D.Yu. Pushchashovsky, Yu.M. Pushchashovsky (MSU them. M.V. Lomonosov)

The composition and structure of the deep shells of the Earth in recent decades continues to be one of the most intriguing problems of modern geology. The number of direct data on the substance of the deep zones is very limited. In this regard, the mineral unit from the Kimberlite Tube Lesotho (South Africa) occupies a special place, which is considered as a representative of mantle breeds, which are at a depth of ~ 250 km. Curne, raised from the deepest well in the world, drilled on the Kola Peninsula and has reached 12,262 m, significantly expanded the scientific ideas about the deep horizons of the earth's crust - a thin near-surface film of the globe. At the same time, the newest data of geophysics and experiments related to the study of structural transformations of minerals are already allowed to simulate many features of the structure, composition and processes occurring in the depths of the Earth, the knowledge of which contributes to the solution of such key problems of modern natural science, as the formation and evolution of the planet, the dynamics Earth crust and mantle, sources of mineral resources, assessment of the risk of grave hazardous waste at large depths, Earth energy resources, etc.

Seismic model of the structure of the Earth

The well-known model of the internal structure of the Earth (dividing it on the core, mantle and earthly bark) was developed by the seismologists of G. Jeffris and B. Gutenberg still in the first half of the 20th century. The decisive factor was the discovery of a sharp decline in the speed of seismic waves inside the globe at a depth of 2,900 km during the radius of 6371 km. The speed of passage of longitudinal seismic waves directly above the specified border is equal to 13.6 km / s, and under it - 8.1 km / s. That's what it is border of mantle and kernel.

Accordingly, the radius of the nucleus is 3471 km. The top border of the mantle is the seismic section Mochorovichich ( Mocho , M), highlighted by the Yugoslav seismologist A. Mohovichich (1857-1936) back in 1909. He separates the earthly boron from the mantle. At this lineup of the speed of the longitudinal waves, which passed through the earth's bark, are jumpingly increasing from 6.7-7.6 to 7.9-8.2 km / s, but it takes place at different depth levels. Under the continents, the depth of the section M (i.e. the soles of the earth's crust) make up the first tens of kilometers, and under some mountain structures (Pamir, Andes) can reach 60 km, while under the ocean depressions, including water, the depth is only 10-12 km . In general, the earth's crust in this scheme is evaporated as a thin shell, while the mantle spreads deep into a depth of 45% of the earth's radius.

But in the middle of the 20th century, ideas about the more fractional deep structure of the Earth entered science. Based on new seismological data it was possible to divide the kernel to the inner and external, and the mantle to the lower and top (Fig. 1). This model that has been widespread is used and now. The Australian seismologist K.E. was laid on her Bullen, who proposed the earth's division into zones at the beginning of the 40s, which denoted by letters: a - Ground Cora, in - zone in the depths interval 33-413 km, C - zone 413-984 km, d - zone 984-2898 km , D - 2898-4982 km, F - 4982-5121 km, G - 5121-6371 km (center of the Earth). These zones are characterized by seismic characteristics. Later zone d, he divided into zones D "(984-2700 km) and d" (2700-2900 km). Currently, this scheme is significantly modified and only a layer D "is widely used in the literature. Its main characteristic is a decrease in seismic velocity gradients compared with the overlying area of \u200b\u200bthe mantle.

Fig. 1. Scheme of the deep structure of the Earth

The greater the seismological studies are carried out, the more seismic borders appear. Global is considered to be the boundaries of 410, 520, 670, 2900 km, where the increase in seismic wave rates is especially noticeable. Along with them, intermediate borders are distinguished: 60, 80, 220, 330, 710, 900, 1050, 2640 km. Additionally, there are instructions of geophysicists to the existence of boundaries 800, 1200-1300, 1700, 1900-2000 km. N.I. Pavlenkovaya recently highlighted the border 100, which corresponds to the lower level of separation of the upper mantle to blocks. Intermediate boundaries have different spatial distribution, which indicates the lateral variability of the physical properties of the mantle, from which they depend. Global boundaries represent a different category of phenomena. They meet the global changes in the mantle medium along the radius of the Earth.

The marked global seismic boundaries are used in the construction of geological and geodynamic models, while intermediate in this sense has not yet attracted attention. Meanwhile, the differences in the scale and intensity of their manifestation create an empirical basis for hypotheses relating to phenomena and processes in the depths of the planet.

Let us consider how the geophysical frontiers relate to the obtained in lately The results of structural changes in minerals under the influence of high pressures and temperatures, the values \u200b\u200bof which correspond to the conditions of earthly depths.

The problem of the composition, structures and mineral associations of deep globe or geospheres, of course, is still far from the final decision, but new experimental results and ideas significantly expand and detail the corresponding views.

According to modern views, a relatively small group of chemical elements prevails as part of the mantle: Si, Mg, Fe, Al, Ca and O. proposed models of geosphere composition First of all, it is based on the difference between the relations of these elements (variations Mg / (Mg + Fe) \u003d 0.8-0.9; (Mg + Fe) / Si \u003d 1.2Р1.9), as well as on differences in Al and Some other more rare for deep breeds of elements. In accordance with the chemical and mineralogical composition, these models received their names: pyrolyte (main minerals - olivine, pyroxen and grenades in respect of 4: 2: 1), plogyte (main minerals - pyroxen and grenade, and the share of olivine decreases to 40%) and the eclogite, in which, along with the Pyroxen-Granaya Association characteristic of the eclogites, there are some more rare minerals, in particular Al2SiO5 kianite (up to 10% by weight.% ). However, all these petrological models relate primarily to breeds of the upper mantle extending to the depths of ~ 670 km. In relation to gross composition, the deeper geopap is only allowed that the ratio of oxides of bivalent elements (MO) to silica (MO / SiO2) ~ 2, turning to olivine (Mg, Fe) 2SiO4 than to Pyroxen (MG, FE) SiO3, and Among minerals predominate perovskite phases (Mg, Fe) SiO3 with various structural distortions, magnesian (Mg, Fe) O with a NaCl type structure and some other phases in significantly smaller quantities.

All proposed models are very generalized and hypothetical. The pyrolite model of the upper mantle with the predominance of Olivina involves it significantly greater proximity for chemical composition with all the deeper mantle. On the contrary, the pylogite model involves the existence of a certain chemical contrast between the upper and the rest of the mantle. A more private eclogite model allows presence in the upper mantle of individual eclogite lenses and blocks.

Of great interest is attempting to coordinate structural and mineralogical and geophysical data related to the upper mantle. For about 20 years, it is assumed that an increase in the velocities of seismic waves at a depth of ~ 410 km is predominantly due to the structural rearrangement of Olivine A- (Mg, Fe) 2SiO4 in Vadsleit B- (Mg, Fe) 2SiO4, accompanied by the formation of a more dense phase with large values \u200b\u200bof coefficients elasticity. According to geophysical data, at such depths in the depths of the Earth, the rate of seismic waves increase by 3-5%, while the structural restructuring of olivine in Vadsleit (in accordance with the values \u200b\u200bof their elastic modules) should be accompanied by an increase in seismic waves rates by about 13%. At the same time, the results of experimental studies of olivine and a mixture of olivine-pyroxen at high temperatures and pressures revealed a complete coincidence of the calculated and experimental increase in seismic waves rates in the depth interval of 200-400 km. Since olivine has about the same elasticity as high-density monoclinic pyroxes, these data would have to indicate the absence of a grenade in the underlying zone with high elasticity, the presence of which in the mantle would inevitably cause a more significant increase in seismic wave rates. However, these ideas about the ignorant mantle entered into a contradiction with petrological models of its composition.

Table 1. Mineral composition of the pyroid (on L. Liu, 1979)

So the idea appeared that the jump in the speeds of seismic waves at a depth of 410 km is mainly connected with the structural rearrangement of the pyroxen-grenade inside the rich Na parts of the upper mantle. Such a model involves almost complete absence of convection in the upper mantle, which contradicts modern geodynamic representations. Overcoming these contradictions can be associated with the recently proposed model of the upper mantle, which admits the entry of iron and hydrogen atoms into the structure of the Vadsleit.

Fig. 2. Changes in volumetric portions of pyratite minerals in increase of pressures (depth), according to M. Akagi (1997). Legend Minerals: OL - Olivine, Gar - Pomegranate, CPX - Monoclinic Pyroxen, OPX - Rhombic Pyroxes, MS - "Modified Spinel", or Wadswake (B- (MG, FE) 2SiO4), Sp - Spinel, MJ - MEDOGIT MG3 (Fe, Al, Si) 2 (SiO4) 3, MW - Magnesian (Mg, Fe) O, Mg-PV -MG-Perovskite, CA-PV-C PVC, X - Preparable Al- Content phases with elemenite type structures, Ferrite and / or Holland

While the olivine polymorphic transition in Vadsleit is not accompanied by a change in the chemical composition, a reaction occurs in the presence of a grenade, which leads to the formation of the Vadslejite enriched with FE compared to the original olivine. Moreover, the vadsleit may contain significantly more compared to olivine hydrogen atoms. The participation of FE and H atoms in the structure of Vadslejite leads to a decrease in its rigidity and, accordingly, reduce the velocities of the distribution of seismic waves passing through this mineral.

In addition, the formation of the enriched FE Vadsleita involves the involvement in the appropriate reaction of a larger amount of olivine, which should be accompanied by a change in the chemical composition of the breed near section 410. The ideas about these transformation are confirmed by modern global substitution data. In general, the mineralogical composition of this part of the upper mantle seems more or less clear. If we talk about the pyrolite mineral association (Table 1), then its transformation up to the depths of ~ 800 km is investigated enough and in generalized form is represented in Fig. 2. At the same time, the global seismic border at a depth of 520 km corresponds to the restructuring of Vadsleit B- (Mg, Fe) 2SiO4 in the ringvudit - G-modification (MG, FE) 2SiO4 with the structure of the spinel. Transformation Pyroxen (MG, FE) SiO3 MG3 grenades (Fe, Al, Si) 2Si3O12 is carried out in the upper mantle in a wider depth interval. Thus, the whole relatively homogeneous shell in the interval of 400-600 km of the upper mantle mainly contains phases with structural types of garnet and spinel.

All currently proposed models of the composition of mantle breeds allow the content of Al2O3 in them in the amount of ~ 4 weight. %, which also affects the specifics of structural transformations. In this case, it is noted that in some areas inhomogeneous according to the composition of the upper mantle Al can be concentrated in minerals as Corundum Al2O3 or Al2SiO5 kenit, which, at pressures and temperatures, corresponding to the depths of ~ 450 km are transformed into corundum and stump - SiO2 modification, structure which contains a frame from SiO6 octahedra. Both of these minerals are preserved not only in the noses of the upper mantle, but also deeper.

The most important component of the chemical composition of the zone 400-670 km is water, the content of which, according to some estimates, is ~ 0.1 weight. % and the presence of which is primarily associated with Mg-silicates. The amount of water stored in this shell so much significantly that it would be a layer with a capacity of 800 m.

The composition of the mantle is below the border of 670 km

The study of structural transitions of minerals conducted in the last two or three to a decade using X-ray high-pressure chambers made it possible to simulate some features of the composition and geophage structure deeper than 670 km border. In these experiments, the crystal under study is placed between two diamond pyramids (anvils), with compression of which pressure is created, commensurate with pressures inside the mantle and the earth's core. Nevertheless, in relation to this part of the mantle, which accounts for more than half of all the bowels of the Earth, there are still many issues. At present, most researchers agree with the idea that all this deep (lower in traditional understanding) of the mantle mainly consists of a perovsk-like phase (MG, FE) SiO3, which accounts for about 70% of its volume (40% of the total land ), and magnesian (MG, FE) O (~ 20%). The remaining 10% are styling and oxide phases containing Ca, Na, K, Al and Fe, the crystallization of which is allowed in the structural types of ilmenite-corundum (solid solution (Mg, Fe) SiO3-Al2O3), cubic perovskite (Casio3) and Ferrite (Naalsio4). The formation of these compounds is associated with various structural transformation minerals of the upper mantle . At the same time, one of the main mineral phases relative to a homogeneous shell lying in the depth interval of 410-670 km, the spinel-like ringvudit is transformed into the association (MG, FE) -Perovskit and Mg-Wystit at the turn of 670 km, where the pressure is ~ 24 GPa. Another most important component of the transition zone is a representative of the grenade family Pirop Mg3Al2Si3O12 experiencing transformation to form a rhombic perovskite (Mg, Fe) SiO3 and a solid solution of corunda-ilmenite (MG, FE) SiO3 - Al2O3 with several large pressures. With this transition, the change in the velocities of seismic waves at the turn of 850-900 km corresponding to one of the intermediate seismic boundaries. The transformation of the co-grenade of theradite with lower pressures of ~ 21 GPa leads to the formation of another mentioned above important component of the lower mantle - Casio3 cubic sa-perovskite. The polar ratio between the main minerals of this zone (Mg, Fe) - Perovskite (Mg, Fe) SiO3 and Mg-Vousitis (Mg, Fe) O varies in fairly wide limits and at a depth of ~ 1170 km at a pressure of ~ 29 GPa and temperatures of 2000- 2800 ° C varies from 2: 1 to 3: 1.

The exceptional stability of MgSiO3 with the structure of the type of rhombic perovskite in a wide range of pressures corresponding to the depths of the bottom of the mantle, allows you to consider it one of the main components of this geosphere. The basis for this conclusion was the experiments, during which samples of Mg-perovskite MgSiO3 were subjected to pressure, 1.3 million times larger than atmospheric, and simultaneously to the sample placed between diamond anvils, a laser beam was influenced with a temperature of about 2000 ° C.

Thus simulated conditions that exist at the depths of ~ 2800 km, that is, near the lower boundary of the lower mantle. It turned out that neither during nor after the experiment, the mineral did not change its structure and composition. Thus, L. Liu, as well as E. Nittl and E. Jellazoz came to the conclusion, according to which the stability of Mg-Perovskite allows it to consider it as the most common mineral on Earth, which seems to be almost half of its mass.

FExo is not less resistant, the composition of which in the conditions of the lower mantle is characterized by the value of the stoichiometric coefficient x< 0,98, что означает одновременное присутствие в его составе Fe2+ и Fe3+. При этом, согласно экспериментальным данным, температура плавления вюстита на границе нижней мантии и слоя D", по данным Р. Болера (1996), оценивается в ~5000 K, что намного выше 3800 0С, предполагаемой для этого уровня (при средних температурах мантии ~2500 0С в основании нижней мантии допускается повышение температуры приблизительно на 1300 0С). Таким образом, вюстит должен сохраниться на этом рубеже в твердом состоянии, а признание фазового контраста между твердой нижней мантией и жидким внешним ядром требует более гибкого подхода и уж во всяком случае не означает четко очерченной границы между ними.

It should be noted that the prevailing phases prevailing at high depths may contain a very limited amount of Fe, and the elevated concentrations of Fe among the minerals of the deep association are characteristic only for magnesian. At the same time, the possibility of transition under the influence of high pressures of the part contained in it, which remains in the mineral structure, is proved for magnesian, while the relevant amount of neutral iron is proved. Based on this data, employees of the Geophysical Laboratory of the Astitute Carnegie H. Mao, P. Bell and T. Yagi put forward new ideas about the differentiation of the substance in the depths of the Earth. At the first stage, thanks to the gravitational instability, Magnesian is immersed at a depth, where, under the influence of pressure, some of the iron is released from it in neutral form. The residual magnesian, characterized by lower density, rises into the upper layers, where he is rejected with perovsk-like phases. Contact with them is accompanied by the restoration of stoichiometry (that is, the integer relationship of elements in chemical formula) Magnesian and leads to the ability to repeat the described process. New data allow you to slightly expand a set of probable for deep mantle of chemical elements. For example, substantiated N. Ross (1997), the stability of the magnesite at pressures corresponding to the depths of ~ 900 km, indicates the possible presence of carbon in its composition.

Selection of individual intermediate seismic borders located below the border 670, correlates with data on structural transformation mantle minerals whose forms can be very diverse. An illustration of changes in many properties of various crystals at high values \u200b\u200bof physicochemical parameters corresponding to the deep mantle, according to R. Jeallanose and R. Heisen, recorded during experiments at pressures 70 gigapascals (GPA) (~ 1700 km) Perestroika Ion-rival bonds Due to the metal type of interatomic interactions. The frontier 1200 may correspond to the predicted on theoretical quantum-mechanical calculations and subsequently simulated at a pressure of ~ 45 GPa and a temperature of ~ 2000 0C Perestroika SiO2 with the structure of the Eachovit to the structural type CaCl2 (Rhombic analogue of rutila TiO2), and 2000 km - its subsequent transformation to the phase With the structure, intermediate between A-PBO2 and ZrO2, characterized by a more dense packaging of silicic salmon octahedra (data LS Dubrovinsky with co-authors). Also, starting with these depths (~ 2000 km) at pressures of 80-90 GPa, the decay of perovsk-like MgSiO3 is allowed, accompanied by an increase in the content of MGO periclase and free silica. With a slightly larger pressure (~ 96 GPa) and the temperature of 800 0, the manifestation of politicization in FEO, associated with the formation of structural fragments of the NIAS nickeline type, alternating with anti-strain domains, in which FE atoms are located in the positions of AS atoms, and atoms are in the positions of atoms Ni. Near the border D "There is a transformation of Al2O3 with the corundum structure in the phase with the structure of RH2O3, which is experimentally modeled at the pressures of ~ 100 GPa, that is, at a depth of ~ 2200-2300 km." The use of the Mössbauer spectroscopy (HS) is justified using the method of Mössbauer spectroscopy In the low-spin state (Ls) FE atoms in the structure of magnesian, that is, the change in their electronic structure. In this connection, it should be emphasized that the structure of the Austit FEO at high pressure is characterized by nonstihiometry of the composition, defects of atomic packaging, politicization, as well as a change in the magnetic ordering associated with the change in the electronic structure (HS \u003d\u003e LS - transition) of FE atoms. The noted features allow us to consider the awit as one of the most complex minerals with unusual propertiesdefining the specifics of the land enriched with the deep zones near the D borders.

Fig. 3. Tetragonal structure of the FE7S-possible component of the internal (solid) kernel, according to D.M. Sherman (1997)

Seismological measurements indicate that the internal (solid) and external (liquid) core of the Earth is characterized by a smaller density compared with the value obtained based on the model of the kernel consisting only of metal iron with the same physicochemical parameters. This decrease in density Most researchers are associated with the presence of such elements in the core as Si, O, S, and even about the forming alloys with iron. Among the phases probable for such "faustic" physicochemical conditions (pressure ~ 250 GPa and a temperature of 4000-6500 ° C) are called FE3S with a well-known structural type Cu3au and Fe7S. , whose structure is depicted in Fig. 3. Another estimated phase is B-FE, the structure of which is characterized by four-layer tight packaging of FE atoms. The melting point of this phase is estimated at 5000 ° C at a pressure of 360 GPa. The presence of hydrogen in the kernel for a long time caused a discussion due to its low solubility in the gland atmospheric pressure. However, recent experiments (data J. Badding, H. Mao and R. Hamley (1992)) allowed to establish that hydride Iron FEH can be formed at high temperatures and pressures and is resistant for pressures exceeding 62 GPa, which corresponds to the depths of ~ 1600 km. In this regard, the presence of significant quantities (up to 40 mol.%) hydrogen The kernel is quite acceptable and reduces its density to the values \u200b\u200bconsistent with the seismology data.

It can be predicted that new data on structural changes in mineral phases at large depths will allow to find an adequate interpretation and other essential geophysical borders recorded in the depths of the Earth. The general conclusion is that on such global seismic borders, as 410 and 670 km, there are significant changes in the mineral composition. mantle breeds . Mineral transformations are also marked at the depths of ~ 850, 1200, 1700, 2000 and 2200-2300 km, that is, within the limits of the lower mantle. This is a very important circumstance that allows you to abandon the idea of \u200b\u200bits homogeneous structure.

By the 80s of the XX century, seismological studies of the methods of longitudinal and transverse seismic waves, capable of penetrating through the entire volume of land, and therefore called voluminous unlike surface, distributing only on its surface, were already so significant that they allowed to make seismic anomalies for Different levels of the planet. Fundamental works in this area are performed by the American seismologist A. Dysiewonski and his colleagues.

In fig. 4 shows samples of such cards from the series published in 1994, although the first publications appeared 10 years earlier. The paper contains 12 cards for the deep sections of the Earth in the range from 50 to 2850 km, that is, practically covering the entire mantle. On these interesting maps it is easy to see that the seismic picture at various levels of depth is different. It can be seen by area and distribution circuits. seismanomalie Areals , features of transitions between them and generally on the general appearance of cards. Separates are distinguished by a large variety and contrast in the distribution of areas with different seismic wave rates (Fig. 5), whereas more smooth and simple relations between them are visible.

In the same, 1994, a similar work of Japanese geophysicists was published. It contains 14 cards for levels from 78 to 2900 km. On both series of cards, the Pacific inhomogeneity is clearly visible, which changes in the outlines, but can be traced until the earth's core. Outside of this major inhomogeneity, the seismic picture is complicated, significantly changing when the transition from one level to another. But, no matter how much the difference between these cards, there are similarities between individuals. They are expressed in some similarity in the placement in the space of positive and negative seismicomali and ultimately in the general features of the deep seismic structure. This allows you to group such cards, which makes it possible to highlight intramician shells of different seismic appearance. And such work was performed. Based on the analysis of Japanese Geophysician cards, it turned out to be made significantly more fractional. the structure of the land shallow structure shown in fig. 5, compared with the traditional model of earth shells.

Fundamentally new are two provisions:

How do the proposed borders of the deep geospheres with previously isolated seismologists seismic turns relate? Comparison shows that the lower boundary of the medium mantle correlates with the frontier 1700, the global significance of which is emphasized in the work. Its upper border approximately corresponds to the turns of 800-900. This concerns the upper mantle, then there are no discrepancies here: its lower boundary is represented by the frontier 670, and the top-line Mochorovichich. We will especially pay attention to the uncertainty of the upper boundary of the lower mantle. In the process of further research, it may be that the recently marked seismic binds of 1900 and 2000 will make adjustments to its capacity. Thus, the results of comparisons indicate the legality of the proposed new model of the structure of the mantle.

Conclusion

The study of the deep structure of the Earth belongs to the largest and most relevant directions of geological sciences. New stratification of mantle The land allows much less schematically than before, to approach the complex problem of deep geodynamics. The difference in the seismic characteristics of the earth's shells ( geospheres) reflecting the difference in their physical properties and mineral composition, creates opportunities for modeling geodynamic processes in each of them separately. The geospheres in this sense, as now perfectly clearly, have a known autonomy. However, this extremely important topic lies beyond this article. From the further development of seismism, as well as some other geophysical studies, as well as the study of the mineral and chemical composition of the depths, significantly more substantiated constructions will depend on the composition, structure, geodynamics and the evolution of the Earth as a whole.

Bibliography

Geotimes. 1994. Vol. 39, N 6. P. 13-15.

ROSS A. The Earths Mantle Remodelled // Nature. 1997. Vol. 385, N 6616. P. 490.

Thompson A.B. Water in the Earthhs Upper Mantle // Nature. 1992. Vol. 358, N 6384. P. 295-302.

Pushchashovsky D.Yu. Deep Minerals Earth // Nature. 1980. N 11. P. 119-120.

SU W., Woodward R.L., Dziewonski A.M. Degree 12 Model of Shear Velocity Heterogeneity In The Mantle // J. Geophys. RES. 1994. Vol. 99, N B4. P. 6945-6980.

J. GEOL. SOC. Japan. 1994. Vol. 100, N 1. P. VI-VII.

Pushchashovsky Yu.M. Seismotomography and structure of the mantle: tectonic perspective // \u200b\u200bReports an 1996. T. 351, N 6. P. 805-809.

Line UMK "Classical Geography" (5-9)

Geography

The internal structure of the Earth. Mir of amazing secrets in one article

We often look into the sky and reflect on how space is arranged. We read about astronauts and satellites. And it seems that all the riddles, unsolved by man, are there - outside the globe. In fact, we live on the planet full of amazing secrets. And we dream of space, without thinking, how difficult and interesting is our land.

The inner structure of the Earth

Planet Earth consists of three main layers: earth crust, mantle and nuclei. You can compare the globe with an egg. Then the egg shell will be an earthly boron, an egg white - a mantle, and yolk - core.

The upper part of the Earth is called lithosphere(Translated from the Greek "Stone Ball"). This is a solid shell of the globe, which includes the earth bark and top part mantle.

The training manual is addressed to students of grade 6 and is included in the CMD "Classical Geography". Modern design, a variety of questions and tasks, the possibility of parallery work with the electronic form of the textbook contributes to an effective assimilation educational material. The training manual complies with the Federal State Educational Standard of the Basic General Education.

Earth's crust

The crust is a stone shell that covers the entire surface of our planet. Under the oceans, its thickness does not exceed 15 kilometers, and on the mainland - 75. If you return to an analogy with the egg, then the earth's crust in relation to the entire planet thinner than the egg shell. This layer of land accounts for only 5% of the volume and less than 1% of the mass of the entire planet.

As part of the earth's crust, scientists have discovered silicon oxides, alkali metal, aluminum and iron. The bark under the oceans consists of a sedimentary and basalt layers, it is heavier continental (mainland). While the shell covering the continental part of the planet has a more complex structure.

Three layers of continental terrestrial crust are isolated:

sedimentary (10-15 km mostly sedimentary breeds);

granite (5-15 km of metamorphic rocks, according to properties similar to granite);

basalt (10-35 km of magmatic breeds).

Mantle

Under the earth's crust is the mantle ( "Cover, cloak"). This layer has a thickness of up to 2900 km. It accounts for 83% of the total volume of the planet and almost 70% of the mass. It consists of mantle of heavy minerals rich in iron and magnesium. This layer has a temperature of over 2000 ° C. Nevertheless, most of the substance of the mantle retains a solid crystalline state due to huge pressure. At a depth of 50 to 200 km, the moving upper layer of the mantle is located. It is called an asthenosphere ( "Impossile Sphere"). Asthenosphere is very plastic, precisely because of it there is an eruption of volcanoes and the formation of mineral deposits. In the thickness of the asthenosphere reaches from 100 to 250 km. The substance that penetrates the asthenosphere into the earth's bark and is poured sometimes to the surface, called magma ("Messa, thick ointment"). When Magma froze on the ground surface, it turns into Lava.

Core

Under the mantle, as if under the bedspread, there is a terrestrial core. It is located 2900 km from the surface of the planet. The kernel has a ball shape with a radius of about 3,500 km. Since people still failed to get to the nucleus of the Earth, the scientists are building guesses about its composition. Presumably, the kernel consists of iron with an admixture of other elements. This is the tight and heavy part of the planet. It accounts for only 15% of the volume of land and as much as 35% of the mass.

It is believed that the kernel consists of two layers - a solid internal nucleus (by a radius of about 1,300 km) and liquid external (about 2,200 km). The inner core seems to float in the external liquid layer. Because of this smooth movement around the Earth, its magnetic field is formed (it protects the planet from hazardous space radiation, and the compass arrow reacts to it). The kernel is the hottest part of our planet. For a long time it was believed that the temperature reaches it, presumably, 4000-5000 ° C. However, in 2013, scientists conducted a laboratory experiment, during which the melting point of iron was determined, which is probably part of the inner earth's nucleus. It turned out that the temperature between the inner solid and external liquid nucleus is equal to the temperature of the surface of the Sun, that is, about 6000 ° C.

The structure of our planet is one of the many unsolved secrets of secrets. Most of the information about it is obtained by indirect methods, no one scientist has failed to produce samples of the earth's core. The study of the structure and composition of the Earth is still conjugate with insurmountable difficulties, but researchers do not surrender and are looking for new ways to extract reliable information about the planet Earth.

When studying the topic "Interior structure of the Earth", students may have difficulties with memorizing titles and order of the globe layers. Latin names will be much easier to remember if the children will create their own earth model. You can offer students to perform a globe model from plasticine or tell about its device on the example of fruits (peel - earth bark, flesh - mantle, bone - core) and items that have a similar structure. Textbook O.A. Climanova will help in the lesson, where you will find colorful illustrations and detailed information on the topic.

Many people know that the planet Earth in the seismic (tectonic) sense consists of a core, mantle and lithosphere (bark). We will look at what mantle is. This is a layer or an intermediate shell, which is between the core and the bark. Mantle is 83% of the volume of the planet Earth. If we take the weight, then 67% of the Earth is mantle.

Two layers of mantle

Even at the beginning of the twentieth century it was considered that the mantle is homogeneous, but by the middle of the century scientists came to the conclusion that it consists of two layers. Close to the kernel layer is the bottom mantle. That layer that borders with a lithosphere is the upper mantle. The upper mantle goes deep into the earth about 600 kilometers. The lower boundary of the lower mantle is located at a depth of 2,900 kilometers.

What makes the mantle

To get to the mantle, scientists have not yet been brought. No drilling has not yet allowed to get closer to it. Therefore, all studies are made not an experienced, but theoretical and mediated path. The scientists make their conclusions about the mantle of the Earth primarily on the basis of geophysical studies. The calculation is taken by electrical conductivity, seismic waves, the speed of their distribution, force.

Japanese scientists declared their intentions to approach the land mantle, drilling oceanic rocks, but while their plans are not yet embodied. At the bottom of the ocean, some places were already found, where the layer of earthly crust is the thinnest, that is, to the top of the mantle, it will be detached to the whole of some 3000 km. The difficulty lies in the fact that drilling must be carried out at the bottom of the ocean and at the same time the Buru will have to undergo areas of heavy-duty rocks, and this can be compared with an attempt to a thread tail break through the walls of the thread. Of course, the ability to study samples of breeds taken directly from the mantle, would give a more accurate picture of its structure and composition.

Diamonds and Peridotos

Informative are the mantle rocks, which, as a result of various geophysical and seismic processes, are on the surface of the Earth. For example, the mantle breeds include diamonds. Some of them suggest researchers, rise from the lower mantle. The most common breeds are peridotes. They are often thrown into the lava by volcanic eruptions. The study of mantle breeds allows scientists with a certain accuracy to talk about the composition and main features of the mantle.

Liquid condition and water

Mantle silicate rocks that are saturated with magnesium and iron. All substances that make up the mantle are in the hottest. molten, liquid state, because the temperature of this layer is large enough - to two and a half thousand degrees. Water is also part of the land mantle. In quantitatively, it is 12 times more than in the World Ocean. The stock of water in the mantle is such that if it were to spill on the surface of the Earth, the water would rise above the surface of 800 meters.

Processes in mantle

The border of the mantle is not a smooth line. On the contrary, in some places, for example, in the area of \u200b\u200bthe Alps, at the bottom of the oceans, mantle, that is, the breed mantle approaches quite close to the surface of the Earth. It is the physical and chemical processes that flow into the mantle affect the fact that it happens in the earth's crust and on the ground surface. We are talking about the formation of mountains, oceans, the movement of continents.

It has a special composition, differing from the composition of the covering of its earth's crust. Data O. chemical composition The mantle was obtained on the basis of analyzes of the most deep magmatic rocks enrolled in the upper horizons of the Earth as a result of powerful tectonic raises with the removal of the mantle material. Such rocks include ultrasound breeds - dunites, peridotitis that occur in mining systems. Mountain breeds of the Islands of St. Paul in the middle part Atlantic OceanAccording to all geological data, relate to the mantle material. Also, the mantle material includes fragments of rocks collected by Soviet oceanographic expeditions from the bottom Indian Ocean In the field of the Indookean ridge. As for the mineralogical composition of the mantle, it is possible to expect significant changes here, ranging from the upper horizons and ending the base of the mantle due to the growth of pressure. The upper mantle is prepared predominantly silicates (olivines, pyroxen, grenades), resistant and limits of relatively low pressures. Lower mantle is composed of high density minerals.

The most common component of the mantle is silica oxide as part of silicates. But at high pressures, silica can go to a more dense polymorphic modification - styling. This mineral is obtained by the Soviet researcher Stischom and named so by his name. If ordinary quartz has a density of 2.533 R / cm 3, then the styling, formed from quartz at a pressure of 150,000 bar, has a density of 4.25 g / cm 3.

In addition, more dense mineral modifications of other compounds are likely in the lower mantle. Based on the above, it is possible to believe with a sufficient reason that, with increasing pressure, ordinary iron-magnesian silicates of olivine and pyroxen are decomposed on oxides, which separately have a higher density than silicates that are resistant in the upper mantle.

Upper mantle consists mainly of ironist-magnesia silicates (olivines, pyroxen). Some aluminosilicates can go here into more dense grenade type minerals. Under the mainland and oceans, the upper mantle has different properties and probably a different composition. One can only assume that in the field of continents, the mantle is more differentiated and has less SiO 2 due to the concentration of this component in aluminosilicate crust. Under the oceans, the mantle is less differentiated. In the upper mantle, more dense polymorphic modifications of olivine with the structure of spinel and others may occur.

The transition layer of the mantle is characterized by a constant increase in the velocities of seismic waves with a depth, which indicates the appearance of more dense polymorphic modifications of the substance. Here, obviously, oxides Feo, MgO, Gao, SiO 2 in the form of a specta, periclase, lime and echovita appear. The amount of them with depth increases, and the number of conventional silicates decreases, and the deeper 1000 km they constitute an insignificant share.

The lower mantle within the depths of 1000-2900 km almost fully consists of dense varieties of minerals - oxides, as evidenced by its high density in the range of 4.08-5.7 g / cm 3. Under the influence of increased pressure, dense oxides are compressed, even more increasing their density. The lower mantle also probably increases the content of iron.

Earth core. The question of the composition and physical nature of the core of our planet refers to the most exciting and mysterious problems of geophysics and geochemistry. Only lately there was a slight enlightenment in solving this problem.

The extensive central core of the Earth, which occupies an internal area of \u200b\u200bdeeper than 2,900 km, consists of a large outer nucleus and small inner. According to seismic data, the external kernel has fluid properties. It does not transmit transverse seismic waves. The lack of clutch forces between the core and the lower mantia, the nature of the tides in the mantle and the crust, the features of moving the axis of the earth's rotation in space, the nature of the passage of seismic waves deeper than 2,900 km say that the external core of the Earth is liquid.

Some authors, the composition of the kernel for the chemically homogeneous model of the Earth was allowed silicate, and under the influence of high pressure, silicates moved to the "metallized" state, acquiring the atomic structure in which external electrons are common. However, the geophysical data listed above contradicts the assumption of the "metallized" state of silicate material in the Earth's kernel. In particular, the lack of adhesion between the nucleus and the mantle can not be compatible with the "metallized" solid core, which was allowed in the hypothesis of the boat duty-razay. Very important indirect data on the core of the Earth were obtained during experiments with silicates under greater pressure. At the same time, pressure reached 5 million atm. Meanwhile, in the center of the Earth, the pressure of 3 million atm., And on the border of the nucleus - approximately 1 million atm. Thus, experimentally managed to overlap the pressure existing in the most depths of the Earth. At the same time, only a linear compression was observed for silicates and the transition to the "metallized" state. In addition, at high and pressures within the depths of 2900-6370 km, silicates cannot be in liquid state, as well as oxides. Their melting point increases with increasing pressure.

Per last years A very interesting results of studies on the effect of very high pressures on the melting point of metals are obtained. It turned out that a number of metals at high pressures (300 thousand atm. And above) goes into a liquid state with relatively low temperatures. According to some calculations, iron alloy with nickel and silicon admixture (76% FE, 10% Ni, 14% Si) at a depth of 2900 km under the influence of high pressure should be in a liquid state at a temperature of 1000 ° C. But the temperature at these depths, According to the most modest estimates of geophysicists, must be significantly higher.

Therefore, in the light of modern data of geophysics and high-pressure physics, as well as the data of the Cosmochemia, indicating the leading role of iron as the most abundant metal in space, it should be assumed that the Earth's core is mainly complex with liquid iron with an admixture of nickel. However, the calculations of the American Geophysics F. Bercha showed that the density of the earth's nucleus is 10% lower than the ironopone-leather alloy at temperatures and pressures that dominate the kernel. It follows that the metal kernel of the Earth must contain a significant amount (10-20%) of some lung. Of all the easiest and most common elements, silicon (Si) and sulfur (S) are maximally likely. The presence of one or other can explain the observed physical properties Ground kernel. Therefore, the question is that the impurity of the earth's nucleus - silicon or sulfur is discussed and is associated with the method of forming our planet in the case.

A. RIDGVUD in 1958 made it that the earth's core contains silicon as a light element, arguing such an assumption that elemental silicon in the amount of several weight percent occurs in the metal phase of some restored chondrite meteorites (enstatam). However, there are no other arguments in favor of the presence of silicon in the earth's core.

The assumption that there is sulfur in the earth's core, follows from the comparison of its distribution in the chondritious material of meteorites and the land mantle. Thus, the comparison of the elementary atomic relationships of some volatile elements in a mixture of cortex and mantle and in chondrites shows a sharp disadvantage of sulfur. In the material of the mantle and the crust, the concentration of sulfur is three orders of magnitude lower than the average material of the solar system, which is accepted by chondrites.

The possibility of sulfur loss at high temperatures of the primary earth disappears, since other more volatile elements than sulfur (for example, H2 in the form of H2O), who have discovered a much smaller deficit, would be lost significantly more. In addition, when cooling solar gas, sulfur is chemically associated with iron and ceases to be a volatile element.

In this regard, it is quite possible, large quantities of sulfur come to the earth's core. It should be noted that, with other things being equal, the melting point of the FE-FES system is significantly lower than the melting point of the melting melting of silicate of the mantle. So, at a pressure of 60 kbar, the melting point of the system (eutectic) Fe-FES will be 990 ° C, while pure iron - 1610 °, and the pyrolyte of the mantle - 1310. Therefore, with an increase in temperature in the depths of the primary homogeneous land, iron melt enriched with gray It will be formed first and because of its low viscosity and high density will be easy to drain into the central parts of the planet, forming iron-sulphate core. Thus, the presence of sulfur in the ironoponecelic medium acts as a flux, reducing its melting temperature as a whole. The hypothesis of the presence in the earth's nucleus of significant amounts of sulfur is very attractive and does not contradict all known data from geochemistry and consochemistry.

Thus, modern ideas about the nature of the subsoil of our planet correspond to the chemically differentiated ground Shar.which turned out to be divided into two different parts: a powerful solid silicate oxide mantle and liquid mainly metal kernel. The earth's crust is the most light upper solid shell consisting of aluminosilicates and having the most complex structure.

Summing up this, you can draw the following conclusions.

1. The earth has a layered zonar structure. It consists of two thirds of the solid silicate oxide shell - the mantle and one-third of the metal liquid core.
2. The main properties of the Earth indicate that the kernel is in liquid state and only iron from the most common metals with an admixture of some light elements (most likely, sulfur) can provide these properties.
3. In the upper horizons, the Earth has an asymmetric structure covering the bark and the upper mantle. Oceanic hemisphere within the upper mantle is less differentiated than the opposite continental hemisphere.

The task of any cosmogonical theory of the Earth's origin is to explain these basic features of its inner nature and composition.

Earth's mantle is the most important plot of our planet, since most of the substances are concentrated here. It is much thicker than the remaining components and, in fact, takes most of the space - about 80%. Studying precisely this part of the planet, scientists have dedicated most of the time.

Structure

The structure of the mantle scientists can only assume, since methods that would definitely give an answer to this question, so far there is no. But, conducted studies made it possible to assume that this section of our planet consists of such layers:

• the first, outdoor - it takes from 30 to 400 kilometers of the earth's surface;
• the transition zone, which is located immediately at the outside layer - by the assumptions of scientists, it goes deep into about 250 kilometers;
• the lower layer is its length of the largest, about 2900 kilometers. It begins immediately after the transition zone and goes straight to the kernel.

It should be noted that in the mantle of the planet there are such rocks that are not in the earth's crust.

Structure

Of course, it is impossible to determine exactly from what the mantle of our planet is, since it is impossible to get there. Therefore, everything that manages to learn scientists occurs with the help of fragments of this sections, which periodically appear on the surface.

So, after a number of studies managed to find out that this section of black and green land. The main composition is rock formations that consist of such chemical elements:

• silicon;
• calcium;
• magnesium;
• iron;
• oxygen.

By appearanceAnd in something even in composition, it is very similar to stone meteorites, which also periodically fall on our planet.

Substances that are in the mantle itself, liquid, viscous, as the temperature in this area exceeds thousands of degrees. Closer to the lands of the Earth, the temperature is reduced. Thus, some cycle occurs - those masses that have already been cooled, descend down, and heated to the limit fall up, so the process of "mixing" never stops.

Periodically, such preheated streams fall into the Correra of the Planet, in which the acting volcanoes are assisted.

Methods of study

It goes without saying that the layers that are at great depths are quite difficult to study and not only because not such technique. The process is also complicated by the fact that the temperature is almost constantly increasing, and at the same time the density increases. Therefore, it can be said that the depth of the layer is the smallest problem, in this case.

At the same time, scientists still managed to advance in learning this issue. To study this section of our planet, the main source of information was chosen just geophysical indicators. In addition, during the study, scientists use such data:

• speed \u200b\u200bof seismic waves;
• gravity;
• characteristics and electrical conductivity indicators;
• the study of the magmatic rocks and fragments of the mantle, which rarely, but still manage to find on the surface of the Earth.

As for the latter, the diamonds deserve particular attention to scientists here - in their opinion, studying the composition and structure of this stone, it is possible to find out a lot of interesting things about the lower layers of the mantle.

Occasionally, but there are mantle breeds. Their study also allows you to produce valuable information, but a distortion will be present to one degree or another. It is due to the fact that various processes occur in the crust, which are somewhat different from those that occur in the depths of our planet.

Separately, you should talk about the technique, with which scientists are trying to get the original mantle breeds. So, in 2005, a special ship was erected in Japan, which, according to the project developers themselves, will be able to make a record deep well. At the moment, work still go, and the start of the project has been scheduled for 2020 - it is not so much to wait.

Now all the study of the structure of the mantle occur within the laboratory. Scientists have already established exactly that the lower layer of this area of \u200b\u200bthe planet, almost all consists of silicon.

Pressure and temperature

The distribution of pressure within the mantle is ambiguous, actually as a temperature regime, but about everything in order. The robe accounts for more than half the weight of the planet, and if you say more precisely, then 67%. In areas under the earth's crust, the pressure is about 1.3-1.4 million collections., At the same time, it should be noted that in places where the oceans are located, the pressure level is significantly subsided.

As for the temperature regime, the data here is ambiguous and based only on theoretical assumptions. So, the sole of the mantle is supposed to be a temperature of 1500-10,000 degrees Celsius. In general, scientists suggested that the temperature level in this section of the planet is closer to the melting point.