Even today, when so many technical equipment and devices have been invented, there are still inaccessible and mysterious worlds. One of them is the bowels of the earth. 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. Everything that scientists know about the bowels of the earth, they learn through the seismic method of study. During tremors inside the planet, vibrations occur that are carried at different speeds. It is known that the speed of propagation depends on the density and composition of substances. Based on the speed data, specialists can already interpret information about which layer the oscillation passed through.
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 believed 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 compared to the previous ones. Its mass does not exceed even 1% of the weight of the entire planet. Humanity lives on its surface, and fossils are extracted from it. In many places, the crust is permeated by wells and mines. Their presence allowed us to collect rock samples, which helped to determine the structure of this shell of the planet.
And the earth's crust consists of rocks, which, in turn, are formed from minerals. They continue and now form in all layers of the shell, even on its surface. According to the conditions in which the rocks were formed, they are divided into:
1. Metamorphic. They form deep underground as a result of intense heating and compression of some rocks and their transformation into other rocks. So, 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 into the overlying layers and is frozen there. The most famous of these rocks is granite. Magma can also rise to the earth's surface in molten form. Then water vapors and gases are sharply released from it, and it turns into lava. Having poured out, she freezes instantly. Thus, igneous rocks form as a result of the volcanic eruption . These include, for example, basalt.
The crust beneath the oceans and on the continents is structured differently. The main differences are in the composition of its layers and in thickness. On this basis, the following types of crust are separately considered:
- continental;
- oceanic.
Experts suggest that the mainland species appeared much later under the influence of seismic processes occurring in the bowels of the planet. The minimum thickness of the continental (or continental) earth's crust is 35 km, and under mountains and other elevations it can be up to 75 km. Three layers form it. Upper - these are sedimentary rocks. Its thickness is from 10 km to 15 km. Then comes a 5-15 km layer of granite. And the last one is basalt. Its thickness is 10-35 km. It consists mainly of basalt, as well as of rocks close to it in physical properties.
The chemical composition of the earth's crust can be determined only by its upper layer, the depth of which does not exceed 20 km. Almost half of it is oxygen, 26% is silicon, about 8% is aluminum, 4.2% is iron, 3.2% is calcium, 2.3% is magnesium and potassium, and 2.2% is sodium. The remaining chemical elements account for no more than a tenth of 1%.
Now scientists have taken up a close study of the oceanic crust and continental. They took as a basis the hypothesis about the movement of the 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.