The bowels of the Earth are very mysterious and practically inaccessible. Unfortunately, there is still no such apparatus with which you can penetrate and study the internal structure of the Earth. The researchers found that at the moment the deepest mine in the world has a depth of 4 km, and the deepest well is located on the Kola Peninsula and is 12 km.
However, certain knowledge about the depths of our planet is still established. Scientists have studied its internal structure using the seismic method. The basis of this method is the measurement of vibrations during an earthquake or artificial explosions produced in the bowels of the Earth. Substances with different density and composition passed vibrations through themselves at a certain speed. This made it possible to measure this speed with the help of special instruments and analyze the results obtained.
Scientists' opinion
The researchers found that our planet has several shells: the earth's crust, mantle and core. Scientists believe that about 4.6 billion years ago, the stratification of the bowels of the Earth began and continues to stratify to this day. In their opinion, all heavy substances descend to the center of the Earth, joining the planet's core, while lighter substances rise up and become the earth's crust. When the internal stratification ends, our planet will turn into a cold and dead one.
Earth's crust
It is the thinnest shell of the planet. Its share is 1% of the total mass of the Earth. People live on the surface of the earth's crust and extract from it everything necessary for survival. In the earth's crust, in many places, there are mines and wells. Its composition and structure is studied using samples collected from the surface.
Mantle
Represents the most extensive shell of the earth. Its volume and mass is 70 - 80% of the entire planet. The mantle is solid but less dense than the core. The deeper the mantle is located, the greater its temperature and pressure become. The mantle has a partially melted layer. With the help of this layer, solids move to the core of the earth.
Core
It is the center of the earth. It has a very high temperature (3000 - 4000 o C) and pressure. The core consists of the densest and heaviest substances. It is approximately 30% of the total mass. The solid part of the core floats in its liquid layer, thereby creating the earth's magnetic field. It is the protector of life on the planet, protecting it from cosmic rays.
Non-fiction film about shaping our world
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The internal structure of the Earth established on the basis of geophysical surveys (the nature of the passage of seismic waves). There are three main shells.
1. Earth's crust - the greatest thickness is up to 70 km.
2. Mantle - from the lower boundary of the earth's crust to a depth of 2900 km.
3. Core - extends to the center of the Earth (to a depth of 6,371 km).
The boundary between the earth's crust and mantle is called border Mohorovichic (Moho), between the mantle and the core - border Gutenberg.
Earth's core divided into two layers. External the core (at a depth of 5,120 km to 2,900 km), the substance is liquid, since transverse waves do not penetrate into it, and the velocity of longitudinal waves drops to 8 km / s (see "Earthquakes"). internal the core (from a depth of 6,371 km to 5,120 km), the substance here is in a solid state (the velocity of longitudinal waves increases to 11 km/s or more). The composition of the core is dominated by an iron-nickel melt with an admixture of silicon and sulfur. The density of the substance in the core reaches 13 g/cc.
Mantle divided into two parts: upper and lower.
Upper mantle consists of three layers, sinks to a depth of 800 - 900 km. top th the layer, up to 50 km thick, consists of a hard and brittle crystalline substance (the velocity of longitudinal waves is up to 8.5 km/s and more). Together with the earth's crust, it forms lithosphere- stone shell of the Earth.
middle layer - asthenosphere(flexible shell) is characterized by an amorphous vitreous state of matter, and partly (by 10%) has a molten viscoplastic state (this is evidenced by a sharp drop in the velocity of seismic waves). The thickness of the middle layer is about 100 km. The asthenosphere lies at different depths. Under the mid-ocean ridges, where the thickness of the lithosphere is minimal, the asthenosphere lies at a depth of several kilometers. On the outskirts of the oceans, as the thickness of the lithosphere grows, the asthenosphere sinks to 60–80 km. Under the continents, it lies at depths of about 200 km, and under the continental rifts, it again rises to a depth of 10–25 km. Lower layer of upper mantle (Golicin layer) are sometimes distinguished as a transitional layer or as an independent part - the middle mantle. It descends to a depth of 800 - 900 km, the substance here is crystalline solid (the speed of longitudinal waves is up to 9 km / s).
Lower mantle extends up to 2,900 km, is composed of a solid crystalline substance (the velocity of longitudinal waves increases to 13.5 km/s). The composition of the mantle is dominated by olivine and pyroxene, its density in the lower part reaches 5.8 g/cm3.
Earth's crust It is subdivided into two main types (continental and oceanic) and two transitional (subcontinental and suboceanic). The types of bark differ in structure and thickness.
Continental the crust, distributed within the continents and the shelf zone, has a thickness of 30 - 40 km in the platform areas and up to 70 km in the highlands. The bottom layer is basaltic (mafic- enriched with magnesium and iron), consists of heavy rocks, its thickness is from 15 to 40 km. Above lies composed of lighter rocks granite-gneiss layer ( sialic- enriched with silicon and aluminum), with a thickness of 10 to 30 km. These layers may overlap on top. sedimentary layer, thickness from 0 to 15 km. The boundary between the basalt and granite-gneiss layers identified by seismic data ( border Conrad) is not always clear.
Oceanic the crust, up to 6 - 8 km thick, also has a three-layer structure. The bottom layer is heavy basaltic, up to 4-6 km thick. The middle layer, about 1 km thick, is composed of interbedded layers dense sedimentary breeds and basalt lava. The top layer is made up of loose sedimentary rocks up to 0.7 km thick.
Subcontinental the crust, which has a structure close to the continental crust, is present on the periphery of marginal and inland seas (in the zones of the continental slope and foot) and under island arcs, and is characterized by a sharply reduced thickness (up to 0 m) of the sedimentary layer. The reason for this decrease in the thickness of the sedimentary layer is the large slope of the surface, which contributes to the sliding of the accumulated sediments. The thickness of this type of crust is up to 25 km, including the basalt layer up to 15 km, granite-gneiss up to 10 km; Konrad's border is poorly expressed.
suboceanic the crust, close in structure to the oceanic, is developed within the deep-water parts of the inland and marginal seas and in deep-sea oceanic trenches. It is distinguished by a sharp increase in the thickness of the sedimentary layer and the absence of a granite-gneiss layer. The extremely high thickness of the sedimentary layer is due to the very low hypsometric level of the surface - under the influence of gravity, giant strata of sedimentary rocks accumulate here. The total thickness of the suboceanic crust also reaches 25 km, including the basalt layer up to 10 km and the sedimentary layer up to 15 km. In this case, the thickness of the layer of dense sedimentary and basalt rocks can be 5 km.
Density and pressure Lands also change with depth. The average density of the Earth is 5.52 g/cu. see. The density of the rocks of the earth's crust varies from 2.4 to 3.0 g / cu. cm (on average - 2.8 g / cc). The density of the upper mantle below the Moho boundary approaches 3.4 g/cu. cm, at a depth of 2,900 km it reaches 5.8 g/cu. cm, and in the inner core up to 13 g / cu. see According to the given data pressure at a depth of 40 km it is 10 3 MPa, at the Gutenberg border 137 * 10 3 MPa, in the center of the Earth 361 * 10 3 MPa. The acceleration of gravity on the surface of the planet is 982 cm/s2, reaches a maximum of 1037 cm/s2 at a depth of 2900 km and is minimal (zero) in the center of the Earth.
A magnetic field
Earth is presumably due to the convective movements of the liquid matter of the outer core that occur during the daily rotation of the planet. The study of magnetic anomalies (variations in the magnetic field strength) is widely used in the search for iron ore deposits.
Thermal properties
The Earths are formed by solar radiation and heat flux propagating from the bowels of the planet. The influence of solar heat does not extend deeper than 30 m. Within these limits, at a certain depth, there is a belt of constant temperature equal to the average annual air temperature of the area. Deeper than this belt, the temperature gradually increases under the influence of the heat flow of the Earth itself. The intensity of the heat flow depends on the structure of the earth's crust and on the degree of activity of endogenous processes. The average planetary value of the heat flow is 1.5 μkal/cm2 * s, on shields about 0.6 - 1.0 μkal/cm 2 * s, in the mountains up to 4.0 μkal/cm 2 * s, and in the mid-ocean rifts up to 8.0 μcal/cm 2 * s. Among the sources that form the internal heat of the Earth, the following are assumed: the decay energy of radioactive elements, chemical transformations of matter, gravitational redistribution of matter in the mantle and core. Geothermal gradient - the amount of temperature increase per unit depth. Geothermal step - the value of the depth beyond which the temperature rises by 1 ° C. These indicators vary greatly in different places on the planet. The maximum values of the gradient are observed in the mobile zones of the lithosphere, while the minimum values are observed in the ancient continental massifs. On average, the geothermal gradient of the upper part of the earth's crust is about 30°C per 1 km, and the geothermal step is about 33 m. It is assumed that with increasing depth, the geothermal gradient decreases, and the geothermal step increases. Based on the hypothesis about the predominance of iron in the composition of the core, its melting temperatures were calculated at different depths (taking into account the regular increase in pressure): 3700° C at the boundary of the mantle and the core, 4300° C at the boundary of the inner and outer core.
Chemical composition
Earth considered to be similar to the average chemical composition of the studied meteorites. Meteorites are composed of:
– iron(nickel iron with an admixture of cobalt and phosphorus) make up 5.6% of those found;
– iron-stone (siderolites- a mixture of iron and silicates) are the least common - they make up only 1.3% of those known;
– stone (aerolites- enriched with iron and magnesium silicates with an admixture of nickel iron) are the most common - 92.7%.
Thus, the average chemical composition of the Earth is dominated by four elements. Oxygen and iron contain approximately 30% each, magnesium and silicon - 15% each. Sulfur accounts for about 2 - 4%; nickel, calcium and aluminum - 2% each.
The composition of the deep shells of the Earth continues to be one of the most intriguing issues of modern science, and yet, at the beginning of the 20th century, seismologists Beno Gutenberg and G. Jefferson developed a model of the internal structure of our planet, according to which the Earth consists of the following layers:
Core;
- mantle;
- Earth's crust.
A modern look at the internal structure of the planet
In the middle of the last century, on the basis of the latest seismological data at that time, scientists came to the conclusion that deep shells have a more complex structure. At the same time, seismologists found out that the earth's core is divided into inner and outer, and the mantle consists of two layers: upper and lower.
The outer shell of the earth
The earth's crust is not only the uppermost, thinnest, but also the most well-studied of all layers. Its thickness (thickness) reaches its maximum under the mountains (about 70 km) and the minimum - under the waters of the oceans (5-10 km), the average The thickness of the earth's crust under the plains varies from 35 to 40 km. The transition from the earth's crust to the mantle is called the Mohorovich or Moho boundary.
It is also worth noting that the earth's crust, together with the upper part of the mantle, form the earth's stone shell - the lithosphere, the thickness of which varies from 50 to 200 km.
Following the lithosphere is the asthenosphere - a softened liquid layer with increased viscosity. In addition to everything, it is this component of the earth's surface that is called the source of volcanism, since it contains pockets of magma that pours into the earth's crust and onto the surface.
In science, it is customary to distinguish several types of the earth's crust
Continental or continental spreads within the boundaries of the continents and shelves, consists of basalt, granite-geiss and sedimentary layers. The transition from the granite-geiss layer to the basalt layer is called the Konrad boundary.
The subcontinental crust is a transitional type, located on the periphery of the internal and also under the island arcs.
The suboceanic crust is similar in structure to the oceanic, and is especially well developed in the deep parts of the seas and at great depths of oceanic trenches.
Middle geosphere
Deep layer of the planet Earth
It is the least studied. There is very little reliable information about it, with full confidence we can only say that its diameter is about 7 thousand kilometers. It is believed that the composition of the earth's core includes an alloy of nickel and iron. It is also worth noting that the outer core of the planet has a large thickness and is in liquid, while the inner one is smaller in thickness and harder in consistency. The so-called Gutenberg boundary separates the earth's core from the mantle.
There is one interesting feature in the structure of our planet: we meet the most complex and diverse structure in the surface layers of the earth's crust; the deeper we descend into the bowels of the Earth, the simpler its structure becomes. One can, of course, express the suspicion that it only seems so to us, because the deeper we go, the more approximate and indefinite our information becomes. Apparently, this is still not the case, and the simplification of the structure with depth is an objective fact, independent of the degree of our knowledge.
We will begin our consideration from above, with the most complex upper layers of the earth's crust. These layers, as we know, are studied mainly with the help of direct geological methods.
Approximately two-thirds of the earth's surface is covered by oceans; one third is on the continents. The structure of the earth's crust under the oceans and continents is different. Therefore, we will first consider the features of the continents, and then turn to the oceans.
Rocks of different ages are found on the surface of the Earth on the continents in different places. Some areas of the continents are composed on the surface of the most ancient rocks - Archeozoic or, as they are more commonly called, Archean, and Proterozoic. Together they are called pre-Paleozoic or Precambrian rocks. Their peculiarity is that most of them are highly metamorphosed: clays have turned into metamorphic schists, sandstones - into crystalline quartzites, limestones - into marbles. An important role among these rocks is played by gneisses, i.e., shale granites, as well as ordinary granites. The areas where these most ancient rocks come to the surface are called crystalline massifs or shields. An example is the Baltic Shield, embracing Karelia, the Kola Peninsula, all of Finland and Sweden. Another shield covers most of Canada. In the same way, most of Africa is a shield, as is much of Brazil, almost all of India, and all of Western Australia. All rocks of the ancient shields are not only metamorphosed and recrystallized, but also very strongly folded into small complex folds.
Other areas on the continents are occupied by mostly younger rocks - Paleozoic, Mesozoic and Cenozoic in age. These are mainly sedimentary rocks, although among them there are also rocks of igneous origin, poured out to the surface in the form of volcanic lava or intruded and solidified at a certain depth. There are two categories of areas: on the surface of some layers of sedimentary rocks lie very quietly, almost horizontally, and in them only rare and small folds are observed. In such places, igneous rocks, especially intrusive ones, play a relatively small role. Such areas are called platforms. In other places, sedimentary rocks are strongly crumpled into folds, riddled with deep cracks. Among them, intruded or erupted igneous rocks are often found. These places usually coincide with mountains. They're called folded zones, or geosynclines.
The differences between individual platforms and folded zones are in the age of the rocks lying calm or crumpled into folds. Among the platforms, ancient platforms stand out, on which all Paleozoic, Mesozoic and Cenozoic rocks lie almost horizontally on top of a highly metamorphosed and folded "crystalline base" composed of Precambrian rocks. An example of an ancient platform is the Russian platform, within which all layers, starting from the Cambrian, are generally very calm.
There are platforms on which not only the Precambrian, but also the Cambrian, Ordovician and Silurian layers are crumpled into folds, and younger rocks, starting from the Devonian, lie quietly on top of these folds on their eroded surface (as they say, “unconformably”). In other places, the "folded foundation" is formed, except for the Precambrian, by all Paleozoic rocks, and only Mesozoic and Cenozoic rocks lie almost horizontally. The platforms of the last two categories are called young. Some of them, as we can see, were formed after the Silurian period (before that there were folded zones), and others - after the end of the Paleozoic era. Thus, it turns out that on the continents there are platforms of different ages, formed earlier or later. Before the platform was formed (in some cases - until the end of the Proterozoic era, in others - until the end of the Silurian period, in others - until the end of the Paleozoic era), a strong collapse of the layers into folds occurred in the earth's crust, igneous molten rocks were introduced into it, sediments were subjected to metamorphization, recrystallization. And only after that came calm, and the subsequent layers of sedimentary rocks, having accumulated horizontally at the bottom of the sea basins, generally retained their calm occurrence in the future.
Finally, in other places all the layers are crumpled into folds and penetrated by igneous rocks - up to the Neogene.
Saying that the platforms could have formed at different times, we also point to different ages of the fold zones. Indeed, on ancient crystalline shields, the collapse of layers into folds, the intrusion of igneous rocks, and recrystallization ended before the beginning of the Paleozoic. Therefore, the shields are zones of Precambrian folding. Where the layers were not disturbed since the Devonian period, the folding of the layers into folds continued until the end of the Silurian, or, as they say, until the end of the early Paleozoic. Consequently, this group of young platforms is at the same time an area of Early Paleozoic folding. The folding of this time is called the Caledonian folding. Where the platform has formed since the beginning of the Mesozoic, we have zones of Late Paleozoic or Hercynian folding. Finally, the areas where all the layers, up to and including the Neogene, are strongly folded into folds, are zones of the youngest, Alpine folding, which left only the layers formed in the Quaternary not folded.
Maps depicting the location of platforms and folded zones of different ages and some other features of the structure of the earth's crust are called tectonic (tectonics is a branch of geology that studies the movements and deformations of the earth's crust). These maps serve as a supplement to the geological maps. The latter are primary geological documents that most objectively illuminate the structure of the earth's crust. Tectonic maps already contain some conclusions: about the age of platforms and folded zones, about the nature and time of formation of folds, about the depth of the folded basement under the calm layers of platforms, etc. The principles for compiling tectonic maps were developed in the 30s by Soviet geologists, mainly Academician A. D. Arkhangelsky. After the Great Patriotic War, tectonic maps of the Soviet Union were compiled under the guidance of Academician N. S. Shatsky. These maps are taken as an example for compiling international tectonic maps of Europe, other continents and the entire Earth as a whole.
The thickness of the sedimentary suites in those places where they lie quietly (ie, on platforms), and where they are strongly folded, is different. For example, Jurassic deposits on the Russian platform are nowhere thicker or "thick" than 200 meters, while their thickness in the Caucasus, where they are strongly crumpled into folds, reaches 8 kilometers in places. Deposits of the Carboniferous period on the same Russian platform have a thickness of no more than a few hundred meters, and in the Urals, where the same deposits are strongly crumpled into folds, their thickness in places grows up to 5-6 kilometers. This indicates that when deposits of the same age accumulated on the platform and in the regions of the folded zone, the earth's crust sagged very little on the platform and sagged much more strongly in the folded zone. Therefore, there was no place on the platform for the accumulation of such thick formations as could be accumulated in deep troughs of the earth's crust in folded zones.
Within platforms and folded zones, the thickness of the accumulated sedimentary rocks does not remain the same everywhere. It varies from site to site. But on platforms, these changes are smooth, gradual, and small. They indicate that during the accumulation of sediments, the platform sagged a little more in some places, a little less in some places, and wide gentle troughs (syneclises) separated by equally gentle uplifts (anteclises) formed in its basement. In contrast, in folded zones, the thickness of sedimentary rocks of the same age varies from site to site very sharply, over short distances, either increasing to several kilometers, or decreasing to several hundred or tens of meters, or even disappearing. This indicates that during the accumulation of sediments in the folded zone, some areas sagged strongly and deeply, others sagged little or even did not sag at all, and still others rose strongly, as evidenced by the coarse clastic deposits found next to them, which formed as a result of erosion of uplifted areas. Moreover, it is significant that all these areas, which were intensively sagging and intensively rising, were narrow and located in the form of strips closely next to each other, which led to very large contrasts in the movements of the earth's crust at close distances.
Bearing in mind all the above features of the movements of the earth's crust: very contrasting and strong subsidence and uplift, strong folding, vigorous magmatic activity, that is, all the features of the historical development of folded zones, these zones are usually called geosynclines, leaving the name "folded zone" only to characterize their modern structure, which was the result of all previous violent events in the earth's crust. We will continue to use the term "geosyncline" when we are talking not about the modern structure of the folded zone, but about the features of its previous development.
Platforms and fold zones differ significantly from each other in terms of the minerals that are located on their territory. There are few igneous rocks on the platforms that have intruded into the calm layers of sedimentary rocks. Therefore, minerals of igneous origin are only rarely found on the platforms. On the other hand, coal, oil, natural gases, as well as rock salt, gypsum, building materials, etc. are widespread in the calmly occurring sedimentary layers of the platform. In folded zones, the advantage is on the side of igneous minerals. These are various metals that were formed in different stages of solidification of magma chambers.
However, when we talk about the predominant confinement of sedimentary minerals to platforms, we must not forget that we are talking about layers that lie quietly, and not about those highly metamorphosed and crumpled crystalline rocks of the ancient "folded foundation" of the platforms, which is best seen on " shields." These basement rocks reflect the era when the platform did not yet exist here, but the geosyncline existed. Therefore, the minerals found in the folded basement are geosynclinal in their type, i.e., predominantly magmatic. Consequently, on the platforms there are, as it were, two floors of minerals: the lower floor is ancient, belonging to the foundation, geosynclinal; it is characterized by metallic ores; the upper floor is actually platform, belonging to the cover of sedimentary rocks lying quietly on the foundation; these are sedimentary, i.e., predominantly non-metallic minerals.
A few words must be said about the folds.
Strong folding in the folded zones and weak folding on the platforms were mentioned above. It should be noted that we should be talking not only about the different intensity of folding, but also about the fact that folds of different types are characteristic of folded zones and platforms. In folded zones, the folds belong to a type called linear, or complete. These are long narrow folds that, like waves, follow each other, adjoining each other in a circle and covering completely large areas. The folds have different shapes: some of them are rounded, others are sharp, some are straight, vertical, others are oblique. But all of them are similar to each other, and most importantly, they cover the folded zone in a continuous series.
On the platforms - folds of a different type. These are separate isolated uplifts of layers. Some of them are table-shaped or, as they say, chest-shaped or box-shaped, many have the appearance of gentle domes or ramparts. The folds here are not elongated, as in the folded zone, into stripes, but are arranged in more complex shapes or scattered rather randomly. This folding is “discontinuous”, or dome-shaped.
Folds of discontinuous type - chest rises, domes and ramparts - are found not only on the platform, but also on the edge of the folded zones. So there is a somewhat gradual transition from platform folds to those typical of fold zones.
On the platforms and on the edge of the folded zones, there is another peculiar type of folds - the so-called "diapiric domes". They are formed where thick layers of rock salt, gypsum or soft clay lie at some depth. The specific gravity of rock salt is less than the specific gravity of other sedimentary rocks (rock salt 2.1, sands and clays 2.3). Thus, lighter salt is under heavier clays, sands, limestones. Due to the ability of rocks to slowly plastically deform under the action of small mechanical forces (the creep phenomenon mentioned above), salt tends to float to the surface, piercing and pushing the overlying heavier layers. This is helped by the fact that salt under pressure is extremely fluid and at the same time strong: it flows easily, but does not break. The salt floats up in columns. At the same time, it lifts the overlying layers, bends them dome-shaped and, sticking out upwards, causes them to split into separate pieces. Therefore, on the surface, such diapiric domes often look like a “broken plate”. In a similar way, diapiric folds are formed, in the “piercing cores” of which we find not salt, but soft clays. But clay diapiric folds usually do not look like round columns, like salt diapiric domes, but long elongated ridges.
The domes (including diapirs) and swells found on the platforms play an important role in the formation of oil and gas accumulations. In folded zones, mineral deposits are mostly associated with cracks.
Let us now turn to the deeper layers of the earth's crust. We will have to leave the area that we know from direct observation from the surface and go to a place where information can be obtained only by geophysical research.
As already mentioned, within the visible part of the earth's crust, metamorphic rocks of the Archean age lie the deepest. Among them, gneisses and granites are the most common. Observations show that the deeper the cut of the earth's crust we observe on the surface, the more granites we encounter. Therefore, one can think that even deeper - a few kilometers below the surface of crystalline shields or about 10 km below the surface of platforms and folded zones - we would have encountered a continuous layer of granite under the continents. The upper surface of this granite layer is very uneven: it either rises to the day surface, or falls 5-10 km below it.
We can only guess the depth of the lower surface of this layer on the basis of some data on the propagation velocity of elastic seismic vibrations in the earth's crust. The speed of movement of the so-called longitudinal seismic waves in granites is on average about 5 km/sec.
In longitudinal waves, particle oscillations occur in the direction of wave movement: forward and backward. The so-called transverse waves are characterized by fluctuations across the direction of wave movement: up - down or right - left.
But in a number of places it was found that at a depth of 10, 15, 20 km, the propagation velocity of the same longitudinal seismic waves becomes greater and reaches 6 or 6.5 km/sec. Since this speed is too high for granite and close to the speed of propagation of elastic vibrations, which characterizes such a rock as basalt in laboratory tests, the layer of the earth's crust with a higher speed of propagation of seismic waves was called basalt. It starts at different depths in different areas - usually at a depth of 15 or 20 km, but in some areas it comes much closer to the surface, and a well 6-8 km deep could reach it.
However, so far not a single well has penetrated into the basalt layer and no one has seen the rocks that lie in this layer. Are these really basalts? There are doubts about this. Some think that instead of basalts we will find there the same gneisses, granites and metamorphic rocks that are characteristic of the overlying granite layer, but which at a greater depth are strongly compacted by the pressure of the overlying rocks, and therefore the speed of propagation of seismic waves in them is greater. The solution of this issue is of great interest and not only theoretical: somewhere in the lower part of the granite and upper part of the basalt layers, the processes of formation of granites and the birth of those hot solutions and gases, from which various ore minerals crystallize above, when they move to the surface, take place. To know what the basalt layer really is means to better understand the processes of formation of metal ores in the earth's crust and the laws of their distribution. That is why the project of drilling ultra-deep wells to study the structure of the entire granite and at least the upper part of the basalt layer deserves every support.
The basalt layer is the lower layer of the continental crust. At the bottom, it is separated from the deeper parts of the Earth by a very sharp division called section of Mohorovicic(named after the Yugoslav seismologist who discovered the existence of this section at the beginning of our century). On this section of the Mohorovichic (or, for short, Moho), the velocity of compressional seismic waves changes abruptly: above the section it is usually 6.5 km/sec, and immediately below it increases to 8 km/sec. This section is considered the lower boundary of the earth's crust. Its distance from the surface, therefore, is the thickness of the earth's crust. Observations show that the thickness of the crust under the continents is far from uniform. On average, it is 35 km, but under the mountains it increases to 50, 60 and even 70 km. At the same time, the higher the mountains, the thicker the earth's crust: a large protrusion of the earth's surface upward corresponds to a much larger protrusion downward; thus, the mountains have, as it were, "roots" that go deep into the deeper layers of the Earth. Under the plains, on the contrary, the thickness of the crust is less than the average. The relative role of the granite and basalt layers in the section of the earth's crust also varies from region to region. It is especially interesting that under some mountains the "roots" are formed mainly due to an increase in the thickness of the granite layer, and under others - due to an increase in the thickness of the basalt layer. The first case is observed, for example, in the Caucasus, the second - in the Tien Shan. Further we will see that the origin of these mountains is different; this was also reflected in the different structure of the earth's crust under them.
One property of the earth's crust, closely related to the "roots" of mountains, should be especially noted: this is the so-called isostasy, or balance. Observations on the magnitude of gravity on the surface of the Earth show, as we have seen, the presence of certain fluctuations in this magnitude from place to place, i.e., the existence of certain anomalies in gravity. However, these anomalies (after subtracting the influence of the geographical and altitude position of the observation point) are extremely small; they can cause a change in a person's weight by just a few grams. Such deviations from the normal force of gravity are extremely small compared with those that might be expected, bearing in mind the topography of the earth's surface. Indeed, if mountain ranges were a heap of superfluous masses on the surface of the Earth, then these masses should create a stronger attraction. On the contrary, over the seas, where instead of dense rocks the attracting body is less dense water, the force of gravity would have to weaken.
In fact, there are no such differences. The force of gravity does not become greater in the mountains and less on the sea, it is approximately the same everywhere, and the observed deviations from the average value are much less than the influence that the unevenness of the relief or the replacement of rocks by sea water should have. From this, only one conclusion is possible: the additional masses on the surface, forming the ridges, must correspond to the lack of masses at depth; only in this case the total mass and the total attraction of the rocks under the mountains will not exceed the normal value. On the contrary, the lack of masses on the surface in the seas must correspond to some heavier masses at depth. The above changes in the thickness of the crust under the mountains and plains just meet these conditions. The average density of the rocks of the earth's crust is 2.7. Beneath the Earth's crust, just below the Moho section, matter has a higher density, reaching 3.3. Therefore, where the earth's crust is thinner (under the lowlands), a heavy subcrustal "substrate" approaches the surface closer to the surface, and its attracting influence compensates for the "lack" of masses on the surface. On the contrary, in mountains, an increase in the thickness of the light crust reduces the total attractive force, thereby compensating for the increase in attraction caused by additional surface masses. Conditions are created under which the earth's crust, as it were, floats on a heavy litter like ice floes on water: a thicker ice floe sinks deeper into the water, but also protrudes above it; a less thick ice floe sinks less, but also protrudes less.
This behavior of ice floes corresponds to the well-known law of Archimedes, which determines the equilibrium of floating bodies. The earth's crust also obeys the same law: where it is thicker, it goes deeper into the substrate in the form of "roots", but also protrudes higher on the surface; where the crust is thinner, the heavy substrate comes closer to the surface, and the surface of the crust is relatively lowered and forms either a plain or a seabed. Thus, the state of the crust corresponds to the equilibrium of floating bodies, which is why this state is called isostasy.
It should be noted that the conclusion about the equilibrium of the earth's crust with respect to its gravity and substrate is valid if we take into account the average thickness of the crust and the average height of its surface for large areas - several hundred kilometers in diameter. If, however, we investigate the behavior of much smaller sections of the earth's crust, we will find deviations from equilibrium, discrepancies between the thickness of the crust and the height of its surface, which are expressed in the form of the corresponding anomalies of gravity. Imagine a big ice floe. Its balance, like a body floating on water, will depend on its average thickness. But in different places, an ice floe can have very different thicknesses, it can be corroded by water and its lower surface can have many small pockets and bulges. Within each pocket or each bulge, the position of the ice in relation to the water can be very different from the equilibrium: if we knock out the corresponding piece of ice from the ice floe, then it will either sink deeper than the surrounding ice floe or float above it. But in general, the ice floe is in equilibrium, and this balance depends on the average thickness of the ice floe.
Under the earth's crust, we enter the next, very powerful shell of the Earth, called Earth's mantle. It extends inland for 2900 km. At this depth, there is the next sharp section in the Earth's substance, separating the mantle from Earth's core. Inside the mantle, as it deepens, the propagation velocity of seismic waves increases and at the bottom of the mantle reaches 13.6 km/sec for longitudinal waves. But the increase in this speed is uneven: it is much faster in the upper part, down to a depth of about 1000 km, and extremely slow and gradual at greater depths. In this regard, the mantle can be divided into two parts - the upper and lower mantle. More and more data are now accumulating, indicating that such a division of the mantle into upper and lower is of great fundamental importance, since the development of the earth's crust, apparently, is directly related to the processes occurring in the upper mantle. The nature of these processes will be discussed later. The lower mantle apparently has little direct effect on the earth's crust.
The material that makes up the mantle is solid. This confirms the nature of the passage of seismic waves through the mantle. Regarding the chemical composition of the mantle, there are differences of opinion. Some people think that the upper mantle is made up of a rock called peridotite. This rock contains very little silica; its main constituent is the mineral olivine, a silicate rich in iron and magnesium. Others suggest that the upper mantle is much richer in silica and similar in composition to basalt, but that the minerals that make up this deep basalt are denser than those of surface basalt. For example, in deep basalt, garnets play a significant role - minerals with a very dense "packing" of atoms in the crystal lattice. Such deep basalt, obtained as if by pressing ordinary surface basalt, is called eclogite.
There are arguments in favor of both points of view. In particular, the second point of view is confirmed by the huge number of basalts that are very uniform in their chemical composition and are erupting now during volcanic eruptions. Their source can only be in the upper mantle.
If this point of view turns out to be correct, then we should consider that on the Moho section there is not a change in the chemical composition of matter, but a transition of the same substance in chemical composition to a new, denser, “deep” state, to another, as they say , "phase". Such transitions are called "phase transitions". This transition depends on the change in pressure with depth. When a certain pressure is reached, ordinary basalt turns into eclogite and less dense feldspars are replaced by denser garnets. Such transitions are also affected by temperature: increasing it at the same pressure makes it difficult for basalt to pass into eclogite. Therefore, the lower boundary of the earth's crust becomes mobile, dependent on temperature changes. If the temperature rises, then some of the eclogite passes back into ordinary basalt, the crustal boundary drops, the crust becomes thicker; while the volume of the substance increases by 15%. If the temperature decreases, then at the same pressure, part of the basalt in the lower layers of the crust passes into eclogite, the boundary of the crust rises, the crust becomes thinner, and the volume of the material that has passed into a new phase decreases by 15%. These processes can explain the fluctuations of the earth's crust up and down: as a result of its thickening, the crust will rise, rise, while reducing the thickness, it will sink, sag.
However, the question of the chemical composition and physical state of the upper mantle will be finally resolved, apparently, only as a result of superdeep drilling, when the boreholes, having passed through the entire crust, reach the substance of the upper mantle.
An important feature of the structure of the upper mantle is the "softening belt", located at a depth of between 100 and 200 km. In this belt, which is also called asthenosphere, the velocity of propagation of elastic vibrations is slightly less than above and below it, and this indicates a somewhat less solid state of the substance. In the future, we will see that the "softening belt" plays a very important role in the life of the Earth.
In the lower mantle, matter becomes much heavier. Its density rises, apparently, to 5.6. It is assumed that it consists of silicates, very rich in iron and magnesium and poor in silica. It is possible that iron sulfide is widespread in the lower mantle.
At a depth of 2900 km, as indicated, the mantle ends and begins core of the earth. The most important feature of the core is that it transmits longitudinal seismic vibrations, but turns out to be impassable for transverse vibrations. Since transverse elastic vibrations pass through solids, but quickly die out in liquids, while longitudinal vibrations pass through both solids and liquids, it should be concluded that the Earth's core is in a liquid state. Of course, it is nowhere near as liquid as water; it is a very thick substance, close to a solid state, but still much more fluid than the substance of the mantle.
Inside the nucleus is allocated more inner core, or nucleolus. Its upper boundary is located at a depth of 5000 km, i.e., at a distance of 1370 km from the center of the Earth. Here, a not very sharp section is observed, at which the speed of seismic oscillations again rapidly drops, and then, towards the center of the Earth, begins to increase again. There is an assumption that the inner core is solid and that only the outer core is in a liquid state. However, since the latter prevents the passage of transverse vibrations, the question of the state of the inner core cannot yet be finally resolved.
There has been a lot of controversy about the chemical composition of the nucleus. They are still going on. Many still adhere to the old point of view, believing that the core of the Earth consists of iron with a small admixture of nickel. The prototype of this composition are iron meteorites. Meteorites are generally considered either as fragments of pre-existing and decayed planets, or as remaining “unused” small cosmic bodies, from which planets were “collected” several billion years ago. In both cases, the meteorites should seem to represent the chemical composition of one or another shell of the planet. Stony meteorites probably correspond to the chemical composition of the mantle, at least the lower one. Heavier, iron meteorites correspond, as many people think, to deeper bowels - the core of the planet.
However, other researchers find arguments against the concept of the iron composition of the core and believe that the core should consist of silicates, in general the same as those that compose the mantle, but that these silicates are in a "metallic" state as a result of the enormous pressure in the core at the upper boundary of the core. it is equal to 1.3 million atmospheres, and in the center of the Earth 3 million atm.). This means that under the influence of pressure, the silicate atoms were partially destroyed and individual electrons broke off from them, which were able to move independently. This, as in metals, is responsible for certain metallic properties of the core: high density; reaching in the center of the Earth 12.6 electrical conductivity, thermal conductivity.
Finally, there is an intermediate point of view, which is now beginning to prevail, namely, that the inner core is iron, and the outer one is composed of silicates in a metallic state.
According to modern theory, the Earth's magnetic field is associated with the outer core. Charged electrons move in the outer core at a depth between 2900 and 5000 km, describing circles or loops, and it is their movement that leads to the creation of a magnetic field. It is well known that Soviet rockets launched to the Moon did not detect a magnetic field in our natural satellite. This is consistent with the assumption that the Moon does not have a core similar to the Earth's.
Consider now the structure of the earth's interior under the oceans.
Although recently, since the International Geophysical Year, the ocean floor and the depths of the Earth under the oceans have been studied extremely intensively (the numerous voyages of the Soviet research ship Vityaz are well known), we still know the geological structure of the ocean territories much worse than the structure of the continents. It has been established, however, that at the bottom of the oceans there are no shields, platforms, or folded zones similar to those known on the continents. According to the bottom relief in the oceans, plains (or basins), oceanic ridges and deep-water ditches can be distinguished as the largest elements.
Plains occupy wide spaces at the bottom of all oceans. They are located almost always at the same depth (5-5.5 km).
Oceanic ridges are broad, bumpy swells. The Atlantic underwater ridge is especially characteristic. It stretches from north to south, exactly along the midline of the ocean, curving parallel to the shores of the fringing continents. Its crest is usually located at a depth of about 2 km, but individual peaks rise above sea level in the form of volcanic islands (Azores, St. Paul, Ascension, Tristan da Cunha). Right on the continuation of the underwater ridge is Iceland with its volcanoes.
The underwater ridge in the Indian Ocean also stretches in the meridional direction along the midline of the ocean. At the Chagos Islands, this range forks. One of its branches goes straight to the north, where huge frozen flows of volcanic basalts (Dekkan plateau) are known on its continuation in the Bombay region. The other branch heads northwest and gets lost before entering the Red Sea.
The Atlantic and Indian submarine ridges are interconnected. In turn, the Indian Ridge connects with the East Pacific Submarine Ridge. The latter stretches in a latitudinal direction to the south of New Zealand, but on the meridian of 120° west longitude it turns sharply to the north. It approaches the coast of Mexico and here is lost in shallow water before entering the Gulf of California.
A number of shorter submarine ridges occupies the central part of the Pacific Ocean. Almost all of them are elongated from the southeast to the northwest. On top of one such underwater ridge are the Hawaiian Islands, on the tops of others - numerous archipelagos of smaller islands.
An example of an underwater oceanic ridge is also the Lomonosov Ridge discovered by Soviet scientists in the Arctic Ocean.
Almost all major underwater ridges are interconnected and form, as it were, a single system. It is still unclear the relationship of the Lomonosov Ridge with other ridges.
Deep-sea oceanic ravines are narrow (100-300 km) and long (several thousand kilometers) trenches in the ocean floor, within which maximum depths are observed. It was in one of these potholes, Mariana, that the Soviet expeditionary vessel Vityaz found the greatest depth of the World Ocean, reaching 11,034 m. Deep-water potholes are located along the periphery of the oceans. Most often they border island arcs. The latter in a number of places are a characteristic feature of the structure of the transition zones between the continents and the ocean. Island arcs are especially widely developed along the western periphery of the Pacific Ocean - between the ocean, on the one hand, and Asia and Australia, on the other. From north to south, the arcs of the islands of the Aleutian, Kuril, Japanese, Bonino-Marian, Philippine, Tonga, Kermadec and New Zealand descend like garlands. Almost all of these arcs are bordered by deep-sea ruts on the outer (convex) side. The same rut borders the Antilles island arc in Central America. Another rut borders the island arc of Indonesia from the side of the Indian Ocean. Some potholes, located on the periphery of the ocean, are not connected with island arcs. Such, for example, is the Atakama ravine off the coast of South America. The peripheral position of deep-sea ruts is, of course, not accidental.
Speaking about the geological structure of the ocean floor, it should first of all be noted that in the open ocean, the thickness of loose sediments accumulated on the bottom is small - no more than a kilometer, and often less. These sediments consist of very thin calcareous silts, formed mainly by microscopically small shells of unicellular organisms - globigerin, as well as from the so-called red deep-sea clays containing the smallest grains of iron and manganese oxides. Recently, in many places at great distances from the coast, entire bands of sediments of detrital origin - sands - have been discovered. They are clearly brought to these areas of the oceans from the coastal regions and by their existence indicate the presence of strong deep currents in the oceans.
Another feature is the huge and widespread development of traces of volcanic activity. At the bottom of all the oceans, a large number of huge cone-shaped mountains are known; these are extinct ancient volcanoes. Many at the bottom of the oceans and active volcanoes. Of these volcanoes, only basalts have erupted and are erupting, and at the same time they are very uniform in composition, the same everywhere. Along the periphery of the oceans, on island arcs, other lavas containing more silica are also known - andesites, but in the middle parts of the oceans volcanic eruptions are only basaltic. And in general, in the middle parts of the oceans, almost no other solid rocks are known, except for basalts. The oceanographic dredge has always lifted only basalt fragments from the bottom, except for some sedimentary rocks. Mention should also be made of huge deep latitudinal fissures, several thousand kilometers long, cutting through the bottom of the northeastern part of the Pacific Ocean. Along these cracks, sharp ledges in the ocean floor can be traced.
The deep structure of the earth's crust in the ocean is much simpler than under the continents. There is no granite layer in the oceans and loose sediments directly lie on the basalt layer, the thickness of which is much less than on the continents: usually it is only 5 km. Thus, the solid part of the earth's crust in the oceans consists of one kilometer of loose sediments and five kilometers of basalt layer. That this layer is indeed composed of basalt is much more probable for the oceans than for the continents, given the wide distribution of basalts on the ocean floor and on oceanic islands. If we add five kilometers of the average thickness of the ocean water layer to this, then the depth of the lower boundary of the earth's crust (the Moho section) under the oceans will be only 11 km - much less than under the continents. Thus, the oceanic crust is thinner than the continental one. Therefore, American engineers began drilling through the entire earth's crust precisely in the ocean, from a floating drilling rig, hoping to reach the upper layers of the mantle there more easily and find out their composition.
There is evidence to suggest that oceanic crust is getting thicker under submarine ridges. There its thickness is 20-25 km and it remains basaltic. It is interesting that the crust has an oceanic structure not only under the open oceans, but also under some deep seas: basaltic crust and the absence of a granite layer were established under the deep part of the Black Sea, under the South Caspian, under the deepest depressions of the Caribbean Sea, under the Sea of Japan and in other places. Seas of intermediate depth also have an intermediate structure of the crust: under them it is thinner than a typical continental one, but thicker than an oceanic one, it has both granite and basalt layers, but the granite layer is much thinner than on the mainland. Such an intermediate crust is observed in shallow areas of the Caribbean Sea, in the Sea of Okhotsk, and elsewhere.
The structure of the mantle and core under the oceans is generally similar to their structure under the continents. The difference is observed in the upper mantle: the "softening belt" (asthenosphere) under the oceans is thicker than under the continents; under the oceans, this belt begins already at a depth of 50 km and continues to a depth of 400 km, while on the continents it is concentrated between 100 and 200 km deep. Thus, differences in structure between continents and oceans extend not only to the entire thickness of the earth's crust, but also to the upper mantle to a depth of at least 400 km. Deeper - in the lower layers of the upper mantle, in the lower mantle, in the outer and inner core - no changes in the structure in the horizontal direction, no differences between the continental and oceanic sectors of the Earth have yet been found.
In conclusion, let us say a few words about some general properties of the globe.
The globe radiates heat. A constant flow of heat flows from the Earth's interior to the surface. In this regard, there is a so-called temperature gradient - an increase in temperature with depth. On average, this gradient is assumed to be 30° per 1 km, i.e., with a depth of 1 km, the temperature rises by 30° Celsius. This gradient, however, varies widely from place to place. In addition, it is correct only for the most superficial parts of the earth's crust. If it remained the same until the center of the Earth, then in the inner regions of the Earth the temperature would be so high that our planet would simply explode. Now there is no doubt that with depth the temperature rises more and more slowly. In the lower mantle and in the core, it rises very weakly and apparently does not exceed 4000° in the center of the Earth.
Based on the temperature gradient near the surface, as well as the thermal conductivity of the rocks, it is possible to calculate how much heat flows from the depth to the outside. It turns out that every second the Earth loses 6 ∙ 10 12 calories from its entire surface. Recently, quite a lot of measurements of the size of the Earth's heat flux have been made in different places - on the continents and at the bottom of the oceans. It turned out that the average heat flow is 1.2 ∙ 10 -6 cal/cm 2 per second. In some of the most common cases, it fluctuates between 0.5 and 3 ∙ 10 -6 cal/cm 2 per second, and there are no differences in heat release on the continents and in the ocean. However, against this uniform background, anomalous zones were found - with a very high heat transfer, 10 times higher than the normal heat flux. Such zones are underwater oceanic ridges. Especially many measurements were made on the East Pacific Ridge.
These observations pose an interesting question for geophysicists. It is now quite clear that the source of heat inside the Earth is radioactive elements. They are present in all rocks, in all the material of the globe, and when they decay, they release heat. If we take into account the average content of radioactive elements in rocks, assume that their content in the mantle is equal to their content in stony meteorites, and the content in the core is considered equal to the content in iron meteorites, then it turns out that the total amount of radioactive elements is more than enough to form the observed flux heat. But it is known that granites contain, on average, 3 times more radioactive elements than basalts, and, accordingly, should generate more heat. Since there is a granitic layer in the earth's crust under the continents and absent under the oceans, one could assume that the heat flux on the continents should be greater than on the ocean floor. In fact, this is not so, in general the flow is the same everywhere, but there are zones with an abnormally high heat flow at the bottom of the oceans. In what follows, we will try to explain this anomaly.
The shape of the Earth, as you know, is a ball, slightly flattened at the poles. Due to oblateness, the radius from the center of the Earth to the pole is 1/300 fraction shorter than the radius directed from the center to the equator. This difference is approximately 21 km. On a globe with a diameter of 1 m, it will be a little more than one and a half millimeters and is almost invisible. It was calculated that a liquid ball, the size of the Earth, rotating at the same speed would have to take such a shape. This means that due to the property of creep, as we discussed above, the material of the Earth, subjected to a very long action of centrifugal force, was deformed and took such an equilibrium shape that (of course, much faster) a liquid would have taken.
The inconsistency of the properties of the matter of the Earth is interesting. The elastic vibrations caused by earthquakes propagate in it as in a very solid body, and in the face of a long-acting centrifugal force, the same substance behaves like a very mobile liquid. Such inconsistency is common for many bodies: they turn out to be solid when a short-term force acts on them, a shock similar to a seismic shock, and become plastic when the force acts on them slowly, gradually. This property has already been mentioned in the description of the crushing of layers of hard rocks into folds. However, data have recently appeared that allow us to think that the substance of the Earth adapts to the action of centrifugal force with some delay. The fact is that the Earth is gradually slowing down its rotation. The reason for this is the tides caused by the attraction of the moon. There are always two bulges on the surface of the World Ocean, one of which is facing the Moon, and the other is in the opposite direction. These bulges move across the surface due to the rotation of the Earth. But due to the inertia and viscosity of water, the crest of the bulge facing the Moon is always a little late, always slightly shifted in the direction of the Earth's rotation. Therefore, the Moon attracts a wave not along a perpendicular to the earth's surface, but along a somewhat inclined line. It is this tilt that leads to the fact that the attraction of the Moon all the time slightly slows down the rotation of the Earth. Braking is very little. Thanks to it, the day increases by two thousandths of a second every 100 years. If such a rate of deceleration remained unchanged during geological time, then in the Jurassic period the day was shorter by one hour, and two billion years ago - at the end of the Archean era - the Earth rotated twice as fast.
Along with the slowing down of rotation, the centrifugal force should also decrease; consequently, the shape of the Earth must change - its oblateness gradually decreases. However, calculations show that the shape of the Earth observed now does not correspond to the current speed of its rotation, but to the one that was approximately 10 million years ago. The substance of the Earth, although fluid under conditions of prolonged pressure, has a significant viscosity, high internal friction, and therefore submits to new mechanical conditions with a noticeable delay.
In conclusion, we point out some interesting consequences of earthquakes. Oscillations caused by ordinary earthquakes have different periods. Some earthquakes have a short period - about a second. Registration of such oscillations is extremely important for the study of earthquakes that occurred near the seismic station, i.e., local earthquakes. With distance from the source of the earthquake, such oscillations quickly decay. On the contrary, oscillations with a long period (18-20 sec.) propagate far; during an earthquake of great strength, they can pass through the globe through or go around it on the surface. Such oscillations are recorded at many seismic stations and are convenient for studying distant earthquakes. It is with the help of long-period oscillations that the seismic station "Moskva" can register earthquakes occurring in South America or the Philippines.
In recent years, vibrations caused by earthquakes with a very long period of about an hour have been found. Super-long seismic waves were, for example, formed by the strongest earthquake in Chile in 1960. Such waves, before dying out, go around the globe seven to eight times, or even more.
Calculations show that ultra-long waves are caused by oscillations of the entire globe. The energy of some earthquakes is so great that they seem to shake the entire globe, causing it to pulsate as a whole. True, the amplitude of such oscillations is insignificant: far from the source of the earthquake, it can only be noticed by sensitive instruments and completely fades away within a few days. However, the phenomenon of "trembling" of the entire Earth as a whole cannot but make an impression. The general fluctuations of the entire earth have proved useful in determining some of the physical properties of the globe.
Our house
The planet on which we live is used by us in absolutely all spheres of our life: we build our cities and dwellings on it; we eat the fruits of plants growing on it; use for our own purposes the natural resources extracted from its bowels. The earth is the source of all the blessings available to us, our home. But few people know what the structure of the Earth is, what are its features and why it is interesting. For people who are specifically interested in this issue, this article is written. Someone, having read it, will refresh the knowledge they already have in their memory. And someone, perhaps, will find out something that he had no idea about. But before moving on to talking about what characterizes the internal structure of the Earth, it is worth saying a little about the planet itself.
Briefly about the planet Earth
Earth is the third planet from the Sun (Venus is in front of it, Mars is behind it). The distance from the Sun is about 150 million km. It belongs to a group of planets called the "earth group" (also includes Mercury, Venus and Mars). Its mass is 5.98 * 10 27, and the volume is 1.083 * 10 27 cm³. The orbital speed is 29.77 km/s. The Earth makes a complete revolution around the Sun in 365.26 days, and a complete revolution around its own axis - in 23 hours 56 minutes. Based on scientific data, scientists have concluded that the age of the Earth is approximately 4.5 billion years. The planet has the shape of a ball, but its outlines sometimes change due to inevitable internal dynamic processes. The chemical composition is similar to that of the rest of the terrestrial planets - it is dominated by oxygen, iron, silicon, nickel and magnesium.
Earth structure
The earth consists of several components - this is the core, the mantle and the earth's crust. A little about everything.
Earth's crust
This is the top layer of the earth. It is he who is actively used by a person. And this layer is the best studied. It contains deposits of rocks and minerals. It consists of three layers. The first is sedimentary. It is represented by softer rocks formed as a result of the destruction of solid rocks, deposits of plant and animal remains, and sedimentation of various substances on the bottom of the world's oceans. The next layer is granite. It is formed from solidified magma (molten substance of the earth's depths that fills cracks in the crust) under conditions of pressure and high temperatures. Also, this layer contains various minerals: aluminum, calcium, sodium, potassium. As a rule, this layer is absent under the oceans. After the granite layer comes the basalt layer, consisting mainly of basalt (a rock of deep origin). This layer contains more calcium, magnesium and iron. These three layers contain all the minerals that a person uses. The thickness of the earth's crust ranges from 5 km (under the oceans) to 75 km (under the continents). The Earth's crust makes up about 1% of its total volume.
Mantle
It is located under the cortex and surrounds the nucleus. It makes up 83% of the total volume of the planet. The mantle is divided into upper (at a depth of 800-900 km) and lower (at a depth of 2900 km) parts. From the upper part, magma is formed, which we mentioned above. The mantle consists of dense silicate rocks, which contain oxygen, magnesium and silicon. Also on the basis of seismological data, scientists came to the conclusion that at the base of the mantle there is an alternately interrupted layer consisting of giant continents. And they, in turn, could have formed as a result of the mixing of the rocks of the mantle itself with the substance of the core. But another possibility is that these areas could represent the bottom of ancient oceans. Notes are details. Further, the geological structure of the Earth continues with the core.
Core
The formation of the core is explained by the fact that in the early historical period of the Earth, substances with the highest density (iron and nickel) settled to the center and formed the core. It is the most dense part, representing the structure of the Earth. It is divided into a molten outer core (approximately 2200 km thick) and a solid inner core (approximately 2500 km in diameter). It makes up 16% of the total volume of the Earth and 32% of its total mass. Its radius is 3500 km. What happens inside the core is hardly imaginable - here the temperature is over 3000 ° C and colossal pressure.
Convection
The heat that was accumulated during the formation of the Earth is still being released from its depths as the core cools and radioactive elements decay. It does not come to the surface only due to the fact that there is a mantle, the rocks of which have excellent thermal insulation. But this heat sets in motion the very substance of the mantle - first, hot rocks rise up from the core, and then, being cooled by it, return again. This process is called convection. It results in volcanic eruptions and earthquakes.
A magnetic field
The molten iron in the outer core has a circulation that creates electrical currents that generate the Earth's magnetic field. It spreads into space and creates a magnetic shell around the Earth, which reflects the flows of the solar wind (charged particles ejected by the Sun) and protects living beings from deadly radiation.
Where is the data from
All information is obtained using various geophysical methods. On the surface of the Earth, seismologists (scientists who study the vibrations of the Earth) set up seismological stations, where any vibrations of the earth's crust are recorded. By observing the activity of seismic waves in different parts of the Earth, the most powerful computers reproduce a picture of what is happening in the depths of the planet in the same way that X-rays “shine through” the human body.
Finally
We only talked a little about what the structure of the Earth is. In fact, this issue can be studied for a very long time, because. it is full of nuances and features. For this purpose, there are seismologists. The rest is enough to have general information about its structure. But in no case should we forget that the planet Earth is our home, without which we would not exist. And it should be treated with love, respect and care.
