Earth's crust in scientific understanding represents 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. He long years 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 part of 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 either loose components (sand, pebbles), cemented components (sandstone), remains of microorganisms ( coal, limestone), chemical reaction products (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 natural factors(earthquake, typhoon, tsunami). These include sand, pebbles, gravel, crushed stone, clay.
- Chemical. They are gradually formed from aqueous solutions one or another minerals(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 as in natural form, and undergoing processing.
Types of useful minerals. Their classification
Depending on the physical condition and aggregations, minerals can be divided into categories:
- Solid (ore, marble, coal).
- Liquid ( mineral water, oil).
- Gaseous (methane).
Characteristics of individual types of minerals
According to the composition and features of application, they are distinguished:
- Combustibles (coal, oil, gas).
- Ore. They include radioactive (radium, uranium) and precious metals(silver, gold, platinum). There are ores of ferrous (iron, manganese, chromium) and non-ferrous metals (copper, tin, zinc, aluminum).
- Non-metallic 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. This Construction Materials(sand, gravel, clay) and chemical substances(sulfur, phosphates, potassium salts). A separate section is devoted to precious and ornamental stones.
Distribution mineral on our planet directly depends on external factors and geological patterns.
Thus, fuel minerals are primarily mined in oil and gas bearing 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 outer shell of our planet. The lower boundary of the mantle is at enormous depth 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 have been discovered to date. chemical elements. 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.
Mineral - comparatively homogeneous substance, which can be located 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. Theory tectonic plates explains that the oceanic crust is relatively young, and its most recent sections 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 voluminous areas it ranges from 5 to 10 kilometers. This type 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.
Lithosphere on earth's surface not homogeneous. It has several layers.
- 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.
- Granite layer. It consists of igneous and metamorphic rocks, which 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.
- 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. She is experiencing seasonal variations temperature. 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 provides for its presence, and its temperature is determined internal heat Earth and increases with depth.
The temperature rise occurs due to the decomposition radioactive substances, which 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 setting 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.
A characteristic feature of the evolution of the Earth is the differentiation of matter, the expression of which is the shell structure of our planet. The lithosphere, hydrosphere, atmosphere, biosphere form the main shells of the Earth, differing in chemical composition, thickness and state of matter.
Internal structure of the Earth
Chemical composition of the Earth(Fig. 1) similar to the composition of other planets terrestrial group, such as Venus or Mars.
In general, elements such as iron, oxygen, silicon, magnesium, and nickel predominate. The content of light elements is low. The average density of the Earth's substance is 5.5 g/cm 3 .
There is very little reliable data on the internal structure of the Earth. Let's look at Fig. 2. It depicts the internal structure of the Earth. The Earth consists of the crust, mantle and core.
Rice. 1. Chemical composition of the Earth
Rice. 2. Internal structure Earth
Core
Core(Fig. 3) is located in the center of the Earth, its radius is about 3.5 thousand km. The temperature of the core reaches 10,000 K, i.e. it is higher than the temperature of the outer layers of the Sun, and its density is 13 g/cm 3 (compare: water - 1 g/cm 3). The core is believed to be composed of iron and nickel alloys.
The outer core of the Earth has a greater thickness than the inner core (radius 2200 km) and is in a liquid (molten) state. Inner core subject to enormous pressure. The substances that compose it are in a solid state.
Mantle
Mantle- the Earth’s geosphere, which surrounds the core and makes up 83% of the volume of our planet (see Fig. 3). Its lower boundary is located at a depth of 2900 km. The mantle is divided into a less dense and plastic upper part (800-900 km), from which it is formed magma(translated from Greek means “thick ointment”; this is the molten substance of the earth’s interior - a mixture chemical compounds and elements, including gases, in a special semi-liquid state); and the crystalline lower one, about 2000 km thick.
Rice. 3. Structure of the Earth: core, mantle and crust
Earth's crust
Earth's crust - the outer shell of the lithosphere (see Fig. 3). Its density is approximately two times less than average density Earth, - 3 g/cm 3.
Separates the earth's crust from the mantle Mohorovicic border(often called the Moho boundary), characterized by a sharp increase in seismic wave velocities. It was installed in 1909 by a Croatian scientist Andrei Mohorovicic (1857- 1936).
Since the processes occurring in the uppermost part of the mantle affect the movements of matter in the earth's crust, they are combined under common namelithosphere(stone shell). The thickness of the lithosphere ranges from 50 to 200 km.
Below the lithosphere is located asthenosphere- less hard and less viscous, but more plastic shell with a temperature of 1200 ° C. It can cross the Moho boundary, penetrating into the earth's crust. The asthenosphere is the source of volcanism. It contains pockets of molten magma, which penetrates into the earth's crust or pours out onto the earth's surface.
Composition and structure of the earth's crust
Compared to the mantle and core, the earth's crust is a very thin, hard and brittle layer. It is composed of a lighter substance, which currently contains about 90 natural chemical elements. These elements are not equally represented in the earth's crust. Seven elements - oxygen, aluminum, iron, calcium, sodium, potassium and magnesium - account for 98% of the mass of the earth's crust (see Fig. 5).
Peculiar combinations of chemical elements form various rocks and minerals. The oldest of them are at least 4.5 billion years old.
Rice. 4. Structure of the earth's crust
Rice. 5. Composition of the earth's crust
Mineral- it is relatively homogeneous in its composition and properties natural body, formed both in the depths and on the surface of the lithosphere. Examples of minerals are diamond, quartz, gypsum, talc, etc. (You will find characteristics of the physical properties of various minerals in Appendix 2.) The composition of the Earth's minerals is shown in Fig. 6.
Rice. 6. General mineral composition Earth
Rocks consist of minerals. They can be composed of one or several minerals.
Sedimentary rocks - clay, limestone, chalk, sandstone, etc. - formed by sedimentation of substances in aquatic environment and on land. They lie in layers. Geologists call them pages of the history of the Earth, because they can learn about natural conditions that existed on our planet in ancient times.
Among sedimentary rocks, organogenic and inorganogenic (clastic and chemogenic) are distinguished.
Organogenic Rocks are formed as a result of the accumulation of animal and plant remains.
Clastic rocks are formed as a result of weathering, destruction by water, ice or wind of the products of destruction of previously formed rocks (Table 1).
Table 1. Clastic rocks depending on the size of the fragments
|
Breed name |
Size of bummer con (particles) |
|
More than 50 cm |
|
|
5 mm - 1 cm |
|
|
1 mm - 5 mm |
|
|
Sand and sandstones |
0.005 mm - 1 mm |
|
Less than 0.005 mm |
Chemogenic Rocks are formed as a result of the precipitation of substances dissolved in them from the waters of seas and lakes.
In the thickness of the earth's crust, magma forms igneous rocks(Fig. 7), for example granite and basalt.
Sedimentary and igneous rocks when immersed to great depths under the influence of pressure and high temperatures undergo significant changes, becoming metamorphic rocks. For example, limestone turns into marble, quartz sandstone into quartzite.
The structure of the earth's crust is divided into three layers: sedimentary, granite, and basalt.
Sedimentary layer(see Fig. 8) is formed mainly by sedimentary rocks. Clays and shales predominate here, and sandy, carbonate and volcanic rocks are widely represented. In the sedimentary layer there are deposits of such mineral, like coal, gas, oil. All of them are of organic origin. For example, coal is a product of the transformation of plants of ancient times. The thickness of the sedimentary layer varies widely - from complete absence in some areas of land up to 20-25 km in deep depressions.
Rice. 7. Classification of rocks by origin
"Granite" layer consists of metamorphic and igneous rocks, similar in their properties to granite. The most common here are gneisses, granites, crystalline schists, etc. The granite layer is not found everywhere, but on continents where it is well expressed, its maximum thickness can reach several tens of kilometers.
"Basalt" layer formed by rocks close to basalts. These are metamorphosed igneous rocks, denser than the rocks of the “granite” layer.
Power and vertical structure the earth's crust are different. There are several types of the earth's crust (Fig. 8). According to the simplest classification, a distinction is made between oceanic and continental crust.
Continental and oceanic crust vary in thickness. Thus, the maximum thickness of the earth's crust is observed under mountain systems. It is about 70 km. Under the plains the thickness of the earth's crust is 30-40 km, and under the oceans it is thinnest - only 5-10 km.
Rice. 8. Types of the earth's crust: 1 - water; 2- sedimentary layer; 3—interlayering of sedimentary rocks and basalts; 4 - basalts and crystalline ultrabasic rocks; 5 – granite-metamorphic layer; 6 – granulite-mafic layer; 7 - normal mantle; 8 - decompressed mantle
The difference between the continental and oceanic crust in the composition of rocks is manifested in the fact that there is no granite layer in the oceanic crust. And the basalt layer of the oceanic crust is very unique. In terms of rock composition, it differs from a similar layer of continental crust.
The boundary between land and ocean (zero mark) does not record the transition of the continental crust to the oceanic one. The replacement of continental crust by oceanic crust occurs in the ocean at a depth of approximately 2450 m.
Rice. 9. Structure of the continental and oceanic crust
There are also transitional types of the earth's crust - suboceanic and subcontinental.
Suboceanic crust located along continental slopes and foothills, can be found in marginal and Mediterranean seas. It represents continental crust with a thickness of up to 15-20 km.
Subcontinental crust located, for example, on volcanic island arcs.
Based on materials seismic sounding - the speed of passage of seismic waves - we obtain data on the deep structure of the earth’s crust. Yes, Kola ultra-deep well, which for the first time made it possible to see rock samples from a depth of more than 12 km, brought many unexpected things. It was assumed that at a depth of 7 km a “basalt” layer should begin. In reality, it was not discovered, and gneisses predominated among the rocks.
Change in temperature of the earth's crust with depth. The surface layer of the earth's crust has a temperature determined by solar heat. This heliometric layer(from the Greek helio - Sun), experiencing seasonal temperature fluctuations. Its average thickness is about 30 m.
Below is an even thinner layer, characteristic feature which is a constant temperature corresponding to the average annual temperature of the observation site. The depth of this layer increases in continental climates.
Even deeper in the earth's crust there is a geothermal layer, the temperature of which is determined by the internal heat of the Earth and increases with depth.
The increase in temperature occurs mainly due to the decay of radioactive elements that make up rocks, primarily radium and uranium.
The amount of temperature increase in rocks with depth is called geothermal gradient. It varies within a fairly wide range - from 0.1 to 0.01 °C/m - and depends on the composition of rocks, the conditions of their occurrence and a number of other factors. Under the oceans, temperature increases faster with depth than on continents. On average, with every 100 m of depth it becomes warmer by 3 °C.
The reciprocal of the geothermal gradient is called geothermal stage. It is measured in m/°C.
The heat of the earth's crust is an important energy source.
The part of the earth's crust that extends to depths accessible to geological study forms bowels of the earth. The Earth's interior requires special protection and reasonable use.
By modern ideas Geology Our planet consists of several layers - geospheres. They differ in physical properties, chemical composition and In the center of the Earth there is a core, followed by the mantle, then the earth's crust, hydrosphere and atmosphere.
In this article we will look at the structure of the earth's crust, which is top part lithosphere. It represents the external hard shell whose power is so small (1.5%) that it can be compared with thin film on a planetary scale. However, despite this, it is the upper layer of the earth’s crust that is of great interest to humanity as a source of minerals.
The earth's crust is conventionally divided into three layers, each of which is remarkable in its own way.
- Upper layer- sedimentary. It reaches a thickness of 0 to 20 km. Sedimentary rocks are formed due to the deposition of substances on land, or their settling at the bottom of the hydrosphere. They are part of the earth's crust, located in it in successive layers.
- The middle layer is granite. Its thickness can vary from 10 to 40 km. It is an igneous rock that formed hard layer as a result of eruptions and subsequent solidification of magma in the earth's thickness during high blood pressure and temperature.
- The lower layer, which is part of the structure of the earth's crust, is basalt, also of magmatic origin. It contains large quantity calcium, iron and magnesium, and its mass is greater than that of granite rock.
The structure of the earth's crust is not the same everywhere. The oceanic crust and the continental crust have especially striking differences. Under the oceans the earth's crust is thinner, and under the continents it is thicker. It is thickest in mountainous areas.
The composition includes two layers - sedimentary and basalt. Below the basalt layer is the Moho surface, and behind it is the upper mantle. The ocean floor has complex relief forms. Among all their diversity special place occupy huge mid-ocean ridges, in which young basaltic oceanic crust is born from the mantle. Magma has access to the surface through a deep fault - a rift, which runs along the center of the ridge along the peaks. Outside, the magma spreads, thereby constantly pushing the walls of the gorge to the sides. This process is called “spreading”.
The structure of the earth's crust is more complex on continents than under the oceans. Continental crust occupies a much smaller area than the oceanic one - up to 40% of the earth's surface, but has a much greater thickness. Below it reaches a thickness of 60-70 km. The continental crust has a three-layer structure - a sedimentary layer, granite and basalt. In areas called shields, a granite layer is on the surface. As an example, it is made of granite rocks.
The underwater extreme part of the continent - the shelf, also has a continental structure of the earth's crust. It also includes the islands of Kalimantan, New Zealand, New Guinea, Sulawesi, Greenland, Madagascar, Sakhalin, etc. As well as internal and marginal seas: Mediterranean, Azov, Black.
It is possible to draw a boundary between the granite layer and the basalt layer only conditionally, since they have a similar speed of passage of seismic waves, which is used to determine the density earth layers and their composition. The basalt layer is in contact with the Moho surface. The sedimentary layer can have different thicknesses, depending on the landform located on it. In the mountains, for example, it is either absent or has a very small thickness, due to the fact that loose particles move down the slopes under the influence external forces. But it is very powerful in foothill areas, depressions and basins. So, it reaches 22 km.
Earth's crust- thin top shell The Earth, which has a thickness of 40-50 km on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth's mass.
Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust.
On continents, the crust has three layers: sedimentary rocks cover granite rocks, and granite rocks overlie basaltic rocks. Under the oceans the crust is of the “oceanic”, two-layer type; sedimentary rocks simply lie on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the margins of the oceans and some areas on continents, for example).
The earth's crust has the greatest thickness in mountainous regions (under the Himalayas - over 75 km), average - in platform areas (under the West Siberian Lowland - 35-40, within the Russian Platform - 30-35), and the least in central regions oceans (5-7 km).
The predominant part of the earth's surface is the plains of continents and the ocean floor. The continents are surrounded by a shelf - a shallow strip with a depth of up to 200 g and an average width of about SO km, which, after a sharp steep bend of the bottom, turns into a continental slope (the slope varies from 15-17 to 20-30° ). The slopes gradually level out and turn into abyssal plains (depths 3.7-6.0 km). Oceanic trenches have the greatest depths (9-11 km), the vast majority of which are located on the northern and western outskirts.
The earth's crust formed gradually: first a basalt layer was formed, then a granite layer; the sedimentary layer continues to form to this day.
The deep strata of the lithosphere, which are studied by geophysical methods, have a rather complex and still insufficiently studied structure, just like the mantle and core of the Earth. But it is already known that the density of rocks increases with depth, and if on the surface it averages 2.3-2.7 g/cm3, then at a depth of about 400 km it is 3.5 g/cm3, and at a depth of 2900 km ( boundary of the mantle and the outer core) - 5.6 g/cm3. In the center of the core, where the pressure reaches 3.5 thousand t/cm2, it increases to 13-17 g/cm3. The nature of the increase in the Earth's deep temperature has also been established. At a depth of 100 km it is approximately 1300 K, at a depth of approximately 3000 km -4800 K, and in the center earth's core- 6900 K.
The predominant part of the Earth's substance is in a solid state, but at the boundary of the earth's crust and the upper mantle (depths of 100-150 km) lies a layer of softened, pasty rocks. This thickness (100-150 km) is called the asthenosphere. Geophysicists believe that other parts of the Earth may also be in a rarefied state (due to decompression, active radio decay of rocks, etc.), in particular, the zone of the outer core. The inner core is located in metal phase, but relative to it material composition consensus not for today.