Before talking about what the earth's crust consists of, we can recall what is supposedly the constituent parts of everything Presumably - because man has not yet been able to penetrate deeper than this earth's crust to the center of the earth. Even the entire thickness of the bark could only be "picked".

Scientists assume, build hypotheses based on the laws of physics, chemistry and other sciences, and according to these data, we have a certain picture of the structure of the entire planet, as well as what large elements the earth's crust consists of. Geography in grades 6-7 gives students precisely these theories in a form facilitated for immature minds.

Due to a small share of data and a large baggage of various laws, planetary models are built in the same way. solar system, and even stars that are far from us. What follows from this? Mainly that you have an absolute right to doubt all this.

Layers of planet Earth

In addition to having layers, the entire earth also consists of three layers. Such a layered culinary masterpiece. The first of these is the core; it has a solid part and a liquid part. It is the movement of the liquid part in the core that presumably creates a bit hot here - the temperature reaches values ​​​​up to 5000 degrees Celsius.

The second is the mantle. It connects the core and the earth's crust. The mantle also has several layers, namely three, and the upper one, adjacent to the earth's crust, is magma. It is directly related to the question of what large elements the earth's crust consists of, since hypothetically it is on it that these largest elements "float". We can talk about its existence with a more or less high degree of probability, since during volcanic eruptions it is this hot substance that comes to the surface, destroying all plant and animal life that is on the slope of the volcano.

And, finally, the third layer of the earth is the earth's crust: the solid layer of the planet, located outside the hot "insides" of the Earth, on which we are used to walking, traveling and living in general. The thickness of the earth's crust, in comparison with the other two layers of the earth, is negligible, but nevertheless it is possible to characterize what large elements the earth's crust consists of, and also to understand its composition.

What are the layers of the earth's crust. Its main chemical elements

The earth's crust also consists of layers - there is basalt, granite and sedimentary. Interestingly, in the chemical composition of the earth's crust, 47% is oxygen.

The substance, which is essentially a gas, combines with other elements and creates a solid crust. Other elements in this case are silicon, aluminum, iron and calcium; the remaining elements are present in minute fractions.

Division into parts by thickness in different areas

It has already been said that the earth's crust is much thinner than the lower mantle or core. If we approach the question of what large elements the earth's crust consists of, precisely in relation to thickness, we can divide it into oceanic and continental. These two parts differ significantly in their thickness, and the oceanic one is about three times, and in some places ten times (if we talk about averages) thinner than the mainland.

What is the difference between the continental and oceanic crust

In addition, the zones of land and oceans differ in layers. Different sources indicate different data, we will give one option. So, according to these data, the continental crust consists of three layers, among which there is a basalt layer, a granite layer and a layer of sedimentary rocks. The plains of the earth's continental crust reach a thickness of 30-50 km, in the mountains these figures can rise to 70-80 km. According to the same source, the oceanic crust consists of two layers. A granite ball falls out, leaving only the upper sedimentary and lower basalt. The thickness of the earth's crust in the region of the oceans is approximately from 5 to 15 kilometers.

Simplified and averaged data as the basis for training

These are the most general and simplified descriptions, because scientists are constantly working to study the features of the surrounding world, and the latest data indicate that the earth's crust in different places has a structure that is much more complicated than the usual standard scheme of the earth's crust that we study at school. Here in many places of the continental crust, for example, there is another layer - diorite.

It is also interesting that these layers are not perfectly even, as is schematically depicted in geographical atlases or from other sources. Each layer can be wedged into another, or kneaded in some cut. In principle, there can be no ideal model of the earth's scheme, for the same reason that volcanic eruptions occur: there, under the earth's crust, something is constantly in motion and has very high temperatures.

All this can be learned if you connect your life with the sciences of geology and geophysics. You can try to keep track of scientific progress through scientific journals and articles. But without a certain amount of knowledge, this can turn out to be a very difficult task, and therefore there is a certain basis that is taught in schools without any explanation that this is just an approximate model.

Presumably, the earth's crust consists of "pieces"

Scientists at the beginning of the 20th century put forward the theory that the earth's crust is not monolithic. Therefore, it is possible to find out what large elements the earth's crust consists of according to this theory. It is assumed that the lithosphere consists of seven large and several small plates that slowly float on the surface of magma.

These movements create a catastrophic kind of phenomena that occur on our earth with great intensity in certain places. There are areas between the lithospheric plates, which are called "seismic belts". It is in these areas that the highest level of anxiety, so to speak. An earthquake and all the ensuing consequences of this is one of the clear signs that demonstrates

Influence of displacements of lithospheric plates on the formation of relief

What large elements the earth's crust consists of, which moving parts are more stable and which are more mobile, throughout the creation earth relief influenced his education. The structure of the lithosphere and the characteristics of the seismic regime distribute the entire lithosphere into stable areas and mobile belts. The first are characterized by flat planes without huge depressions, hills and similar relief variations. They are also called abyssal plains. In principle, this is the answer to the question of what large elements the earth's crust consists of, what stable primary objects it is formed from. The earth's crust underlies all continents. The boundaries of these plates are easily visible by the zones of mountain formation, as well as by the degree of intensity of earthquakes. The most active places on our planet, where earthquakes and many active volcanoes are located, are the locations of Japan, the islands of Indonesia, the Aleutian Islands, the South American Pacific coast.

Are the continents bigger than we used to think?

That is, simply speaking, what the earth's crust consists of is pieces of the lithosphere, which move more or less through magma. And the boundaries of these "pieces" do not always coincide with the boundaries of the continents. Technically, they often never match. In addition, we are used to hearing that the oceans account for approximately 70% of the surface, and the continental component - only 30%. Geographically, it is, but here's what's interesting - in terms of geology, the continents account for about 40%. Ten percent of the continental crust is covered by sea and ocean waters.

A characteristic feature of the Earth's evolution 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, power and state of matter.

The internal structure of the Earth

The chemical composition of the Earth(Fig. 1) is similar to the composition of other planets terrestrial group like 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 matter is 5.5 g/cm 3 .

There is very little reliable data on the internal structure of the Earth. Consider Fig. 2. It depicts the internal structure of the Earth. The earth consists of the earth's crust, mantle and core.

Rice. 1. The chemical composition of the Earth

Rice. 2. The 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 core temperature 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 presumably consists of alloys of iron and nickel.

The outer core of the Earth has a greater power than the inner core (radius 2200 km) and is in a liquid (molten) state. The inner core is under enormous pressure. The substances that compose it are in a solid state.

Mantle

Mantle- the geosphere of the Earth, 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 less dense and plastic upper part(800-900 km), from which magma(translated from Greek means "thick ointment"; this is the molten substance of the earth's interior - a mixture chemical compounds and elements, including gases, in a special semi-liquid state); and a crystalline lower one, about 2000 km thick.

Rice. 3. Structure of the Earth: core, mantle and earth's 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(it is often called the Moho boundary), characterized by a sharp increase in seismic wave velocities. It was installed in 1909 by a Croatian scientist Andrey Mohorovichich (1857- 1936).

Since the processes occurring in the uppermost part of the mantle affect the movement of matter in the earth's crust, they are combined under the general name lithosphere(stone shell). The thickness of the lithosphere varies from 50 to 200 km.

Below the lithosphere is 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 is introduced into the earth's crust or poured onto the earth's surface.

The 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, aluminium, iron, calcium, sodium, potassium, and magnesium—account for 98% of the mass of the earth's crust (see Figure 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. The structure of the earth's crust

Rice. 5. The composition of the earth's crust

Mineral is a relatively homogeneous in its composition and properties of a natural body, formed both in the depths and on the surface of the lithosphere. Examples of minerals are diamond, quartz, gypsum, talc, etc. (Characteristic physical properties various minerals you will find in Appendix 2.) The composition of the minerals of the Earth is shown in fig. 6.

Rice. 6. General mineral composition of the Earth

Rocks are made up of minerals. They can be composed of one or more minerals.

Sedimentary rocks - clay, limestone, chalk, sandstone, etc. - formed by precipitation of substances in aquatic environment and on dry land. They lie in layers. Geologists call them pages of the history of the Earth, since they can learn about natural conditions that existed on our planet in ancient times.

Among sedimentary rocks, organogenic and inorganic (detrital and chemogenic) are distinguished.

Organogenic rocks are formed as a result of the accumulation of the remains of animals and plants.

Clastic rocks are formed as a result of weathering, the formation of destruction products of previously formed rocks with the help of water, ice or wind (Table 1).

Table 1. Clastic rocks depending on the size of the fragments

Breed name	Size of bummer con (particles)
	Over 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 sedimentation from the waters of the seas and lakes of substances dissolved in them.

In the thickness of the earth's crust, magma forms igneous rocks(Fig. 7), such as 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. So, for example, limestone turns into marble, quartz sandstone into quartzite.

Three layers are distinguished in the structure of the earth's crust: sedimentary, "granite", "basalt".

Sedimentary layer(see Fig. 8) is formed mainly by sedimentary rocks. Clays and shales predominate here, 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 areas of land 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 the 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, oceanic and continental crust are distinguished.

Continental and oceanic crust are different in thickness. So, 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 the thinnest - only 5-10 km.

Rice. 8. Types of the earth's crust: 1 - water; 2 - sedimentary layer; 3 - interbedding of sedimentary rocks and basalts; 4, basalts and crystalline ultramafic rocks; 5, granite-metamorphic layer; 6 - granulite-mafic layer; 7 - normal mantle; 8 - decompressed mantle

The difference between the continental and oceanic crust in terms of rock composition is manifested in the absence of a granite layer in the oceanic crust. Yes, and the basalt layer of the oceanic crust is very peculiar. In terms of rock composition, it differs from the analogous layer of the continental crust.

The boundary of land and ocean (zero mark) does not fix the transition of the continental crust into the oceanic one. The replacement of the continental crust by oceanic occurs in the ocean approximately at a depth of 2450 m.

Rice. 9. The structure of the continental and oceanic crust

There are also transitional types of the earth's crust - suboceanic and subcontinental.

Suboceanic crust located along the continental slopes and foothills, can be found in the marginal and Mediterranean seas. It is a continental crust up to 15-20 km thick.

subcontinental crust located, for example, on volcanic island arcs.

Based on materials seismic sounding - seismic wave velocity - we get data on the deep structure of the earth's crust. Yes, Kola ultradeep 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 surprises. It was assumed that at a depth of 7 km, a “basalt” layer should begin. In reality, however, it was not discovered, and gneisses predominated among the rocks.

Change in the temperature of the earth's crust with depth. The surface layer of the earth's crust has a temperature determined by solar heat. This is heliometric layer(from the Greek Helio - the Sun), experiencing seasonal temperature fluctuations. Its average thickness is about 30 m.

Below is an even thinner layer, feature which is a constant temperature corresponding to the average annual temperature of the observation site. The depth of this layer increases in the continental climate.

Even deeper in the earth's crust, a geothermal layer is distinguished, 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 the rocks, primarily radium and uranium.

The magnitude of the increase in temperature of rocks with depth is called geothermal gradient. It varies over a fairly wide range - from 0.1 to 0.01 ° C / m - and depends on the composition of the rocks, the conditions of their occurrence and a number of other factors. Under the oceans, the temperature rises faster with depth than on the continents. On average, with every 100 m of depth it becomes warmer by 3 °C.

The reciprocal of the geothermal gradient is called geothermal step. 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 extending to the depths available for geological study forms bowels of the earth. The bowels of the Earth require special protection and reasonable use.

In the 80s of the last century, the American scientist Clark set out to determine the average chemical composition of the earth's crust. To do this, he collected all the chemical analyzes of the rocks known in his time and deduced the average from them. Of course, Clark knew that various rocks, loose and soft, like sand or clay, and hard, like granite or basalt, are distributed on the surface of the Earth very unevenly: some rocks compose large areas of the earth's surface, while others are rare and only in small spots. For example, more than half of the area of ​​Canada, almost all of Sweden and all of Finland are covered with continuous granite outcrops on the earth's surface. Huge areas are composed of granites and similar rocks in Africa, South America, India, Australia and other places. At the same time, there are such rocks (for example, alkaline, containing increased quantities potassium or sodium), which can be found on the surface of the Earth only in the form of individual small spots, the total area of ​​\u200b\u200bwhich for all continents does not exceed several hundred thousand square kilometers.

But Clark, in making his calculations, proceeded from the assumption that the more often this or that rock is found on the earth's surface, the more samples of it were subjected to chemical analysis and that therefore the relative number of chemical analyzes for each rock fairly well reflects the relative abundance of rocks on the surface. .

Subsequently, many scientists pointed out that this bold assumption of Clark could not be considered correct: some of the rarest rocks were subjected to chemical research disproportionately precisely because, because of their rarity and unusualness, they attracted the attention of geologists more. As later studies showed, the data obtained by Clark, as an average of 6000 analyzes, for the most common chemical elements, were still close to the truth. The values ​​that he obtained for less common elements were later significantly changed. To note the merit of Clark, who first introduced us, at least approximately, to the general chemical composition of the earth's surface, scientists agreed to call the percentage of an element in the earth's crust the "clarke" of this element. Clark's table was published in 1889.

The Finnish geologist Sederholm made an attempt to calculate the average chemical composition of the earth's crust, given the relative size of the area occupied by each rock. He could not do this for the entire globe and limited his calculations only to the territory of Finland. The discrepancy with Clark's data turned out to be quite large. So, for example, the average content of silica (SiO 2) in the rocks of Finland at Sederholm turned out to be 67.70%, while at Clark, the average content of silica in the rocks of the whole world was 60.58%. On the contrary, the content of alumina (Al 2 O 3), iron sesquioxide (Fe 2 O 3), calcium oxides (CaO), magnesium (MgO), sodium (Na 2 O) turned out to be much less than Clarke expected.

Since then, many prominent scientists have been engaged in refining data on the chemical composition of the earth's crust: abroad - Washington, Vogt, I. and V. Noddaki, Goldschmidt, Geveshi, etc., in our country - V. I. Vernadsky, A. E. Fersman, V. G. Khlopin, A. P. Vinogradov and others. Particularly accurate clarke tables of all elements were compiled Soviet academician A. E. Fersman.

The table shows the content (in weight percent) of the elements most common in the earth's crust. There are only 12 of them here; the remaining 80 elements form an insignificant fraction of the weight of the earth's crust.

The average composition of the earth's crust (according to A. E. Fersman)

Weight percent

Indeed, if we were to give the clarks of all the elements, the first thing that would strike us would be the unevenness of their distribution. The amount of oxygen, the most common element, reaches 49.13% (by weight), and protactinium is only 7∙10 -11%. The most common elements have clarks billions of times higher than the rarest elements. This uneven distribution of chemical elements can be illustrated in another way. If we arrange the elements in descending order of their clarks, we will see that the first three elements (oxygen, silicon and aluminum) make up 82.58% by weight, the first nine elements already make up 98.13%, and the first twelve - 99.29% . The same can be expressed graphically.

So, we see that the earth's crust, by weight, is almost half oxygen, about a quarter of silicon, a thirteenth of aluminum, a twenty-fourth of iron, etc. Taking into account the large size of oxygen atoms, it can be said that the earth's crust, like bricks, is built of oxygen atoms, and only in the gaps between them, as if cementing them, are other elements located.

From the average content of elements, it is not difficult to calculate their absolute masses contained in a particular volume, corresponding in composition to the average composition of the earth's crust. So, it can be determined that 1 km 3 of rocks will contain on average: iron 130 ∙ 10 6 t, aluminum 230 ∙ 10 6 t, copper 260,000 t, tin 100,000 t, etc.

The elements that make up the earth's crust are in various combinations with each other. These compounds, formed as a result of natural processes, are called minerals. In total, several thousand minerals are known, but only a few dozen of them are most widely used. Here again we see the same disproportion in the distribution of various minerals as in the distribution of individual elements.

The predominance of oxygen, silicon and aluminum in the earth's crust determines that most of the minerals belong to the category silicates and aluminosilicates, i.e., it is salts of silicic and aluminum-silicic acids. In addition, sulfides, sulfates and oxides are common among minerals.

An example of aluminosilic acid (not existing in free form) is the compound H 2 Al 2 Si 2 O 8 , or (if written in the form of a combination of oxides) H 2 O ∙ Al 2 O 3 ∙ 2SiO 2 . Among silicic acids, there are: orthosilicic acid H 4 SiO 4, or 2H 2 O ∙ SiO 2, and metasilicic acid H 2 SiO 3, or H 2 O ∙ SiO 2.

When the hydrogen of aluminosilic acid is replaced by potassium, sodium or calcium, minerals are obtained, called feldspars. An example of feldspar is the orthoclase mineral having the composition K 2 O ∙ Al 2 O 3 ∙ 6SiO 2 .

Aqueous aluminosilicates form various mica, both light (containing potassium or sodium) and dark (containing magnesium and iron). For example, light mica or muscovite has the composition: K 2 O ∙ 3Al 2 O 3 ∙ 6SiO 2 ∙ 2H 2 O.

When the hydrogen of silicic acids is replaced by magnesium, iron and calcium, dark-colored minerals are obtained - olivines, pyroxenes and amphiboles.

Statistics show that feldspars are the most common among minerals in the earth's crust (55.0%). Meta - and ortho-silicates form 15%, and quartz (SiO 2) - 12%. Among other minerals, micas (3%) and magnetite (Fe 3 O 4) together with hematite (Fe 2 O 3) (3%) are relatively common. The remaining minerals in the composition of the earth's crust are much less. Most minerals are crystalline.

Minerals in the earth's crust are not randomly distributed. They are grouped into some natural associations, forming the so-called rocks. The rock is, for example, granite, characterized by a certain association of minerals, among which feldspars, quartz, and micas predominate. There are rocks consisting almost or completely of one mineral. Such, for example, is quartzite, consisting almost entirely of quartz, or marble, composed almost exclusively of calcite. More often, however, several minerals are involved in the rock, more or less evenly distributed in it in a certain quantitative relationship.

The rocks that make up the earth's crust are divided into groups depending on their origin. Most of the earth's crust is composed of rocks of igneous origin, formed as a result of penetration into the earth's crust from a depth or outpouring to the surface and solidification of molten stone masses. This group includes many rocks: granite, basalt, andesite, diorite, etc.

A few percent of the earth's crust is folded sedimentary rocks formed as a result of the deposition and accumulation of mineral material on the surface of the Earth, mainly at the bottom of sea basins, but also at the bottom of lakes, river flows, in swamps and simply on the land surface.

Finally, in the earth's crust are common metamorphic rocks, which are the result of chemical and physical changes in sedimentary rocks under the influence of high temperature and high pressure. Sedimentary rocks undergo such changes where they sank to great depths during the bowing of the earth's crust and, being buried under heavy strata of later rocks, found themselves in a zone of high temperatures and under high pressure. In addition, metamorphic rocks are formed in those places where molten magma intrudes into sedimentary rocks and affects them with its temperature, as well as chemically.

The belonging of a rock to one or another genetic group leaves an imprint on its mineralogical composition and internal composition.

Rocks of igneous origin, in turn, are divided into intruded, or intrusive rocks, and outflowing, or effusive rocks. Intruded rocks are the result of solidification of molten mineral matter at some depth below the earth's surface. We can see them only after the overlying rocks are destroyed by erosion and the mass of intruded rock (the so-called intrusion) is exposed on the surface. Intruded rocks are characterized, as a rule, by dense coarse-grained composition, and the sizes of crystals of different minerals are usually close in size: from 0.2 to 1 cm. Granite is a typical rock of this group - in general, the most common rock among intruders.

Erupted rocks, among which basalt is the most common, are characterized either by a glassy, ​​amorphous composition, or by fine-grained, formed as a result of volcanic glass crystallization over time. Rapid solidification after outpouring to the surface prevents the formation of large crystals in the erupted rocks.

According to their composition, igneous rocks, intruded and erupted, are divided into acidic, medium, basic and ultrabasic, depending on the content of silica in them.

In acid rocks, silica is more than 65%, in medium rocks - from 52 to 65%, in basic rocks - from 40 to 52%, and in ultrabasic rocks - less than 40%. Interestingly, among the intruded rocks, the acidic rock - granite, sharply predominates, while the main rock basalt dominates among the erupted rocks. Medium breeds are relatively rare. Usually, alkaline rocks enriched in potassium and sodium are also isolated.

Sedimentary rocks are usually divided into three genetic groups: clastic, organogenic and chemical. The first of them are products of mechanical destruction of other rocks, displacement and redeposition of their fragments. Sometimes (for example, in breccias and pebbles) we deal with the accumulation of large fragments that have remained angular or have undergone rounding. In other cases, clastic rock is composed of small fragments of minerals, as in sandstone. Finally, mineral fragments often turn out to be worn into an extremely thin mass, which, after its redeposition by water, forms clay. The mineralogical composition of clastic rocks depends on the composition of the original rock, as well as on the strength of individual minerals, on their resistance to grinding and dissolution during transfer. Since the most durable mineral, among the widely distributed ones, is quartz, a significant part of clastic rocks consists of large or small fragments of quartz.

Organogenic sedimentary rocks are formed by the accumulation of the remains of organisms. main role at the same time, the skeletons of organisms play. In marine organisms, they are predominantly calcareous; these are shells, segments, membranes, needles, etc. From the accumulation of calcareous skeletons of organisms, limestones are formed. The remains of some organisms have a different composition: siliceous, phosphate, ferruginous, etc. In accordance with this, organogenic rocks have a different composition, along with limestones, siliceous diatomites and flasks, phosphorites, etc. are found.

Organogenic sedimentary rocks also include coals, oil shale and oil, which are products of the transformation in the earth of the remains of plant and animal soft matter.

Chemical rocks in their formation are associated mainly with the chemical precipitation of salts from aqueous solutions. From saturated solutions, found in some lakes and sea lagoons, fall out salt, gypsum, calcite, sulfate and chloride salts of magnesium, calcium, potassium, as well as various salts of complex composition.

Metamorphic rocks are formed when sedimentary rocks come into contact with molten magma in the earth's crust. They also arise in the deep zones of the earth's crust, where high temperatures prevail everywhere. The phenomenon of metamorphism is facilitated by the simultaneous crushing of the rock or its cracking under the influence of pressure acting in the earth's crust. In metamorphic rocks, depending on the degree of metamorphism, a composition is found that is intermediate between sedimentary and igneous rocks. With strong heating of the sedimentary rock and when pressure is applied to it, the rock first of all recrystallizes. Amorphous constituents pass into. crystalline state, small crystals are combined and enlarged. A typical example is the transformation of limestone into marble - a dense coarse-grained calcite rock.

During recrystallization, some ions are rearranged and new compounds are formed that were previously absent in the sedimentary rock. So, for example, during the metamorphization of limestone containing an admixture of quartz (usually in the form of grains of sand or in the form of siliceous inclusions), the mineral wollastonite - calcium silicate (CaSiO 3) is often formed.

From the magma acting on the sedimentary rock, gases and liquids are released, which, penetrating into the surrounding rocks, can cause various chemical changes. Under these conditions, the sedimentary rock can, for example, undergo silicification, i.e., become saturated with quartz when gases or solutions bring silica.

The pressure developing in the earth's crust under the influence of tectonic forces (see below) crushes rocks. As a result, the rocks often acquire a slate structure - they are divided into thin parallel plates or tiles. This process is usually accompanied by the formation of new flat minerals (mica, chlorite, etc.). This is how various metamorphic schists are formed.

A few words should be said about ore minerals. This is the name of minerals in which the content of certain metals is sufficient for their practically beneficial isolation. Iron ore is minerals with a sufficiently high iron content, molybdenum ore is minerals with a sufficiently high molybdenum content, etc. The percentage of metal required for a given mineral to be considered an ore is extremely different for different metals, as well as for different conditions of their occurrence. in the earth's crust. In some cases, mining is carried out where the content of the desired metal in the ore is measured in small fractions of a percent, in other cases, tens of percent of the metal content is needed for the ore to attract the attention of geologists. The requirements for the quality of ore are also changing as the technology of its extraction and enrichment improves.

In terms of their chemical composition, ore minerals are very different: many of them belong to the group of sulfates (for example, realgar HgS - mercury ore), others are oxides (for example, hematite Fe 2 O 3 - iron ore), silicates, carbonates or have a complex composition .

Apart from chemical composition ore minerals, the concentration is extremely important a large number them inside one or another volume of rocks. If single ore minerals are scattered in a large volume of rock far apart, then the extraction of such minerals is extremely unprofitable or simply impossible. Another thing is if they are located closely, in a dense mass, and it is relatively easy to get them in large numbers by constructing mines and adits. Accumulations of ore minerals that are profitable to develop are called ore deposits.

Accumulations of ore minerals (ore deposits) are formed in the earth's crust in various ways. Many of them arise when igneous rocks and the hot aqueous solutions accompanying them rise from a depth, others are concentrated in sedimentary rocks, and still others are found in metamorphic rocks. In the future, when considering the processes developing in the earth's crust, we will briefly talk about the conditions for the formation of ore and other minerals.

MOU "Secondary school p.Novopushkinskoye"

The scenario of the lesson in geography on the topic:

What is the earth's crust made of?

Prepared and hosted:

Geography teacher

Iqualifying

2017

Lesson topic: What is the earth's crust made of

Target: To form students' understanding of the diversity of rocks and minerals.

Tasks:

1. Continue the formation of ideas about the structure of the earth's crust,

2. To ensure that students acquire knowledge of the terms: "minerals", "rocks", the most common rocks, minerals of the Saratov region, properties of rocks and minerals.

3. Create conditions for the development of speech, the ability to work in a group, draw an analogy between objects and symbols denoting them

4. Promote the development of comradely relations and mutual understanding in group work.

Lesson type : learning new material

Equipment: collections of rocks and minerals, physical map hemispheres, multimedia presentation,Geography. Initial course: Grade 5: a textbook for students of educational organizations / A.A. Letyagin; edited by V.P. Dronov. - M .: Ventana - Graf, 2016.

During the classes:

I .Organizing time (greeting students, checking readiness for the lesson, filling out a weather diary, a phenolologist table).

II .Repetition.

Students perform a written check in the “Diary of a Pathfinder Geographer” (figure of a volcano diagram).

Quiz:

1. The largest massif of the earth's crust (mainland).

2. What is the name of our planet? (Earth)

3. What happens in the sky after the rain? (Rainbow)

4. The top layer of the earth on which plants grow? (the soil)

5. What is the name of the line that cannot be reached? (horizon)

6. Ability to find the sides of the horizon? (orient)

7. He does not know grief, but cries bitterly. (cloud)

III . Goal setting.

What is the lithosphere?

What parts does it consist of?

What is the structure of the earth's crust and mantle?

On the screen in the presentation, the teacher displays minerals and rocks.

Guys, what do you see on the screen (children's answers)

Studying the course "The World Around You" you learned that all natural objects are made up of substances. Give examples of substances (children's answers)

IV .Primary development

- Today in the lesson we will get acquainted with the variety of rocks and minerals and learn about the minerals of our area.

Find on page 41 of the textbook what rocks are according to the conditions of education (children's answers)

By origin, rocks and minerals can be divided into igneous, sedimentary, metamorphic. (On the slide in the presentation)

1. Independent work in groups

1 group. Pages 41-42 of the textbook

Igneous rocks were formed as a result of solidification of magma on the surface and in the depths of the Earth.

deep

poured out

2 group pp. 42-43 of the textbook

Sedimentary rocks were formed on the surface of the Earth as a result of the deposition of rock fragments in water and on land.

Sedimentary clastic rocks

Sedimentary chemical origin

organic sedimentary origin(sandstones, limestones).

3 group page 43 of the textbook

Metamorphic rocks are any rocks that have undergone significant changes under the influence of high temperatures and pressures.

Limestone - marble,

Sandstone - quartzite,

Granite - gneiss

2. Workshop in small groups using the collection of rocks and minerals "Properties of rocks and minerals."

3. Rocks and minerals of the Saratov region (in presentation)

Oil, gas, clay, sand, sandstone, phosphorite, peat, oil shale, table and potash salt, gold. limestone, chalk.

4.Fixing the material :

What rocks and minerals of the Saratov region do you know?

What is the earth's crust made up of?

What groups of origin are rocks and minerals divided into?

What groups are igneous rocks divided into?

What groups are sedimentary rocks divided into?

How are metamorphic rocks formed?

V .Result of the lesson, grading.

VI . Reflection They raise a smiley with a different facial expression, which makes it clear whether they liked the lesson or not.

VII .Homework: Paragraph 8, make a crossword "Rocks"

(no more than 15 words), page 45 back 6, video geography, project "Formation of rocks"

Appendix

Practicum in small groups using a collection of rocks and minerals. "Properties of rocks and minerals"

origin

Colour

shine

transparency

hardness

Study of internal structure planets, including our Earth, is an extremely difficult task. We cannot physically "drill" the earth's crust down to the core of the planet, so all the knowledge we have received at the moment is knowledge obtained "by touch", and in the most literal way.

How seismic exploration works on the example of oil exploration. We “call” the ground and “listen” to what the reflected signal will bring us

The fact is that the simplest and most reliable way to find out what is under the surface of the planet and is part of its crust is to study the propagation velocity seismic waves in the depths of the planet.

It is known that the velocity of longitudinal seismic waves increases in denser media and, on the contrary, decreases in loose soils. Accordingly, knowing the parameters different types rocks and having calculated data on pressure, etc., “listening” to the received answer, one can understand through which layers of the earth’s crust the seismic signal passed and how deep they are under the surface.

Studying the structure of the earth's crust using seismic waves

Seismic vibrations can be caused by two types of sources: natural and artificial. Earthquakes are natural sources of vibrations, the waves of which carry necessary information about the density of the rocks through which they penetrate.

The arsenal of artificial vibration sources is more extensive, but first of all, artificial vibrations are caused by an ordinary explosion, but there are also more “subtle” ways of working - generators of directed impulses, seismic vibrators, etc.

Conducting blasting and studying the velocities of seismic waves is engaged in seismic exploration- one of the most important branches of modern geophysics.

What did the study of seismic waves inside the Earth give? An analysis of their propagation revealed several jumps in the change in speed when passing through the bowels of the planet.

Earth's crust

The first jump, at which speeds increase from 6.7 to 8.1 km / s, according to geologists, registers bottom of the earth's crust. This surface is located in different places on the planet at different levels, from 5 to 75 km. The boundary of the earth's crust and the underlying shell - the mantle, is called "Mohorovicic surfaces", named after the Yugoslav scientist A. Mohorovichich, who first established it.

Mantle

Mantle lies at depths up to 2,900 km and is divided into two parts: upper and lower. The boundary between the upper and lower mantle is also fixed by the jump in the propagation velocity of longitudinal seismic waves (11.5 km/s) and is located at depths from 400 to 900 km.

The upper mantle has complex structure. In its upper part there is a layer located at depths of 100-200 km, where transverse seismic waves attenuate by 0.2-0.3 km / s, and the velocities of longitudinal waves, in essence, do not change. This layer is called waveguide. Its thickness is usually 200-300 km.

The part of the upper mantle and the crust overlying the waveguide is called lithosphere, and the layer of low velocities itself - asthenosphere.

Thus, the lithosphere is a rigid hard shell underlain by a plastic asthenosphere. It is assumed that processes arise in the asthenosphere that cause the movement of the lithosphere.

The internal structure of our planet

Earth's core

At the base of the mantle, there is a sharp decrease in the propagation velocity of longitudinal waves from 13.9 to 7.6 km/s. At this level lies the boundary between the mantle and the core of the earth, deeper than which transverse seismic waves no longer propagate.

The radius of the core reaches 3500 km, its volume: 16% of the planet's volume, and mass: 31% of the mass of the Earth.

Many scientists believe that the core is in a molten state. Its outer part is characterized by sharply reduced P-wave velocities, while in the inner part (with a radius of 1200 km), seismic wave velocities increase again to 11 km/s. The density of the core rocks is 11 g/cm 3 , and it is determined by the presence of heavy elements. So heavy element could be iron. Most likely, iron is an integral part of the core, since the core of a purely iron or iron-nickel composition should have a density that is 8-15% higher than the existing density of the core. Therefore, oxygen, sulfur, carbon and hydrogen appear to be attached to the iron in the core.

Geochemical method for studying the structure of planets

There is another way to study the deep structure of planets - geochemical method. The identification of various shells of the Earth and other terrestrial planets by physical parameters finds a fairly clear geochemical confirmation based on the theory of heterogeneous accretion, according to which the composition of the cores of the planets and their outer shells in its main part is initially different and depends on the earliest stage of their development.

As a result of this process, the heaviest ( iron-nickel) components, and in the outer shells - lighter silicate ( chondrite), enriched in the upper mantle with volatiles and water.

The most important feature of the terrestrial planets ( , Earth, ) is that their outer shell, the so-called bark, consists of two types of matter: mainland" - feldspar and " oceanic» - basalt.

Continental (continental) crust of the Earth

The continental (continental) crust of the Earth is composed of granites or rocks similar in composition to them, that is, rocks with a large amount of feldspars. The formation of the "granite" layer of the Earth is due to the transformation of older sediments in the process of granitization.

The granite layer should be considered as specific the shell of the Earth's crust - the only planet on which the processes of differentiation of matter with the participation of water and having a hydrosphere, an oxygen atmosphere and a biosphere have been widely developed. On the Moon and, probably, on the terrestrial planets, the continental crust is composed of gabbro-anorthosites - rocks consisting of a large number feldspar, however, of a slightly different composition than in granites.

These rocks form the most ancient (4.0-4.5 billion years) surfaces of the planets.

Oceanic (basalt) crust of the Earth

Oceanic (basalt) crust The earth was formed as a result of stretching and is associated with zones of deep faults, which caused the penetration of the upper mantle to the basalt chambers. Basalt volcanism is superimposed on previously formed continental crust and is a relatively younger geological formation.

Manifestations of basalt volcanism on all terrestrial planets are apparently similar. The wide development of basalt "seas" on the Moon, Mars, and Mercury is obviously associated with stretching and the formation of permeability zones as a result of this process, along which basalt melts of the mantle rushed to the surface. This mechanism of manifestation of basaltic volcanism is more or less similar for all planets of the terrestrial group.

The satellite of the Earth - the Moon also has a shell structure, which, on the whole, repeats the earth's, although it has a striking difference in composition.

Heat flow of the Earth. It is hottest in the region of faults in the earth's crust, and colder in the regions of ancient continental plates.

Method for measuring heat flow for studying the structure of planets

Another way to study the deep structure of the Earth is to study its heat flow. It is known that the Earth, hot from the inside, gives off its heat. The heating of deep horizons is evidenced by volcanic eruptions, geysers, and hot springs. Heat is the main energy source of the Earth.

The increase in temperature with deepening from the Earth's surface averages about 15 ° C per 1 km. This means that at the boundary of the lithosphere and asthenosphere, located approximately at a depth of 100 km, the temperature should be close to 1500 ° C. It has been established that at this temperature basalt melts. This means that the asthenospheric shell can serve as a source of basaltic magma.

With depth, the change in temperature occurs according to a more complex law and depends on the change in pressure. According to the calculated data, at a depth of 400 km the temperature does not exceed 1600°C, and at the core-mantle boundary it is estimated at 2500-5000°C.

It is established that the release of heat occurs constantly over the entire surface of the planet. Heat is the most important physical parameter. Some of their properties depend on the degree of heating of rocks: viscosity, electrical conductivity, magneticness, phase state. Therefore, according to the thermal state, one can judge the deep structure of the Earth.

Measuring the temperature of our planet at great depths is a technically difficult task, since only the first kilometers of the earth's crust are available for measurements. However, the internal temperature of the Earth can be studied indirectly when measuring the heat flux.

Despite the fact that the main source of heat on Earth is the Sun, the total power of the heat flow of our planet exceeds the power of all power plants on Earth by 30 times.

The measurements showed that the average heat flow on the continents and in the oceans is the same. This result is explained by the fact that in the oceans, most of the heat (up to 90%) comes from the mantle, where the process of transfer of matter by moving streams occurs more intensively - convection.

Convection is a process in which a heated liquid expands, becomes lighter, and rises, while colder layers sink. Since the mantle substance is closer in its state to a solid body, convection in it proceeds under special conditions, at low material flow rates.

What is the thermal history of our planet? Its initial heating is probably associated with the heat generated by the collision of particles and their compaction in their own gravity field. Then the heat was the result of radioactive decay. Under the influence of heat, a layered structure of the Earth and the terrestrial planets arose.

Radioactive heat in the Earth is released even now. There is a hypothesis according to which, at the boundary of the molten core of the Earth, the processes of matter splitting with the release of huge amount thermal energy heating the mantle.