The structure of the earth's crust and the composition of its layers. Types of structure of the earth's crust

The earth's crust is the upper part of the lithosphere. On the scale of the entire globe, it can be compared to the thinnest film - its thickness is so insignificant. But we don’t know even this uppermost shell of the planet very well. How can one learn about the structure of the earth’s crust if even the deepest wells drilled into the crust do not go beyond the first ten kilometers? Seismic location comes to the aid of scientists. By deciphering the speed of seismic waves passing through different media, it is possible to obtain data on the density of the earth's layers and draw conclusions about their composition. Under continents and ocean basins, the structure of the earth's crust is different.

OCEANIC CRUST

The oceanic crust is thinner (5-7 km) than the continental crust, and consists of two layers - lower basalt and upper sedimentary. Below the basalt layer is the Moho surface and the upper mantle. The topography of the ocean floor is very complex. Among the various landforms, the huge mid-ocean ridges stand out. In these places, the birth of young basaltic oceanic crust from mantle material occurs. Through a deep fault running along the peaks in the center of the ridge - a rift - magma comes to the surface, spreading in different directions in the form of underwater lava flows, constantly pushing the walls of the rift gorge in different directions. This process is called spreading.

Mid-ocean ridges rise several kilometers above the ocean floor, and their length reaches 80 thousand km. The ridges are cut by parallel transverse faults. They are called transformative. Rift zones are the most turbulent seismic zones on Earth. The basalt layer is overlain by layers of marine sedimentary deposits - silts and clays of various compositions.

CONTINENTAL CRUST

The continental crust occupies a smaller area (about 40% of the Earth's surface - approx.), but has a more complex structure and much greater thickness. Under high mountains its thickness is measured 60-70 kilometers. The structure of the continental crust is three-membered - basalt, granite and sedimentary layers. The granite layer comes to the surface in areas called shields. For example, the Baltic Shield, part of which is occupied by the Kola Peninsula, is composed of granite rocks. It was here that deep drilling was carried out, and the Kola superdeep well reached 12 km. But attempts to drill through the entire granite layer were unsuccessful.

The shelf - the underwater margin of the continent - also has continental crust. The same applies to the large islands - New Zealand, the islands of Kalimantan, Sulawesi, New Guinea, Greenland, Sakhalin, Madagascar and others. Marginal seas and internal seas, such as the Mediterranean, Black, and Azov, are located on continental-type crust.

It is possible to talk about basalt and granite layers of the continental crust only conditionally. This means that the speed of passage of seismic waves in these layers is similar to the speed of their passage in rocks of basalt and granite composition. The boundary between the granite and basalt layers is not very clearly defined and varies in depth. The basalt layer borders the Moho surface. The upper sedimentary layer changes its thickness depending on the surface topography. So, in mountainous regions it is thin or absent altogether, since the external forces of the Earth move loose material down the slopes - approx.. But in the foothills, on the plains, in basins and depressions it reaches significant thicknesses. For example, in the Caspian lowland, which is undergoing subsidence, the sedimentary layer reaches 22 km.

FROM THE HISTORY OF THE KOLA SUPERDEEP WELL

Since the start of drilling this well in 1970, scientists have set a purely scientific goal for this experiment: to determine the boundary between the granite and basalt layers. The location was chosen taking into account the fact that it is in the areas of the shields that the granite layer, not covered by the sedimentary one, can be passed “through and through”, which would allow one to touch the rocks of the basalt layer and see the difference. It was previously assumed that such a boundary on the Baltic Shield, where ancient igneous rocks come to the surface, should be located at a depth of approximately 7 km.

Over several years of drilling, the well repeatedly deviated from the specified vertical direction, intersecting layers with different strengths. Sometimes the drills broke, and then we had to start drilling again, using bypass shafts. The material that was delivered to the surface was studied by various scientists and constantly brought amazing discoveries. Thus, at a depth of about 2 km, copper-nickel ores were found, and from a depth of 7 km, a core was delivered (this is the name of a rock sample from a drill in the form of a long cylinder - approx. from the site), in which the fossilized remains of ancient organisms were discovered.

But, having traveled more than 12 km by 1990, the well never went beyond the granite layer. In 1994, drilling was stopped. The Kola superdeep well is not the only well in the world that was laid for deep drilling. Similar experiments were carried out in different places by several countries. But only Kola reached such marks, for which it was included in the Guinness Book of Records.

The Earth's crust is the hard surface layer of our planet. It was formed billions of years ago and constantly changes its appearance under the influence of external and internal forces. Part of it is hidden under water, the other forms land. The earth's crust is made up of various chemicals. Let's find out which ones.

Surface of the planet

Hundreds of millions of years after the Earth's origins, its outer layer of boiling molten rock began to cool and formed the Earth's crust. The surface changed from year to year. Cracks, mountains, and volcanoes appeared on it. The wind smoothed them out, so that after a while they appeared again, but in different places.

Thanks to the external and internal, the solid layer of the planet is heterogeneous. From the point of view of structure, the following elements of the earth's crust can be distinguished:

• geosynclines or folded areas;
• platforms;
• marginal faults and troughs.

The platforms are vast, low-moving areas. Their upper layer (to a depth of 3-4 km) is covered by sedimentary rocks that occur in horizontal layers. The lower level (foundation) is severely crumpled. It is composed of metamorphic rocks and may contain igneous inclusions.

Geosynclines are tectonically active areas where mountain building processes occur. They arise at the junction of the ocean floor and the continental platform, or in the trough of the ocean floor between the continents.

If mountains form close to a platform boundary, marginal faults and troughs may occur. They reach up to 17 kilometers in depth and stretch along the mountain formation. Over time, sedimentary rocks accumulate here and mineral deposits are formed (oil, rock and potassium salts, etc.).

Composition of the bark

The mass of the bark is 2.8 1019 tons. This is only 0.473% of the mass of the entire planet. The content of substances in it is not as diverse as in the mantle. It is formed by basalts, granites and sedimentary rocks.

99.8% of the earth's crust consists of eighteen elements. The rest account for only 0.2%. The most common are oxygen and silicon, which make up the bulk of the mass. In addition to them, the bark is rich in aluminum, iron, potassium, calcium, sodium, carbon, hydrogen, phosphorus, chlorine, nitrogen, fluorine, etc. The content of these substances can be seen in the table:

The rarest element is considered to be astatine, an extremely unstable and toxic substance. Rare minerals also include tellurium, indium, and thallium. They are often scattered and do not contain large concentrations in one place.

Continental crust

Continental or continental crust is what we commonly call land. It is quite old and covers about 40% of the entire planet. Many of its areas reach an age of 2 to 4.4 billion years.

The continental crust consists of three layers. It is covered on top by a discontinuous sedimentary cover. The rocks in it lie in layers or strata, as they are formed due to the compression and compaction of salt sediments or microorganism residues.

The lower and more ancient layer is represented by granites and gneisses. They are not always hidden under sedimentary rocks. In some places they come to the surface in the form of crystalline shields.

The lowest layer consists of metamorphic rocks like basalts and granulites. The basalt layer can reach 20-35 kilometers.

Oceanic crust

The part of the earth's crust hidden under the waters of the World Ocean is called oceanic. It is thinner and younger than the continental one. The age of the crust is less than two hundred million years, and its thickness is approximately 7 kilometers.

The continental crust is composed of sedimentary rocks from deep-sea remains. Below is a basalt layer 5-6 kilometers thick. Below it begins the mantle, represented here mainly by peridotites and dunites.

Every hundred million years the crust is renewed. It is absorbed in subduction zones and formed again at mid-ocean ridges with the help of minerals that come out.

Earth's crust- the thin upper shell of the Earth, which has a thickness of 40-50 km on the continents, 5-10 km under the oceans and makes up only about 1% of the Earth’s mass.

Eight elements - oxygen, silicon, hydrogen, aluminum, iron, magnesium, calcium, sodium - form 99.5% of the earth's crust.

On continents, the crust is three-layered: sedimentary rocks cover granite rocks, and granite rocks overlie basaltic rocks. Under the oceans the crust is of the “oceanic”, two-layer type; sedimentary rocks simply lie on basalts, there is no granite layer. There is also a transitional type of the earth's crust (island-arc zones on the margins of the oceans and some areas on continents, for example).

The earth's crust is greatest in mountainous regions (under the Himalayas - over 75 km), average in platform areas (under the West Siberian Lowland - 35-40, within the Russian Platform - 30-35), and least in the central regions of the oceans (5-7 km).

The predominant part of the earth's surface is the plains of continents and the ocean floor. The continents are surrounded by a shelf - a shallow strip with a depth of up to 200 g and an average width of about SO km, which, after a sharp steep bend of the bottom, turns into a continental slope (the slope varies from 15-17 to 20-30° ). The slopes gradually level out and turn into abyssal plains (depths 3.7-6.0 km). The oceanic trenches have the greatest depths (9-11 km), the vast majority of which are located on the northern and western outskirts.

The earth's crust formed gradually: first a basalt layer was formed, then a granite layer; the sedimentary layer continues to form to this day.

The deep strata of the lithosphere, which are studied by geophysical methods, have a rather complex and still insufficiently studied structure, just like the mantle and core of the Earth. But it is already known that the density of rocks increases with depth, and if on the surface it averages 2.3-2.7 g/cm3, then at a depth of about 400 km it is 3.5 g/cm3, and at a depth of 2900 km ( boundary of the mantle and the outer core) - 5.6 g/cm3. In the center of the core, where the pressure reaches 3.5 thousand t/cm2, it increases to 13-17 g/cm3. The nature of the increase in the Earth's deep temperature has also been established. At a depth of 100 km it is approximately 1300 K, at a depth of approximately 3000 km -4800 K, and in the center of the earth's core - 6900 K.

The predominant part of the Earth's substance is in a solid state, but at the boundary of the earth's crust and the upper mantle (depths of 100-150 km) lies a layer of softened, pasty rocks. This thickness (100-150 km) is called the asthenosphere. Geophysicists believe that other parts of the Earth may also be in a rarefied state (due to decompression, active radio decay of rocks, etc.), in particular, the zone of the outer core. The inner core is in the metallic phase, but today there is no consensus regarding its material composition.

There are 2 main types of the earth's crust: continental and oceanic, and 2 transitional types - subcontinental and suboceanic (see figure).

1- sedimentary rocks;

2- volcanic rocks;

3- granite layer;

4- basalt layer;

5- Mohorovicic border;

6- upper mantle.

The continental type of the earth's crust has a thickness of 35 to 75 km, in the shelf area - 20 - 25 km, and pinches out on the continental slope. There are 3 layers of continental crust:

1st – upper, composed of sedimentary rocks with a thickness of 0 to 10 km. on platforms and 15 – 20 km. in tectonic deflections of mountain structures.

2nd – medium “granite-gneiss” or “granite” - 50% granites and 40% gneisses and other metamorphosed rocks. Its average thickness is 15–20 km. (in mountain structures up to 20 - 25 km.).

3rd – lower, “basalt” or “granite-basalt”, composition close to basalt. Power from 15 – 20 to 35 km. The boundary between the “granite” and “basalt” layers is the Conrad section.

According to modern data, the oceanic type of the earth’s crust also has a three-layer structure with a thickness of 5 to 9 (12) km, more often 6–7 km.

1st layer – upper, sedimentary, consists of loose sediments. Its thickness ranges from several hundred meters to 1 km.

2nd layer – basalts with interlayers of carbonate and silicon rocks. Thickness from 1 – 1.5 to 2.5 – 3 km.

The 3rd layer is the bottom one, not opened by drilling. It is composed of basic igneous rocks of the gabbro type with subordinate, ultrabasic rocks (serpentinites, pyroxenites).

The subcontinental type of earth's surface is similar in structure to the continental one, but does not have a clearly defined Conrad section. This type of crust is usually associated with island arcs - the Kuril, Aleutian and continental margins.

1st layer – upper, sedimentary – volcanic, thickness – 0.5 – 5 km. (on average 2 – 3 km.).

2nd layer – island arc, “granite”, thickness 5 – 10 km.

The 3rd layer is “basalt”, at depths of 8 – 15 km, with a thickness from 14 – 18 to 20 – 40 km.

The suboceanic type of the earth's crust is confined to the basin parts of the marginal and inland seas (Okhotsk, Japan, Mediterranean, Black, etc.). It is close in structure to the oceanic one, but is distinguished by an increased thickness of the sedimentary layer.

1st upper – 4 – 10 or more km, located directly on the third oceanic layer with a thickness of 5 – 10 km.

The total thickness of the earth's crust is 10–20 km, in some places up to 25–30 km. due to an increase in the sedimentary layer.

A peculiar structure of the earth's crust is observed in the central rift zones of the mid-ocean ridges (Mid-Atlantic). Here, under the second oceanic layer, there is a lens (or protrusion) of low-speed material (V = 7.4 - 7.8 km / s). It is believed that this is either a protrusion of an abnormally heated mantle, or a mixture of crustal and mantle matter.

Structure of the earth's crust

On the surface of the Earth, on continents, rocks of different ages are found in different places.

Some areas of the continents are composed on the surface of the most ancient rocks of Archean (AR) and Proterozoic (PT) age. They are highly metamorphosed: clays turned into metamorphic shales, sandstones into crystalline quartzites, limestones into marbles. There are many granites among them. The areas on the surface of which these most ancient rocks emerge are called crystalline massifs or shields (Baltic, Canadian, African, Brazilian, etc.).

Other areas on the continents are occupied by rocks of predominantly younger age - Paleozoic, Mesozoic, Cenozoic (Pz, Mz, Kz). These are mainly sedimentary rocks, although among them there are also rocks of igneous origin, erupted on the surface in the form of volcanic lava or embedded and frozen at some depth. There are two categories of land areas: 1) platforms - plains: layers of sedimentary rocks lie calmly, almost horizontally, with rare and small folds observed in them. There is very little igneous, especially intrusive, rock in such rocks; 2) folded zones (geosynclines) - mountains: sedimentary rocks are strongly folded, penetrated by deep cracks; Intruded or erupted igneous rocks are often encountered. The differences between platforms or folded zones lie in the age of the resting or folded rocks. Therefore, there are ancient and young platforms. By saying that the platforms could have formed at different times, we thereby indicate different ages of the folded zones.

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. They serve as a complement to geological maps, which represent the most objective geological documents illuminating the structure of the earth's crust.

Types of the earth's crust

The thickness of the earth's crust is not the same under continents and oceans. It is larger under mountains and plains, thinner under oceanic islands and oceans. Therefore, there are two main types of the earth's crust - continental and oceanic.

The average thickness of the continental crust is 42 km. But in the mountains it increases to 50-60 and even 70 km. Then they talk about “the roots of the mountains.” The average thickness of the oceanic crust is about 11 km.

Thus, the continents represent, as it were, unnecessary accumulations of masses. But these masses should create a stronger attraction, and in the oceans, where the attracting body is lighter water, the force of gravity should weaken. But in reality there are no such differences. The force of gravity is approximately the same everywhere on the continents and oceans. This leads to the conclusion: continental and oceanic masses are balanced. They obey the law of isostasy (equilibrium), which reads like this: additional masses on the surface of the continents correspond to a lack of masses at depth, and vice versa - the lack of masses on the surface of the oceans must correspond to some heavy masses at depth.

What is the earth's crust

This hard shell of the Earth, on which we walk, on which oceans splash and baobab trees grow.

It was formed due to the fact that our planet (being initially a red-hot ball of fire) still slowly cooled down, becoming covered with a “brown crust”. Now only its “fiery” core, which sometimes appears outward with volcanic eruptions, reminds us of our planet’s formidable past.

What is the earth's crust made of?

This is how you look at it. From a geographical (more precisely from a geomorphological) point of view, it consists of:

And here from the point of view of geochemistry, the earth's crust is formed:

• silicon (17%);
• oddly enough, oxygen (53%);
• aluminum (6%) and a dozen other elements.

In general, scientists have argued a lot and heatedly about this. After all, how can we say what the surface of the Earth consists of when the entire periodic table is scattered and floating on it?

Determination of the composition of the earth's crust

The first attempt to analyze this “earth cocktail” was made by an American Frank Clark. He did what for many years analyzed the composition he came across rocks, and when I had analyzed enough, I decided that it was possible to summarize the data and obtain the composition “ average earth's crust" Many scientists found this idea controversial, and new debates began.

But a Swiss researcher came to Frank's aid. Victor Goldshmit who suggested that the glaciers that “traveled” (during the Ice Age) across the Earth’s surface tore off and mixed the top layer of rocks, the chemical composition of which was of interest to scientists.

Therefore, it is possible to analyze "glacial" clays settled, for example, in the Barents Sea, and understand what exactly the glacier “attached” along the way. Imagine the public's surprise when the results obtained by Goldschmit coincided with the results of Clark's work.

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The Earth's crust is, first of all, the outer shell of the Earth, what we stand on. It lies to a depth of more than seventy kilometers, and its composition includes more than forty different substances. For example, the fundamental elements of its composition are silicon and oxygen (26% and 49%, respectively). They are followed (by volume) by aluminum (7.3%), iron (4.5%), calcium (3.4%), sodium (2.7%), magnesium (2.3%). Plus many other elements that have an extremely small percentage of the total mass of the crust.

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Back in school, I (like, most likely, many of you) were told about the what does our planet consist of?. It was then that I remembered that what we walk on is called earth's crust. In my childhood mind, associations immediately arose with tree bark, but in fact, their compositions have nothing in common with each other. So What exactly does the earth's crust consist of?

2 barks

I think everyone imagines a picture from a geography textbook with a cross-section of the earth. on her the earth's crust is the topmost layer, but in some places there is still an ocean on top of it - the hydrosphere. Indeed, a question that seems simple at first glance hides many difficulties to answer. For example, earth's crust bThere are two types:

• Oceanic.
• Continental.

Let's try to figure it out their differences and composition, because that’s what interests you.

What is the oceanic crust made of?

As the name suggests - oceanic crust covered by the ocean, or rather, the hydrosphere. The age of even its oldest components is much less than the age of the continental crust, although for us 156 million years sounds impressive.

Here is its composition:

Composition of the continental crust

Continental crust, in its turn, covered not by the ocean, but by the atmosphere, but that’s not exactly what I’m talking about now. It is much older than the oceanic crust, its age can reach 4 billion years! This is the age of minerals that includes one of layers of continental crust - “granite”. You and I can see it, and probably everyone has encountered it more than once, because the “granite” layer is most mountains, not covered sedimentary rocks. Accordingly, the composition of the continental crust looks like this:

• Sedimentary rocks.
• "Granite layer"
• Basalt covers.
• Mantle.

It happens that some scientists distinguish another layer - Moho section, which is boundary between other layers.

It would be nice for everyone to know all this, because not having an idea of ​​what you walk on every day is like not knowing anything about a person close to you.

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Since my school days, I remember that one of the components of the Earth is the earth's crust. But it, in turn, is also divided into components. I want to answer the question of exactly what parts the Earth’s crust is divided into.

The mantle as one of the components of the earth's crust

The Earth's mantle can be called that part that is located higher than the core, but is located under the crust itself. It contains a larger amount of earth matter. Its location is determined from approximately 20 to 3000 kilometers below the earth's surface. The mantle consists of rocks that have complex and incomprehensible names, but are its important components:

• peridotites;
• perovskites;
• eclogites.

We can say with confidence that all processes that occur in the Earth’s mantle affect its surface. These factors also explain earthly cataclysms, as well as the formation of new ore deposits.

Basalt part

It is the lower layer that makes up the upper part of the earth's surface. It can be called a product of magma. Located above the mantle. We can say that the basalt layer is the place where all minerals accumulate. And minerals form combinations of various elements from the periodic table. It contains huge reserves of magnesium, iron and calcium. The layer is intermediate between the mantle and the granite layer.

Granite part

This layer is about 10-40 kilometers. The composition of the layer can be considered magma or igneous rock. This rock formed a hard layer due to volcanic eruptions and the solidification of magma that came out of the volcano. This all happened at very high temperature and pressure in the earth's thickness.

Sedimentary part

The layer that is located above granite and basalt. Its thickness reaches 20 kilometers. The layer is formed due to the fact that various substances are deposited on land, and ultimately they create sedimentary rocks. Seismic waves in this place reach a speed of four and a half kilometers per second. For the most part, sediment predominates on land more than in water.

These are all the main parts that make up the earth's crust.

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I would never need clear concepts and definitions of the subject “The World Around Us,” I thought, until my little brother came up to me with a notebook and asked for help with his homework. According to the assignment, it was necessary to depict a cross-section of the Earth with all the components of the earth's crust. I was already getting ready to draw, when I suddenly realized that everything had flown out of my head. I know that there is a core in the center of the Earth, and everything else is like a fog. “Well, let’s figure it out,” I told my brother and began searching for information.

What is the Earth made of?

If you imagine a globe, then the earth’s crust is like a protective shell along its contour, which is continuous throughout its entire length. Transfer this mentally to the Earth and you will understand that there is an earth’s crust. In almost all textbooks the earth's crust is called the solid shell of the Earth, and so it is.

Structure of the earth's crust

It is unreasonable to believe that the earth's crust will lie in a cast layer consisting of a single rock. Years of formation developed the earth's crust, and scientists were able to identify its components:

• sedimentary rocks;
• "granite" layer;
• "basalt" layer;

The sedimentary layer is the topmost layer of the earth's crust. It is the thinnest, formed by rocks that weather from the surface of the Earth. In some areas such a layer does not exist at all, it can be so thin. Let me consider the composition of the layers.

Composition of the layers of the earth's crust

The Earth's crust is the thinnest part of the shell that protects our Earth. Let me look at what percentage this part consists of:

• oxygen - 49.1%;
• silicon - 26.0%;
• aluminum - 7.5%;
• iron - 4.2%;
• calcium - 3.3%;
• potassium - 2.4%;
• magnesium - 2.4%;
• sodium - 2.4%;
• other elements - 2.9%.

All these substances interact with each other, forming new elements. They can even form new rocks.

I will also describe a small but interesting fact for those who are interested in planets. The Earth's crust is in many ways similar to the crust of other planets, or more precisely, it is not they that are similar, but their structure.

I hope I helped you deal with this issue!