The continents were once formed frommassifs of the crust, which in varying degrees, above the water level in the form of land. These clumps of the crust for more than one million years split, shifted, parts of them crushed to appear in the form that we know now.
Today we will consider the largest and smallest thickness of the earth's crust and features of its structure.
At the beginning of the formation of our planet herethere were multiple volcanoes, there were constant collisions with comets. Only after the bombing stopped, the red-hot surface of the planet froze.
That is, scientists believe that initially ourthe planet was a barren desert without water and vegetation. Where did so much water come from on it - still remains a mystery. But not so long ago, under the ground were found large reserves of water, perhaps they became the basis of our oceans.
Увы, все гипотезы о происхождении нашей планеты и its composition are assumptions rather than facts. According to the statements of A. Wegener, the earth was originally covered with a thin layer of granite, which in the Paleozoic era was transformed into Pangea's great motherland. In the Mesozoic era, Pangea began to split into parts, the resulting continents gradually sailed from each other. The Pacific Ocean, Wegener argues, is the remnant of the primary ocean, while the Atlantic and Indian are considered secondary.
The composition of the crust is almost the same asthe 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 more recently, scientists are confident that the collision of Earth with another planet, called Thea, caused the merging of two celestial bodies, and the Moon formed from a splinter fragment. This explains the fact 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 ocean.
The crust is only 1% of the mass of the Earth.It consists mainly 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, the crust of the Earth is a thin and fragile shell, consisting mainly of light substances. Heavy substances, as geologists believe, 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 shown in the figure below.
The crust of the Earth has 3 layers, each of whichuneven layers cover the previous one. Most of its surface is the continental and oceanic plains. The continents are also surrounded by a shelf, which, after a broken curvature, passes into the continental slope (the area of the continental margin).
The continental crust is divided into layers:
1. Sedimentary.
2. Granite.
3. Basalt.
Sedimentary cover sedimentary, metamorphic and igneous rocks. The thickness of the continental crust is the smallest percentage.
Sedimentary rocks areclusters, among which are clay, carbonate, volcanic rocks and other solids. This is a kind of sediment, which was formed as a result of those or other natural conditions that previously existed on Earth. It allows researchers to draw conclusions about the history of our planet.
The granite layer consists of magmatic andmetamorphic rocks similar to granite in their properties. That is, not only granite constitutes the second layer of the earth's crust, but these substances are very similar in composition to it 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.
Базальтовый слой слагается из веществ, по составу similar to basalts. It is more dense in comparison with the granite layer. Under the basalt layer flows the fiery mantle of solids. Conventionally, the mantle is separated from the crust by the so-called Mohorovichich frontier, which, in fact, separates the 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 crustis a fragile barrier separating us from the red-hot mantle. The thickness of the mantle itself is an average of 3,000 km. Along with the mantle, tectonic plates also move, which, as part of the lithosphere, are part of the earth's crust.
Below we consider the power of the continental crust. It is up to 35 km.
The thickness of the crust varies from 30 to 70 km. And if under the plains its layer is only 30-40 km, then under the mountain systems it reaches 70 km. Under the Himalayas, the thickness of the layer reaches 75 km.
The capacity of the continental crust ranges from 5up to 80 km and directly depends on her age. So, cold ancient platforms (East European, Siberian, West Siberian) have a rather high power - 40-45 km.
In addition, each of the layers has its own power and thickness, which may vary in different regions of the continent.
The thickness of the continental crust is:
1. Sedimentary layer - 10-15 km.
2. Granite layer - 5-15 km.
3. The basalt layer - 10-35 km.
The temperature rises as you deepen into it.It is believed that the core temperature is up to 5,000 ° C, but these figures remain conditional, since the form and composition of it are still not clear to scientists. As it goes deeper into the Earth’s crust, its temperature rises every 100 m, but its numbers vary depending on the composition of elements and depth. Oceanic crust has a higher temperature.
Изначально, по предположениям ученых, Земля it was covered by the oceanic layer of the crust, which is somewhat different in thickness and composition from the continental layer. The oceanic crust probably originated from the upper differentiated layer of the mantle, that is, in composition it is very close to it. The power of the earth's crust of the oceanic type 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 differs insignificantly from each other.
The power of the oceanic crust is:
1. A layer of ocean water whose thickness is 4 km.
2. Layer of loose precipitation. Capacity is 0.7 km.
3Basalt-folded layer with carbonate and siliceous rocks. The average power is 1.7 km. It does not stand out sharply and is characterized by compaction of the sedimentary layer. This variant of its structure is called suboceanic.
4. The basalt layer, not differing from the continental crust. The thickness of the oceanic crust in this layer is 4.2 km.
Basalt layer of oceanic crust in zonessubduction (a zone in which one layer of the crust absorbs the other) turns into eclogites. Their density is so high that they sink deeper into the crust to a depth of more than 600 km, and then descend into the lower mantle.
Considering that the lowest crustal thicknessobserved under the oceans and is only 5-10 km, scientists have long had the idea to start drilling the crust at the depths of the oceans, which would allow a more detailed study of the internal structure of the Earth. However, the layer of oceanic crust is very durable, and research in the depths of the ocean makes this task even more difficult.
The crust is probably the only layer detailedstudied by mankind. But what is under it, still worries geologists. One can only hope that once the unexplored depths of our Earth will be explored.
