The structure of the earth's crust

According to modern concepts of geology, our planet consists of several layers - the geospheres. They differ in physical properties, chemical composition and aggregate state. 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 is an outer solid shell of the globe, whose thickness 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 mankind as a source of minerals.

The earth's crust is conditionally divided into three layers, each of which is remarkable in its own way.

1. The upper layer is sedimentary. It reaches a thickness of 0 to 20 km. Sedimentary rocks are formed due to the deposition of substances on land, or their subsidence at the bottom of the hydrosphere. They are part of the earth's crust, located in it replacing each other layers.
2. The middle layer is granite. Its thickness can vary from 10 to 40 km. It is a magmatic rock that has formed a hard layer as a result of eruptions and subsequent solidification of magma in the earth's thickness at high pressure and temperature.
3. The lower layer, which is part of the structure of the earth's crust - basaltic, also has a magmatic origin. It contains more calcium, iron and magnesium, and its mass is greater than that of granite.

The structure of the earth's crust is not the same everywhere. Especially striking differences have oceanic crust and continental. Under the oceans, the earth's crust is thinner, and under the continents is thicker. The greatest thickness it has in areas of mountain massifs.

The composition of the oceanic crust includes two layers - sedimentary and basaltic. Under the basalt layer is the surface of the Moho, and behind it the upper mantle. The ocean bottom has the most complicated relief forms. Among all their diversity, a special place is occupied by huge mid-ocean ridges, in which a young basaltic oceanic crust originates from the mantle. Magma has access to the surface through a deep rift rift that passes through the center of the ridge along the peaks. Outside, the magma spreads, thereby constantly pushing the walls of the gorge to the sides. This process was called "spreading".

The structure of the earth's crust is more complex on the continents, rather 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 much more power. Under the rocks, it reaches a thickness of 60-70 km. The continental crust has a three-layer structure - a sedimentary layer, granite and basaltic. On the areas called shields, the granite layer is on the surface. As an example - the Baltic shield, composed of granite rocks.

The underwater extreme of the continent is 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 inner and outer seas: the Mediterranean, the Azov and the Black.

The boundary between the granite layer and the basalt can only be made conditional, since they have a similar velocity of seismic waves, which determine the density of the earth's layers and their composition. Basalt layer is in contact with the Moho surface. The sedimentary layer can have different thicknesses, which depends on the relief shape located on it. In the mountains, for example, it is either absent or has a very small thickness, since loose particles move down the slopes under the influence of external forces. But he is very powerful in the foothill areas, hollows and hollows. So, in the Caspian lowland it reaches 22 km.