If our planet were an orange and we could cut it in half, we would see several of its parts. The earth's crust is located on the outer layer, which resembles the skin of a fruit. The soil on which we walk in the yard, in the park, in the field is the outer part of the shell, which descends 24-48 km deep. Breaking through sand or dust in order to find out where the earth's crust is located, in the end you can get to the stones.
Earth structure
Most of the crust under the continents consists of layers of granite. In places like the Grand Canyon, where water has partially damaged the shell, such places can be seen with the naked eye. Under the ocean floor, it extends only 5 km and consists mainly of another stone - bas alt.
The Earth's crust accounts for 0.8% of the total mass of the planet. The solid core is surrounded by a liquid shell, which consists mainly of iron in a liquid state. This two-layered core, in turn, is surrounded by a mantle of molten silicon and magnesium, as well as a thick layer of magma. The last substance has a unique composition. Magma is a mixture of molten rock and gases that is constantly under high pressure. Since the earth's crust is located on the mantle, sometimes the volcanic mass pours intoeruption time. At the same time, it penetrates into splits and holes on the surface. Volcanoes, erupting, from time to time weaken the pressure of magma.
Under the layer where the earth's crust is located, lies a huge mantle, 2880 km thick. Scientists do not know much about the structure of this layer of the planet. Its upper part is composed mainly of a stone called peridotite. The Earth's crust is located on the mantle, under which is the core of the Earth. It is another 3200 km down to the very center.
The oldest and youngest parts of the earth's crust
The oldest part of the earth's shell is located in West Greenland, which appeared 4 billion years ago. This is 1 billion years after hot clouds of cosmic gas and dust created the planet. Where is the earth's youngest crust located? Infants compared to the age of the Earth are considered the Canary Islands, located off the West African coast. They appeared after underwater volcanic eruptions. For example, the island of La Palma is only 1 million years old.
The lithosphere and the earth's crust
As for the lithosphere, it is known for sure that two layers belong to it - the earth's crust and the solid part of the mantle located under it. In other words, the lithosphere is a solid shell of our planet that lies above the asthenosphere.
It is interesting that the average thickness of the earth's shell is 33 km, but on the continents it varies from 25-45 km - on the platforms and up to 45-75 km - in the mountainssystems. Depending on where the earth's crust is located, the density of matter and its chemical composition change. Such a difference is noticeable at the border of the transition to the mantle.
In terms of mineral composition, it is characterized mainly by fusible silicates with most of the aluminosilicates, and in terms of chemical composition, it is characterized by an increased concentration of silica, alkali and rare metals with a low content of magnesium and elements of the iron group.
Types of the earth's shell
According to the features of the geological structure, geophysical properties and chemical composition, the earth's crust is divided into 2 types - continental and oceanic. In addition, a transitional (or intermediate) type is also distinguished.
Sedimentary, granite and bas alt layers are located in the continental shell. Why is that? The names of the granite and bas alt layers are arbitrary, taking into account not only the advantage of the respective rocks, but also geophysical properties. It also has to do with composition. The name of the bas alt layer is also conditional. Because in addition to the main bas alts, it contains many other igneous rocks, but they are similar in geophysical properties.
Transitional crust has the properties of both continental and oceanic. Depending on what features prevail in it, two subtypes are distinguished, such as suboceanic and subcontinental.
Sedimentary layer
The earth's crust is located on sedimentary rocks. It also has features. The sedimentary layer consists of sedimentary rocks of marine and continental origin,It has a predominant distribution on the continents and on the bottom of the oceans and seas. In places where it comes to the surface of the land, it is often completely absent. But within large depressions it reaches many kilometers, and in the Caspian depression - up to 25 km. Here is the largest thickness of sedimentary rocks on our planet. Their average density is 2.2 g/cm3, the temperature is less than 100 °С.
Granite layer
Granite layer lies under the sedimentary layer and is distributed on all continents. In many places it can be observed directly in river valleys and gullies. The rock density in this case is 2.4-2.6 g/cm3. The thickness of the layer within the platforms is on average about 20 km, and under the mountain ranges - up to 40 km.
Bas alt layer
The bas alt layer does not come to the surface, and those bas alt rocks that can be seen are lava outpourings on the surface as a result of ancient volcanic activity. They can be observed in the walls of the rift valleys of the mid-ocean ridges with the help of television cameras, and sampling is carried out by drilling and automatic submersibles. But it doesn't always happen that way. In the Red Sea, geologists selected rocks with their own hands. The bas alt layer lies under the granite layer and has a continuous distribution on the Earth. Its thickness on the continents is close to granite: mainly 20-25 km, and a maximum of 40 km. Under the ocean, it becomes much thinner and varies mainly from 4 to 10 km. Rock density – 2, 8-3, 3 g/cm3.
The inconstancy of the earth's crust
The Earth's crust is located in such a way that it is in constant motion: the continents rotate very slowly but persistently on the liquid basis of the Earth. They connect with each other and diverge. The earth looked very different 200 million years ago. Then it was a huge single piece of land, surrounded by the sea. Later, separate blocks broke away from this ancient continent. 65 million years ago there were such parts of the Earth: the Eurasian continent, the united African American continent, as well as the part that formed today's Antarctica. The land area where India is today was an island in those days.
The process of renewal of the Earth is ongoing. Africa is approaching Europe at a rate of a few millimeters a year, America is moving further and further away from Africa. And in the place where India is pressed closer and closer to the Asian part of the land every year, the mountain ranges of the Himalayas rise. Because of this, the Himalayas are constantly growing, becoming higher and higher. Tibet, located on this mountain range, has grown 3 km upwards in the last 2 million years during the existence of human life.
If the continents move at the previous speed, then in the future the Earth will have a completely different look. After 50 million years, Alaska will join Siberia. The Mediterranean Sea will disappear, and as a result, Asia, Europe and Africa may form a single piece of land.
