The continental crust has layers. The structure of the earth - a diagram of the internal and external structure, the names of the layers

10.04.2020

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

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

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

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

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

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

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

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

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

Earth's crust

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

Mantle

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

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

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

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

The internal structure of our planet

Earth's core

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

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

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

Geochemical method for studying the structure of planets

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

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

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

Continental (continental) crust of the Earth

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

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

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

Oceanic (basalt) crust of the Earth

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

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

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

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

Method for measuring heat flow for studying the structure of planets

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

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

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

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

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

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

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

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

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

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

The upper layer of the Earth, which gives life to the inhabitants of the planet, is just a thin shell covering many kilometers of inner layers. Little more is known about the hidden structure of the planet than about outer space. the deepest Kola well, drilled into the earth's crust to study its layers, has a depth of 11 thousand meters, but this is only four hundredth of the distance to the center of the globe. Only seismic analysis can get an idea of the processes taking place inside and create a model of the Earth's device.

Inner and outer layers of the Earth

The structure of the planet Earth is heterogeneous layers of inner and outer shells, which differ in composition and role, but are closely related to each other. The following concentric zones are located inside the globe:

The core - with a radius of 3500 km.
Mantle - approximately 2900 km.
The earth's crust is an average of 50 km.

The outer layers of the earth make up a gaseous shell, which is called the atmosphere.

Center of the planet

The central geosphere of the Earth is its core. If we raise the question of which layer of the Earth is practically the least studied, then the answer will be - the core. It is not possible to obtain exact data on its composition, structure and temperature. All information that is published in scientific papers has been obtained by geophysical, geochemical methods and mathematical calculations and is presented to the general public with the proviso "presumably". As the results of the analysis of seismic waves show, the earth's core consists of two parts: internal and external. The inner core is the most unexplored part of the Earth, since seismic waves do not reach its limits. The outer core is a mass of hot iron and nickel, with a temperature of about 5 thousand degrees, which is constantly in motion and is a conductor of electricity. It is with these properties that the origin of the Earth's magnetic field is associated. The composition of the inner core, according to scientists, is more diverse and is supplemented by even lighter elements - sulfur, silicon, and possibly oxygen.

Mantle

The geosphere of the planet, which connects the central and upper layers of the Earth, is called the mantle. It is this layer that makes up about 70% of the mass of the globe. The lower part of the magma is the shell of the core, its outer boundary. Seismic analysis shows here a sharp jump in the density and velocity of compressional waves, which indicates a material change in the composition of the rock. The composition of the magma is a mixture of heavy metals, dominated by magnesium and iron. The upper part of the layer, or asthenosphere, is a mobile, plastic, soft mass with a high temperature. It is this substance that breaks through the earth's crust and splashes to the surface in the process of volcanic eruptions.

The thickness of the magma layer in the mantle is from 200 to 250 kilometers, the temperature is about 2000 ° C. The mantle is separated from the lower globe of the earth's crust by the Moho layer, or the border of Mohorovichich, a Serbian scientist who determined abrupt change seismic wave velocities in this part of the mantle.

hard shell

What is the name of the layer of the Earth that is the hardest? This is the lithosphere, a shell that connects the mantle and the earth's crust, it is located above the asthenosphere, and cleans the surface layer from its hot influence. The main part of the lithosphere is part of the mantle: out of the entire thickness from 79 to 250 km, the earth's crust accounts for 5-70 km, depending on the location. The lithosphere is heterogeneous, it is divided into lithospheric plates, which are in constant slow motion, sometimes diverging, sometimes approaching each other. Such fluctuations of the lithospheric plates are called tectonic movement, it is their fast tremors that cause earthquakes, splits in the earth's crust, and magma splashing onto the surface. The movement of lithospheric plates leads to the formation of troughs or hills, the frozen magma forms mountain ranges. Plates do not have permanent boundaries, they join and separate. Territories of the Earth's surface, above the faults of tectonic plates, are places of increased seismic activity, where earthquakes, volcanic eruptions occur more often than in others, and minerals are formed. At this time, 13 lithospheric plates have been recorded, the largest of them: American, African, Antarctic, Pacific, Indo-Australian and Eurasian.

Earth's crust

Compared to other layers, the earth's crust is the thinnest and most fragile layer of the entire earth's surface. The layer in which organisms live, which is most saturated chemicals and trace elements, is only 5% of the total mass of the planet. The earth's crust on planet Earth has two varieties: continental or mainland and oceanic. The continental crust is harder, consists of three layers: basalt, granite and sedimentary. The ocean floor is made up of basalt (basic) and sedimentary layers.

Basalt rocks- These are igneous fossils, the densest of the layers of the earth's surface.
granite layer- absent under the oceans, on land it can approach a thickness of several tens of kilometers of granite, crystalline and other similar rocks.
Sedimentary layer formed during the destruction of rocks. In some places it contains deposits of minerals of organic origin: coal, table salt, gas, oil, limestone, chalk, potassium salts and others.

Hydrosphere

Characterizing the layers of the Earth's surface, one cannot fail to mention the vital water shell of the planet, or the hydrosphere. The water balance on the planet is maintained by ocean waters (the main water mass), groundwater, glaciers, inland waters of rivers, lakes and other bodies of water. 97% of the entire hydrosphere falls on salt water seas and oceans, and only 3% - fresh drinking water, of which the bulk is in glaciers. Scientists suggest that the amount of water on the surface will increase over time due to deep balls. Hydrospheric masses are in constant circulation, they pass from one state to another and closely interact with the lithosphere and atmosphere. The hydrosphere has a great influence on all earthly processes, the development and life of the biosphere. It was the water shell that became the environment for the origin of life on the planet.

The soil

The thinnest fertile layer of the Earth called soil, or soil, together with the water shell, is of the greatest importance for the existence of plants, animals and humans. This ball arose on the surface as a result of erosion of rocks, under the influence of organic decomposition processes. Processing the remnants of life, millions of microorganisms have created a layer of humus - the most favorable for crops of all kinds of land plants. One of the important indicators of high soil quality is fertility. The most fertile soils are those with an equal content of sand, clay and humus, or loam. Clay, rocky and sandy soils are among the least suitable for agriculture.

Troposphere

The air shell of the Earth rotates together with the planet and is inextricably linked with all processes occurring in the earth's layers. The lower part of the atmosphere through the pores penetrates deep into the body of the earth's crust, the upper part gradually connects with space.

The layers of the Earth's atmosphere are heterogeneous in composition, density and temperature.

At a distance of 10 - 18 km from the earth's crust extends the troposphere. This part of the atmosphere is heated by the earth's crust and water, so it gets colder with height. The temperature drop in the troposphere occurs by about half a degree every 100 meters, and in highest points reaches from -55 to -70 degrees. This part of the airspace occupies the largest share - up to 80%. It is here that the weather is formed, storms, clouds gather, precipitation and winds form.

high layers

Stratosphere - ozone layer planet, which absorbs the ultraviolet radiation of the Sun, preventing it from destroying all life. The air in the stratosphere is rarefied. Ozone maintains a stable temperature in this part of the atmosphere from -50 to 55 ° C. In the stratosphere, an insignificant part of moisture, therefore, clouds and precipitation are not characteristic of it, in contrast to air currents that are significant in speed.
Mesosphere, thermosphere, ionosphere- the air layers of the Earth above the stratosphere, in which a decrease in the density and temperature of the atmosphere is observed. The layer of the ionosphere is the place where the glow of charged gas particles occurs, which is called the aurora.
Exosphere- sphere of dispersion of gas particles, blurred border with space.

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 is the core, followed by the mantle, then - the earth's crust, hydrosphere and atmosphere.

In this article, we will consider the structure of the earth's crust, which is the upper part of the lithosphere. It is an outer hard shell whose thickness is so small (1.5%) that it can be compared with a thin film on a global scale. However, despite this, it is the upper layer of the earth's crust that is of great interest to mankind as a source of minerals.

The crust of the earth is conditionally divided into three layers, each of which is remarkable in its own way.

The top layer is sedimentary. It reaches a thickness of 0 to 20 km. Sedimentary rocks are formed as a result of 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. This is an igneous rock that formed a solid layer as a result of eruptions and subsequent solidification of magma in the earth's thickness at high pressure and temperature.
The lower layer, which is part of the structure of the earth's crust - basalt, also has a magmatic origin. It contains more 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. Particularly striking differences are between the oceanic and continental crusts. Under the oceans, the earth's crust is thinner, and thicker under the continents. It has the greatest thickness in areas of mountain ranges.

The composition includes two layers - sedimentary and basalt. Beneath the basaltic layer is the Moho surface, and behind it is the upper mantle. The ocean floor has the most complex relief forms. Among all their diversity special place occupy huge mid-ocean ridges, in which young basalt oceanic crust is born from the mantle. Magma has access to the surface through a deep fault - a rift that 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 the continents than under the oceans. The continental crust occupies a much smaller area than the oceanic - up to 40% of the earth's surface, but has a much greater thickness. Under 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, the granite layer is on the surface. As an example - composed of granite rocks.

The underwater extreme part of the mainland - the shelf, also has continental structure earth's crust. It includes the islands of Kalimantan, New Zealand, New Guinea, Sulawesi, Greenland, Madagascar, Sakhalin, etc. As well as inland and marginal seas: the 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 seismic wave propagation velocity, 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 a different thickness, which depends on the relief form located on it. In the mountains, for example, it is either completely absent or has a very small thickness, due to the fact that loose particles move down the slopes under the influence of external forces. But on the other hand, it is very powerful in the foothill regions, depressions and hollows. So, in it reaches 22 km.

Such a question as the structure of the Earth is of interest to many scientists, researchers and even believers. With the rapid development of science and technology since the beginning of the 18th century, many worthy workers of science have spent a lot of effort in order to understand our planet. The daredevils descended to the bottom of the ocean, flew to the highest layers of the atmosphere, drilled deep wells to explore the soil.

Today there is a fairly complete picture of what the Earth consists of. True, the structure of the planet and all its regions is still not 100% known, but scientists are gradually expanding the boundaries of knowledge and getting more and more objective information about this.

The shape and size of the planet Earth

The shape and geometric dimensions of the Earth are the basic concepts by which it is described as heavenly body. In the Middle Ages, it was believed that the planet has a flat shape, is located in the center of the universe, and the Sun and other planets revolve around it.

But such bold naturalists as Giordano Bruno, Nicolaus Copernicus, Isaac Newton refuted such judgments and mathematically proved that the Earth has the shape of a ball with flattened poles and revolves around the Sun, and not vice versa.

The structure of the planet is very diverse, despite the fact that its dimensions are quite small by the standards of even solar system- the length of the equatorial radius is 6378 kilometers, the polar radius - 6356 km.

The length of one of the meridians is 40,008 km, and the equator extends for 40,007 km. This also shows that the planet is somewhat "flattened" between the poles, its weight is 5.9742 × 10 24 kg.

Earth shells

The earth consists of many shells that form peculiar layers. Each layer is centrally symmetrical with respect to the base center point. If you visually cut the soil along its entire depth, then layers with different composition, state of aggregation, density, etc. will open.

All shells are divided into two large groups:

The internal structure is described, respectively, by internal shells. They are the earth's crust and mantle.
The outer shells, which include the hydrosphere and atmosphere.

The structure of each shell is the subject of study of individual sciences. Scientists still, in the age of stormy technical progress, not all questions were clarified to the end.

The earth's crust and its types

The Earth's crust is one of the shells of the planet, occupying only about 0.473% of its mass. The depth of the crust is 5 - 12 kilometers.

It is interesting to note that scientists practically did not penetrate deeper, and if we draw an analogy, then the bark is like the skin on an apple in relation to its entire volume. Further and more precise study requires a completely different level of development of technology.

If you look at the planet in a section, then according to the different depths of penetration into its structure, the following types of the earth's crust can be distinguished in order:

oceanic crust- consists mainly of basalts, is located at the bottom of the oceans under huge layers of water.
Continental or mainland crust- covers the land, consists of a very rich chemical composition, including 25% silicon, 50% oxygen, and 18% other main elements of the periodic table. For the purpose of convenient study of this bark, it is also divided into lower and upper. The most ancient belong to the lower part.

The temperature of the crust increases as it deepens.

Mantle

The main volume of our planet is the mantle. It occupies the entire space between the crust and the nucleus discussed above and consists of many layers. The smallest thickness to the mantle is about 5-7 km.

The current level of development of science and technology does not allow direct study of this part of the Earth, therefore, indirect methods are used to obtain information about it.

Very often, the birth of a new earth's crust is accompanied by its contact with the mantle, which is especially active in places under ocean waters.

Today, it is believed that there is an upper and lower mantle that are separated by the Mohorovicic boundary. The percentages of this distribution are calculated quite accurately, but require clarification in the future.

outer core

The core of the planet is also not homogeneous. Huge temperatures and pressure make many chemical processes take place here, the distribution of masses and substances is carried out. The nucleus is divided into inner and outer.

The outer core is about 3,000 kilometers thick. Chemical composition this layer: iron and nickel, which are in the liquid phase. The temperature of the environment here ranges from 4400 to 6100 degrees Celsius as you approach the center.

inner core

The central part of the Earth, the radius of which is approximately 1200 kilometers. The lowest layer, which also consists of iron and nickel, as well as some impurities of light elements. The aggregate state of this nucleus is similar to the amorphous one. The pressure here reaches an incredible 3.8 million bar.

Do you know how many kilometers to the core of the earth? The distance is approximately 6371 km, which is easily calculated if you know the diameter and other parameters of the ball.

Comparison of the thickness of the inner layers of the Earth

The geological structure is sometimes estimated by such a parameter as the thickness of the inner layers. It is believed that the mantle is the most powerful, since it has the largest thickness.

Outer spheres of the globe

Planet Earth differs from any other space object known to scientists in that it also has outer spheres, to which they belong:

hydrosphere;
atmosphere;
biosphere.

The research methods of these spheres are significantly different, because they all differ greatly in their composition and object of study.

Hydrosphere

The hydrosphere is understood as the entire water shell of the Earth, including both the huge oceans, which occupy approximately 74% of the surface, and the seas, rivers, lakes, and even small streams and reservoirs.

The greatest thickness of the hydrosphere is about 11 km and is observed in the area of the Mariana Trench. It is water that is considered the source of life and what distinguishes our ball from all the others in the Universe.

The hydrosphere occupies approximately 1.4 billion km 3 of volume. Life is in full swing here, and the conditions for the functioning of the atmosphere are provided.

Atmosphere

The gaseous shell of our planet, reliably closing its bowels from space objects (meteorites), cosmic cold and other phenomena incompatible with life.

The thickness of the atmosphere is, according to various estimates, about 1000 km. Near the ground surface, the density of the atmosphere is 1.225 kg/m 3 .

78% of the gas envelope consists of nitrogen, 21% of oxygen, the rest is accounted for by elements such as argon, carbon dioxide, helium, methane and others.

Biosphere

Regardless of how scientists study the issue under consideration, the biosphere is the most important part of the structure of the Earth - this is the shell that is inhabited by living beings, including people themselves.

The biosphere is not only inhabited by living beings, but also constantly changing under their influence, in particular, under the influence of man and his activities. A holistic doctrine of this area was developed by the great scientist V. I. Vernadsky. This very definition was introduced by the Austrian geologist Suess.

Conclusion

The surface of the Earth, as well as all the shells of its external and internal structure, are a very interesting subject of study for entire generations of scientists.

Although at first glance it seems that the considered spheres are rather disparate, in fact they are connected by indestructible ties. For example, life and the entire biosphere are simply impossible without the hydrosphere and atmosphere, the same, in turn, originate from the depths.

A distinctive feature of the earth's lithosphere, associated with the phenomenon of the global tectonics of our planet, is the presence of two types of crust: continental, which makes up continental masses, and oceanic. They differ in composition, structure, thickness and nature of the prevailing tectonic processes. An important role in the functioning of a single dynamic system, which is the Earth, belongs to the oceanic crust. To clarify this role, it is first necessary to turn to the consideration of its inherent features.

general characteristics

The oceanic type of crust forms the largest geological structure of the planet - the ocean bed. This crust has a small thickness - from 5 to 10 km (for comparison, the thickness of the continental-type crust is on average 35-45 km and can reach 70 km). It occupies about 70% of the total surface area of the Earth, but in terms of mass it is almost four times inferior to the continental crust. The average density of rocks is close to 2.9 g/cm 3 , that is, higher than that of the continents (2.6-2.7 g/cm 3 ).

Unlike isolated blocks of the continental crust, the oceanic one is a single planetary structure, which, however, is not monolithic. The Earth's lithosphere is divided into a number of mobile plates formed by sections of the crust and the underlying upper mantle. The oceanic type of crust is present on all lithospheric plates; there are plates (for example, the Pacific or Nazca) that do not have continental masses.

Plate tectonics and crustal age

In the oceanic plate, such large structural elements, as stable platforms - thalassocratons - and active mid-ocean ridges and deep-sea trenches. Ridges are areas of spreading, or moving apart of plates and the formation of new crust, and trenches are subduction zones, or subduction of one plate under the edge of another, where the crust is destroyed. Thus, its continuous renewal takes place, as a result of which the age of the most ancient crust of this type does not exceed 160-170 million years, that is, it was formed in the Jurassic period.

On the other hand, it should be borne in mind that the oceanic type appeared on Earth earlier than the continental type (probably at the turn of the Catarcheans - Archeans, about 4 billion years ago), and is characterized by a much more primitive structure and composition.

What and how is the earth's crust under the oceans

Currently, there are usually three main layers of oceanic crust:

Sedimentary. It is formed mainly by carbonate rocks, partly by deep-water clays. Near the slopes of the continents, especially near the deltas major rivers, there are also terrigenous sediments entering the ocean from land. In these areas, the thickness of precipitation can be several kilometers, but on average it is small - about 0.5 km. Precipitation is practically absent near mid-ocean ridges.
Basaltic. These are pillow-type lavas erupted, as a rule, under water. In addition, this layer includes a complex complex of dikes located below - special intrusions - of dolerite (that is, also basalt) composition. Its average thickness is 2-2.5 km.
Gabbro-serpentinite. It is composed of an intrusive analogue of basalt - gabbro, and in the lower part - serpentinites (metamorphosed ultrabasic rocks). The thickness of this layer, according to seismic data, reaches 5 km, and sometimes more. Its sole is separated from the upper mantle underlying the crust by a special interface - the Mohorovichic boundary.

The structure of the oceanic crust indicates that, in fact, this formation can, in a sense, be considered as a differentiated upper layer of the earth's mantle, consisting of its crystallized rocks, which is overlain from above by a thin layer of marine sediments.

"Conveyor" of the ocean floor

It is clear why there are few sedimentary rocks in this crust: they simply do not have time to accumulate in significant quantities. Growing from spreading zones in the areas of mid-ocean ridges due to the influx of hot mantle matter during the convection process, lithospheric plates, as it were, carry the oceanic crust further and further away from the place of formation. They are carried away by the horizontal section of the same slow but powerful convective current. In the subduction zone, the plate (and the crust in its composition) plunges back into the mantle as a cold part of this flow. At the same time, a significant part of the sediments is torn off, crushed, and ultimately goes to increase the crust of the continental type, that is, to reduce the area of the oceans.

The oceanic type of crust is characterized by such an interesting property as strip magnetic anomalies. These alternating areas of direct and reverse magnetization of basalt are parallel to the spreading zone and are located symmetrically on both sides of it. They arise during the crystallization of basaltic lava, when it acquires remanent magnetization in accordance with the geo direction. magnetic field in one era or another. Since it repeatedly experienced inversions, the direction of magnetization periodically changed to the opposite. This phenomenon is used in paleomagnetic geochronological dating, and half a century ago it served as one of the strongest arguments in favor of the correctness of the theory of plate tectonics.

Oceanic type of crust in the cycle of matter and in the heat balance of the Earth

Participating in the processes of lithospheric plate tectonics, the oceanic crust is an important element of long-term geological cycles. Such, for example, is the slow mantle-oceanic water cycle. The mantle contains a lot of water, and a considerable amount of it enters the ocean during the formation of the basalt layer of the young crust. But during its existence, the crust, in turn, is enriched due to the formation of the sedimentary layer with ocean water, a significant proportion of which, partly in bound form, escapes into the mantle during subduction. Similar cycles operate for other substances, for example, for carbon.

Plate tectonics play a key role in the Earth's energy balance, allowing heat to move slowly away from hot interiors and away from the surface. Moreover, it is known that in the entire geological history of the planet gave up to 90% of the heat through the thin crust under the oceans. If this mechanism did not work, the Earth would get rid of excess heat in a different way - perhaps, like Venus, where, as many scientists suggest, there was a global destruction of the crust when the superheated mantle substance broke through to the surface. Thus, the importance of the oceanic crust for the functioning of our planet in a regime suitable for the existence of life is also exceptionally great.