Even in our days, when so much has been inventedtechnical equipment, apparatuses, the worlds still remain inaccessible and mysterious. One of them is the earth's interior. The deepest well in the world was drilled on the Kola Peninsula, its depth reaches 12 km, which is only 1/500 of the radius of our planet. All that scientists know about the terrestrial interior, they learn by seismic method of study. During shaking, fluctuations occur within the planet, which occur at different speeds. It is known that the speed of propagation depends on the density and composition of substances. Based on the data on speed, specialists can already interpret information about the layer through which the oscillation passed.
In this way it was found that the planet is covered with several shells. This is the earth's crust, then the mantle and the next - the core.
The latter is the densest and heaviest. It is assumed that the core consists of iron.
The mantle of all three shells has the largest volume and weight. It consists of a solid substance, but not as dense as in the core.
And, finally, the earth's crust. This outer shell of the planet is much thinner than the previous ones. Its mass does not exceed even 1% of the weight of the entire planet. Humanity lives on its surface, fossils are extracted from it. In many places the earth's crust is penetrated by wells and mines. Their presence allowed to collect samples of rocks, which helped to determine the structure of this shell of the planet.
A consists of the earth's crust of rocks, which, inturn, are formed from minerals. They continue and now form in all layers of the shell, even on its surface. For those conditions in which rocks have been formed, they are divided into:
1. Metamorphic. They are formed deep underground as a result of strong heating and compression of some rocks and their transformation into other rocks. For example, ordinary limestone is transformed into marble.
2. Sedimentary. They are formed by the gradual accumulation of various minerals on the earth's surface. Since this process is slow, sedimentary rocks often consist of several layers.
3. Magmatic. They are formed by the substance of the mantle, which has risen in the overlying layers and is frozen there. The most famous of these rocks is granite. Magma can also rise to the ground in a molten form. Then from it sharply stand out water vapor and gases, and it turns into lava. Outpoured, it freezes instantly. Thus, as a result of the eruption of the volcano, magmatic rocks are formed. These include, for example, basalt.
The Earth's crust under the oceans and on the continents is arranged in different ways. The main differences are in the composition of its layers and in thickness. On this basis, separately consider the following types of crust:
Experts suggest that the mainlandappeared much later under the influence of seismic processes occurring in the bowels of the planet. The minimum thickness of the continental (or continental) crust is 35 km, and under the mountains and other elevations it can be up to 75 km. Form it three layers. The upper is sedimentary rocks. Its thickness is from 10 km to 15 km. Then there is a 5-15-kilometer layer of granite. And the last one is basalt. Its thickness is 10-35 km. It consists mainly of basalt, and also of rocks close to it in physical properties.
The chemical composition of the earth's crust can be determinedOnly on its upper layer, the depth of which does not exceed 20 km. Almost half of it is oxygen, 26% silicon, about 8% aluminum, 4.2% iron, 3.2% calcium, 2.3% magnesium and potassium, and 2.2% sodium. The remaining chemical elements account for no more than a tenth of 1%.
Now scientists have taken a closer lookoceanic crust and continental. They took as a basis the hypothesis of the displacement of continents, put forward more than a century ago by A. Wegener, and formed their theory of the structure of the outer shell of the planet.