the processes of metamorphism take place.

Under the influence of endogenous energy flows, deep rocks are remelted, forming magma - the source of new igneous rocks. After the rise of these rocks to the surface of the Earth, under the influence of the processes of weathering and transport, they are again transformed into new sedimentary rocks.

Thus, a large circulation is due to the interaction of the solar (exogenous) energy with the deep (endogenous) energy of the Earth. It redistributes substances between the biosphere and the deeper horizons of our planet.

Rice. 3. Large (geological) circulation of substances (thin arrows) and change in diversity in the earth's crust (solid wide arrows - growth, dashed - decrease in diversity)

Big circle also called the water cycle between the hydrosphere, atmosphere and lithosphere, which is driven by the energy of the sun. Water evaporates from the surface of water bodies and land and then returns to the Earth in the form of precipitation. Evaporation exceeds precipitation over the ocean, and vice versa over land. These differences are compensated by river flows. Land vegetation plays an important role in the global water cycle. Transpiration of plants in certain areas of the earth's surface can be up to 80-90% of the precipitation falling here, and on average for all climatic zones - about 30%. In contrast to the large cycle, the small cycle of substances occurs only within the biosphere. The relationship between the large and small water cycles is shown in fig. 4.

Cycles on a planetary scale are created from countless local cyclic movements of atoms driven by the vital activity of organisms in individual ecosystems, and those movements that are caused by the action of landscape and geological factors (surface and underground runoff, wind erosion, movement of the seabed, volcanism, mountain building, etc. ).

Rice. 4. Relationship between the large geological cycle (GBC) of water and the small biogeochemical cycle (MBC) of water

Unlike energy, which is once used by the body, turns into heat and is lost, substances in the biosphere circulate, creating biogeochemical cycles. Of the more than ninety elements found in nature, living organisms need about forty. The most important for them are required in large quantities - carbon, hydrogen, oxygen, nitrogen. The cycles of elements and substances are carried out through self-regulating processes in which all components participate. These processes are non-waste. Exists the law of global closure of the biogeochemical circulation in the biosphere operating at all stages of its development. In the process of evolution of the biosphere, the role of the biological component in the closure of the biogeochemical
whom the cycle. Man has an even greater influence on the biogeochemical cycle. But its role is manifested in the opposite direction (circulations become open). The basis of the biogeochemical circulation of substances is the energy of the Sun and the chlorophyll of green plants. Other most important cycles - water, carbon, nitrogen, phosphorus and sulfur - are associated with biogeochemical and contribute to it.

The water cycle in the biosphere

Plants use water hydrogen during photosynthesis to build organic compounds, releasing molecular oxygen. In the processes of respiration of all living beings, during the oxidation of organic compounds, water is formed again. In the history of life, all the free water of the hydrosphere has repeatedly gone through cycles of decomposition and neoformation in the living matter of the planet. About 500,000 km 3 of water are involved in the water cycle on Earth every year. The water cycle and its reserves are shown in fig. 5 (in relative terms).

The oxygen cycle in the biosphere

The Earth owes its unique atmosphere with a high content of free oxygen to the process of photosynthesis. The formation of ozone in the high layers of the atmosphere is closely related to the oxygen cycle. Oxygen is released from water molecules and is essentially a by-product of photosynthetic activity in plants. Abiotically, oxygen arises in the upper atmosphere due to the photodissociation of water vapor, but this source is only thousandths of a percent of those supplied by photosynthesis. Between the oxygen content in the atmosphere and the hydrosphere there is a mobile equilibrium. In water, it is about 21 times less.

Rice. Fig. 6. Scheme of the oxygen cycle: bold arrows - the main flows of oxygen supply and consumption

The released oxygen is intensively spent on the processes of respiration of all aerobic organisms and on the oxidation of various mineral compounds. These processes occur in the atmosphere, soil, water, silts and rocks. It has been shown that a significant part of the oxygen bound in sedimentary rocks is of photosynthetic origin. The exchange fund of O in the atmosphere is no more than 5% of the total production of photosynthesis. Many anaerobic bacteria also oxidize organic matter during anaerobic respiration using sulfates or nitrates for this.

The complete decomposition of organic matter created by plants requires exactly the same amount of oxygen that was released during photosynthesis. The burial of organics in sedimentary rocks, coals, and peat served as the basis for maintaining the oxygen exchange fund in the atmosphere. All the oxygen it contains passes full cycle through living organisms for about 2000 years.

At present, a significant part of atmospheric oxygen is bound as a result of transport, industry and other forms of anthropogenic activity. It is known that mankind already spends more than 10 billion tons of free oxygen from its total amount of 430-470 billion tons supplied by photosynthesis processes. If we take into account that only a small part of photosynthetic oxygen enters the exchange fund, the activity of people in this respect begins to acquire alarming proportions.

The oxygen cycle is closely related to the carbon cycle.

The carbon cycle in the biosphere

Carbon as a chemical element is the basis of life. He can different ways combine with many other elements, forming simple and complex organic molecules that make up living cells. In terms of distribution on the planet, carbon occupies the eleventh place (0.35% of the weight of the earth's crust), but in living matter it averages about 18 or 45% of dry biomass.

In the atmosphere, carbon is included in the composition of carbon dioxide CO 2 , to a lesser extent - in the composition of methane CH 4 . In the hydrosphere, CO 2 is dissolved in water, and its total content is much higher than atmospheric. The ocean serves as a powerful buffer for the regulation of CO 2 in the atmosphere: with an increase in its concentration in the air, the absorption of carbon dioxide by water increases. Some of the CO 2 molecules react with water, forming carbonic acid, which then dissociates into HCO 3 - and CO 2- 3 ions. These ions react with calcium or magnesium cations to precipitate carbonates. Similar reactions underlie the buffer system of the ocean, keeping the pH of the water constant.

Carbon dioxide of the atmosphere and hydrosphere is an exchange fund in the carbon cycle, from where it is drawn by terrestrial plants and algae. Photosynthesis underlies all biological cycles on Earth. The release of fixed carbon occurs during the respiratory activity of the photosynthetic organisms themselves and all heterotrophs - bacteria, fungi, animals included in the food chain at the expense of living or dead organic matter.

Rice. 7. Carbon cycle

Especially active is the return of CO 2 to the atmosphere from the soil, where the activity of numerous groups of organisms is concentrated, decomposing the remains of dead plants and animals and the respiration of the root systems of plants is carried out. This integral process is referred to as "soil respiration" and makes a significant contribution to the replenishment of the CO 2 exchange fund in the air. In parallel with the processes of mineralization of organic matter, humus is formed in soils - a complex and stable molecular complex rich in carbon. Soil humus is one of the important reservoirs of carbon on land.

In conditions where the activity of destructors is inhibited by environmental factors (for example, when an anaerobic regime occurs in soils and at the bottom of water bodies), organic matter accumulated by vegetation does not decompose, turning over time into rocks such as coal, peat, sapropels , oil shale and others rich in accumulated solar energy. They replenish the reserve fund of carbon, being switched off from the biological cycle for a long time. Carbon is also temporarily deposited in living biomass, in dead litter, in dissolved organic matter of the ocean, etc. However the main reserve fund of carbon on the write are not living organisms and not combustible fossils, but sedimentary rocks are limestones and dolomites. Their formation is also associated with the activity of living matter. The carbon of these carbonates is buried for a long time in the bowels of the Earth and enters the circulation only during erosion when rocks are exposed in tectonic cycles.

Only fractions of a percent of carbon from its total amount on Earth participate in the biogeochemical cycle. Atmospheric and hydrosphere carbon repeatedly passes through living organisms. Land plants are able to exhaust its reserves in the air in 4-5 years, reserves in soil humus - in 300-400 years. The main return of carbon to the exchange fund occurs due to the activity of living organisms, and only a small part of it (thousandths of a percent) is compensated by the release from the Earth's interior as part of volcanic gases.

At present, the extraction and burning of huge reserves of fossil fuels is becoming a powerful factor in the transfer of carbon from the reserve to the exchange fund of the biosphere.

Nitrogen cycle in the biosphere

The atmosphere and living matter contain less than 2% of all nitrogen on Earth, but it is he who supports life on the planet. Nitrogen is one of the most important organic molecules- DNA, proteins, lipoproteins, ATP, chlorophyll, etc. In plant tissues, its ratio with carbon is on average 1: 30, and in seaweed I: 6. Therefore, the biological cycle of nitrogen is also closely related to carbon.

The molecular nitrogen of the atmosphere is not available to plants, which can absorb this element only in the form of ammonium ions, nitrates, or from soil or water solutions. Therefore, nitrogen deficiency is often a factor limiting primary production- the work of organisms associated with the creation of organic substances from inorganic. Nevertheless, atmospheric nitrogen is widely involved in the biological cycle due to the activity of special bacteria (nitrogen fixers).

Ammonifying microorganisms also take an important part in the nitrogen cycle. They decompose proteins and other nitrogen-containing organic substances into ammonia. In the ammonium form, nitrogen is partly reabsorbed by the roots of plants, and partly intercepted by nitrifying microorganisms, which is opposite to the functions of a group of microorganisms - denitrifiers.

Rice. 8. Nitrogen cycle

Under anaerobic conditions in soils or waters, they use the oxygen of nitrates to oxidize organic matter, obtaining energy for their life activity. Nitrogen is reduced to molecular nitrogen. Nitrogen fixation and denitrification in nature are approximately balanced. The nitrogen cycle thus depends predominantly on bacterial activity, while plants enter it by using the intermediate products of this cycle and greatly increasing the nitrogen circulation in the biosphere through the production of biomass.

The role of bacteria in the nitrogen cycle is so great that if only 20 of their species are destroyed, life on our planet will cease.

Non-biological fixation of nitrogen and the entry of its oxides and ammonia into soils also occur with rainfall during atmospheric ionization and lightning discharges. The modern fertilizer industry fixes atmospheric nitrogen in excess of natural nitrogen fixation in order to increase crop production.

At present, human activity is increasingly affecting the nitrogen cycle, mainly in the direction of exceeding its conversion into bound forms over the processes of returning to the molecular state.

Phosphorus cycle in the biosphere

This element, necessary for the synthesis of many organic substances, including ATP, DNA, RNA, is absorbed by plants only in the form of orthophosphoric acid ions (PO 3 4 +). It belongs to the elements limiting primary production both on land and especially in the ocean, since the exchange fund of phosphorus in soils and waters is small. The circulation of this element on the scale of the biosphere is not closed.

On land, plants draw phosphates from the soil, released by decomposers from decaying organic residues. However, in alkaline or acidic soil, the solubility of phosphorus compounds drops sharply. The main reserve fund of phosphates is contained in rocks created on the ocean floor in the geological past. In the course of rock leaching, part of these reserves passes into the soil and is washed out into water bodies in the form of suspensions and solutions. In the hydrosphere, phosphates are used by phytoplankton, passing through food chains to other hydrobionts. However, in the ocean, most of the phosphorus compounds are buried with the remains of animals and plants at the bottom, followed by a transition with sedimentary rocks into a large geological cycle. At depth, dissolved phosphates bind with calcium, forming phosphorites and apatites. In the biosphere, in fact, there is a unidirectional flow of phosphorus from the rocks of the land to the depths of the ocean, therefore, its exchange fund in the hydrosphere is very limited.

Rice. 9. Phosphorus cycle

Ground deposits of phosphorites and apatites are used in the production of fertilizers. The ingress of phosphorus into fresh water is one of the main reasons for their "bloom".

Sulfur cycle in the biosphere

The cycle of sulfur, necessary for the construction of a number of amino acids, is responsible for the three-dimensional structure of proteins, and is supported in the biosphere by a wide range of bacteria. Aerobic microorganisms, which oxidize the sulfur of organic residues to sulfates, as well as anaerobic sulfate reducers, which reduce sulfates to hydrogen sulfide, participate in separate links of this cycle. In addition to the listed groups of sulfur bacteria, they oxidize hydrogen sulfide to elemental sulfur and further to sulfates. Plants absorb only SO 2-4 ions from soil and water.

The ring in the center illustrates the oxidation (O) and reduction (R) processes that exchange sulfur between the available sulfate pool and the iron sulfide pool deep in the soil and sediment.

Rice. 10. Sulfur cycle. The ring in the center illustrates the oxidation (0) and reduction (R) processes that exchange sulfur between the available sulfate pool and the iron sulfide pool deep in soil and sediment.

The main accumulation of sulfur occurs in the ocean, where sulfate ions are continuously supplied from land with river runoff. When hydrogen sulfide is released from the waters, sulfur is partially returned to the atmosphere, where it is oxidized to dioxide, turning into sulfuric acid in rainwater. The industrial use of large amounts of sulphates and elemental sulfur and the combustion of fossil fuels release large amounts of sulfur dioxide into the atmosphere. This harms vegetation, animals, people and serves as a source of acid rain, which exacerbates the negative effects of human intervention in the sulfur cycle.

The rate of circulation of substances

All cycles of substances occur at different speeds (Fig. 11)

Thus, the cycles of all biogenic elements on the planet are supported by a complex interaction of different parts. They are formed by the activity of groups of organisms with different functions, by the system of runoff and evaporation connecting the ocean and land, by the processes of circulation of water and air masses, by the action of gravitational forces, by lithospheric plate tectonics, and by other large-scale geological and geophysical processes.

The biosphere acts as a single complex system in which various cycles of substances take place. The main engine of these cycles is the living substance of the planet, all living organisms, providing processes of synthesis, transformation and decomposition of organic matter.

Rice. 11. The rate of circulation of substances (P. Cloud, A. Jibor, 1972)

The basis of the ecological view of the world is the idea that every living being is surrounded by many different factors influencing it, which together form its habitat - a biotope. Hence, biotope - a piece of territory that is homogeneous in terms of living conditions for certain types of plants or animals(the slope of a ravine, an urban forest park, a small lake or part of a large one, but with homogeneous conditions - the coastal part, the deep-water part).

Organisms characteristic of a particular biotope are life community, or biocenosis(animals, plants and microorganisms of the lake, meadow, coastal strip).

The life community (biocenosis) forms a single whole with its biotope, which is called ecological system (ecosystem). An anthill, a lake, a pond, a meadow, a forest, a city, a farm can serve as an example of natural ecosystems. A classic example of an artificial ecosystem is a spaceship. As you can see, there is no strict spatial structure here. Close to the concept of an ecosystem is the concept biogeocenosis.

The main components of ecosystems are:

• inanimate (abiotic) environment. These are water, minerals, gases, as well as organic substances and humus;
• biotic components. These include: producers or producers (green plants), consumers, or consumers (living creatures that feed on producers), and decomposers, or decomposers (microorganisms).

Nature is extremely economical. Thus, the biomass created by organisms (the substance of the bodies of organisms) and the energy contained in them are transferred to other members of the ecosystem: animals eat plants, these animals are eaten by other animals. This process is called food or trophic chain. In nature, food chains often intersect, forming a food web.

Examples of food chains: plant - herbivore - predator; cereal - field mouse - fox, etc. and the food web are shown in fig. 12.

Thus, the state of equilibrium in the biosphere is based on the interaction of biotic and abiotic environmental factors, which is maintained due to the continuous exchange of matter and energy between all components of ecosystems.

In closed cycles of natural ecosystems, along with others, the participation of two factors is mandatory: the presence of decomposers and the constant supply of solar energy. There are few or no decomposers in urban and artificial ecosystems, so liquid, solid and gaseous wastes accumulate, polluting the environment.

Rice. 12. Food web and direction of matter flow

Large cycle of substances in nature due to the interaction of solar energy with the deep energy of the Earth and redistributes matter between the biosphere and deeper horizons of the Earth.

Sedimentary rocks formed due to the weathering of igneous rocks in the mobile zones of the earth's crust again plunge into the zone of high temperatures and pressures. There they are melted down and form magma - the source of new igneous rocks. After the rise of these rocks to the earth's surface and the action of weathering processes, they are again transformed into new sedimentary rocks. The new cycle of circulation does not exactly repeat the old one, but introduces something new, which over time leads to very significant changes.

driving force great (geological) circulation are exogenous and endogenous geological processes.

Endogenous processes(processes of internal dynamics) occur under the influence of the internal energy of the Earth, released as a result of radioactive decay, chemical reactions of the formation of minerals, crystallization of rocks, etc. (for example, tectonic movements, earthquakes, magmatism, metamorphism).

Exogenous processes(processes of external dynamics) proceed under the influence of the external energy of the Sun. Examples: weathering of rocks and minerals, removal of destruction products from some areas of the earth's crust and their transfer to new areas, deposition and accumulation of destruction products with the formation of sedimentary rocks. To Ex.pr. relation geological activity of the atmosphere, hydrosphere, as well as living organisms and humans.

The largest landforms (continents and oceanic depressions) and large landforms (mountains and plains) were formed due to endogenous processes, while medium and small landforms (river valleys, hills, ravines, dunes, etc.), superimposed on larger landforms, were formed due to account of exogenous processes. Thus, endogenous and exogenous processes are opposite. The former lead to the formation of large landforms, the latter to their smoothing.

Examples of the geological cycle. Igneous rocks are transformed into sedimentary rocks as a result of weathering. In the mobile zones of the earth's crust, they sink into the depths of the Earth. There, under the influence of high temperatures and pressures, they melt and form magma, which, rising to the surface and, solidifying, forms igneous rocks.

An example of a large cycle is the circulation of water between land and ocean through the atmosphere (Fig. 2.1).

Rice. 2.1. The generally accepted scheme of hydrological (climatic)

water cycle in nature

Moisture evaporated from the surface of the World Ocean (which consumes almost half of the solar energy coming to the Earth's surface) is transferred to land, where it falls in the form of precipitation, which again returns to the ocean in the form of surface and underground runoff. The water cycle also occurs according to a simpler scheme: evaporation of moisture from the surface of the ocean - condensation of water vapor - precipitation on the same water surface of the ocean.

The water cycle as a whole plays a major role in shaping the natural conditions on our planet. Taking into account the transpiration of water by plants and its absorption in the biogeochemical cycle, the entire supply of water on Earth decays and is restored in 2 million years.

Thus, the geological circulation of substances proceeds without the participation of living organisms and redistributes matter between the biosphere and the deeper layers of the Earth.