According to modern concepts of geology, our planet consists of several layers - geospheres. They differ in physical properties, chemical composition and state of aggregation. In the center of the earth is the core, followed by the mantle, then the earth’s crust, hydrosphere and atmosphere.
In this article, we will consider the structure of the earth's crust, which is the upper part of the lithosphere. It represents the outer hard shell of the globe, the power of which is so small (1.5%) that it can be compared with a thin film on a global scale. However, despite this, it is the upper layer of the earth’s crust that is of great interest to humanity as a source of minerals.
The earth's crust is conditionally divided into three layers, each of which is remarkable in its own way.
- The top layer is sedimentary. It reaches a thickness of 0 to 20 km. Sedimentary rocks are formed due to deposition of substances on land, or their sedimentation at the bottom of the hydrosphere. They are part of the earth's crust, located in it alternating layers.
- The middle layer is granite. Its thickness can vary from 10 to 40 km. This is igneous rock, which formed a solid layer as a result of eruptions and subsequent solidification of magma in the earth's thickness at high pressure and temperature.
- The lower layer included in the structure of the earth's crust - basalt, also has a magmatic origin. It contains a greater amount of calcium, iron and magnesium, and its mass is greater than that of granite rock.
The structure of the earth's crust is not the same everywhere. Particularly striking differences are the oceanic crust and continental. Under the oceans, the earth's crust is thinner and thicker under the continents. It has the greatest thickness in the areas of mountain ranges.
The oceanic crust consists of two layers - sedimentary and basalt. Under the basaltic layer is the surface of Moho, followed by the upper mantle. The ocean floor has the most complicated relief forms. Among all their diversity, a special place is occupied by huge sizes of mid-ocean ridges, in which a young basaltic oceanic crust originates from the mantle. Magma has access to the surface through a deep fault - a rift that runs along the center of the ridge along the peaks. Outside, magma spreads, thereby constantly pushing the walls of the gorge to the sides. This process is called "spreading."
The structure of the earth's crust is more complex on the continents than under the oceans. The continental crust occupies a much smaller area than the oceanic crust - up to 40% of the earth's surface, but has a much greater thickness. Under the rocks, it reaches a thickness of 60-70 km. The continental crust has a three-layer structure - sedimentary layer, granite and basalt. In areas called shields, the granite layer is on the surface. As an example - the Baltic shield, composed of granite rocks.
The underwater extreme part of the continent - the shelf, also has a continental structure of the earth's crust. It includes the islands of Kalimantan, New Zealand, New Guinea, Sulawesi, Greenland, Madagascar, Sakhalin, etc. And also the inland and marginal seas: Mediterranean, Azov, Black.
It is only possible to draw a boundary between a granite layer and a basalt layer, since they have a similar velocity of seismic waves, which determine the density of the earth layers and their composition. The basalt layer is in contact with the surface of Moho. The sediment layer may have a different thickness, which depends on the shape of the relief located on it. In the mountains, for example, it is either completely absent or has a very small thickness, due to the fact that loose particles move down the slopes under the influence of external forces. But on the other hand, it is very powerful in foothill areas, hollows and hollows. So, in the Caspian lowland, it reaches 22 km.