Elemental Composition of Living Matter and OM of Combustible Fossils
Combustible fossils contain in their composition the same elements as the substance of living organisms, so the elements - carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus called or biogenic, or biophilic, or organogenic.
Hydrogen, carbon, oxygen and nitrogen account for over 99% both the mass and the number of atoms that make up all living organisms. In addition to them, in significant quantities in living organisms, another eye can be concentrated.
lo 20-22 chemical elements. 12 elements make up 99.29%, the rest 0.71%
Space abundance: H, He, C, N.
Up to 50% - C, up to 20% - O, up to 8% - H, 10-15% - N, 2-6% - P, 1% - S, 1% - K, ½% - Mg and Ca, 0 .2% - Fe, in trace amounts - Na, Mn, Cu, Zn.
The structure of the atom, isotopes, distribution of hydrogen, oxygen, sulfur and nitrogen in the earth's crust
HYDROGEN - the main element of the cosmos, the most common element of the universe . Chem e-t 1 group, atomic number 1, atomic mass 1.0079. In modern editions of the periodic table, H is also placed in group VII above F, since some properties of H are similar to the properties of halogens. Three H isotopes are known. Two stable ones are protium 1 H - P (99.985%), deuterium 2 H - D (0.015%), and one radioactive is tritium 3 H - T, T 1/2 = 12.262 years. One more is artificially obtained - the fourth extremely unstable isotope - 4 H. In the separation of P and D under natural conditions, evaporation plays the main role, however, the mass of the world's oceans is so large that the deuterium content in it changes slightly. In tropical countries, the content of deuterium in precipitation is higher than in the polar zone. In the free state, H is a colorless gas, odorless and tasteless, the lightest of all gases, 14.4 times lighter than air. H becomes liquid at -252.6°C, solid at -259.1°C. H is an excellent reducing agent. It burns in O with a non-luminous flame, forming water. In the earth's crust, H is much smaller than in stars and on the Sun. Its weight clarke in the earth's crust is 1%. In natural chemical compounds, H forms ionic, covalent And hydrogen bonds . Hydrogen bonds play an important role in biopolymers (carbohydrates, alcohols, proteins, nucleic acids), determine the properties and structure of kerogen geopolymers and GI molecules. Under certain conditions, the H atom is able to combine simultaneously with two other atoms. As a rule, it forms a strong covalent bond with one of them, and a weak one with the other, which is called hydrogen bond.
OXYGEN - The most common element of the earth's crust, it is 49.13% by weight. O has serial number 8, is in period 2, group VI, atomic mass 15.9994. Three stable isotopes of O are known - 16 O (99.759%), 17 O (0.0371%), 18 O (0.2039%). There are no long-lived radioactive isotopes of O. Artificial radioactive isotope 15 O (T 1/2 = 122 seconds). The isotope ratio 18 O/16 O is used for geological reconstructions, which in natural objects varies by 10% from 1/475 to 1/525. The polar ices have the lowest isotopic coefficient, the highest - CO 2 of the atmosphere. When comparing the isotopic composition, the value is used d 18 O, which is calculated by the formula: d 18 O‰= . Behind standard the average ratio of these isotopes in ocean water is taken. Variations in the isotopic composition of O in gp, water are determined by the temperature at which the process of formation of specific minerals proceeds. The lower T, the more intensive isotope fractionation will be. It is believed that the O isotope composition of the ocean has not changed over the past 500 million years. The main factor determining the isotopic shift (variations in the isotopic composition in nature) is the kinetic effect determined by the reaction temperature. O under normal conditions, the gas is invisible, tasteless, odorless. In reactions with the overwhelming majority of atoms, O acts as oxidizing agent. Only in the reaction with F is the oxidizing agent F. O exists in biallotropic modifications . First - molecular oxygen - O 2 The second modification is ozone - O 3, arr under the action of electrical discharges in air and pure O, in radioactive processes, by the action of ultraviolet rays on ordinary O. In nature About 3 formed constantly under the action of UV rays in the upper atmosphere. At an altitude of about 30-50 km there is an "ozone screen" that traps the bulk of UV rays, protecting the organisms of the biosphere from the harmful effects of these rays. At low concentrations, About 3 pleasant, refreshing smell, but if in the air more than 1% O 3 it is highly toxic .
NITROGEN - concentrated in the biosphere: it prevails in the atmosphere (75.31% by weight, 78.7% by volume), and in the earth's crust it weight clark - 0.045%. Chemical element of group V, 2 periods atomic number 7, atomic mass 14.0067. Three N isotopes are known - two stable 14 N (99.635%) and 15 N (0.365%) and radioactive 13 N, T 1/2 = 10.08 min. General scatter of ratio values 15 N/ 14 N small . The oils are enriched in the 15 N isotope, while the accompanying natural gases are depleted in it. Oil shale is also enriched in heavy isotope N 2 colorless gas, tasteless and odorless. N unlike O does not support breathing, the mixture N with O is most acceptable for the breath of most of the inhabitants of our planet. N is chemically inactive. It is part of the GI of all organisms. The low chemical activity of nitrogen is determined by the structure of its molecule. Like most gases, except for inert ones, the molecule N consists of two atoms. In the formation of a bond between them, 3 valence electrons of the outer shell of each atom participate, forming triple covalent chemical bond , which gives the most stable of all known diatomic molecules. "Formal" valency from -3 to +5, "true" valence 3. Forming strong covalent bonds with O, H and C, it is part of the complex ions: -, -, +, which give easily soluble salts.
SULFUR - e-t ZK, in the mantle (ultrabasic rocks) it is 5 times less than in the lithosphere. Clark in ZK - 0,1%. Chemical element group VI, 3 periods, atomic number 16, atomic mass 32.06. Highly electronegative el-t, exhibits non-metallic properties. In hydrogen and oxygen compounds, it is in the composition of various ions. Arr acid and salt. Many sulfur-containing salts are sparingly soluble in water. S can have valences: (-2), (0), (+4), (+6), of which the first and last are the most characteristic. Both ionic and covalent bonds are characteristic. The main value for natural processes is the complex ion - 2 S - non-metal, chemically active element. Only with Au and Pt S does not interact. Of the inorganic compounds, in addition to sulfates, sulfides and H2SO4, oxides of SO 2 - a gas that strongly pollutes the atmosphere, and SO 3 (solid), as well as hydrogen sulfide, are common on Earth. Elementary S is characterized by three allotropic varieties : S rhombic (most stable), S monoclinic (cyclic molecule - eight-membered ring S 8) and plastic S 6 are linear chains of six atoms. 4 stable isotopes of S are known in nature: 32S (95.02%), 34S (4.21%), 33S (0.75%), 36S (0.02%). Artificial radioactive isotope 35 S c T 1/2 = 8.72 days. S is accepted as standard. troilite(FeS) from the Canyon Diablo meteorite (32 S/ 34 S= 22.22) Oxidation and reduction reactions can cause isotopic exchange, which is expressed in an isotopic shift. In nature, it is bacterial, but thermal is also possible. In nature, to date, there has been a clear division of the S of the earth's crust into 2 groups - biogenic sulfides and gases enriched in the light isotope 32 S, and sulfates, included in the salts of oceanic water of ancient evaporites, gypsum containing 34 S. The gases associated with oil deposits vary in isotopic composition and differ markedly from oils.
The chemical composition of the earth's crust was determined from the results of the analysis of numerous samples of rocks and minerals that come to the surface of the earth during mountain-building processes, as well as taken from mine workings and deep boreholes.
At present, the earth's crust has been studied to a depth of 15-20 km. It consists of chemical elements that are part of the rocks.
The most widespread in the earth's crust are 46 elements, of which 8 make up 97.2-98.8% of its mass, 2 (oxygen and silicon) - 75% of the mass of the Earth.
The first 13 elements (with the exception of titanium), which are most often found in the earth's crust, are part of the organic matter of plants, participate in all vital processes and play an important role in soil fertility. A large number of elements involved in chemical reactions in the bowels of the Earth leads to the formation of a wide variety of compounds. Chemical elements, which are most in the lithosphere, are part of many minerals (they mainly consist of different rocks).
Separate chemical elements are distributed in the geospheres as follows: oxygen and hydrogen fill the hydrosphere; oxygen, hydrogen and carbon form the basis of the biosphere; oxygen, hydrogen, silicon and aluminum are the main components of clays and sands or weathering products (they mostly make up the upper part of the Earth's crust).
Chemical elements in nature are found in a variety of compounds called minerals. These are homogeneous chemicals of the earth's crust, which were formed as a result of complex physicochemical or biochemical processes, for example, rock salt (NaCl), gypsum (CaS04 * 2H20), orthoclase (K2Al2Si6016).
In nature, chemical elements take an unequal part in the formation of different minerals. For example, silicon (Si) is found in over 600 minerals and is also very common in the form of oxides. Sulfur forms up to 600 compounds, calcium-300, magnesium -200, manganese-150, boron - 80, potassium - up to 75, only 10 lithium compounds are known, and even less iodine.
Among the best known minerals in the earth's crust is dominated by a large group of feldspars with three main elements - K, Na and Ca. In soil-forming rocks and their weathering products, feldspars occupy the main position. Feldspars gradually weather (decompose) and enrich the soil with K, Na, Ca, Mg, Fe and other ash substances, as well as trace elements.
Clarke number- numbers expressing the average content of chemical elements in the earth's crust, hydrosphere, Earth, cosmic bodies, geochemical or cosmochemical systems, etc., in relation to the total mass of this system. Expressed in % or g/kg.
Types of clarks
There are weight (in %, in g/t or in g/g) and atomic (in % of the number of atoms) clarks. Generalization of data on chemical composition of various rocks that make up the earth's crust, taking into account their distribution to depths of 16 km, was first done by the American scientist F. W. Clark (1889). The numbers obtained by him for the percentage of chemical elements in the composition of the earth's crust, later somewhat refined by A. E. Fersman, at the suggestion of the latter were called Clark numbers or clarks.
The structure of the molecule. Electrical, optical, magnetic and other properties of molecules are related to wave functions and energies of various states of molecules. Information about the states of molecules and the probability of transition between them is provided by molecular spectra.
The vibration frequencies in the spectra are determined by the masses of the atoms, their arrangement, and the dynamics of interatomic interactions. The frequencies in the spectra depend on the moments of inertia of molecules, the determination of which from spectroscopic data makes it possible to obtain exact values of interatomic distances in a molecule. The total number of lines and bands in the vibrational spectrum of a molecule depends on its symmetry.
Electronic transitions in molecules characterize the structure of their electron shells and the state of chemical bonds. The spectra of molecules that have a greater number of bonds are characterized by long-wavelength absorption bands that fall into the visible region. Substances that are built from such molecules are characterized by color; such substances include all organic dyes.
Ions. As a result of electron transitions, ions are formed - atoms or groups of atoms in which the number of electrons is not equal to the number of protons. If an ion contains more negatively charged particles than positively charged ones, then such an ion is called negative. Otherwise, the ion is called positive. Ions are very common in substances, for example, they are in all metals without exception. The reason is that one or more electrons from each metal atom are separated and move inside the metal, forming the so-called electron gas. It is because of the loss of electrons, that is negative particles, metal atoms become positive ions. This is true for metals in any state - solid, liquid or gaseous.
The crystal lattice models the arrangement of positive ions inside the crystal of a homogeneous metallic substance.
It is known that in the solid state all metals are crystals. The ions of all metals are arranged in an orderly manner, forming a crystal lattice. In molten and vaporized (gaseous) metals, there is no ordered arrangement of ions, but the electron gas still remains between the ions.
Isotopes- varieties of atoms (and nuclei) of a chemical element that have the same atomic (ordinal) number, but different mass numbers. The name is due to the fact that all isotopes of one atom are placed in the same place (in one cell) of the periodic table. Chemical properties atoms depend on the structure of the electron shell, which, in turn, is determined mainly by the charge of the nucleus Z (that is, the number of protons in it), and almost do not depend on its mass number A (that is, the total number of protons Z and neutrons N). All isotopes of the same element have the same nuclear charge, differing only in the number of neutrons. Usually, an isotope is denoted by the symbol of the chemical element to which it belongs, with the addition of an upper left index indicating the mass number. You can also write the name of the element with a hyphenated mass number. Some isotopes have traditional proper names (for example, deuterium, actinon).
There are the following forms of finding chemical elements in the earth's crust : 1) independent mineral species; 2) impurities and mixtures - a) non-structural (scattering state), b) structural (isomorphic impurities and mixtures); 3) silicate melts; 4) aqueous solutions and gas mixtures; 5) biogenic form. The most studied are the first two forms.
Independent mineral species(minerals) represent the most important form of existence of chemical elements in the earth's crust. By prevalence, minerals are divided into five groups: very common, common, common ore, rare, very rare.
Non-structural impurities they do not have a crystallochemical bond with the crystal lattice of the host mineral and are in a state of scattering (according to A.E. Fersman - endocrypt scattering). This form of occurrence is typical for a group of radioactive elements, as well as for elements that do not form independent mineral species. The atmosphere and hydrosphere are especially favorable for scattering. The content of 1 atom in 1 cm 3 of a substance is conditionally taken as the lower limit of scattering.
Structural impurities usually called isomorphic. isomorphism called the property of atoms of one chemical element to replace atoms of another chemical element at the nodes of the crystal lattice with the formation of a homogeneous (homogeneous) mixed crystal of variable composition. The formation of an isomorphic mixture is determined primarily by the proximity of the crystal lattice parameters of the components being mixed. Components that have a similar structure, but do not form a homogeneous mixed crystal, are called isostructural (for example, halite NaCl and galena PbS).
Currently there are several types of isomorphism taking into account the following features: 1) the degree of isomorphic miscibility - perfect and imperfect; 2) the valency of the ions involved in the substitutions - isovalent and heterovalent; 3) the mechanism of entry of an atom into the crystal lattice - polar. For an isovalent isomorphism exists rule : if ions of larger or smaller radii participate in the substitution, then the ion of a smaller radius enters the crystal lattice first of all, in the second place - an ion of a larger radius. Heterovalent isomorphism obeys law of diagonal rows periodic system D.I. Mendeleev, established by A.E. Fersman.
The formation of isomorphic mixtures is due to several factors, among which internal and external are distinguished. Internal factors are determined by the features inherent in the atom (ion or molecule); these include the following: chemical indifference of atoms, sizes of atoms (ions), similarities in the type of chemical bond and crystal structures; preservation of electrostatic equilibrium during the formation of an isomorphic mixture. External factors of isomorphism include physical and chemical conditions of the environment - temperature, pressure, concentration of isomorphic components. At high temperatures, the isomorphic miscibility of the components increases. With a decrease in temperature, the mineral is freed from impurities. This is the phenomenon of A.E. Fersman was named autolysia (self-cleaning). As the pressure increases, atoms with smaller radii preferentially enter the crystal lattice of the host mineral. The joint role of temperature and pressure is illustrated by V.I. Vernadsky.
Isomorphic mixtures are stable while maintaining the physicochemical conditions of their formation. A change in these conditions leads to the fact that the mixtures decompose into constituent components. Under endogenous conditions, the main factors of decomposition are temperature and pressure. Under exogenous conditions, the reasons for the decomposition of isomorphic mixtures are more diverse: a change in the valency of chemical elements isomorphically replacing each other, accompanied by a change in ionic radii; change in the type of chemical bond; change in the pH of hypergene solutions.
The phenomenon of isomorphism is widely used to solve various geological problems, in particular paleothermometry. The decomposition of isomorphic mixtures often leads to the formation of easily soluble compounds, which, as a result of leaching, enter the composition of groundwater, which is the object of hydrogeochemical studies (1.140–159; 2.128–130; 3.96–102).
Answers on questions,
submitted to the exam in the discipline "Physical and chemical processes in environment» for third-year students of the specialty "Environmental Management and Audit in Industry"
The abundance of atoms in the environment. Clarke elements.
element clark - a numerical estimate of the average content of an element in the earth's crust, hydrosphere, atmosphere, the Earth as a whole, various types of rocks, space objects, etc. The clarke of an element can be expressed in units of mass (%, g / t), or in atomic%. Introduced by Fersman, named after Frank Unglisort, an American geochemist.
The quantitative distribution of chemical elements in the earth's crust was first established by Clark. He also included the hydrosphere and atmosphere in the earth's crust. However, the mass of the hydrosphere is a few%, and the atmosphere - hundredths of a% of the mass of the solid earth's crust, so the Clark numbers mainly reflect the composition of the solid earth's crust. So, in 1889 clarks were calculated for 10 elements, in 1924 - for 50 elements.
Modern radiometric, neutron activation, atomic absorption and other methods of analysis make it possible to determine the content of chemical elements in rocks and minerals with great accuracy and sensitivity. Ideas about Clarks have changed. N-r: Ge in 1898, Fox considered the clark equal to n * 10 -10%. Ge was poorly studied and had no practical value. In 1924, the Clark was calculated for him as n * 10 -9% (Clark and G. Washington). Later, Ge was found in coals, and its clarke increased to 0.n%. Ge is used in radio engineering, the search for germanium raw materials, a detailed study of the geochemistry of Ge showed that Ge is not so rare in the earth's crust, its clarke in the lithosphere is 1.4 * 10 -4%, almost the same as that of Sn, As, it is much more in the earth's crust than Au, Pt, Ag.
The abundance of atoms in
Vernadsky introduced the concept of the scattered state of chemical elements, and it was confirmed. All elements are everywhere, we can only talk about the lack of sensitivity of the analysis, which does not allow determining the content of one or another element in the environment under study. This provision on the general dispersion of chemical elements is called the Clark-Vernadsky law.
Based on the clarks of elements in the solid earth's crust (about Vinogradova), almost ½ of the solid earth's crust consists of O, that is, the earth's crust is an "oxygen sphere", an oxygen substance.
The clarks of most elements do not exceed 0.01-0.0001% - these are rare elements. If these elements have a weak ability to concentrate, they are called sharp scattered (Br, In, Ra, I, Hf).
NR: For U and Br, the clarke values are ≈ 2.5*10 -4 , 2.1* 10-4 respectively, but U is just a rare element because its deposits are known, and Br is a rare scattered, because. it is not concentrated in the earth's crust. Trace elements - elements contained in this system in small quantities (≈ 0.01% or less). Thus, Al is a trace element in organisms and a macroelement in silicate rocks.
Classification of elements according to Vernadsky.
In the earth's crust, elements related in the periodic system behave differently - they migrate into the earth's crust in different ways. Vernadsky took into account the most important moments in the history of elements in the earth's crust. The main importance was given to such phenomena and processes as radioactivity, reversibility and irreversibility of migration. Ability to provide minerals. Vernadsky identified 6 groups of elements:
noble gases (He, Ne, Ar, Kr, Xe) - 5 elements;
noble metals (Ru, Rh, Pd, Os, Ir, Pt, Au) - 7 elements;
cyclic elements (participating in complex cycles) - 44 elements;
scattered elements - 11 elements;
highly radioactive elements (Po, Ra, Rn, Ac, Th, Pa, U) - 7 elements;
elements of rare earths - 15 elements.
Elements of the 3rd group by mass predominate in the earth's crust; they mainly consist of rocks, water, and organisms.
Representations from everyday experience do not match the real data. So, Zn, Cu are widespread in everyday life and technology, and Zr (zirconium) and Ti are rare elements for us. Although Zr in the earth's crust is 4 times more than Cu, and Ti - 95 times. The "rarity" of these elements is explained by the difficulty of extracting them from ores.
Chemical elements interact with each other not in proportion to their masses, but in accordance with the number of atoms. Therefore, clarks can be calculated not only in mass %, but also in % of the number of atoms, i.e. taking into account atomic masses (Chirvinsky, Fersman). At the same time, the clarks of heavy elements decrease, while those of light elements increase.
For example:The calculation for the number of atoms gives a more contrasting picture of the abundance of chemical elements - an even greater predominance of oxygen and the rarity of heavy elements.
When the average composition of the earth's crust was established, the question arose of the reason for the uneven distribution of elements. These flocks are associated with the structural features of atoms.
Consider the relationship between the value of clarks and the chemical properties of elements.
So the alkali metals Li, Na, K, Rb, Cs, Fr are chemically close to each other - one valence electron, but the clarke values differ - Na and K - ≈ 2.5; Rb - 1.5 * 10 -2; Li - 3.2 * 10 -3; Cs - 3.7 * 10 -4; Fr - an artificial element. Clarke values for F and Cl, Br and I, Si (29.5) and Ge (1.4*10 -4), Ba (6.5*10 -2) and Ra (2*10 -10) differ sharply .
On the other hand, chemically different elements have close clarks - Mn (0.1) and P (0.093), Rb (1.5 * 10 -2) and Cl (1.7 * 10 -2).
Fersman plotted the dependence of the values of atomic clarks for even and odd elements of the Periodic Table on the ordinal number of the element. It turned out that with the complication of the structure of the atomic nucleus (heavier), the clarks of the elements decrease. However, these dependencies (curves) turned out to be broken.
Fersman drew a hypothetical middle line, which gradually decreased as the atomic number of the element increased. The elements located above the middle line, forming peaks, the scientist called excess (O, Si, Fe, etc.), and those located below the line - deficient (inert gases, etc.). It follows from the dependence obtained that light atoms predominate in the earth's crust, occupying the initial cells of the Periodic system, the nuclei of which contain a small amount of protons and neutrons. Indeed, after Fe (No. 26) there is not a single common element.
Further Oddo (Italian scientist) and Harkins (American scientist) in 1925-28. another feature of the abundance of elements was established. The Earth's crust is dominated by elements with even numbers and atomic masses. Among neighboring elements, the clarkes of even elements are almost always higher than those of odd ones. For the 9 most common elements (8 O, 14 Si, 13 Al, 26 Fe, 20 Ca, 11 Na, 19 K, 12 Mg, 22 Ti), the mass clarks of even ones add up to 86.43%, and odd - 13.05 %. The clarks of elements whose atomic mass is divisible by 4 are especially large, these are O, Mg, Si, Ca.
According to Fersman's research, 4q-type nuclei (q is an integer) make up 86.3% of the earth's crust. Less common are 4q+3 nuclei (12.7%) and very few 4q+1 and 4q+2 nuclei (1%).
Among the even elements, starting with He, every sixth has the largest clarks: O (No. 8), Si (No. 14), Ca (No. 20), Fe (No. 26). For odd elements - a similar rule (starting with H) - N (No. 7), Al (No. 13), K (No. 19), Mg (No. 25).
So, in the earth's crust, nuclei with a small and even number of protons and neutrons predominate.
Clarks have changed over time. So, as a result of radioactive decay, there was less U and Th, but more Pb. Such processes as dissipation of gases, fallout of meteorites also played a role in changing the values of clarks of elements.
The main trends of chemical changes in the earth's crust. Large circulation of matter in the earth's crust.
CIRCULATION OF SUBSTANCES. The substance of the earth's crust is in continuous motion, caused by a variety of reasons associated with the physical. properties of matter, planetary, geological, geographical and biol. earth conditions. This movement invariably and continuously occurs during geological time, not less than one and a half and apparently not more than three billion years. IN last years a new science of the geological cycle has grown - geochemistry, which has the task of studying chem. elements that build our planet. The main subject of its study are the movements of chemical. elements of the earth's substance, no matter what causes these movements may be caused. These movements of elements are called chemical migrations. elements. Among the migrations there are those during which the chem. the element after a longer or shorter period of time inevitably returns to its initial state; the history of such chem. elements in the earth's crust can be reduced so. to a reversible process and is presented in the form of a circular process, circulation. This kind of migration is not typical for all elements, but for a significant number of them, including the vast majority of chemical elements. elements that build plant or animal organisms and the environment around us - oceans and waters, rocks and air. For such elements, all or the overwhelming majority of their atoms are in the circulation of substances, for others only an insignificant part of them is covered by cycles. Undoubtedly, most of the matter of the earth's crust to a depth of 20-25 km is covered by gyres. For the following chem. elements of circular processes are characteristic and dominant among their migrations (the figure indicates the ordinal number). H, Be4, B5, C', N7, 08, P9, Nan, Mg12, Aha, Sii4, Pi5, Sie, Cli7, K19, Ca2o, Ti22, V23, Cr24, Mn25, Fe2e, Co27, Ni28, Cu29, Zn30 , Ge32, As33, Se34, Sr38, Mo42, Ag47, Cd48, Sn50, Sb51, Te62, Ba56) W74, Au79, Hg80, T]81, Pb82, Bi83. These elements can be separated from other elements on this basis as cyclic or organogenic elements. That. cycles characterize 42 elements out of 92 included in the Mendeleev system of elements, and this number includes the most common dominant terrestrial elements.
Let us dwell on the K. of the first kind, which include biogenic migrations. These climates capture the biosphere (i.e., the atmosphere, hydrosphere, and weathering crust). Under the hydrosphere, they capture a basalt shell approaching the ocean floor. Under land, in a sequence of depressions, they embrace the thickness of sedimentary rocks (stratosphere), metamorphic and granite shells and enter the basalt shell. From the earth's depths lying behind the basalt shell, the earth's matter does not fall into the observed K. It also does not fall into them from above because of the limits of the upper parts of the stratosphere. That. chemical cycles. elements are surface phenomena that occur in the atmosphere up to heights of 15-20 km (not higher), and in the lithosphere, no deeper than 15-20 km. Any K., in order for it to be constantly renewed, requires an influx of external energy. There are two main ones and no doubt. source of such energy: 1) cosmic energy - radiation of the sun (biogenic migration almost entirely depends on it) and 2) atomic energy associated with the radioactive decay of elements "78 of the series uranium, thorium, potassium, rubidium. With a lesser degree of accuracy, mechanical energy can be isolated , associated with the movement (due to gravity) of the earth's masses, and probably cosmic energy penetrating from above (Hess rays).
The cycles, which capture several earthly shells, go slowly, with stops and can be seen only in geological time. Often they cover several geologist periods. They are caused by geologists, land and ocean displacements. Parts of K. can go quickly (eg biogenic migration).
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Until now, speaking about the atomic theory, about how substances that are completely different from each other are obtained from several types of atoms connected to each other in a different order, we have never asked the “childish” question - where did the atoms themselves come from? Why are there a lot of atoms of some elements, and very few of others, and they are very unevenly distributed. For example, just one element (oxygen) makes up half of the earth's crust. Three elements (oxygen, silicon and aluminum) in total already account for 85%, and if we add iron, potassium, sodium, potassium, magnesium and titanium to them, we will get 99.5% of the earth's crust. The share of several dozen other elements accounts for only 0.5%. The rarest metal on Earth is rhenium, and there is not so much gold with platinum, it is not for nothing that they are so expensive. And here is another example: there are about a thousand times more iron atoms in the earth's crust than copper atoms, a thousand times more copper atoms than silver atoms, and a hundred times more silver than rhenium atoms.
The elements on the Sun are distributed in a completely different way: there is the most hydrogen (70%) and helium (28%), and only 2% of all other elements. If we take the entire visible Universe, then there is even more hydrogen in it. Why is that? In ancient times and in the Middle Ages, questions about the origin of atoms were not asked, because they believed that they always existed in an unchanged form and quantity (and according to the biblical tradition, they were created by God on the same day of creation). And even when the atomistic theory won and chemistry began to develop rapidly, and D. I. Mendeleev created his famous system of elements, the question of the origin of atoms continued to be considered frivolous. Of course, occasionally one of the scientists mustered up the courage and proposed his theory. As already mentioned. In 1815, William Prout suggested that all elements originated from atoms of the lightest element, hydrogen. As Prout wrote, hydrogen is the same "first matter" of the ancient Greek philosophers. which by "condensing" gave all the other elements.
In the 20th century, through the efforts of astronomers and theoretical physicists, a scientific theory of the origin of atoms was created, which in general terms answered the question of the origin of chemical elements. In a very simplified way, this theory looks like this. At first, all matter was concentrated at one point with an incredibly high density (K) * "g / cm") and temperature (1027 K). These numbers are so large that there are no names for them. About 10 billion years ago, as a result of the so-called Big Bang, this super-dense and super-hot spot began to expand rapidly. Physicists have a fairly good idea of how events developed 0.01 seconds after the explosion. The theory of what happened before was developed much worse, because in the then-existing clot of matter, the now known physical laws were poorly observed (and the sooner, the worse). Moreover, the question of what happened before the Big Bang was essentially not even considered, because then there was no time itself! After all, if there is no material world, that is, no events, then where does time come from? Who or what will count it? So, the matter began to rapidly scatter and cool down. The lower the temperature, the more opportunities for the formation of various structures (for example, at room temperature, millions of different organic compounds can exist, at +500 ° C - only a few, and above +1000 ° C, probably, no organic substances can exist, - All of them break down into their component parts at high temperatures. According to scientists, 3 minutes after the explosion, when the temperature dropped to a billion degrees, the process of nucleosynthesis began (this word comes from the Latin nucleus - “core” and the Greek “synthesis” - “connection, combination”), i.e. the process of connection protons and neutrons into the nuclei of various elements. In addition to protons - hydrogen nuclei, helium nuclei also appeared; these nuclei could not yet add electrons and form agoms due to too high a temperature. The Primary Universe consisted of hydrogen (about 75%) and helium, with a small amount of the next largest element, lithium (its core has three protons). This composition has not changed for about 500 thousand years. The universe continued to expand, cool, and become increasingly rarefied. When the temperature dropped to +3000 "C. the electrons got the opportunity to combine with the nuclei, which led to the formation of stable hydrogen and helium atoms.
It would seem that the Universe, consisting of hydrogen and helium, should continue to expand and cool to infinity. But then there would be not only other elements, but also galaxies, stars, and also us. The forces of universal gravitation (gravity) counteracted the infinite expansion of the Universe. The gravitational compression of matter in different parts of the rarefied Universe was accompanied by repeated strong heating - the stage of mass formation of stars began, which lasted about 100 million years. In those regions of space consisting of gas and dust, where the temperature reached 10 million degrees, the process of thermonuclear fusion of helium began by fusion of hydrogen nuclei.These nuclear reactions were accompanied by the release of huge amount energy that was radiated into the surrounding space: so it lit up new star. As long as there was enough hydrogen in it, the compression of the star under the influence of gravitational forces was counteracted by radiation, which "pressed from the inside." Our Sun also shines by "burning" hydrogen. This process is very slow, since the approach of two positively charged protons is prevented by the Coulomb repulsion force. So our luminary judges yeshe long years life.
When the supply of hydrogen fuel comes to an end, the synthesis of helium gradually stops, and with it the powerful radiation fades. The forces of gravity again compress the star, the temperature rises and it becomes possible for helium nuclei to merge with each other to form carbon nuclei (6 protons) and oxygen (8 protons in the nucleus). These nuclear processes are also accompanied by the release of energy. But sooner or later helium stocks will come to an end. And then comes the third stage of compression of the star by the forces of gravity. And then everything depends on the mass of the star at this stage. If the mass is not very large (like our Sun), then the effect of the increase in temperature during the compression of the star will not be sufficient for carbon and oxygen to enter into further nuclear fusion reactions; such a star becomes a so-called white dwarf. Heavier elements are "manufactured" in stars that astronomers call red giants - their mass is several times that of the Sun. In these stars, the reactions of synthesis of heavier elements from carbon and oxygen take place. As astronomers figuratively express themselves, stars are nuclear fires, the ashes of which are heavy chemical elements.
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The energy released at this stage of the life of a star greatly "inflates" the outer layers of the red giant; if our Sun were such a star. The earth would be inside this giant ball - the prospect for everything on the earth is not the most pleasant. Stellar wind.
"breathing" from the surface of red giants, brings to outer space the chemical elements synthesized by these stars, which form nebulae (many of them are visible through a telescope). Red giants live relatively short lives - hundreds of times less than the Sun. If the mass of such a star exceeds the mass of the Sun by 10 times, then conditions arise (temperature of the order of a billion degrees) for the synthesis of elements up to iron. Yalro iron is the most stable of all cores. This means that the reactions of synthesis of elements that are lighter than iron proceed with the release of energy, while the synthesis of heavier elements requires energy. With the expenditure of energy, reactions of the decomposition of iron into lighter elements also occur. Therefore, in stars that have reached the "iron" stage of development, dramatic processes take place: instead of releasing energy, it is absorbed, which is accompanied by a rapid decrease in temperature and compression to a very small volume; astronomers call this process gravitational collapse (from the Latin word collapsus - “weakened, fallen”; it’s not for nothing that doctors call a sudden drop in blood pressure, which is very dangerous for humans). During the gravitational collapse, a huge number of neutrons are formed, which, due to the absence of a charge, easily penetrate into the nuclei of all available elements. Nuclei supersaturated with neutrons undergo a special transformation (called beta decay), during which a proton is formed from a neutron; as a result, the next element is obtained from the nucleus of this element, in the nucleus of which there is already one more proton. Scientists have learned to reproduce such processes in terrestrial conditions; Fine famous example- synthesis of the plutonium-239 isotope, when, when natural uranium (92 protons, 146 neutrons) is irradiated with neutrons, its nucleus captures one neutron and an artificial element neptunium (93 protons, 146 neutrons) is formed, and from it the same deadly plutonium (94 protons, 145 neutrons), which is used in atomic bombs. In stars that undergo gravitational collapse, as a result of neutron capture and subsequent beta decays, hundreds of different nuclei of all possible isotopes of chemical elements are formed. The collapse of a star ends with a grandiose explosion, accompanied by the ejection of a huge mass of matter into outer space - a supernova is formed. The ejected substance, containing all the elements from the periodic table (and our body contains those same atoms!), Scatters around at a speed of up to 10,000 km / s. and a small remainder dead star shrinks (collaises) to form a superdense neutron star or even a black hole. Occasionally, such stars flare up in our sky, and if the outbreak does not occur too far, the supernova outshines all other stars in brightness. And no wonder: the brightness of a supernova can exceed the brightness of an entire galaxy consisting of a billion stars! One of these " new "stars, according to the Chinese chronicles, flared up in 1054. Now in this place is the famous Crab nebula in the constellation Taurus, and in its center there is a rapidly rotating (30 revolutions per second!) Neutron star. Fortunately (for us , and not for the synthesis of new elements), such stars have flared so far only in distant galaxies ...
As a result of the "burning" of stars and the explosion of supernovae, all known chemical elements turned out to be in outer space. The remnants of supernovae in the form of expanding nebulae, “heated up” by radioactive transformations, collide with each other, condense into dense formations, from which new generation stars arise under the influence of gravitational forces. These stars (including our Sun) from the very beginning of their existence contain an admixture of heavy elements in their composition; the same elements are contained in the gas and dust clouds surrounding these stars, from which the planets are formed. So the elements that make up all the things around us, including our body, were born as a result of grandiose cosmic processes ...
Why are some elements formed a lot, and others - a little? It turns out that in the process of nucleosynthesis, nuclei consisting of a small even number of schutons and neutrons are most likely to be formed. Heavy nuclei, "overflowing" with protons and neutrons, are less stable and there are fewer of them in the Universe. There is a general rule: the greater the charge of the nucleus, the heavier it is, the less such nuclei in the Universe. However, this rule is not always followed. For example, there are few light nuclei of lithium (3 protons, 3 neutrons) and boron (5 protons and 5 or 6 neutrons) in the earth's crust. It is assumed that for a number of reasons these nuclei cannot be formed in the interiors of stars, but under the action of cosmic rays they “break off” from heavier nuclei accumulated in interstellar space. Thus, the ratio of various elements on Earth is an echo of the turbulent processes in space that took place billions of years ago, at the later stages of the development of the Universe.