What is called the earth's crust. Structure of the earth's crust

The continents were once formed from massifs earth's crust, which to one degree or another protrudes above the water level in the form of land. These blocks of the earth's crust have been splitting, shifting, and parts of them have been crushed for millions of years in order to appear in the form that we know now.

Today we will look at the greatest and smallest thickness of the earth's crust and the features of its structure.

A little about our planet

At the beginning of the formation of our planet, multiple volcanoes were active here, and constant collisions with comets occurred. Only after the bombardment stopped did the hot surface of the planet freeze.
That is, scientists are sure that initially our planet was a barren desert without water and vegetation. Where so much water came from is still a mystery. But not so long ago, large reserves of water were discovered underground, and perhaps they became the basis of our oceans.

Alas, all hypotheses about the origin of our planet and its composition are more assumptions than facts. According to A. Wegener, the Earth was originally covered thin layer granite, which is Paleozoic era transformed into the proto-continent Pangea. During the Mesozoic era, Pangea began to split into pieces, and the resulting continents gradually floated away from each other. The Pacific Ocean, Wegener argues, is a remnant of the primary ocean, while the Atlantic and Indian are considered secondary.

Earth's crust

The composition of the earth's crust is almost similar to the composition of the planets of ours solar system- Venus, Mars, etc. After all, the same substances served as the basis for all the planets of the solar system. And recently, scientists are confident that the collision of the Earth with another planet, called Theia, caused the merger of two celestial bodies, and the Moon was formed from the broken fragment. This explains what mineral composition The composition of the moon is similar to our planet. Below we will look at the structure of the earth's crust - a map of its layers on land and ocean.

The crust makes up only 1% of the Earth's mass. It mainly consists of silicon, iron, aluminum, oxygen, hydrogen, magnesium, calcium and sodium and 78 other elements. It is assumed that, in comparison with the mantle and core, the Earth's crust is a thin and fragile shell, consisting mainly of light substances. Heavy substances, according to geologists, descend to the center of the planet, and the heaviest are concentrated in the core.

The structure of the earth's crust and a map of its layers are presented in the figure below.

Continental crust

The Earth's crust has 3 layers, each of which covers the previous one in uneven layers. Most of its surfaces are continental and oceanic plains. The continents are also surrounded by a shelf, which, after a steep bend, passes into the continental slope (the area of ​​​​the underwater margin of the continent).
The earth's continental crust is divided into layers:

1. Sedimentary.
2. Granite.
3. Basalt.

The sedimentary layer is covered by sedimentary, metamorphic and igneous rocks. The thickness of the continental crust is the smallest percentage.

Types of continental crust

Sedimentary rocks are accumulations that include clay, carbonate, volcanic rocks, and other solids. This is a kind of sediment that was formed as a result of certain natural conditions that previously existed on Earth. It allows researchers to draw conclusions about the history of our planet.

The granite layer consists of igneous and metamorphic rocks similar to granite in their properties. That is, not only granite makes up the second layer of the earth’s crust, but these substances are very similar in composition to it and have approximately the same strength. The speed of its longitudinal waves reaches 5.5-6.5 km/s. It consists of granites, crystalline schists, gneisses, etc.

The basalt layer is composed of substances similar in composition to basalts. It is more dense compared to the granite layer. Beneath the basalt layer flows a viscous mantle of solids. Conventionally, the mantle is separated from the crust by the so-called Mohorovicic boundary, which, in fact, separates layers of different chemical compositions. Characterized by a sharp increase in the speed of seismic waves.
That is, a relatively thin layer of the earth’s crust is a fragile barrier separating us from the hot mantle. The thickness of the mantle itself is on average 3,000 km. Together with the mantle, tectonic plates also move, which, as part of the lithosphere, are part of the earth's crust.

Below we consider the thickness of the continental crust. It is up to 35 km.

Thickness of the continental crust

The thickness of the earth's crust varies from 30 to 70 km. And if under the plains its layer is only 30-40 km, then under mountain systems reaches 70 km. Under the Himalayas, the thickness of the layer reaches 75 km.

The thickness of the continental crust ranges from 5 to 80 km and directly depends on its age. Thus, cold ancient platforms (East European, Siberian, West Siberian) have a fairly high thickness - 40-45 km.

Moreover, each layer has its own thickness and thickness, which can vary in different areas of the continent.

The thickness of the continental crust is:

1. Sedimentary layer - 10-15 km.

2. Granite layer - 5-15 km.

3. Basalt layer - 10-35 km.

Temperature of the Earth's crust

The temperature rises as you go deeper into it. It is believed that the temperature of the core is up to 5,000 C, but these figures remain arbitrary, since its type and composition are still not clear to scientists. As you go deeper into the earth's crust, its temperature rises every 100 m, but its numbers vary depending on the composition of the elements and depth. The oceanic crust has a higher temperature.

Oceanic crust

Initially, according to scientists, the Earth was covered with an oceanic layer of crust, which is somewhat different in thickness and composition from the continental layer. probably arose from the upper differentiated layer of the mantle, that is, it is very close to it in composition. The thickness of the earth's crust of the oceanic type is 5 times less than the thickness of the continental type. Moreover, its composition in deep and shallow areas of seas and oceans differs insignificantly from each other.

Continental crust layers

The thickness of the oceanic crust is:

1. Layer ocean water, whose thickness is 4 km.

2. Layer of loose sediments. The thickness is 0.7 km.

3. A layer composed of basalts with carbonate and siliceous rocks. The average thickness is 1.7 km. It does not stand out sharply and is characterized by compaction of the sedimentary layer. This variant of its structure is called suboceanic.

4. Basalt layer, no different from the continental crust. The thickness of the oceanic crust in this layer is 4.2 km.

The basaltic layer of oceanic crust in subduction zones (zones in which one layer of crust absorbs another) turns into eclogites. Their density is so high that they plunge deep into the crust to a depth of more than 600 km and then descend into the lower mantle.

Considering that the thinnest thickness of the Earth's crust is observed under the oceans and is only 5-10 km, scientists have long been toying with the idea of ​​starting to drill into the crust at the depths of the oceans, which would allow them to study the internal structure of the Earth in more detail. However, the layer of oceanic crust is very strong, and research in the deep ocean makes this task even more difficult.

Conclusion

The earth's crust is perhaps the only layer studied in detail by mankind. But what lies underneath still worries geologists. We can only hope that one day the unexplored depths of our Earth will be explored.

Until recently, ideas about the thickness of the Earth's crust under the ocean floor were based on rather rare seismic profiles of deep structure studies.

Some data on the possible thickness of the crust under the ocean floor were obtained by V. F. Bonchkovsky based on the study of surface waves of earthquakes.

R. M. Demenitskaya, having developed new method determination of the thickness of the earth's crust, based on its known connections with gravity anomalies (in the Bouguer reduction) and with relief earth's surface, constructed schematic maps of the distribution of the thickness of the earth's crust of continents and oceans. Judging by these maps, the thickness of the earth's crust in the oceans is as follows.

IN Atlantic Ocean, within the continental shelf, the thickness of the crust varies from 35 to 25 km. It does not differ from that in the adjacent parts of the continent, since the continental structures directly continue on the shelf. In the area of ​​the continental slope, with increasing depth, the thickness of the crust decreases from 25-15 km in the upper part of the slope to 15-10 and even less than 10 km in the lower part. The bottom of the basins of the Atlantic Ocean is characterized by a crust of small thickness - from 2 to 7 km, but where it makes up underwater ridges or plateaus, its thickness increases to 15-25 km (Bermuda underwater plateau, Telegraph plateau).

We see a similar picture in the Arctic basin of the North Arctic Ocean with a crust thickness of 15 to 25 km; only in its central parts it is less than 10-5 km. In the Scandic Basin, the crustal thickness (15 to 25 km) differs from that typical of oceanic basins. On the continental slope, the thickness of the crust changes in the same way as in the Atlantic Ocean. We see the same analogy in the crust of the continental shallows of the Arctic Ocean with a crustal thickness of 25 to 35 km; it thickens in the Laptev Sea, as well as in adjacent parts of the Kara and East Siberian Seas and further on the Lomonosov Ridge. It is possible that the increase in crustal thickness here is associated with the spread of young - Mesozoic folded structures.

In the Indian Ocean there is a relatively thick crust (more than 25 km) in the Mozambique Channel and partly east of Madagascar up to and including the Seychelles Ridge. Sredinny ridge Indian Ocean the thickness of the crust is no different from the Mid-Atlantic Ridge. The southern part of the Arabian Sea and the Bay of Bengal are distinguished by a relatively thin crust, despite their comparative youth.

The thickness of the earth's crust in the Pacific Ocean is characterized by certain features. In the Bering and Okhotsk Seas, the crust is more than 25 km thick. It is thinner only in the southern deep-water part of the Bering Sea. In the Sea of ​​Japan, the thickness decreases sharply (to 10-15 km), in the seas of Indonesia it increases again (more than 25 km), remaining the same further south - up to and including the Arafura Sea. In the western part Pacific Ocean, directly adjacent to the belt of geosynclinal seas, the prevailing thicknesses are from 7 to 10 km, but in some depressions of the ocean floor they decrease to 5 km, while in areas of seamounts and islands they increase to 10-15 and often up to 20-25 km.

In the central part of the Pacific Ocean - the region of the deepest basins, as in other oceans, the thickness of the crust is the smallest - ranging from 2 to 7 km. In some depressions of the ocean floor, the crust is thinner. In the most elevated parts of the ocean floor - on the middle underwater ridges and adjacent spaces - the thickness of the crust increases to 7-10 km. The same crustal thicknesses are characteristic of the eastern and southeastern parts of the ocean along the strike of the South Pacific and East Pacific ridges, as well as the underwater Albatross Plateau.

Maps of the thickness of the earth's crust compiled by R. M. Demenitskaya give an idea of ​​​​the total thickness of the crust. To clarify the structure of the crust, you need to turn to data obtained through seismic studies.

The thickness of the earth's crust is not the same on all parts of the earth. Minimum thickness under the seas and oceans - within 5 kilometers. And the maximum is on the mainland and can reach 70 kilometers (this is in mountainous areas).

According to information, or rather assumptions of the scientific community, the thickness of the earth’s crust in different areas of the earth is from 7 to 70 kilometers. Under the oceans in places of volcanic activity the crust is thinner, on land it is thicker.

The earth's crust is not even a thin crust, it is a film similar to the one that forms on boiled milk and protects this milk from quickly cooling. Once you tear this film, the milk instantly becomes cold. Likewise, the earth’s crust protects the Earth from wasting internal heat, which, while it exists, gives life to all the inhabitants of the planet. The thickness of the earth's crust is 35-70 kilometers under the continents and only 7-10 kilometers in the ocean. It is not surprising that there are many times more underwater volcanoes than volcanoes on the continents. The diameter of the Earth is more than 12 thousand kilometers, so what is the crust if not a thin film?

The thickness of the earth's crust is not uniform, it varies from 5 to 130 kilometers. The thinnest part is at the bottom of the ocean, the widest, as you might guess, is in the mountains. You can calculate the average length by adding 5 and 130 and then dividing in half. The result is 67.5 km. But this is quite conditional.

Our Earth is covered with a crust, like a huge shell consisting of rock formations. Inner forces extraordinary power constantly changes its surface: new oceans are formed, mountains rise, huge abysses open up. The earth's crust is deformed due to earthquakes and volcanic eruptions. measurements of the thickness of the earth's crust were made. Thus, the thickness of the earth's crust under the ocean turned out to be 5 km, under the continents its thickness reaches 30-40 km, and under high mountains, on land - 60-70 km.

The thickness of the earth's crust is not constant. It differs in different areas globe. For example, in oceanic areas it is several kilometers, and in mountainous areas of continents it reaches several tens of kilometers.

From a theory that has existed for more than 300 years, it follows that the current continents merged at one time and one giant continent was formed, to which researchers gave the name Pangea (from the Greek, the whole earth). Due to still unclear reasons, about 200 million years ago, Pangea began to fragment again. First, the northern half of Pangea (from which Europe, North America, and part of Asia were later formed) moved away from the southern half (which included Australia, South America, India, Antarctica and Africa). Then new giant cracks called rifts began to form, and these two landmasses broke into modern continents.

Moving with lithospheric plates, these arrays gradually occupied the position we see today. However, the continents continue to move in our time. Europe and North America are quietly moving away from each other. Consequently, the Atlantic Ocean is expanding. And the Red Sea is located in a still young rift zone of the earth’s crust, and over time it will most likely become an ocean, perhaps wider than the Atlantic, provided that new volcanic material continues to pour out from the bowels of the Earth onto its bottom.

I will not redo the text. Just for those poor students who put downvotes, I’ll give you a link to the Geographical site. I will quote just a few paragraphs:

Continental crust of reduced thickness (less than 30 km), with a less clearly defined granite layer, is sometimes called subcontinental. Seismic sections in the crust are often the boundaries of zones of regional metamorphism or zones of increased fragmentation and permeability of rocks, rather than changes in their composition. The oceanic crust is up to 5-10 km thick. In modern geological time she is under sea ​​waters, if their depth is more than 3.5 km, and is divided into three layers: the upper (less than 1 km) sedimentary, the middle mainly basaltic, and the lower, composed of gabbro, serpentinites, ultrabasic rocks with a silica content of less than 40%......

Request to the Losers: familiarize yourself with and fill the gap in school education.

The thickness of the earth's crust varies in different places on Earth. So, under the ocean the thickness of the earth’s crust is at least 5 kilometers. Despite its name, the bark is quite thick. Somewhere there are 70 kilometers (this is where the mountains are).

The earth's crust is a solid shell (geosphere), and below the earth's crust is the mantle. The entire mass of the Earth's crust is only about 0.5% of the total mass of the planet. The thickness of the earth's crust varies in different parts of the earth, from 5-7 kilometers to 120-130 kilometers.



It is impossible to name the exact thickness of the earth's crust, which would be the same for all parts of the earth's surface. The fact is that it is different for continents and oceans. The thickness of the earth's crust under the ocean is 5-10 kilometers, and it decreases with depth. The average thickness of the earth's crust on the continents is 35-45 kilometers, and in mountainous areas it reaches 70 kilometers.

• Thickness of the earth's crust

  

  There are two types of earth's crust - oceanic crust and continental crust. The continental crust consists mainly of light granitic rocks. The oceanic crust is composed of dark basaltic rocks. One of the main differences between them is density. Continental crust has an average density of 2.6 g/cm3, while oceanic crust has an average density of 3 g/cm3. In this regard, the average height of the continents is 600 meters above sea level, the average height (depth) of the ocean floor is 3000 meters below sea level.

  The average thickness of the earth's crust in the ocean is 5-10 kilometers. The average thickness of the continental crust is 35 kilometers, but can reach up to 70 kilometers.

Earth's crust called the outer solid shell of the Earth, limited from below by the Mohorovicic surface, or Moho, which is distinguished by a sharp increase in the speed of elastic waves as they pass from the Earth’s surface into its depths.

Below the Mohorovicic surface is the following solid shell - upper mantle . The uppermost part of the mantle, together with the earth's crust, is the hard and brittle solid shell of the Earth — lithosphere (stone). It is underlain by more plastic and susceptible to deformation, less viscous layers of the mantle - asthenosphere (weak). In it, the temperature is close to the melting point of the mantle substance, but due to high pressure the substance does not melt, but is in an amorphous state and can flow while remaining solid, like a glacier in the mountains. It is the asthenosphere that is the plastic layer on which individual blocks of the lithosphere float.

The thickness of the earth's crust on the continents is about 30-40 km, under mountain ranges it increases to 80 km (continental type of earth's crust). Under the deep-sea part of the oceans, the thickness of the earth's crust is 5-15 km (oceanic type of the earth's crust). On average, the base of the earth's crust (Mohorovicic surface) lies under the continents at a depth of 35 km, and under the oceans at a depth of 7 km, i.e., the oceanic earth's crust is approximately five times thinner than the continental crust.

In addition to differences in thickness, there are differences in the structure of the earth's crust of continental and oceanic types.

Continental crust consists of three layers: upper - sedimentary, extending to an average depth of 5 km; medium granite (the name is due to the fact that the speed of seismic waves in it is the same as in granite) with an average thickness of 10-15 km; the lower one is basaltic, about 15 km thick.

Oceanic crust also consists of three layers: upper - sedimentary to a depth of 1 km; medium with a little-known composition, occurring at depths from 1 to 2.5 km; the lower one is basaltic with a thickness of about 5 km.

A visual representation of the nature of the distribution of land heights and depths of the ocean floor is given by hypsographic curve (Fig. 1). It reflects the ratio of the areas of the Earth's solid shell with different heights on land and with different depths in the sea. Using the curve, the average land height (840 m) and average sea depth (-3880 m) were calculated. If we do not take into account the mountainous areas and deep-sea depressions, which occupy a relatively small area, then two predominant levels are clearly distinguished on the hypsographic curve: the level of the continental platform with a height of approximately 1000 m and the level of the oceanic bed with elevations from -2000 to -6000 m. A transitional level connecting them the zone is a relatively sharp ledge and is called the continental slope. Thus, the natural boundary separating the ocean and continents is the invisible coastline, and the outer boundary of the slope.

Rice. 1. Hypsographic curve (A) and generalized profile of the ocean floor (B). (I - underwater continental margins, II - transition zone, III - ocean floor, IV - mid-ocean ridges).

Within the oceanic part of the gypsographic (bathygraphic) The curve distinguishes four main stages of bottom relief: continental shallows or shelf (0-200 m), continental slope (200-2000 m), ocean floor (2000-6000 m) and deep-sea depressions (6000-11000 m).

Shelf (continental shelf)- an underwater continuation of the mainland. This is an area of ​​the continental crust, which is generally characterized by a flat topography with traces of flooded river valleys, Quaternary glaciation, and ancient coastlines.

The outer limit of the shelf is edge - a sharp bend in the bottom, beyond which the continental slope begins. The average depth of the shelf edge is 130 m, but in specific cases its depth may vary.

The width of the shelf varies over a very wide range: from zero (in some areas of the African coast) to thousands of kilometers (off the northern coast of Asia). In general, the shelf occupies about 7% of the area of ​​the World Ocean.

continental slope- the area from the edge of the shelf to the continental foot, i.e., before the transition of the slope to a flatter ocean bed. The average angle of inclination of the continental slope is about 6o, but often the steepness of the slope can increase to 20-30 0, and in some cases almost vertical ledges are possible. The width of the continental slope due to the steep dip is usually small - about 100 km.

The relief of the continental slope is characterized by great complexity and diversity, but its most characteristic form is underwater canyons . These are narrow gutters with a large angle of incidence along the longitudinal profile and steep slopes. The tops of underwater canyons often cut into the edge of the shelf, and their mouths reach the continental foot, where in such cases alluvial cones of loose sedimentary material are observed.

Mainland foot- the third element of the ocean floor relief, located within the continental crust. The continental foothills are a vast sloping plain formed by sedimentary rocks up to 3.5 km thick. The width of this slightly hilly plain can reach hundreds of kilometers, and its area is close to that of the shelf and continental slope.

ocean bed- the deepest part of the ocean floor, occupying more than 2/3 of the entire area of ​​the World Ocean. The prevailing depths of the ocean floor range from 4 to 6 km, and the bottom topography is the calmest. The main elements of the ocean floor topography are ocean basins, mid-ocean ridges and oceanic rises.

Ocean basins- extensive depressions in the bottom of the World Ocean with depths of about 5 km. The leveled surface of the bottom of basins is called abyssal (bottomless) plains, and it is caused by the accumulation of sedimentary material brought from land. Abyssal plains in the World Ocean occupy about 8% of the ocean floor.

Mid-ocean ridges- tectonically active zones in the ocean in which new formation of the earth’s crust occurs. They are composed of basaltic rocks formed as a result of the entry of upper mantle material from the interior of the Earth. This determined the uniqueness of the earth's crust at mid-ocean ridges and its classification as a rifting type.

Oceanic rises- large positive forms of relief of the ocean floor, not associated with mid-ocean ridges. They are located within the oceanic type of the earth's crust and are distinguished by large horizontal and vertical dimensions.

In the deep ocean, isolated seamounts of volcanic origin have been discovered. Flat-topped seamounts located at depths greater than 200 m are called guyots.

Deep-sea depressions (trenches)— zones of the greatest depths of the World Ocean, exceeding 6000 m.

The deepest trench is the Mariana Trench, discovered in 1954 by the research vessel Vityaz. Its depth is 11022 m.

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Internal structure of the Earth

The structure of the Earth has three main shells: the earth's crust, mantle and core.

Diagram of the internal structure of the Earth

The surface of the Earth is covered by a shell of rock - Earth's crust. Its thickness under the oceans is only 3–15 km, and on the continents it reaches 75 km. It turns out that in relation to the entire planet, the earth's crust is thinner than the skin of a peach. The upper layer of the crust is formed by sedimentary rocks; under it there are “granite” and “basalt” layers, which are named so conventionally.

Located under the earth's crust mantle. The mantle is the inner shell covering the Earth's core. WITH Greek language"mantle" is translated as "veil". Scientists assume that the upper part of the mantle consists of dense rocks, that is, it is solid. However, at a depth of 50-250 km from the Earth’s surface there is a partially molten layer called magma.

Earth's crust

It is relatively soft and plastic, capable of flowing slowly and thus moving. The speed of magma movement is low - a few centimeters per year. However, it plays a decisive role in the movements of the earth's crust. The temperature of the upper layer of magma is about +2000 °C, and in the lower layers the heat can reach +5000 °C. The earth's crust along with top layer the hot mantle is called the lithosphere.

Hidden under the mantle, at a depth of about 2900 km from the surface Earth's core. It has the shape of a ball with a radius of almost 3500 km. In the nucleus there is an outer and inner part, which differ in composition, temperature and density. The inner core is the hottest and densest part of our planet, consisting, scientists believe, mainly of iron and nickel. In the inner core the pressure is so high that, despite the enormous temperature (+6000...+10,000 °C), it is solid. The outer core is in a liquid state, its temperature is 4300 °C.

Structure of the earth's crust

Most of the crust on the outside is covered with the hydrosphere, and a smaller part borders on the atmosphere. In accordance with this, the earth's crust is distinguished oceanic And mainland types, and they have different structures.

The continental (continental) crust occupies a smaller area (about 40% of the entire surface of the Earth), but has a more complex structure. Under high mountains its thickness reaches 60-70 km. The continental crust consists of 3 layers - basalt, granite And sedimentary. The oceanic crust is thinner - only 5-7 km. It consists of two layers: the lower - basalt and the upper - sedimentary.

The earth's crust is best studied to a depth of 20 km. Based on the results of the analysis of numerous samples of rocks and minerals exposed on the surface of the earth during mountain-forming processes, as well as taken from mine workings and deep boreholes, the average composition was calculated chemical elements earth's crust.

The boundary layer separating the mantle and crust of the Earth is called the Mohorovicic boundary, or Moho surface, in honor of the Croatian scientist A. Mohorovicic. In 1909, he was the first to point out the characteristic command of seismic waves when crossing a boundary, which can be traced throughout the globe at a depth of 5 to 70 km.

How is the mantle studied?

The mantle is deep below the Earth, and even the deepest drill holes do not reach it. But sometimes, when gases break through the earth's crust, so-called kimberlite pipes are formed. Through them, mantle rocks and minerals reach the surface. The most famous of these is the diamond, the deepest fragment of our planet that we can study. Thanks to such tubes, we can judge the structure of the mantle.

The kimberlite pipe in Yakutia, where diamonds are mined, has been developed for a long time. Huge quarries have been built in place of such pipes. Their very name comes from the city of Kimberley in South Africa.

Until recently, ideas about the thickness of the Earth's crust under the ocean floor were based on rather rare seismic profiles of deep structure studies.

Some data on the possible thickness of the crust under the ocean floor were obtained by V. F. Bonchkovsky based on the study of surface waves of earthquakes.

R. M. Demenitskaya, having developed a new method for determining the thickness of the earth's crust, based on its known connections with gravity anomalies (in the Bouguer reduction) and with the relief of the earth's surface, constructed schematic maps of the distribution of the thickness of the earth's crust of the continents and oceans. Judging by these maps, the thickness of the earth's crust in the oceans is as follows.

In the Atlantic Ocean, within the continental shallows, the thickness of the crust varies from 35 to 25 km. It does not differ from that in the adjacent parts of the continent, since the continental structures directly continue on the shelf. In the area of ​​the continental slope, with increasing depth, the thickness of the crust decreases from 25-15 km in the upper part of the slope to 15-10 and even less than 10 km in the lower part. The bottom of the basins of the Atlantic Ocean is characterized by a crust of small thickness - from 2 to 7 km, but where it makes up underwater ridges or plateaus, its thickness increases to 15-25 km (Bermuda underwater plateau, Telegraph plateau).

We see a similar picture in the Arctic basin of the Arctic Ocean with a crustal thickness of 15 to 25 km; only in its central parts it is less than 10-5 km. In the Scandic Basin, the crustal thickness (15 to 25 km) differs from that typical of oceanic basins. On the continental slope, the thickness of the crust changes in the same way as in the Atlantic Ocean. We see the same analogy in the crust of the continental shallows of the Arctic Ocean with a crustal thickness of 25 to 35 km; it thickens in the Laptev Sea, as well as in adjacent parts of the Kara and East Siberian Seas and further on the Lomonosov Ridge.

Internal structure of the Earth

It is possible that the increase in crustal thickness here is associated with the spread of young - Mesozoic folded structures.

In the Indian Ocean there is a relatively thick crust (more than 25 km) in the Mozambique Channel and partly east of Madagascar up to and including the Seychelles Ridge. The Mid-Indian Ocean Ridge is no different in crustal thickness from the Mid-Atlantic Ridge. The southern part of the Arabian Sea and the Bay of Bengal are distinguished by a relatively thin crust, despite their comparative youth.

The thickness of the earth's crust in the Pacific Ocean is characterized by certain features. In the Bering and Okhotsk Seas, the crust is more than 25 km thick. It is thinner only in the southern deep-water part of the Bering Sea. In the Sea of ​​Japan, the thickness decreases sharply (to 10-15 km), in the seas of Indonesia it increases again (more than 25 km), remaining the same further south - up to and including the Arafura Sea. In the western part of the Pacific Ocean, directly adjacent to the belt of geosynclinal seas, thicknesses from 7 to 10 km predominate, but in some depressions of the ocean floor they decrease to 5 km, while in areas of seamounts and islands they increase to 10-15 and often up to 20- 25 km.

In the central part of the Pacific Ocean - the region of the deepest basins, as in other oceans, the thickness of the crust is the smallest - ranging from 2 to 7 km. In some depressions of the ocean floor, the crust is thinner. In the most elevated parts of the ocean floor - on the middle underwater ridges and adjacent spaces - the thickness of the crust increases to 7-10 km. The same crustal thicknesses are characteristic of the eastern and southeastern parts of the ocean along the strike of the South Pacific and East Pacific ridges, as well as the underwater Albatross Plateau.

Maps of the thickness of the earth's crust compiled by R. M. Demenitskaya give an idea of ​​​​the total thickness of the crust. To clarify the structure of the crust, you need to turn to data obtained through seismic studies.

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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 Earth(Fig. 1) is similar to the composition of other terrestrial planets, such as Venus or Mars.

In general, elements such as iron, oxygen, silicon, magnesium, and nickel predominate. The content of light elements is low. The average density of the Earth's substance is 5.5 g/cm 3 .

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

Rice. 1. Chemical composition of the Earth

Rice. 2. Internal structure Earth

Core

Core(Fig. 3) is located in the center of the Earth, its radius is about 3.5 thousand km. The core temperature reaches 10,000 K, i.e. it is higher than the temperature outer layers The sun, and its density is 13 g/cm 3 (compare: water - 1 g/cm 3). The core is believed to be composed of iron and nickel alloys.

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

Mantle

Mantle- the Earth’s geosphere, which surrounds the core and makes up 83% of the volume of our planet (see Fig. 3). Its lower boundary is located at a depth of 2900 km. The mantle is divided into less dense and plastic top 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 the general name lithosphere(stone shell). The thickness of the lithosphere ranges from 50 to 200 km.

Below the lithosphere is located asthenosphere- less hard and less viscous, but more plastic shell with a temperature of 1200 ° C. It can cross the Moho boundary, penetrating into the earth's crust. The asthenosphere is the source of volcanism. It contains pockets of molten magma, which penetrates into the earth's crust or pours out onto the earth's surface.

Composition and structure of the earth's crust

Compared to the mantle and core, the earth's crust is a very thin, hard and brittle layer. It is composed of a lighter substance, which currently contains about 90 natural chemical elements. These elements are not equally represented in the earth's crust. Seven elements - oxygen, aluminum, iron, calcium, sodium, potassium and magnesium - account for 98% of the mass of the earth's crust (see Fig. 5).

Peculiar combinations of chemical elements form various rocks and minerals. The oldest of them are at least 4.5 billion years old.

Rice. 4. Structure of the earth's crust

Rice. 5. Composition of the earth's crust

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

Rice. 6. General mineral composition of the 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

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, How coal, gas, oil. All of them are of organic origin. For example, coal is a product of the transformation of plants of ancient times. The thickness of the sedimentary layer varies widely - from complete absence in some land areas to 20-25 km in deep depressions.

Rice. 7. Classification of rocks by origin

"Granite" layer consists of metamorphic and igneous rocks, similar in their properties to granite. The most common here are gneisses, granites, crystalline schists, etc. The granite layer is not found everywhere, but on the continents where it is well expressed, it maximum power can reach several tens of kilometers.

"Basalt" layer formed by rocks close to basalts. These are metamorphosed igneous rocks, denser than the rocks of the “granite” layer.

The thickness and vertical structure of the earth's crust are different. There are several types of the earth's crust (Fig. 8). According to the simplest classification, a distinction is made between oceanic and continental crust.

Continental and oceanic crust vary in thickness. Thus, the maximum thickness of the earth’s crust is observed under mountain systems. It is about 70 km. Under the plains the thickness of the earth's crust is 30-40 km, and under the oceans it is thinnest - only 5-10 km.

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

The difference between the continental and oceanic crust in the composition of rocks is manifested in the fact that there is no granite layer in the oceanic crust. And the basalt layer of the oceanic crust is very unique. In terms of rock composition, it differs from a similar layer of continental crust.

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

Rice. 9. Structure of the continental and oceanic crust

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

Suboceanic crust located along continental slopes and foothills, can be found in marginal and Mediterranean seas. It represents continental crust with a thickness of up to 15-20 km.

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

Based on materials seismic sounding - the speed of passage of seismic waves - we obtain data on the deep structure of the earth’s crust. 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 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 internal heat Earth and increases with depth.

The increase in temperature occurs mainly due to the decay of radioactive elements that make up rocks, primarily radium and uranium.

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

The reciprocal of the geothermal gradient is called geothermal stage. It is measured in m/°C.

The heat of the earth's crust is an important energy source.

The part of the earth's crust that extends to depths accessible to geological study forms bowels of the earth. The Earth's interior requires special protection and wise use.