The globe has several shells: - an air shell, - a water shell, - a solid shell.
The third planet beyond the distance from the Sun, Earth, has a radius of 6370 km, an average density of 5.5 g/cm2. In the internal structure of the Earth, it is customary to distinguish the following layers:
Earth's crust- the upper layer of the Earth in which living organisms can exist. The thickness of the earth's crust can be from 5 to 75 km.
mantle- a solid layer that is located below the earth's crust. Its temperature is quite high, but the substance is in a solid state. The thickness of the mantle is about 3,000 km.
core- the central part of the globe. Its radius is approximately 3,500 km. The temperature inside the core is very high. The core is believed to consist mainly of molten metal,
presumably iron.
Earth's crust
There are two main types of the earth's crust - continental and oceanic, plus an intermediate, subcontinental.
The earth's crust is thinner under the oceans (about 5 km) and thicker under the continents (up to 75 km). It is heterogeneous; three layers are distinguished: basalt (lying at the bottom), granite and sedimentary (upper). The continental crust consists of three layers, while the oceanic crust has no granite layer. The earth's crust formed gradually: first a basalt layer was formed, then a granite layer; the sedimentary layer continues to form to this day.
- the substance that makes up the earth's crust. Rocks are divided into the following groups:
1. Igneous rocks. They are formed when magma solidifies deep within the earth's crust or on the surface.
2. Sedimentary rocks. They are formed on the surface, formed from the products of destruction or change of other rocks and biological organisms.
3. Metamorphic rocks. They are formed in the thickness of the earth's crust from other rocks under the influence of certain factors: temperature, pressure.
A characteristic feature of the evolution of the Earth is the differentiation of matter, the expression of which is the shell structure of our planet. The lithosphere, hydrosphere, atmosphere, biosphere form the main shells of the Earth, differing in chemical composition, thickness and state of matter.
Internal structure of the Earth
Chemical composition of the Earth(Fig. 1) is similar to the composition of other terrestrial planets, such as Venus or Mars.
In general, elements such as iron, oxygen, silicon, magnesium, and nickel predominate. The content of light elements is low. The average density of the Earth's substance is 5.5 g/cm 3 .
There is very little reliable data on the internal structure of the Earth. Let's look at Fig. 2. It depicts the internal structure of the Earth. The Earth consists of the crust, mantle and core.
Rice. 1. Chemical composition of the Earth
Rice. 2. Internal structure of the Earth
Core
Core(Fig. 3) is located in the center of the Earth, its radius is about 3.5 thousand km. The temperature of the core reaches 10,000 K, i.e. it is higher than the temperature of the outer layers of the Sun, and its density is 13 g/cm 3 (compare: water - 1 g/cm 3). The core is believed to be composed of iron and nickel alloys.
The outer core of the Earth has a greater thickness than the inner core (radius 2200 km) and is in a liquid (molten) state. The inner core is subject to enormous pressure. The substances that compose it are in a solid state.
Mantle
Mantle- the Earth’s geosphere, which surrounds the core and makes up 83% of the volume of our planet (see Fig. 3). Its lower boundary is located at a depth of 2900 km. The mantle is divided into a less dense and plastic upper part (800-900 km), from which it is formed magma(translated from Greek means “thick ointment”; this is the molten substance of the earth’s interior - a mixture of chemical compounds and elements, including gases, in a special semi-liquid state); and the crystalline lower one, about 2000 km thick.
Rice. 3. Structure of the Earth: core, mantle and crust
Earth's crust
Earth's crust - the outer shell of the lithosphere (see Fig. 3). Its density is approximately two times less than the average density of the Earth - 3 g/cm 3 .
Separates the earth's crust from the mantle Mohorovicic border(often called the Moho boundary), characterized by a sharp increase in seismic wave velocities. It was installed in 1909 by a Croatian scientist Andrei Mohorovicic (1857- 1936).
Since the processes occurring in the uppermost part of the mantle affect the movements of matter in the earth's crust, they are combined under the general name lithosphere(stone shell). The thickness of the lithosphere ranges from 50 to 200 km.
Below the lithosphere is located asthenosphere- less hard and less viscous, but more plastic shell with a temperature of 1200 ° C. It can cross the Moho boundary, penetrating into the earth's crust. The asthenosphere is the source of volcanism. It contains pockets of molten magma, which penetrates into the earth's crust or pours out onto the earth's surface.
Composition and structure of the earth's crust
Compared to the mantle and core, the earth's crust is a very thin, hard and brittle layer. It is composed of a lighter substance, which currently contains about 90 natural chemical elements. These elements are not equally represented in the earth's crust. Seven elements - oxygen, aluminum, iron, calcium, sodium, potassium and magnesium - account for 98% of the mass of the earth's crust (see Fig. 5).
Peculiar combinations of chemical elements form various rocks and minerals. The oldest of them are at least 4.5 billion years old.
Rice. 4. Structure of the earth's crust
Rice. 5. Composition of the earth's crust
Mineral is a relatively homogeneous natural body in its composition and properties, formed both in the depths and on the surface of the lithosphere. Examples of minerals are diamond, quartz, gypsum, talc, etc. (You will find characteristics of the physical properties of various minerals in Appendix 2.) The composition of the Earth's minerals is shown in Fig. 6.
Rice. 6. General mineral composition of the Earth
Rocks consist of minerals. They can be composed of one or several minerals.
Sedimentary rocks - clay, limestone, chalk, sandstone, etc. - were formed by the precipitation of substances in the aquatic environment and on land. They lie in layers. Geologists call them pages of the history of the Earth, since they can learn about the natural conditions that existed on our planet in ancient times.
Among sedimentary rocks, organogenic and inorganogenic (clastic and chemogenic) are distinguished.
Organogenic Rocks are formed as a result of the accumulation of animal and plant remains.
Clastic rocks are formed as a result of weathering, destruction by water, ice or wind of the products of destruction of previously formed rocks (Table 1).
Table 1. Clastic rocks depending on the size of the fragments
|
Breed name |
Size of bummer con (particles) |
|
More than 50 cm |
|
|
5 mm - 1 cm |
|
|
1 mm - 5 mm |
|
|
Sand and sandstones |
0.005 mm - 1 mm |
|
Less than 0.005 mm |
Chemogenic Rocks are formed as a result of the precipitation of substances dissolved in them from the waters of seas and lakes.
In the thickness of the earth's crust, magma forms igneous rocks(Fig. 7), for example granite and basalt.
Sedimentary and igneous rocks, when immersed to great depths under the influence of pressure and high temperatures, undergo significant changes, turning into metamorphic rocks. For example, limestone turns into marble, quartz sandstone into quartzite.
The structure of the earth's crust is divided into three layers: sedimentary, granite, and basalt.
Sedimentary layer(see Fig. 8) is formed mainly by sedimentary rocks. Clays and shales predominate here, and sandy, carbonate and volcanic rocks are widely represented. In the sedimentary layer there are deposits of such mineral, like coal, gas, oil. All of them are of organic origin. For example, coal is a product of the transformation of plants of ancient times. The thickness of the sedimentary layer varies widely - from complete absence in some land areas to 20-25 km in deep depressions.
Rice. 7. Classification of rocks by origin
"Granite" layer consists of metamorphic and igneous rocks, similar in their properties to granite. The most common here are gneisses, granites, crystalline schists, etc. The granite layer is not found everywhere, but on continents where it is well expressed, its maximum thickness can reach several tens of kilometers.
"Basalt" layer formed by rocks close to basalts. These are metamorphosed igneous rocks, denser than the rocks of the “granite” layer.
The thickness and vertical structure of the earth's crust are different. There are several types of the earth's crust (Fig. 8). According to the simplest classification, a distinction is made between oceanic and continental crust.
Continental and oceanic crust vary in thickness. Thus, the maximum thickness of the earth’s crust is observed under mountain systems. It is about 70 km. Under the plains the thickness of the earth's crust is 30-40 km, and under the oceans it is thinnest - only 5-10 km.
Rice. 8. Types of the earth's crust: 1 - water; 2- sedimentary layer; 3—interlayering of sedimentary rocks and basalts; 4 - basalts and crystalline ultrabasic rocks; 5 – granite-metamorphic layer; 6 – granulite-mafic layer; 7 - normal mantle; 8 - decompressed mantle
The difference between the continental and oceanic crust in the composition of rocks is manifested in the fact that there is no granite layer in the oceanic crust. And the basalt layer of the oceanic crust is very unique. In terms of rock composition, it differs from a similar layer of continental crust.
The boundary between land and ocean (zero mark) does not record the transition of the continental crust to the oceanic one. The replacement of continental crust by oceanic crust occurs in the ocean at a depth of approximately 2450 m.
Rice. 9. Structure of the continental and oceanic crust
There are also transitional types of the earth's crust - suboceanic and subcontinental.
Suboceanic crust located along continental slopes and foothills, can be found in marginal and Mediterranean seas. It represents continental crust with a thickness of up to 15-20 km.
Subcontinental crust located, for example, on volcanic island arcs.
Based on materials seismic sounding - the speed of passage of seismic waves - we obtain data on the deep structure of the earth’s crust. Thus, the Kola superdeep well, which for the first time made it possible to see rock samples from a depth of more than 12 km, brought a lot of unexpected things. It was assumed that at a depth of 7 km a “basalt” layer should begin. In reality, it was not discovered, and gneisses predominated among the rocks.
Change in temperature of the earth's crust with depth. The surface layer of the earth's crust has a temperature determined by solar heat. This heliometric layer(from the Greek helio - Sun), experiencing seasonal temperature fluctuations. Its average thickness is about 30 m.
Below is an even thinner layer, the characteristic feature of which is a constant temperature corresponding to the average annual temperature of the observation site. The depth of this layer increases in continental climates.
Even deeper in the earth's crust there is a geothermal layer, the temperature of which is determined by the internal heat of the Earth and increases with depth.
The increase in temperature occurs mainly due to the decay of radioactive elements that make up rocks, primarily radium and uranium.
The amount of temperature increase in rocks with depth is called geothermal gradient. It varies within a fairly wide range - from 0.1 to 0.01 °C/m - and depends on the composition of rocks, the conditions of their occurrence and a number of other factors. Under the oceans, temperature increases faster with depth than on continents. On average, with every 100 m of depth it becomes warmer by 3 °C.
The reciprocal of the geothermal gradient is called geothermal stage. It is measured in m/°C.
The heat of the earth's crust is an important energy source.
The part of the earth's crust that extends to depths accessible to geological study forms bowels of the earth. The Earth's interior requires special protection and wise use.
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Earth's crust – the outer solid shell of the Earth, the upper part of the lithosphere. The earth's crust is separated from the Earth's mantle by the Mohorovicic surface.
It is customary to distinguish continental and oceanic crust, which differ in their composition, power, structure and age. Continental crust located under continents and their underwater margins (shelves). The earth's crust of continental type, with a thickness of 35-45 km, is located under the plains up to 70 km in the area of young mountains. The most ancient sections of the continental crust have a geological age exceeding 3 billion years. It consists of the following shells: weathering crust, sedimentary, metamorphic, granite, basalt.
Oceanic crust much younger, its age does not exceed 150-170 million years. It has less power – 5-10 km. There is no boundary layer within the oceanic crust. In the structure of the oceanic crust, the following layers are distinguished: unconsolidated sedimentary rocks (up to 1 km), volcanic oceanic, which consists of compacted sediments (1-2 km), basalt (4-8 km).
The rocky shell of the Earth does not represent a single whole. It consists of separate blocks – lithospheric plates. In total, there are 7 large and several smaller plates on the globe. The large ones include the Eurasian, North American, South American, African, Indo-Australian (Indian), Antarctic and Pacific plates. Within all major plates, with the exception of the last, continents are located. The boundaries of lithospheric plates usually run along mid-ocean ridges and deep-sea trenches.
Lithospheric plates constantly changing: two plates can be soldered into a single one as a result of a collision; As a result of rifting, the slab may split into several parts. Lithospheric plates can sink into the earth's mantle, reaching the earth's core. Therefore, the division of the earth's crust into plates is not unambiguous: with the accumulation of new knowledge, some plate boundaries are recognized as non-existent, and new plates are identified.
Within lithospheric plates there are areas with different types of earth's crust. Thus, the eastern part of the Indo-Australian (Indian) plate is a continent, and the western part is located at the base of the Indian Ocean. The African Plate has continental crust surrounded on three sides by oceanic crust. The mobility of the atmospheric plate is determined by the relationship between the continental and oceanic crust within its boundaries.
When lithospheric plates collide, a folding of rock layers. Pleated belts – mobile, highly dissected areas of the earth's surface. There are two stages in their development. At the initial stage, the earth's crust experiences predominantly subsidence, and sedimentary rocks accumulate and metamorphose. At the final stage, the subsidence gives way to uplift, and the rocks are crushed into folds. Over the past billion years, there have been several eras of intense mountain building on Earth: the Baikal, Caledonian, Hercynian, Mesozoic and Cenozoic orogenies. In accordance with this, various folding areas are distinguished.
Subsequently, the rocks that make up the folded region lose their mobility and begin to collapse. Sedimentary rocks accumulate on the surface. Stable areas of the earth's crust are formed –
platforms. They usually consist of a folded foundation (remains of ancient mountains), covered on top by layers of horizontally occurring sedimentary rocks that form a cover. According to the age of the foundation, ancient and young platforms are distinguished. Areas of rock where the foundation is buried deep and covered by sedimentary rocks are called slabs. The places where the foundation reaches the surface are called shields. They are more typical for ancient platforms. At the base of all continents there are ancient platforms, the edges of which are folded areas of different ages. 
The spread of platform and fold regions can be seen on a tectonic geographical map, or on a map of the structure of the earth's crust.
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The Earth's crust, or geosphere, is the outer solid shell of the Earth. Beneath the crust is the mantle, which differs from it in composition and physical properties. The structure of the mantle is more dense, as it contains mainly refractory components. The mantle is separated from the crust by the Mohorovicic boundary, or Moho, at which the speed of seismic waves increases sharply. Most of the outer crust is covered with hydrosphere, the smaller part borders with atmospheric air. In accordance with this, the earth's crust is distinguished between oceanic and continental types, which have different structures. The total mass of the earth's crust, according to scientists, is only 0.5% of the total mass of the planet.
Structure and composition
The oceanic crust is dominated by a basalt layer. According to the theory of plate tectonics, this type of crust forms continuously at mid-ocean ridges, then moves away from them and is absorbed into the mantle in subduction regions. Therefore, the oceanic crust is considered relatively young. In different geographical zones, the thickness of the oceanic crust varies from 5 to 7 km. It consists of basalt and sedimentary layers. Its thickness practically does not change over time because it depends on the amount of melt released from the mantle in the areas of mid-ocean ridges. Also, the thickness of the oceanic crust is partially determined by the thickness of the sedimentary layer at the bottom of the oceans and seas. The thickness of the earth's crust increases with distance from areas of mid-ocean ridges. The continental (continental) crust is characterized by a three-layer structure. The top layer is a cover of sedimentary rocks, interrupted in places. This cover is well developed, but rarely reaches great thickness. The middle granitic layer of the continental crust makes up most of the total crust. It consists of gneisses and granite, has a low density and an ancient history of formation. A large proportion of the mass of these rocks was formed about 3 billion years ago. The lower basalt layer consists of metamorphic rocks - granulites and similar substances. The average thickness of the continental crust is about 35 km, the maximum under the mountain ranges is 70-75 km. The bark of this species contains many chemical elements and their compounds. About half of the mass is oxygen, a quarter is silicon, the rest is Al, Fe, Ca, Na, K, Mg, H, Ti, C, Cl, P, S, N, Mn, F, Ba.
In the transition zone from continents to oceans, a crust of transitional (intermediate) type (suboceanic or subcontinental) was formed. The transitional crust is characterized by a complex combination of features of the earth's crust of the two types described above. Intermediate crust corresponds to areas such as shelves, island arcs, and ocean ridges.
In the vast majority of areas, the earth's crust is in a state of relative isostatic equilibrium. Violation of isostatic compensation is observed on volcanic islands, oceanic basins, and island arcs. Here the earth's crust is constantly subject to tectonic movements. Large faults in the earth's crust can be considered as a result of the shift of tectonic plates in the areas of their junctions. In the structure of the crust, a distinction is made between relatively quiet areas (platforms) and mobile ones (folded belts).
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