The continents at one time were formed from the masses of the earth's crust, which to one degree or another protrudes above the water level in the form of land. These blocks of the earth’s crust have been split, shifted for more than a million years, parts of them crumpled to appear in the form that we now know.
Today we will consider the largest and smallest thickness of the earth's crust and the features of its structure.
A little bit about our planet
At the beginning of the formation of our planet, numerous volcanoes acted here, there were constant collisions with comets. Only after the bombing stopped, the red-hot surface of the planet froze.
That is, scientists are sure that initially our planet was a barren desert without water and vegetation. Where did so much water come from is still a mystery. But not so long ago, large reserves of water were discovered underground, perhaps it was they that became the basis of our oceans.
Alas, all hypotheses about the origin of our planet and its composition are more likely assumptions than facts. According to A. Wegener, initially a thin layer of granite covered the Earth, which in the Paleozoic era was transformed into the foremother Pangea. In the Mesozoic era, Pangea began to split into parts, the formed continents gradually sailed from each other. The Pacific Ocean, Wegener claims, is the remnant of the primary ocean, while the Atlantic and Indian are regarded as secondary.
Earth's crust
The composition of the Earth's crust is almost similar to the composition of the planets of our solar system - Venus, Mars, etc. After all, the same substances served as the basis for all the planets of the solar system. And recently, scientists are sure that the collision of the Earth with another planet, called Thea, caused the merger of two celestial bodies, and the moon was formed from the splinter. This explains that the mineral composition of the moon is similar to the composition of our planet. Below we consider the structure of the earth's crust - a map of its layers on land and the ocean.
The crust is only 1% of the mass of the Earth. Mostly it consists of silicon, iron, aluminum, oxygen, hydrogen, magnesium, calcium and sodium and another 78 elements. It is assumed that, in comparison with the mantle and core of the Earth’s crust, the shell is thin and fragile, consisting mainly of light substances. Heavy materials, according to geologists, descend to the center of the planet, and the heaviest are concentrated in the core.
The structure of the earth's crust and a map of its layers are presented in the figure below.
Continental crust
The Earth's crust has 3 layers, each of which covers the previous one with uneven layers. Most of its surface is continental and oceanic plains. Continents are also surrounded by the shelf, which after a bent bend passes into the continental slope (the area of the underwater margin of the mainland).
The Earth’s mainland crust is divided into layers:
1. Sedimentary.
2. Granite.
3. Basalt.
The sedimentary layer is covered by sedimentary, metamorphic and igneous rocks. The thickness of the continental crust is the smallest percentage.
Types of the continental crust
Sedimentary rocks are clusters, among which are clay, carbonate, volcanic rocks and other solids. This is a kind of sediment that formed as a result of certain environmental conditions that previously existed on Earth. It allows researchers to draw conclusions about the history of our planet.
The granite layer consists of igneous and metamorphic rocks, similar to granite in their properties. That is, not only granite makes up the second layer of the earth's crust, but these substances are very similar in composition and have approximately the same strength. The speed of its longitudinal waves reaches 5.5-6.5 km / s. It consists of granites, crystalline schists, gneisses, etc.
The basalt layer is composed of substances similar in composition to basalts. It is more dense in comparison with the granite layer. A viscous mantle of solids flows under the basaltic layer. Conventionally, the mantle from the crust is separated by the so-called Mokhorovichich border, which, in fact, separates layers of different chemical composition. It is characterized by a sharp increase in the speed of seismic waves.
That is, a relatively thin layer of the earth's crust is a fragile barrier that separates us from the red-hot mantle. The thickness of the mantle itself averages 3,000 km. Together with the mantle, tectonic plates move, which, as part of the lithosphere, are part of the earth's crust.
Below we consider the thickness of the continental crust. It makes up to 35 km.
The power of the mainland crust
The thickness of the earth's crust varies from 30 to 70 km. And if under the plains its layer is only 30-40 km, then under mountain systems it reaches 70 km. Under the Himalayas, the layer thickness reaches 75 km.
The thickness of the continental crust is from 5 to 80 km and depends on its age. So, cold ancient platforms (East European, Siberian, West Siberian) have a fairly high power - 40-45 km.
Moreover, each of the layers has its own thickness and thickness, which can vary in different areas of the continent.
The thickness of the continental crust is:
1. The sedimentary layer is 10-15 km.
2. Granite layer - 5-15 km.
3. The basalt layer - 10-35 km.
Earth's crust temperature
The temperature rises as you go deeper into it. It is believed that the temperature of the core is up to 5,000 C, however, these figures remain conditional, since the type and composition of it are still not clear to scientists. As it deepens into the earth's crust, its temperature rises every 100 m, however, its numbers vary depending on the composition of elements and depth. The oceanic crust has a higher temperature.
Oceanic crust
Initially, according to scientists, the Earth was covered precisely with the oceanic layer of the crust, which is somewhat different in thickness and composition from the mainland layer. The oceanic crust probably arose from the upper differentiated layer of the mantle, that is, in composition it is very close to it. The thickness of the oceanic crust is 5 times less than the thickness of the continental type. Moreover, its composition in the deep and shallow areas of the seas and oceans from each other does not differ significantly.
Layers of the mainland crust
The thickness of the oceanic crust is:
1. A layer of ocean water, the thickness of which is 4 km.
2. A layer of loose precipitation. Power is 0.7 km.
3. A layer composed of basalts with carbonate and siliceous rocks. Average power - 1.7 km. It does not stand out sharply and is characterized by compaction of the sedimentary layer. This version of its structure is called suboceanic.
4. Basaltic layer, not different from the continental crust. The thickness of the oceanic crust in this layer is 4.2 km.
The basaltic layer of the oceanic crust in subduction zones (a zone in which one layer of the crust absorbs the other) turns into eclogites. Their density is so high that they plunge deep into the crust to a depth of more than 600 km, and then sink into the lower mantle.
Given that the smallest thickness of the earth’s crust is observed under the oceans and is only 5-10 km, scientists have long been hatching the idea to start drilling the crust deep in the oceans, which would allow a more detailed study of the Earth’s internal structure. However, the layer of the oceanic crust is very strong, and studies at the depths of the ocean make this task even more difficult.
Conclusion
The earth’s crust is perhaps the only layer studied in detail by humanity. But what is underneath it still worries geologists. One can only hope that once the unknown depths of our Earth will be studied.