Earth's crust types. Types of the earth's crust

My daughter was in Crimea for the first time last summer. She saw the mountains and asked me: “Why are they so high?” This was followed by another question: “Why is the sea deep?” The child is 3 years old, and she is already interested in such questions. Have you ever wondered why that is? What mountains differ from the sea? Now I want to talk about types earth's crust.

What types of earth's crust are there?

I think you know that under the ocean and on the plain there is a different crust of the earth. In the first case it is thinner, and in the second it is much thicker.

Earth's crust – it is a solid ball of lithosphere with a thickness ranging from 5 km (under the ocean) to 70 km (under mountains). Depending on the composition and thickness of the rocks, I distinguish 2 types of the earth’s crust: continental and oceanic.

Mainland (continental)) the earth's crust has thickness from 40 to 70 km. It consists of 3 layers:

• sedimentary- the top layer from the ground. Its thickness is 10-15 km;
• granite-metamorphic layer– thickness 5-15 km;
• basaltic– 10-30 km.

Unlike the mainland,the oceanic crust does not have a middle granite-metamorphic layer. It contains sedimentary and basalt layers. Its thickness is only 5 – 15 km.

Ocean ridges have a unique structure to the earth's crust.. Beneath the second oceanic layer is lens(or ledge). The rocks in their composition are not similar to the rocks in the mountains that are found on earth.

Research of the earth's crust

Scientists have long proven that the earth's crust under a plain (or mountain) is different from the earth's crust under an ocean. But even today, with the latest technical equipment, there are many unexplored places on earth. On Kola Peninsula, for example, they broke through the deepest well in the world. Its depth is 12 km, which is only 1/500 of the radius of our planet.

Everything we know, scientists know thanks to seismic method. During earthquakes and volcanic activity, magma and other rocks fall to the ground and accumulate inside our planet. Research is being conducted on them.

The earth consists of several concentric shells, each of which has a special chemical composition, physical properties and state of aggregation. The Earth's shells are grouped into 3 main layers:

1. external – the earth’s crust;

2. intermediate – mantle;

3. internal – core.

Core presumably composed of oxides of iron and nickel in a molten state.

Mantle consists of rocks whose main components are silicates of magnesium and iron.

Earth's crust in relation to the entire planet is about 1.5% of its volume (0.8% of mass). The thickness of the earth's crust under the continents is 35–70 km (on average 50 km), under the oceans – 5–10 km. The following chemical elements predominate in the earth's crust:

· oxygen (47 - 49.1%) – it is present in most minerals;

· silicon (26 – 28%): silica (silicon oxide), quartz, silicates.

· aluminum (7.4 – 8.7%);

· iron (4.2-5.1%);

· calcium (3.3 – 3.6%);

· sodium (2.6%);

· potassium (2.6%);

· magnesium (2.1%).

A distinction is made between continental and oceanic crust. Upper part continental crust folded so-called sedimentary cover, granite and basalt layers are located below. Oceanic crust has a mainly basaltic composition (contains silicon and magnesium). The density of the continental crust is 2.7 g/cm 3 , and that of the oceanic crust is 2.9 g/cm 3 .

Continental crust	SiO2	69%
	Al2O3	14%
	Fe 2 O 3 + FeO	4%
Oceanic crust	SiO2	48%
	Al2O3	15%
	Fe 2 O 3 + FeO	12%
	MgO	9%

Lithosphere- This is the solid shell of the Earth, including the earth's crust and the upper layer of the mantle. The thickness of the lithosphere ranges from 50 to 200 km.

The most common chemical elements in the lithosphere are oxygen, silicon, aluminum and magnesium; their total share accounts for 92% of the mass of the lithosphere. Oxygen, silicon and aluminum form the most common compounds in the earth's crust - silicates and aluminosilicates.

The earth's crust consists of rocks. Rocks- These are geological formations consisting of minerals and having a relatively constant chemical composition and properties. The main groups of rocks are: igneous, sedimentary and metamorphic.

Igneous rocks– are the result of the solidification of volcanic magma that has spread over the surface of the land or penetrated deep into the earth’s crust. At a depth of 15-30 km, igneous rocks are mainly represented by granite.

Sedimentary rocks – These are predominantly surface formations that arose during the destruction and redeposition of other – previously formed – rocks (crushed stone, gravel, sand, sandstones, clays).

Metamorphic rocks- these are products of changes in igneous and sedimentary rocks as a result of the influence of physical and chemical processes (mainly high temperatures and pressure).

Minerals- these are natural organic compounds, consisting of one or more chemical compounds. Most minerals are found in crystalline state, and has a relatively constant composition. About 3,000 minerals have been discovered in the earth's crust, the vast majority of them (90%) are formed by silicates of aluminum, iron, calcium, magnesium, potassium and sodium. Thus, the most common minerals are feldspars (58%), simple silicates (16.8%), quartz (12.6%), mica (3.6%).

An important component of the lithosphere is groundwater, the total volume of which in the sedimentary cover is 61.4 million km 3. Water is present in the earth's thickness as in free state, and in related form, as well as in various states of aggregation: in the form of vapor, ice and liquid. Free waters The underground hydrosphere is mineralized to varying degrees; fresh groundwater accounts for 2%. Fresh groundwater is mainly groundwater that is directly connected to surface sources (rivers, lakes). General underground mineralization fresh water is no more than 1 g/l; in composition they belong to hydrocarbonate. Groundwater They are characterized by a high content of dissolved organic matter, the concentration of which can be more than 35 mg/l; the waters of the arid (arid) zone contain the least amount of organic matter - less than 20 mg/l.

The biosphere includes only the upper part of the earth's crust, and the position of the lower boundary of the biosphere is not clearly established. The position of the biosphere boundary in the lithosphere is determined geological structure terrain, hydrogeological conditions of the area and geothermal gradient. The geothermal gradient characterizes the increase in the temperature of rocks with deepening for every 100 m. On average, it is 3 0 C, but depending on conditions it ranges from 1 to 20 0 C.

In general, the distribution of living matter in the lithosphere is observed only up to several tens of meters. Some microorganisms with groundwater reach depths of up to 2...3 km.

Soil

Soil is an independent natural organo-mineral body that arises on the surface of the earth’s land as a result of prolonged exposure to biotic, abiotic and anthropogenic factors. The soil consists of solid mineral and organic particles, water and air; it has a set of properties that determine the conditions for the growth and development of plants. Soil is the loose surface horizon of land capable of producing crops. It is the most important element of terrestrial ecosystems; it is a product of the interaction of biota and underlying rocks.

Soil is considered as a special natural body that plays an extremely important role in global biogeochemical processes. Soil is connected to the Earth's geospheres as follows:

1. With the lithosphere:

· Participates in biochemical transformation upper layers lithosphere;

· Is a source for the formation of minerals, minerals, rocks.

· Participates in the transfer of accumulated solar energy into the deep layers of the lithosphere;

· Protects the lithosphere from excessive erosion.

2. With the hydrosphere:

· Transforms surface water into groundwater;

· Participates in the formation of river flow;

· Is a factor in the bioproductivity of reservoirs due to the supplied biogenic compounds;

· Is a sorption barrier that protects against pollution.

3. With Atmosphere:

· Absorbs and reflects solar radiation;

· Regulates the water circulation of the atmosphere;

· Source of solid matter and microorganisms entering the atmosphere;

· Regulation of the gas regime of the atmosphere.

4. With biosphere:

· Habitat, battery and source of matter and energy for terrestrial organisms;

· Protective barrier;

· Connecting link of biological and geological cycles.

Soil-forming rocks is the substrate on which soils are formed. They consist of various mineral components that, to varying degrees, participate in soil formation. Mineral matter makes up 60–90% of the total weight of the soil. The physical properties of the soil depend on the nature of the parent rocks: its water and thermal regimes, the speed of movement of substances in the soil, mineralogical and chemical composition, and the initial content of nutrients for plants.

Organic components of soil are formed as a result of the vital activity of plants, animals and microorganisms. The main role here belongs to vegetation. Green plants are practically the only creators of primary organic substances. Absorbing carbon dioxide from the atmosphere, water and minerals from the soil, and using energy sunlight, they create complex organic compounds through the process of photosynthesis. Largest quantity organic substances are provided by forest communities, especially in the humid tropics.

In the process of the death of both whole plants and their individual parts, organic substances enter the soil (root and ground decay). The amount of annual decline varies widely: in wet forests it reaches 250 c/ha, in arctic tundra– less than 10 c/ha. On the soil surface, organic matter is under the influence of animals, bacteria, fungi, as well as physical and chemical factors decomposes to form soil humus. Ash substances replenish the mineral part of the soil. Undecomposed plant material forms the so-called. forest floor(in forests) or felt (in steppes and meadows). These formations influence soil gas exchange, sediment permeability, the thermal regime of the top layer of soil, soil fauna and the vital activity of microorganisms.

The main function of living organisms in the soil is the transformation of organic matter. Both soil and terrestrial animals take part in soil formation. IN soil environment animals are represented mainly by invertebrates and protozoa. Soil animals are divided into 2 groups: biophages, which feed on living organisms or tissues of animal organisms, and saprophages, which use organic matter as food. The main number of soil living organisms are saprophages: nematodes, earthworms.

The most important property of soil is its fertility, i.e. ability to provide organic and mineral nutrition to plants. Fertility depends on physical and chemical properties soils, which together represent edaphic factors.

Soil formation factors: soil-forming rocks, plant and animal organisms, climate, relief, age, water (soil and ground), economic activity person.

The top, most fertile layer of soil, containing the products of decay of organic matter, is called humus (humus layer). The chemical composition of humus includes free ulmic and humic acids, as well as their calcium, iron and magnesium salts.

Below the humus layer there is a low-fertility layer. Nutrients washed out of it by water or acids, which is why it is called a leaching horizon.

Organic matter, entering the soil with dead tissues of organisms, include lignin, proteins, lipids, as well as the end products of plant metabolism (waxes, resins, tannins).

Organic residues in the soil are mineralized to form simple products– water, carbon dioxide, ammonia.

The most important characteristics soils are: salt concentration in the soil solution, acidity (affects the activity of microorganisms).

Types of the earth's crust

Most for the most part The lithosphere is the earth's crust. The Earth's crust is the outermost solid shell of the Earth. The lower boundary of the earth's crust is considered to be the interface, when passing from top to bottom, longitudinal seismic waves abruptly increase the speed from 6.7-7.6 km/sec to 7.9-8.2 km/sec - the Mohorovicic boundary (Moho section).

The earth's crust is different on continents and under the ocean. Seismic studies show that there are two main types of earth's crust - continental and oceanic.

The continental crust (Fig. 1.1.) usually has a thickness of 35-45 km, in areas mountainous countries- up to 70 km. It consists of three layers - a sedimentary cover, a granite layer and a basalt layer.

The sedimentary cover is up to 10 km thick and consists of unaltered or slightly altered sedimentary and volcanic rocks of different ages. The layers are often folded, torn and displaced along the gap. In some places (on shields) the sedimentary shell is absent;

The granite layer is denser, its thickness is 10-15 km, it is composed of granites and gneisses;

The basalt layer is even denser, 15-35 km thick, composed of basalts, gabbro and very highly metamorphosed sedimentary rocks in various proportions.

The oceanic crust has a thickness of 5-10 km (together with the water column - 9-12 km). It is divided into 3 layers: under a thin (less than 1 km) layer of marine sediments there is a “second” layer with longitudinal seismic wave velocities of 4-6 km/sec; its thickness is 1-2.5 km. It is probably composed of serpentinite and basalt, perhaps with interlayers of sediments. The lower, “oceanic” layer, with an average thickness of about 5 km, has seismic wave speeds of 6.4-7.0 km/sec; it is probably composed of gabbro. The thickness of the sediment layer on the ocean floor is variable, and in some places there is none at all.

In the transition zone from the continent to the ocean, a transitional type of crust is observed.

The earth's crust of geosynclinal belts of transitional type is formed at the junction of oceanic and continental platforms, while the formation of a granite layer occurs as a result of deep metamorphization of igneous and sedimentary rocks in subduction zones, it is distinguished by its diversity and complexity of structure, the earth's crust of transitional type is oceanic ( marginal seas Pacific Ocean, Caspian Sea, etc.) and continental (island arcs, etc.). The earth's crust of transitional type, like the oceanic crust, consists of a basalt layer, on top of which there is a thick, up to 10-20 km, sedimentary layer.

The rift type of the earth's crust (5-7 km) occurs in spreading zones (rifts), where Mantle material reaches the surface and mid-ocean ridges arise, and a young oceanic earth's crust is born.

Even today, when so much has been invented technical equipment, devices, there are still inaccessible and mysterious worlds. One of them is the bowels of the earth. in the world it has been drilled to a depth of 12 km, which is only 1/500 of the radius of our planet. Everything that scientists know about the interior of the earth, they learn through the seismic method of study. During tremors, vibrations occur inside the planet that travel from at different speeds. It is known that the speed of propagation depends on the density and composition of substances. Based on the velocity data, experts can already interpret information about which layer the vibration passed through.

This is how it was established that the planet is covered with several shells. This is the earth's crust, then the mantle and next is the core.

The last one is the densest and heaviest. The core is believed to be composed of iron.

Of all three shells, the mantle has the largest volume and weight. It consists of a solid substance, but not as dense as in the core.

And finally, the earth's crust. This outer shell of the planet is much thinner compared to the previous ones. Its mass does not exceed even 1% of the weight of the entire planet. Humanity lives on its surface, and fossils are mined from it. In many places, the earth's crust is penetrated by wells and mines. Their presence made it possible to collect rock samples, which helped determine the structure of this shell of the planet.

And the earth’s crust consists of rocks, which, in turn, are formed from minerals. They continue to form in all layers of the shell, even on its surface. According to the conditions in which they were formed, they are divided into:

1. Metamorphic. They are formed deep underground as a result of strong heating and compression of some rocks and their transformation into other rocks. For example, ordinary limestone is converted into marble.

2. Sedimentary. They are formed by gradual accumulation on earth's surface various minerals. Because this process is slow, sedimentary rocks often consist of several layers.

3. Igneous. They are formed by mantle material that rose to the overlying layers and froze there. The most famous of these rocks is granite. Magma can rise in molten form to the earth's surface. Then water vapor and gases are sharply released from it, and it turns into lava. Having poured out, it freezes instantly. Thus, as a result, they are formed. These include, for example, basalt.

The earth's crust under the oceans and on the continents is structured differently. The main differences lie in the composition of its layers and thickness. On this basis, the following types of earth's crust are considered separately:

Continental;

Oceanic.

Experts suggest that the continental species appeared much later under the influence of seismic processes occurring in the bowels of the planet. The minimum thickness of the continental (or continental) crust is 35 km, and under mountains and other elevations it can be up to 75 km. It is formed by three layers. The upper one is Its thickness - from 10 km to 15 km. Then there is a 5-15 km layer of granite. And the last one is basalt. Its thickness is 10-35 km. It consists mainly of basalt, as well as rocks similar to it in physical properties.

Chemical composition The earth's crust can only be determined by its upper layer, the depth of which does not exceed 20 km. Almost half of it is oxygen, 26% is silicon, about 8% is aluminum, 4.2% is iron, 3.2% is calcium, 2.3% each is magnesium and potassium, and 2.2% is sodium. The remaining chemical elements account for no more than a tenth of 1%.

Now scientists have begun a close study of the oceanic and continental crust. They took as a basis the hypothesis about the movement of continents, put forward more than a century ago by A. Wegener, and formed their own theory of the structure of the outer shell of the planet.

1.Types of the earth's crust.

There are 2 main types of the earth's crust: continental and oceanic, and 2 transitional types - subcontinental and suboceanic.

The continental type of the earth's crust has a thickness of 35 to 75 km, in the shelf area - 20 - 25 km, and pinches out on the continental slope. There are 3 layers of continental crust:

1st - upper, composed of sedimentary rocks with a thickness of 0 to 10 km. on platforms and 15 - 20 km. in tectonic deflections of mountain structures.

2nd - average “granite-gneiss” or “granite” - 50 - granites and 40% gneisses and other metamorphosed rocks. Its average thickness is 15 - 20 km. (in mountain structures up to 20 - 25 km.).

3rd - lower, “basalt” or “granite-basalt”, composition close to basalt. Power from 15 - 20 to 35 km. The boundary between the “granite” and “basalt” layers is the Conrad section.

According to modern data, the oceanic type of the earth's crust also has a three-layer structure with a thickness of 5 to 9 (12) km, more often 6-7 km.

1st layer - upper, sedimentary, consists of loose sediments. Its thickness ranges from several hundred meters to 1 km.

2nd layer - basalts with interlayers of carbonate and silicon rocks. Thickness from 1 - 1.5 to 2.5 - 3 km.

The 3rd layer is the bottom one, not opened by drilling. It is composed of basic igneous rocks of the gabbro type with subordinate, ultrabasic rocks (serpentinites, pyroxenites).

The subcontinental type of earth's surface is similar in structure to the continental one, but does not have a clearly defined Conrad section. This type of crust is usually associated with island arcs - the Kuril, Aleutian and continental margins.

1st layer - upper, sedimentary - volcanogenic, thickness - 0.5 - 5 km. (on average 2 - 3 km.).

2nd layer - island-arc, “granite”, thickness 5 - 10 km.

3rd layer - “basalt”, at depths of 8 - 15 km, thickness from 14 - 18 to 20 - 40 km.

The suboceanic type of the earth's crust is confined to the basin parts of the marginal and inland seas (Okhotsk, Japan, Mediterranean, Black, etc.). Its structure is similar to that of the ocean, but is distinguished by the increased thickness of the sedimentary layer.

1st upper - 4 - 10 or more km, located directly on the third oceanic layer with a thickness of 5 - 10 km.

The total thickness of the earth's crust is 10 - 20 km, in some places up to 25 - 30 km. due to an increase in the sedimentary layer.

A peculiar structure of the earth's crust is observed in the central rift zones of the mid-ocean ridges (Mid-Atlantic). Here, under the second oceanic layer, there is a lens (or protrusion) of low-speed material (V = 7.4 - 7.8 km/s). It is believed that this is either a protrusion of an abnormally heated mantle, or a mixture of crustal and mantle matter.

2. Hypotheses of the tectonic development of the Earth and the earth’s crust.

Continental drift hypothesis.

The most complete hypothesis of continental drift was developed in 1912 by the famous German geophysicist A. Wegener.

According to the ideas of A. Wegener, the entire surface of the Earth was originally covered with a continuous thin granite layer. During the Paleozoic era, all granite material was collected into one block. A single proto-continent was formed - Pangea (Greek “pan” - universal, “ge” - earth). He towered above the level of the boundless ocean that surrounded him. The reason for this could be the influence of tidal and centrifugal forces. Tidal forces are related to the gravitational pull of the Sun and Moon; they act on the earth's surface from east to west. Centrifugal forces are caused by the rotation of the Earth and are directed from the poles to the equator. In the middle Mesozoic era Pangea began to split into separate blocks - continents. Under the influence of the same forces, they began to sail away from each other in a latitudinal direction. For example, America broke away from Europe and Africa and moved west. In the interval between them there arose Atlantic Ocean. South America and Africa experienced a clockwise turn in their movement. As a result of the movement of Antarctica to the south, Australia to the southeast, and Hindustan to the northeast, the Indian Ocean was formed between them. Thus, in Wegener's hypothesis, the Atlantic and Indian Oceans are considered secondary, and Pacific Ocean- as a remnant of the primary ocean. Its area consistently decreased as a result of continents advancing on it from all sides.

Earth expansion hypothesis.

Proponents of this hypothesis suggest that the volume of the globe was originally much smaller than it is now. The radius of the Earth was 3500 - 4000 km, and its surface was half that of today. Oceans did not yet exist. The continental crust covered the entire globe. According to some researchers, the expansion of the Earth began from the end Paleozoic era. Others believe that this happened in Cretaceous period. From this moment on, the radius of the Earth began to increase annually by approximately 0.6 mm. Due to expansion, the initially single continental crust cracked. Separate continents formed and moved further and further away from each other as the Earth continued to expand. In the intervals between the continents, the subcrustal layer was exposed. The mantle material rising from below penetrated here, forming a new oceanic type crust.

Pulsation hypothesis.

At the beginning of the twentieth century. The idea was expressed that epochs of expansion of the Earth are replaced by epochs of its compression.

According to their ideas, the epochs of compression correspond to mountain-building phases, and the epochs of expansion correspond to periods of rest and subsidence of basins. The extension of the earth's crust is concentrated mainly in rift zones. It is compensated by compression of the crust in the area of ​​deep-sea trenches and mountain-fold systems. The effects of compression and expansion are distributed unevenly on the Earth's surface. Due to repeated alternating compression and stretching, blocks of the earth's crust drift from tension zones to compression zones. For example, the Syrian-Arabian plate moves from the grabens of the Red Sea and the Gulf of Aden towards the folded ridges of the Taurus, Zagros and Caucasus.

3. Hypothesis of the movement of lithospheric plates.

Features of the movement of lithospheric plates were described in the late 60s by V. Jason Morgan, Xavier Le Pinnon and others. According to their ideas, the Earth's surface is divided into 9 main ones (1. Pacific; 2. North American; 3. Eurasian; 4. Coconut; 5. Nazca; 6. South American; 7. African; 8. Indo-Australian; 9. Antarctic) and several small hard lithospheric plates. They include not only continents, but also adjacent parts ocean floor. The main boundaries of the lithospheric plates are rifts of mid-ocean ridges, deep-sea trenches and folded mountains along the margins of continents.

From the line of the mid-ocean ridges, due to the new formation of the oceanic crust here, a spreading occurs (in different sides) lithospheric plates. The buildup of oceanic crust along the axes of rift valleys is compensated by its destruction on the opposite edge of the plate - in the zone of the deep-sea trench. It is assumed that here the plate of oceanic lithosphere moving from the median ridge bends and plunges into the asthenosphere at an angle of 45° under the plate of continental lithosphere moving towards it. This dive occurs to a depth of 700 km (see figure).

A number of scientists believe that such ideas are poorly substantiated.

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 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 common namelithosphere(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, in which 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. (Characteristics physical properties various minerals can be found in Appendix 2.) The composition of the Earth's minerals is shown in Fig. 6.

Rice. 6. General mineral composition Earth

Rocks consist of minerals. They can be composed of one or several minerals.

Sedimentary rocks - clay, limestone, chalk, sandstone, etc. - formed by sedimentation of substances in aquatic environment and on land. They lie in layers. Geologists call them pages of the history of the Earth, because they can learn about 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 0.005mm

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 minerals, How 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 areas of land up 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. So, maximum thickness 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. Yes, Kola ultra-deep well, which for the first time made it possible to see rock samples from a depth of more than 12 km, brought many 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, characteristic feature which is the constant temperature corresponding average annual temperature observation sites. 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.