According to modern concepts of geology Our planet consists of several layers - Geospheres.They differ in their 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 look at the structure of the crust, which is the upper portion of the lithosphere.It is the outer hard shell of the globe, the capacity of which is so small (1.5%), which can be compared to a thin film on a global scale.However, despite this, it is the top layer of the earth's crust is of great interest to mankind as a source of minerals.
crust of the Earth is conditionally divided into three layers, each of which in its own way remarkable.
- top layer - sediment.It reaches a thickness of from 0 to 20 km.Sedimentary rocks are formed due to the deposition of substances on the land, or their sedimentation on the bottom of the hydrosphere.They are part of the earth's crust, lying in her successive layers.
- middle layer - granite.Its thickness can vary from 10 to 40 km.This igneous rock formed a hard layer by the eruption and subsequent solidification of magma in the Earth's thicker at high pressure and temperature.
- lower layer, part of the structure of the Earth's crust - basalt, too, has a magmatic origin.It contains large amounts of calcium, iron and magnesium, and its mass is greater than that of granite rock.
structure of the earth's crust is not the same everywhere.Particularly striking differences are continental and oceanic crust.Under the oceans the crust is thinner and thicker under the continents.The greatest thickness of it is in areas of mountain ranges.
The structure of the oceanic crust consists of two layers - sedimentary and basaltic.Under a layer of basalt is the Moho, and her upper mantle.The ocean floor has a complex relief forms.Among all their diversity occupy a special place huge mid-ocean ridges, where the mantle of emerging young basaltic oceanic crust.Magma has access to the surface through deep fault - the rift that runs down the middle along the ridge tops.Outside the magma flows, thus constantly pushing the walls to the sides of the gorge.This process is called "spreading."
Crustal structure more complex on the continents than under the ocean.Continental crust occupies a much smaller area than the ocean - to 40% of the earth's surface, but has a much larger capacity.Under the rocks it reaches a thickness of 60-70 km.The continental crust has a three-layer structure - sediment, granite and basalt.An area called shields, granite layer is at the surface.As an example - the Baltic Shield, built of granite rocks.
Underwater extreme of the continent - the shelf also has a continental structure of the Earth's crust.It includes and Kalimantan, New Zealand, New Guinea, Sulawesi, Greenland, Madagascar, Sakhalin and others. Also, internal and marginal seas: the Mediterranean, the Sea of Azov, the Black Sea.
draw the line between the granite and basalt layer can be only conditionally, because they have a similar speed of the seismic waves, which is determined by the density of the Earth's layers and their composition.Basalt layer in contact with the surface of the Moho.Sediment layer may have different thicknesses, depending on the shape it is located on the relief.In the mountains, for example, he or absent, or has a very small thickness, due to the fact that the loose particles move down the slopes under the influence of external forces.But it is very powerful in the foothill areas, depressions and hollows.For example, in the Caspian lowlands it reaches 22 km.
