The average density of earth is. Earth Density: Definition, Meaning and Interesting Facts

Plan

Earth's crust (continental, oceanic, transitional).

The main components of the earth's crust are chemical elements, minerals, rocks, and geological bodies.

Basics of classification of igneous rocks.

Earth's crust (continental, oceanic, transitional)

Based on deep seismic sounding data, a number of layers are identified in the earth’s crust, characterized by different rates of elastic vibrations. Of these layers, three are considered primary. The uppermost of them is known as the sedimentary shell, the middle one is granite-metamorphic and the lower one is basaltic (Fig.).

Rice. . Scheme of the structure of the crust and upper mantle, including the solid lithosphere

and plastic asthenosphere

Sedimentary layer composed mainly of the softest, loosest and densest (due to cementation of loose) rocks. Sedimentary rocks usually occur in strata. The thickness of the sedimentary layer on the Earth's surface is very variable and varies from several m to 10-15 km. There are areas where the sedimentary layer is completely absent.

Granite-metamorphic layer composed mainly of igneous and metamorphic rocks rich in aluminum and silicon. Places where there is no sedimentary layer and a granite layer comes to the surface are called crystal shields(Kolsky, Anabarsky, Aldansky, etc.). The thickness of the granite layer is 20-40 km; in some places this layer is absent (at the bottom of the Pacific Ocean). According to the study of the speed of seismic waves, the density of rocks at the lower boundary from 6.5 km/sec to 7.0 km/sec changes sharply. This boundary of the granite layer, separating the granite layer from the basalt layer, is called Conrad's borders.

Basalt layer stands out at the base of the earth's crust, is present everywhere, its thickness ranges from 5 to 30 km. The density of the substance in the basalt layer is 3.32 g/cm 3; its composition differs from granites and is characterized by a significantly lower silica content. At the lower boundary of the layer, an abrupt change in the speed of passage of longitudinal waves is observed, which indicates a sharp change in the properties of the rocks. This boundary is taken to be the lower boundary of the earth's crust and is called the Mohorovicic boundary, as discussed above.

In different parts of the globe, the earth's crust is heterogeneous both in composition and thickness. Types of the earth's crust - continental or continental, oceanic and transitional. The oceanic crust occupies about 60%, and the continental crust about 40% of the earth's surface, which differs from the distribution of the area of ​​the oceans and land (71% and 29%, respectively). This is due to the fact that the boundary between the types of crust under consideration passes along the continental foot. Shallow seas, such as, for example, the Baltic and Arctic seas of Russia, belong to the World Ocean only from a geographical point of view. In the area of ​​oceans there are oceanic type, characterized by a thin sedimentary layer, under which there is a basalt layer. Moreover, the oceanic crust is much younger than the continental crust - the age of the former is no more than 180 - 200 million years. The earth's crust under the continent contains all 3 layers, has a large thickness (40-50 km) and is called mainland. The transitional crust corresponds to the underwater continental margins. Unlike the continental one, the granite layer here sharply decreases and disappears into the ocean, and then the thickness of the basalt layer decreases.

Sedimentary, granite-metamorphic and basalt layers together form a shell, which is called sial - from the words silicium and aluminum. It is usually believed that in the sialic shell it is advisable to identify the concept of the earth's crust. It has also been established that throughout geological history, the earth’s crust absorbs oxygen and to date it consists of 91% of it by volume.

The main components of the earth's crust are chemical elements, minerals, rocks, geological bodies

The substance of the Earth consists of chemical elements. Within the rock shell, chemical elements form minerals, minerals form rocks, and rocks, in turn, form geological bodies. Our knowledge of the chemistry of the Earth, or otherwise geochemistry, decreases catastrophically with depth. Below 15 km, our knowledge is gradually replaced by hypotheses.

American chemist F.W. Clarke, together with G.S. Washington, having begun the analysis of various rocks (5159 samples) at the beginning of the last century, published data on the average contents of about ten of the most common elements in the earth's crust. Frank Clark proceeded from the position that the solid earth's crust to a depth of 16 km consists of 95% igneous rocks and 5% sedimentary rocks formed from igneous rocks. Therefore, for the calculation, F. Clark used 6000 analyzes of various rocks, taking their arithmetic average. Subsequently, these data were supplemented by average data on the contents of other elements. It turned out that the most common elements of the earth’s crust are (wt.%): O – 47.2; Si – 27.6; Al – 8.8; Fe – 5.1; Ca – 3.6; Na – 2.64; Mg – 2.1; K – 1.4; H – 0.15, which adds up to 99.79%. These elements (except hydrogen), as well as carbon, phosphorus, chlorine, fluorine and some others are called rock-forming or petrogenic.

Subsequently, these figures were repeatedly clarified by various authors (table).

Comparison of various estimates of the composition of the continental crust,

Type of bark	Upper continental crust				Continental crust
		Goldschmidt, 1938	Vinogradov, 1962	Ronov et al., 1990	Ronov et al., 1990

The average mass fractions of chemical elements in the earth's crust were named at the suggestion of Academician A.E. Fersman Clarks. The latest data on the chemical composition of the Earth's spheres are summarized in the following diagram (Figure).

All matter in the earth's crust and mantle consists of minerals that vary in shape, structure, composition, abundance and properties. Currently, more than 4,000 minerals have been identified. It is impossible to give an exact figure because every year the number of mineral species is replenished with 50-70 names of mineral species. For example, about 550 minerals were discovered on the territory of the former USSR (320 species are stored in the A.E. Fersman Museum), of which more than 90% were discovered in the 20th century.

The mineral composition of the earth's crust is as follows (vol.%): feldspars - 43.1; pyroxenes - 16.5; olivine - 6.4; amphiboles - 5.1; mica - 3.1; clay minerals - 3.0; orthosilicates – 1.3; chlorites, serpentines - 0.4; quartz – 11.5; cristobalite - 0.02; tridymite - 0.01; carbonates - 2.5; ore minerals - 1.5; phosphates - 1.4; sulfates - 0.05; iron hydroxides - 0.18; others - 0.06; organic matter - 0.04; chlorides - 0.04.

These numbers are, of course, very relative. In general, the mineral composition of the earth's crust is the most varied and rich in comparison with the composition of deeper geospheres and meteorites, the substance of the Moon and the outer shells of other terrestrial planets. So, 85 minerals have been identified on the moon, and 175 in meteorites.

Natural mineral aggregates that make up independent geological bodies in the earth's crust are called rocks. The concept of “geological body” is a multi-scale concept; it includes volumes from a mineral crystal to continents. Each rock forms a three-dimensional body in the earth’s crust (layer, lens, massif, cover...), characterized by a certain material composition and specific internal structure.

The term “rock” was introduced into Russian geological literature at the end of the 18th century by Vasily Mikhailovich Severgin. The study of the earth's crust has shown that it is composed of various rocks, which, based on their origin, can be divided into 3 groups: igneous or igneous, sedimentary and metamorphic.

Before moving on to a description of each of the groups of rocks separately, it is necessary to dwell on their historical relationships.

It is generally accepted that the globe was originally a molten body. From this primary melt or magma, the solid earth's crust was formed by cooling, initially composed entirely of igneous rocks, which should be considered as the historically most ancient group of rocks.

Only in a later phase of the Earth's development could rocks of a different origin arise. This became possible after the emergence of all its outer shells: the atmosphere, the hydrosphere, the biosphere. Primary igneous rocks were destroyed under their influence and solar energy, the destroyed material was moved by water and wind, sorted and cemented again. This is how sedimentary rocks arose, which are secondary to the igneous rocks from which they were formed.

Both igneous and sedimentary rocks served as materials for the formation of metamorphic rocks. As a result of various geological processes, large areas of the earth's crust subsided, and sedimentary rocks accumulated within these areas. During these subsidences, the lower parts of the strata fall to ever greater depths in the region of high temperatures and pressures, in the region of penetration of various vapors and gases from the magma and the circulation of hot water solutions, introducing new chemical elements into the rocks. The result of this is metamorphism.

The distribution of these breeds varies. It is estimated that the lithosphere is composed of 95% igneous and metamorphic rocks and only 5% sedimentary rocks. On the surface the distribution is somewhat different. Sedimentary rocks cover 75% of the earth's surface and only 25% are igneous and metamorphic rocks.

Remember

• What do you know about the internal structure of the Earth? What rocks do you know? By what properties do they differ?

The interior of the Earth is a mysterious and much less accessible world than the space surrounding our planet. Such a device has not yet been invented in which it would be possible to penetrate into the depths of the planet. The world's deepest mine has a depth of 4 km, the deepest borehole on the Kola Peninsula is 12 km. This is only 1/500th of the radius of the Earth!

However, people have learned to “look” into the depths of the earth. The main method of studying them is seismic (from the Greek “seismos” - earthquake). From earthquakes or artificial explosions, vibrations spread in the bowels of the Earth. In substances of different composition and density they propagate at different speeds. Using instruments, specialists measure these speeds and decipher the information.

It has been established that the interior of our planet is divided into several shells: the core, the mantle and the earth’s crust (Fig. 33).

Core- the central part of the globe. It has very high pressure and temperature of 3000-4000 °C. The core consists of the densest and heaviest substance, presumably iron. The core accounts for about 30% of the Earth's mass, but only 15% of its volume. The inner solid part of the core seems to float in the outer, liquid layer. Due to this movement around the Earth, a magnetic field arises. It protects life on our planet from harmful cosmic rays. The compass needle reacts to the magnetic field.

Rice. 33. Internal structure of the Earth

According to scientists, the separation of the Earth's substance into the core, mantle and crust has occurred since the formation of the planet 4.6 billion years ago and continues to the present day. Heavier substances sink to the center of the Earth and become even more dense, while lighter substances rise upward and form the earth's crust. When the Earth's matter is redistributed, heat is released - the main source of internal energy of the Earth. When the separation of the Earth's interior is completely completed, the Earth will become a cold and dead planet. According to calculations, this could happen in 1.5 billion years.

Mantle(from the Greek “mantle” - cover, cloak) - the largest of the internal shells of the Earth. The mantle accounts for the bulk (more than 80%) and mass (almost 70%) of our planet. The mantle material is solid, but less dense than in the core. Pressure and temperature in the mantle increase with depth. At the top of the mantle there is a layer where the material is partially molten and plastic. The hard layers lying above move along this plastic layer.

Earth's crust- the thinnest outer shell of the Earth. The earth's crust accounts for less than 1% of the earth's mass. It is on the surface of the earth's crust that people live, from which they extract minerals. In different places, the earth's crust is pierced by numerous mines and boreholes. Millions of samples taken from them and from the Earth's surface made it possible to determine the composition and structure of the earth's crust.

Feldspars make up half the mass of the earth's crust. They even received the name “field” due to their widespread distribution. They can be found everywhere: in the mountains, in the fields...

Quartz is one of the most common minerals. Colorless quartz is called rock crystal. Varieties of quartz of other colors are known: purple, yellow, brown, black.

What is the earth's crust made of? The Earth's crust is made up of rocks, and rocks are made up of minerals. (Remember what minerals you are familiar with. Where did you manage to see them?)

Minerals are natural substances with different composition, properties and external characteristics.

Minerals are distinguished by such characteristics as color, hardness, luster, transparency, and density. Minerals were formed and continue to form both in the deep layers of the earth's crust and on its surface.

Rice. 34. The most common minerals on Earth: a - feldspar; b - quartz; c - mica

People know about 3000 minerals. Most of them are rare. Rare minerals include diamond, platinum, silver, and graphite. There are only a few dozen widespread minerals that make up rocks. The most abundant minerals on Earth are feldspars, quartz, and mica (Fig. 34). Minerals form rocks.

Rocks are natural bodies composed of one or more minerals.

Mineral crystals in rock can vary in size. In many breeds they can only be seen under a microscope. Crystals of minerals are connected to each other with different strengths. Therefore, some rocks are hard and monolithic, others are porous and light, and others are loose and friable. The composition of minerals in a rock and the strength of their connection depend on the conditions in which the rock was formed. According to the conditions of formation, all rocks are divided into three large groups: igneous, sedimentary and metamorphic.

Questions and tasks

1. What has more mass - the core, the mantle or the earth's crust?
2. What state is the substance in the mantle? in the core?
3. What is rock? How is it different from a mineral?
4. Give examples of rocks and minerals that are common in your area.

The earth's crust in the scientific sense is the uppermost and hardest geological part of the shell of our planet.

Scientific research allows us to study it thoroughly. This is facilitated by repeated drilling of wells both on continents and on the ocean floor. The structure of the earth and the earth's crust in different parts of the planet differs both in composition and characteristics. The upper boundary of the earth's crust is the visible relief, and the lower boundary is the zone of separation of the two environments, which is also known as the Mohorovicic surface. It is often referred to simply as the “M boundary.” It received this name thanks to the Croatian seismologist Mohorovicic A. For many years he observed the speed of seismic movements depending on the depth level. In 1909, he established the existence of a difference between the earth's crust and the hot mantle of the earth. The M boundary lies at the level where the speed of seismic waves increases from 7.4 to 8.0 km/s.

Chemical composition of the Earth

Studying the shells of our planet, scientists have made interesting and even stunning conclusions. The structural features of the earth's crust make it similar to the same areas on Mars and Venus. More than 90% of its constituent elements are represented by oxygen, silicon, iron, aluminum, calcium, potassium, magnesium, and sodium. Combining with each other in various combinations, they form homogeneous physical bodies - minerals. They can be included in rocks in different concentrations. The structure of the earth's crust is very heterogeneous. Thus, rocks in a generalized form are aggregates of more or less constant chemical composition. These are independent geological bodies. They mean a clearly defined area of ​​the earth's crust, which has the same origin and age within its boundaries.

Rocks by group

1. Igneous. The name speaks for itself. They arise from cooled magma flowing from the mouths of ancient volcanoes. The structure of these rocks directly depends on the rate of lava solidification. The larger it is, the smaller the crystals of the substance. Granite, for example, was formed in the thickness of the earth's crust, and basalt appeared as a result of the gradual outpouring of magma onto its surface. The variety of such breeds is quite large. Looking at the structure of the earth's crust, we see that it consists of 60% igneous minerals.

2. Sedimentary. These are rocks that were the result of the gradual deposition of fragments of certain minerals on land and the ocean floor. These can be loose components (sand, pebbles), cemented components (sandstone), remains of microorganisms (coal, limestone), or products of chemical reactions (potassium salt). They make up up to 75% of the entire earth's crust on the continents.
According to the physiological method of formation, sedimentary rocks are divided into:

• Clastic. These are the remains of various rocks. They were destroyed under the influence of natural factors (earthquake, typhoon, tsunami). These include sand, pebbles, gravel, crushed stone, clay.
• Chemical. They are gradually formed from aqueous solutions of certain mineral substances (salt).
• Organic or biogenic. Consist of the remains of animals or plants. These are oil shale, gas, oil, coal, limestone, phosphorites, chalk.

3. Metamorphic rocks. Other components can be converted into them. This occurs under the influence of changing temperature, high pressure, solutions or gases. For example, you can get marble from limestone, gneiss from granite, and quartzite from sand.

Minerals and rocks that humanity actively uses in its life are called minerals. What are they?

These are natural mineral formations that affect the structure of the earth and the earth's crust. They can be used in agriculture and industry, both in their natural form and through processing.

Types of useful minerals. Their classification

Depending on their physical state and aggregation, minerals can be divided into categories:

1. Solid (ore, marble, coal).
2. Liquid (mineral water, oil).
3. Gaseous (methane).

Characteristics of individual types of minerals

According to the composition and features of application, they are distinguished:

1. Combustibles (coal, oil, gas).
2. Ore. They include radioactive (radium, uranium) and noble metals (silver, gold, platinum). There are ores of ferrous (iron, manganese, chromium) and non-ferrous metals (copper, tin, zinc, aluminum).
3. Nonmetallic minerals play a significant role in such a concept as the structure of the earth's crust. Their geography is vast. These are non-metallic and non-combustible rocks. These are building materials (sand, gravel, clay) and chemicals (sulfur, phosphates, potassium salts). A separate section is devoted to precious and ornamental stones.

The distribution of minerals on our planet directly depends on external factors and geological patterns.

Thus, fuel minerals are primarily mined in oil, gas and coal basins. They are of sedimentary origin and form on the sedimentary covers of platforms. Oil and coal rarely occur together.

Ore minerals most often correspond to the basement, overhangs, and folded areas of platform plates. In such places they can create huge belts.

Core

The earth's shell, as is known, is multi-layered. The core is located in the very center, and its radius is approximately 3,500 km. Its temperature is much higher than that of the Sun and is about 10,000 K. Accurate data on the chemical composition of the core has not been obtained, but it presumably consists of nickel and iron.

The outer core is in a molten state and has even greater power than the inner one. The latter is subject to enormous pressure. The substances of which it consists are in a permanent solid state.

Mantle

The Earth's geosphere surrounds the core and makes up about 83 percent of the entire surface of our planet. The lower boundary of the mantle is located at a huge depth of almost 3000 km. This shell is conventionally divided into a less plastic and dense upper part (it is from this that magma is formed) and a lower crystalline one, the width of which is 2000 kilometers.

Composition and structure of the earth's crust

In order to talk about what elements make up the lithosphere, we need to give some concepts.

The earth's crust is the outermost shell of the lithosphere. Its density is less than half the average density of the planet.

The earth's crust is separated from the mantle by the boundary M, which was already mentioned above. Since the processes occurring in both areas mutually influence each other, their symbiosis is usually called the lithosphere. It means "stone shell". Its power ranges from 50-200 kilometers.

Below the lithosphere is the asthenosphere, which has a less dense and viscous consistency. Its temperature is about 1200 degrees. A unique feature of the asthenosphere is the ability to violate its boundaries and penetrate the lithosphere. It is the source of volcanism. Here there are molten pockets of magma, which penetrates the earth's crust and pours out to the surface. By studying these processes, scientists were able to make many amazing discoveries. This is how the structure of the earth's crust was studied. The lithosphere was formed many thousands of years ago, but even now active processes are taking place in it.

Structural elements of the earth's crust

Compared to the mantle and core, the lithosphere is a hard, thin and very fragile layer. It is made up of a combination of substances, in which more than 90 chemical elements have been discovered to date. They are distributed heterogeneously. 98 percent of the mass of the earth's crust is made up of seven components. These are oxygen, iron, calcium, aluminum, potassium, sodium and magnesium. The oldest rocks and minerals are over 4.5 billion years old.

By studying the internal structure of the earth's crust, various minerals can be identified.
A mineral is a relatively homogeneous substance that can be found both inside and on the surface of the lithosphere. These are quartz, gypsum, talc, etc. Rocks are made up of one or more minerals.

Processes that form the earth's crust

The structure of the oceanic crust

This part of the lithosphere mainly consists of basaltic rocks. The structure of the oceanic crust has not been studied as thoroughly as the continental crust. Plate tectonic theory explains that the oceanic crust is relatively young, and the most recent portions of it can be dated to the Late Jurassic.
Its thickness practically does not change over time, since it is determined by the amount of melts released from the mantle in the zone of mid-ocean ridges. It is significantly influenced by the depth of sedimentary layers on the ocean floor. In the most extensive areas it ranges from 5 to 10 kilometers. This type of earth's shell belongs to the oceanic lithosphere.

Continental crust

The lithosphere interacts with the atmosphere, hydrosphere and biosphere. In the process of synthesis, they form the most complex and reactive shell of the Earth. It is in the tectonosphere that processes occur that change the composition and structure of these shells.
The lithosphere on the earth's surface is not homogeneous. It has several layers.

1. Sedimentary. It is mainly formed by rocks. Clays and shales predominate here, and carbonate, volcanic and sandy rocks are also widespread. In sedimentary layers you can find minerals such as gas, oil and coal. All of them are of organic origin.
2. Granite layer. It consists of igneous and metamorphic rocks that are closest in nature to granite. This layer is not found everywhere; it is most pronounced on the continents. Here its depth can be tens of kilometers.
3. The basalt layer is formed by rocks close to the mineral of the same name. It is denser than granite.

Depth and temperature changes in the earth's crust

The surface layer is heated by solar heat. This is the heliometric shell. It experiences seasonal temperature fluctuations. The average thickness of the layer is about 30 m.

Below is a layer that is even thinner and more fragile. Its temperature is constant and approximately equal to the average annual temperature characteristic of this region of the planet. Depending on the continental climate, the depth of this layer increases.
Even deeper in the earth's crust is another level. This is a geothermal layer. The structure of the earth's crust allows for its presence, and its temperature is determined by the internal heat of the Earth and increases with depth.

The temperature rise occurs due to the decay of radioactive substances that are part of rocks. First of all, these are radium and uranium.

Geometric gradient - the magnitude of the temperature increase depending on the degree of increase in the depth of the layers. This parameter depends on various factors. The structure and types of the earth's crust influence it, as well as the composition of rocks, the level and conditions of their occurrence.

The heat of the earth's crust is an important energy source. Its study is very relevant today.

The Earth's crust is of great importance for our life, for research of our planet.

This concept is closely related to others that characterize processes occurring inside and on the surface of the Earth.

What is the earth's crust and where is it located?

The Earth has a holistic and continuous shell, which includes: the earth's crust, the troposphere and stratosphere, which are the lower part of the atmosphere, the hydrosphere, the biosphere and the anthroposphere.

They interact closely, penetrating each other and constantly exchanging energy and matter. The earth's crust is usually called the outer part of the lithosphere - the solid shell of the planet. Most of its outer side is covered by the hydrosphere. The remaining, smaller part is affected by the atmosphere.

Beneath the Earth's crust is a denser and more refractory mantle. They are separated by a conventional border named after the Croatian scientist Mohorovic. Its peculiarity is a sharp increase in the speed of seismic vibrations.

Various scientific methods are used to gain insight into the earth's crust. However, obtaining specific information is only possible by drilling to great depths.

One of the objectives of such research was to establish the nature of the boundary between the upper and lower continental crust. The possibilities of penetrating the upper mantle using self-heating capsules made of refractory metals were discussed.

Structure of the earth's crust

Beneath the continents are its sedimentary, granite and basalt layers, the total thickness of which is up to 80 km. Rocks, called sedimentary rocks, are formed by the deposition of substances on land and in water. They are located mainly in layers.

• clay
• shale
• sandstones
• carbonate rocks
• rocks of volcanic origin
• coal and other rocks.

The sedimentary layer helps to gain a deeper understanding of the natural conditions on earth that existed on the planet in time immemorial. This layer can have different thicknesses. In some places it may not exist at all, in other, mainly large depressions, it can be 20-25 km.

Temperature of the earth's crust

An important energy source for the inhabitants of the Earth is the heat of its crust. The temperature increases as you go deeper into it. The 30-meter layer closest to the surface, called the heliometric layer, is associated with the heat of the sun and fluctuates depending on the season.

In the next, thinner layer, which increases in a continental climate, the temperature is constant and corresponds to the indicators of a specific measurement location. In the geothermal layer of the crust, the temperature is related to the internal heat of the planet and increases as you go deeper into it. It is different in different places and depends on the composition of the elements, depth and conditions of their location.

It is believed that the temperature increases on average by three degrees as you go deeper for every 100 meters. Unlike the continental part, temperatures under the oceans are rising faster. After the lithosphere there is a plastic high-temperature shell, the temperature of which is 1200 degrees. It is called the asthenosphere. There are places with molten magma in it.

Penetrating into the earth's crust, the asthenosphere can pour out molten magma, causing volcanic phenomena.

Characteristics of the Earth's crust

The Earth's crust has a mass of less than half a percent of the total mass of the planet. It is the outer shell of the stone layer in which the movement of matter occurs. This layer, which has a density half that of the Earth. Its thickness varies between 50-200 km.

The uniqueness of the earth's crust is that it can be of continental and oceanic types. The continental crust has three layers, the top of which is formed by sedimentary rocks. The oceanic crust is relatively young and its thickness varies slightly. It is formed due to mantle substances from oceanic ridges.

earth's crust characteristics photo

The thickness of the crust layer under the oceans is 5-10 km. Its peculiarity is constant horizontal and oscillatory movements. Most of the crust is basalt.

The outer part of the earth's crust is the solid shell of the planet. Its structure is distinguished by the presence of movable areas and relatively stable platforms. Lithospheric plates move relative to each other. The movement of these plates can cause earthquakes and other disasters. The patterns of such movements are studied by tectonic science.

Functions of the earth's crust

The main functions of the earth's crust are:

• resource;
• geophysical;
• geochemical.

The first of them indicates the presence of the Earth's resource potential. It is primarily a collection of mineral reserves located in the lithosphere. In addition, the resource function includes a number of environmental factors that ensure the life of humans and other biological objects. One of them is the tendency of a hard surface deficit to form.

You can't do that. let's save our Earth photo

Thermal, noise and radiation effects implement the geophysical function. For example, the problem of natural background radiation arises, which is generally safe on the earth’s surface. However, in countries such as Brazil and India it can be hundreds of times higher than permissible. It is believed that its source is radon and its decay products, as well as certain types of human activity.

The geochemical function is associated with problems of chemical pollution harmful to humans and other representatives of the animal world. Various substances with toxic, carcinogenic and mutagenic properties enter the lithosphere.

They are safe when they are in the bowels of the planet. Zinc, lead, mercury, cadmium and other heavy metals extracted from them can pose a great danger. In processed solid, liquid and gaseous form, they enter the environment.

What is the Earth's crust made of?

Compared to the mantle and core, the Earth's crust is a fragile, hard and thin layer. It consists of a relatively light substance, which includes about 90 natural elements. They are found in different places in the lithosphere and with varying degrees of concentration.

The main ones are: oxygen, silicon, aluminum, iron, potassium, calcium, sodium magnesium. 98 percent of the earth's crust consists of them. About half of this is oxygen, and over a quarter is silicon. Thanks to their combinations, minerals such as diamond, gypsum, quartz, etc. are formed. Several minerals can form a rock.

• An ultra-deep well on the Kola Peninsula made it possible to get acquainted with mineral samples from a 12-kilometer depth, where rocks close to granites and shales were discovered.
• The greatest thickness of the crust (about 70 km) was revealed under mountain systems. Under flat areas it is 30-40 km, and under the oceans it is only 5-10 km.
• Much of the crust forms an ancient, low-density upper layer consisting primarily of granites and shales.
• The structure of the earth's crust resembles the crust of many planets, including the Moon and their satellites.

Introduction

The three outer shells of the Earth, differing in phase state - the solid crust, the liquid hydrosphere and the gas atmosphere - are closely interconnected, and the substance of each of them penetrates into the boundaries of the others. Groundwater permeates the upper part of the earth's crust; a significant volume of gases is not in the atmosphere, but is dissolved in the hydrosphere and fills voids in the soil and rocks. In turn, water and small solid mineral particles saturate the lower layers of the atmosphere.

The outer shells are connected not only spatially, but also genetically. The origin of shells, the formation of their composition and its further evolution are interconnected. Currently, this connection is largely due to the fact that the outer part of the planet is covered by the geochemical activity of living matter.

The masses of the shells vary greatly. The mass of the earth's crust is estimated at 28.46 × 10 18 tons, the World Ocean - 1.47 × 10 18 tons, the atmosphere - 0.005 × 10 18 tons. Consequently, the earth's crust contains the main reserve of chemical elements that are involved in migration processes under the influence living matter. The concentrations and distribution of chemical elements in the earth's crust have a strong influence on the composition of living organisms on land and all living matter on Earth.

Considering the problem of the composition of living matter, V.I. Vernadsky noted: “... the chemical composition of organisms is closely related to the chemical composition of the earth’s crust; organisms adapt to it.”

Chemists and petrographers since the second half of the 19th century. studied the chemical composition of rocks using methods of gravimetric and volumetric chemical analysis. Summarizing the results of numerous analyzes of rocks, F. Clark showed that eight chemical elements predominate in the earth's crust: oxygen, silicon, aluminum, iron, magnesium, calcium, potassium and sodium. This main conclusion has been repeatedly confirmed by the results of subsequent studies. The methods of chemical analysis used in the 19th century made it impossible to determine low concentrations of elements. Fundamentally different approaches were required.

A powerful impetus to the study of chemical elements with very low concentrations in the earth's crust was given by the use of a more sensitive method - spectroscopic analysis. New facts allowed V.I. Vernadsky to formulate the principle of “everywhereness” of all chemical elements. In a report at the XII Congress of Russian Naturalists and Doctors in December 1909, he stated: “In every drop and speck of matter on the earth’s surface, as the subtlety of our research increases, we discover more and more new elements... In a grain of sand or in a drop, as in the microcosm, the general composition of the cosmos is reflected.”

The idea of ​​the “everywhere” of chemical elements has long aroused caution even on the part of prominent scientists. This was due to the fact that elements contained in quantities below the sensitivity level of the method were not detected during the analysis. The illusion of their complete absence was created, which was reflected in the terminology. Terms arose in geochemistry rare elements(dieselteneElementen – German; rareelements – English), frequency(dieHaufigkeit – German) detection. In reality, what is happening is not the real rarity or low frequency of occurrence of the element in analyses, but its low concentration in the samples being studied, which cannot be determined by insufficiently sensitive analytical methods.

The low sensitivity of the method often did not make it possible to determine the amount of an element, but only to state the presence of its “traces”. Since then, the term has been widely used in the geochemical literature? used by V.M. Goldschmidt and his colleagues in the 1930s: trace elements(dieSpurelemente – German; traceelements – English; deselementstraces – French).

As a result of the efforts of scientists from different countries in the 20s. XX century a general idea of ​​the composition of the earth's crust has emerged. Average values ​​of the relative content of chemical elements in the earth's crust and other global and cosmic systems, the famous geochemist A.E. Fersman suggested calling Clarks in honor of the scientist who charted the path to quantifying the distribution of chemical elements.

Clarke is a very important quantity in geochemistry. Analysis of clarke values ​​allows us to understand many patterns of distribution of chemical elements on Earth, in the Solar System and in the part of the Universe accessible to our observations. The Clarke chemical elements of the earth's crust differ by more than ten mathematical orders of magnitude. Such a significant quantitative difference should be reflected in the qualitatively different role of the two groups of elements in the earth’s crust. This is most clearly manifested in the fact that the elements of the first group, contained in relatively large quantities, form independent chemical compounds, while the elements of the second group with small clarkes are predominantly dispersed, scattered among the chemical compounds of other elements. The elements of the first group are called the main ones elements of the second – absent-minded. Their synonyms in English are minorelements, rareelements, the most commonly used synonym is traceelements. The conditional boundary between groups of major and trace elements in the earth's crust can be 0.1%, although the clarkes of most trace elements are much smaller and are measured in thousandths and smaller fractions of a percent. The concept of the state of dispersion of chemical elements, as well as their “ubiquity”, was introduced into science by V.I. Vernadsky.

The complete chemical composition of the upper, so-called granite, layer of the continental block of the earth's crust is given in Table. 1.1.

Table 1.1 Clarks of chemical elements of the granite layer of the continental crust

Chemical element	Atomic number	Average content, 1 × 10 -4 %	Chemical element	Atomic number	Average content, 1 × 10 -4 %
ABOUT	8	481 000	Mg	12	12000
Si	14	399 000	Ti	22	3300
A1	13	80 000	H	1	1000
Fe	26	36000	P	15	800
TO	19	27000	F	9	700
Sa	20	25000	Mn	25	700
Na	11	22000	Va	56	680
S	16	400	Eg	68	3,6
WITH	6	300	Yb	70	3,6
Sr	38	230	Hf	72	3,5
Rb	37	180	Sn	50	2,7
Cl	17	170	And	92	2,6
Zr	40	170	Be	4	2,5
Xie	58	83	Br	35	2,2
V	23	76	Ta	73	2,1
Zn	30	51	As	33	1,9
La	57	46	W	74	1,9
Yr	39	38	Ho	67	1,8
Cl	24	34	Tl	81	1,8
Nd	60	33	Eu	63	1,4
Li	3	30	Tb	65	1,4
N	7	26	Ge	32	1,3
Ni	28	26	Mo	42	1,3
Cu	29	22	Lu	71	1,1
Nb	41	20	I	53	0,5
Ga	31	18	Tu	69	0,3
Pb	82	16	In	49	0,25
Th	90	16	Sb	51	0,20
Sc	21	11	Cd	48	0,16
IN	5	10	Se	34	0,14
Sm	62	9	Ag	47	0,088
Gd	64	9	Hg	80	0,033
Pr	59	7,9	Bi	83	0,010
Co	27	7,3	Au	79	0,0012
Dy	66	6,5	Those	52	0,0010
Cs	55	3,8	Re	75	0,0007

For the formation of any chemical compound, a concentration of the starting components is required that is no less than the minimum, below which the reaction is impossible. Therefore, chemical compounds of the main elements with high clarke predominate in the earth's crust. Despite the fact that the total amount of natural chemical compounds is minerals – is 2-3 thousand species, the number of minerals that form common rocks is small. More than 80% of the mass of the earth's crust is represented by silicates of aluminum, iron, calcium, magnesium, potassium and sodium; about 12% is silicon oxide. All these minerals have a crystalline structure, which determines the general features of the crystal chemistry of the earth’s crust.

V.M. Goldschmidt showed that the silicate composition and crystalline structure of the earth's crust are very important for the distribution of minor, trace elements. According to Goldschmidt's concept, in crystal chemical structures, ions behave like hard spheres (hard balls). Therefore, the radius of each ion is considered as a constant value.

The main feature of ions in crystal chemical structures is that the radii of negatively charged ions (anions) are much larger than the radii of positively charged ions (cations). Let's imagine anions in the form of large balls, and cations in the form of small ones. Then the model of a crystalline substance with an ionic type of bond will be a space filled with tightly adjacent large balls - anions, between which small balls - cations - should be placed. According to Goldschmidt's ideas, this framework plays the role of a kind of geochemical filter that promotes the differentiation of chemical elements based on the size of their ions. A specific crystal chemical structure cannot include any elements that have the required valence, but only those whose ions have the appropriate radius size.

The formation of common minerals is accompanied by a kind of sorting of trace elements. To explain this process, let's turn to a common mineral - feldspar. Its crystal chemical structure is formed by groups consisting of three silicon cations and one aluminum, each of which is associated with four oxygen anions. The group as a whole is a complex anion, with eight oxygen ions, three silicon and one aluminum. This creates a single negative charge, which is balanced by the monovalent potassium cation. As a result, there is a three-chamber structure, the composition of which corresponds to formula K.

The radius of the potassium ion is 0.133 nm. Its place in the structure can only be taken by a cation with a similar radius. This is the divalent barium cation, the radius of which is 0.134 nm. Barium is less common than potassium. It is usually present as a minor impurity in feldspars. Only in special cases is its significant concentration created and the rare mineral celsian (barium feldspar) is formed.

Similarly, in common minerals and rocks, chemical elements are selectively retained, the concentration of which is not so high for the formation of independent minerals. The mutual substitution of ions in the crystal structure due to the proximity of their radii is called isomorphism. This phenomenon was discovered at the beginning of the 19th century, but its significance for the global differentiation of trace chemical elements was established only a century later.

As a result of isomorphism, trace elements are naturally concentrated in certain minerals. Feldspars serve as carriers of barium, strontium, and lead; olivines – nickel and cobalt; zircons – hafnium, etc. Elements such as rubidium, rhenium, and hafnium do not form independent compounds in the lithosphere and are completely dispersed in the crystal chemical structures of host minerals.

Isomorphic substitutions are not the only form of finding scattered elements. The phenomenon of scattering in the earth's crust manifests itself in different forms at different levels of dispersion.

The most coarsely dispersed form of dispersion is well-crystallized, very small (usually less than 0.01 - 0.02 mm in diameter) accessory minerals. They form mechanical inclusions in rock-forming minerals (Fig. 1.1).

Rice. 1.1 Inclusion of accessory apatite (1) and zircon (2) in feldspar grains. Transparent section, magnification 160 ´

The content of accessory elements is very small, but the concentration of scattered elements in them is so high that these elements form independent compounds. In crystalline rocks, zircon Zr, rutile, less commonly anatase and brookite, having the same composition TiO 2, apatite Ca 5 [PO 4 ] 3 F, magnetite Fe 2+ Fe 2 3+ O 4, ilmenite FeTiO 3, monazite CePO are present as accessories. 4, xenotime YPO 4, cassiterite SnO 2, chromite ECr 2 O 4 and other apatite weeds (7) and minerals of the spinel group, minerals of the columbite group (Fe, Mg) (Nb, Ta) 2 O 6, etc. The content of accessories in some rock-forming minerals, especially in mica, is quite noticeable.

In some minerals, mainly among sulfides and similar compounds, so-called solid solution decomposition structures are widespread - small separations of an impurity mineral in the substance of the host mineral. Examples of these include “emulsion dissemination” of chalcopyrite CuFeS 2 and frame Cu 2 FeSnS 4 in ZnS sphalerite, thin lamellar segregations of ilmenite FeTiO 3 in magnetite Fe 2+ Fe 2 3+ O 4 , and small segregations of silver minerals in galena PbS. As a result, lead sulfide contains a noticeable admixture of silver, copper sulfide contains an admixture of tin, and magnetite contains an admixture of titanium.

The use of a polarizing microscope and transparent sections made it possible to detect in minerals not only solid inclusions, but also micro-cavities filled with the remains of solutions from which crystallization took place (Fig. 1.2).

Rice. 1.2. Microcavities in quartz: 1 – sylvite crystal; 2 – halite crystal; 3 – gas bubble; 4 – liquid phase. Transparent section, magnification 900 ´

This phenomenon, first specifically considered in 1858 by the founder of optical petrography G. Sorbi, has now been comprehensively studied. Microcavities in minerals usually contain liquid and gas phases, sometimes with small crystals added to them. The problem of liquid inclusions was thoroughly analyzed by W. Newhouse, who noted the presence of heavy metals in liquids (up to several percent).

Some of the admixture of trace elements, easily extracted from finely ground monomineral samples, is associated precisely with liquid inclusions. N.P. Ermakov (1972), having studied microinclusions from fluorite, found in them n×10 -1% zinc, manganese, n×10 -2% barium, chromium, copper, nickel and lead, n×10 -3% titanium. Later, other trace elements were discovered in liquid inclusions.

At the same time, careful analysis of monomineral samples and the use of electronic probing showed that all rock-forming minerals, without exception, contain trace elements in such a highly dispersed form that they cannot be detected not only using optical, but also electron microscopy. In this case, scattering of elements occurs at the level of ions and molecules. The forms of such scattering are not limited to the previously considered isomorphism phenomena. There are numerous cases of the presence of chemical elements in minerals that have no connection with isomorphism.

The results of many thousands of analyzes carried out in different countries over the past 50 years suggest that all rock-forming minerals are carriers of trace elements. It is in them that the bulk of the trace elements contained in the earth's crust is concentrated. Knowing the content of carrier minerals and the concentration of trace elements in them, it is possible to calculate the balance within a particular rock.

When studying the granites of the Tien Shan, it was discovered that quartz, despite the insignificant concentration of lead, contains more than 5% of the total mass of this metal contained in the rock (Table 1.2).

Table 1.2. Distribution of lead in minerals composing granites of the Jumgol ridge

It is impossible to assume the isomorphic occurrence of lead, zinc or other metal in the quartz structure formed by a combination of silicon and oxygen ions. Meanwhile, quartz serves as a carrier of many trace elements. A special method has been developed for assessing the potential ore content of rocks and veins based on the content of lithium, rubidium, and boron in quartz.

In an experimental study of the strength of fixation of trace metals in rock-forming minerals, it was discovered that when a finely ground mineral mass is treated with successive portions of weak acid-base solvents, a significant part of the metals is easily extracted during the first extraction, and this extraction is not accompanied by destruction of the crystallochemical structure of the minerals. With further processing, the amount of extracted metals is sharply reduced or stopped altogether. This allowed us to make the assumption that some of the scattered elements are not included in the actual crystal chemical structure, but are confined to defects in real crystals. Defects are various types of cracks, and they are so small that they cannot be detected by an optical microscope. The ease of extraction of trace metals is explained by the fact that they are bound to the surface of the carrier mineral by sorption forces. In rock-forming silicates, this form of occurrence of trace metals accounts for 10–20% of the total mass of trace metals. In particular, the loosely bound form of lead in Tien Shan granites accounts for 12 to 18% of the total mass of the trace element.

The following forms of occurrence of trace elements in the crystalline matter of the earth’s crust can be distinguished:

I. Micromineralogical forms:

1. Elements included in accessory minerals.

2. Elements contained in microscopic secretions as a result of the decomposition of solid solutions.

3. Elements found in inclusions of residual solutions. P. Non-mineralogical forms:

4. Elements sorbed by the surface of defects in real crystals.

5. Elements included in the structure of the carrier mineral according to the laws of isomorphism.

6. Elements that are in a disordered state in the structure of the carrier mineral.

The combination of the considered forms of occurrence of scattered elements varies greatly depending on many factors. Accordingly, the total content of trace elements in different parts of the earth's crust also changes.

3. Features of chemical distribution elements in the earth's crust

The variation in element content in different samples is due to many independent reasons. When the distribution of a quantity is determined by a sufficiently large number of approximately resultant and mutually independent causes, then it obeys the so-called normal Gauss law. Its graphical expression is a curve with symmetrical branches on both sides of the maximum ordinate. With a normal distribution, the most probable value is arithmetic mean x, which coincides with the most frequently occurring values ​​– fashion. The extension of a symmetrical curve along the abscissa axis, i.e. the spread of values ​​upward and downward from the mode is characterized by standard deviation A.

A normal distribution can also appear not for the value itself, but for its logarithm (logarithmically normal, or lognormal, distribution law). In this case, the mode coincides with the geometric mean, and the spread of values ​​is characterized by the logarithm a.

In 1940 N.K. Razumovsky empirically discovered that the content of metals in ores corresponds to a lognormal distribution. L.X. Arena in 1954, having processed extensive material, independently of Razumovsky, established that the distribution of trace elements in igneous rocks is approximated by a logarithmically normal law. Numerous facts indicate that the distribution of elements with high clarkes usually obeys the normal law, while those of scattered elements obey the lognormal law. This once again confirms the fundamental difference between the main and scattered elements.

The high variability of low-clark elements is associated with their ability to reach a high degree of concentration. The maximum degree of concentration of the main elements is 10 - 20 times relative to their clarke, and for trace elements - hundreds and thousands of times more. For example, in ores from industrial deposits, the concentration of lead, nickel, tin, chromium is 1000× P.

Speaking about the huge masses of heavy metals concentrated in ore deposits, it should be remembered that these masses are an insignificant part of the total amount of metals scattered in the earth’s crust. In particular, the global reserves of zinc, copper, lead, and nickel ores constitute only thousandths of a percent of the masses of these metals scattered in the upper kilometer layer of the continents' crust.

Ore deposits are connected to the surrounding rocks by gradual transitions. Ore bodies are located, as it were, in a case of gradually decreasing concentrations of metals. Such formations are called scattering halos Primary, syngenetic ore aureoles arise simultaneously with ore bodies and as a result of the same processes. They have a varied configuration, depending on the geological structure, the composition of the host rocks and the conditions of ore formation.

In ores, along with one or more main ore-forming elements, there are accompanying elements, the concentration of which is also increased, but not as much as the main ones. Satellite elements often form isomorphic substitutions of the main ones. For example, zinc ores constantly contain cadmium, and in smaller quantities indium, gallium, and germanium. Copper-nickel ores contain a significant admixture of cobalt, and smaller amounts of selenium and tellurium. All accompanying elements are also dispersed around the ore bodies. Possessing unequal geochemical mobility, they form transition zones of different lengths. As a result, the composition and structure of scattering halos are very complex.

The average content of a chemical element is the norm - geochemical background– for a given type of rock in a certain area. Stand out against the geochemical background geochemical anomalies– areas of rocks with an increased concentration of trace elements. If they are associated with ore deposits, then these are dispersion halos. If the metal concentrations do not reach the ore standard, then such anomalies are called false. Using statistical processing of mass analytical data, it is possible to detect regular changes in the value of the geochemical background in space and identify geochemical provinces. Within provinces, rocks of the same type have consistent statistical parameters, primarily the average content of one or more trace elements. The average content of some elements in rocks of the same type from different geochemical provinces can vary greatly (several times). At the same time, the chemical composition of these rocks, determined by the content of the main elements, remains the same or has very slight differences. For example, in granites from different provinces, which have almost the same amount of silicon, aluminum, iron, potassium, the content of tin, lead, molybdenum, and uranium can differ by 2–3 times.

The presented material indicates the uneven distribution of trace elements in the earth's crust. Therefore, along with the definition of clarks, i.e. the average concentration of elements in the earth’s crust as a whole, it is necessary to take into account their ability to concentrate or disperse in various objects - different types of rocks or in rocks of the same type, but located in different geochemical provinces, in ores, etc. To quantitatively assess the heterogeneity of chemical elements in the earth’s Kore, V.I. Vernadsky introduced a special indicator - clarke concentration Kc. Its numerical value characterizes the deviation of the element content in a given volume from the clarke:

K K = A/K,

Where A– content of a chemical element in a rock, ore, mineral, etc.;

TO– clarke of this element in the earth’s crust. If the clarke concentration is greater than one, this indicates enrichment in the element; if less, it means a decrease in its content compared to data for the earth’s crust as a whole.

Changes in the concentration of chemical elements in space, deviations from the global or local geochemical norm Mb1 __ are not isolated cases, but a characteristic feature of the geochemical structure of the earth's crust. This is very important for the composition of photosynthetic organisms on land, which form the bulk of the mass of living matter on the Earth.

Literature

1. Alekseenko V.A. Environmental geochemistry. – M.: Logos, 2000. – 627 p.

2. Arena L. X. Distribution of elements in igneous rocks // Chemistry of the Earth’s crust. – M.: Nauka, 1964. – T. 2. – P. 293–300.

3. Vernadsky V.I. Essays on geochemistry // Izbr. cit.: In 5 vols. – M.: Publishing House of the USSR Academy of Sciences, 1954. – T. 1. – P. 7–391.

4. Voitkevich G.V., Miroshnikov A.E., Povarenykh A.S., Prokhorov V.G. A short guide to geochemistry. – M.: Nedra, 1977. – 183 p.

5. Goldshmit V.M. Principles of distribution of chemical elements in minerals and rocks // Collection of articles. Art. on geochemistry of rare elements. – M. – L.: GONTI NKTP USSR, 1930. – P. 215–242.

6. Dobrovolsky V.V. Geography of trace elements. Global dispersion. – M.: Mysl, 1983. – 269 p.

7. Perelman A.I. Geochemistry. – M.: Higher. school, 1989. – 528 p.

8. Ronov A.B., Yaroshevsky A.A. A new model of the chemical composition of the earth’s crust // Geochemistry. – 1976. – No. 12. – S. 1763–1795.