The lithosphere

  • The geosphere is divided into four subsystems: atmosphere, biosphere, hydrosphere and geosphere.
  • The lithosphere is composed of the Earth's crust and the outer mantle, with a thickness of approximately 100 km.
  • The theory of plate tectonics explains the movement of lithospheric plates through convection currents in the mantle.
  • There are different types of plate boundaries: divergent, convergent, and transform, which generate seismic and volcanic activity.
Germán Portillo

The lithosphere

As we saw in the article on the Earth's internal layers , there are four terrestrial subsystems: the atmosphere, the biosphere, the hydrosphere, and the geosphere . Within the geosphere, we find the different layers that make up our planet. Humankind has attempted to delve deeper through soundings to study what lies beneath our feet. However, we have only managed to penetrate a few kilometers. We have only scratched the thin skin of an apple.

To study the rest of Earth's interior, we must use indirect methods. This has led to two models that explain the formation of Earth's layers based on the composition of the materials and their dynamics. On the one hand, we have the static model, in which Earth's layers are composed of the crust, mantle, and core . On the other hand, we have the dynamic model, whose layers are the lithosphere, asthenosphere, mesosphere, and endosphere.

Static model

Reviewing the static model, we find that the Earth's crust is divided into continental crust and oceanic crust. The continental crust contains materials of varying composition and age, while the oceanic crust is more homogeneous and younger. To learn more about how mountains form, you can consult the section on mountain formation.

We also have the Earth's mantle, which is much more uniform and contains convection currents . And finally, the Earth's core, composed of iron and nickel and characterized by its high density and temperature.

Dynamic model

We're going to focus on the dynamic model. As mentioned earlier, according to the dynamic model, the Earth's layers are the lithosphere, asthenosphere, mesosphere, and endosphere. Today we'll talk more specifically about the lithosphere.

dynamic and static model of the inner layers of the earth

Source: https://tectonicadeplacasprimeroc.wikispaces.com/02.+MODEL+EST%C3%81TICO+DEL+INTERIOR+DEL+INTERIOR+DE+LA+TERRA

Lithosphere

The lithosphere is composed of what, in the static model, would be the Earth's crust and outer mantle. Its structure is quite rigid and it has a thickness of about 100 km. Its rigidity at such depths is known because the speed of seismic waves increases steadily with depth. For a better understanding of its formation, you can consult isostasy and subsidence.

In the lithosphere, temperature and pressure reach values ​​that allow rocks to melt in some areas. You can also learn about the parts of an earthquake in the parts of an earthquake section.

According to the type of crust that the lithosphere contains, we differentiate it into two types:

  • Continental lithosphere: It is the lithosphere that is formed by the continental crust and the external part of the earth's mantle. In it are the continents, mountain systems, etc. The thickness is only about 120 km and it is of an older geological age since there are rocks that more than 3.800 years old.
  • Oceanic lithosphere: It is formed by the oceanic crust and the earth's outer mantle. They make up the ocean floor and are thinner than the continental lithosphere. Its thickness is 65 km. It is made up mostly of basalts and in it there are the oceanic ridges. These are mountain ranges at the bottom of the ocean in which the thickness is only 7 km.

Continental and ocean lithosphere

Source: http://www.aula2005.com/html/cn1eso/04lalitosfera/04lalitosferaes.htm

The lithosphere rests on the asthenosphere, which contains the rest of Earth's outer mantle. The lithosphere is divided into different lithospheric or tectonic plates that are constantly moving. To learn more about these plates, you can read about tectonic plate boundaries.

Theory of continental drift

Until the beginning of the 20th century, terrestrial phenomena such as volcanoes, earthquakes, and folds were unexplained. There was no way to explain the shape of the continents, the formation of mountain ranges, and so on. From 1910 onward, thanks to the German geologist Alfred Wegener , who proposed the Theory of Continental Drift, it became possible to provide an explanation and connect all these concepts and ideas.

The theory was proposed in 1912 and accepted in 1915. Wegener hypothesized that the continents are in motion based on various tests.

  • Geological tests. They were based on the correlation between the geological structures on both sides of the Atlantic Ocean. That is, the shapes of the continents seem to fit together because they were once together. The global continent that was once united and home to all the planet's flora and fauna was named Pangaea. You can learn more about this phenomenon by visiting .

Geological evidence continental drift

The continents fit together. Source: http://recursos.cnice.mec.es/biosfera/alumno/4ESO/MedioNatural1I/contente2.htm

  • Paleontological evidence. These tests analyzed the presence of very similar fossil flora and fauna in continental areas that are currently separated by oceans. In addition, there are differences between volcanic islands and island arcs that can be consulted. here.

Paleontological evidence of continental drift

Source:: http://www.geologia.unam.mx:8080/igl/index.php/difusion-y-divulgacion/temas-selectos/568-la-teoria-de-la-tectonica-de-placas-y -the-continental-drift

  • Paleoclimatic tests. These tests studied the location of rocks that presented climatic conditions different from the place where they currently reside.

Initially, this theory of continental drift was rejected by the scientific community because it lacked a mechanism to explain the movement of the continents. What force moved the continents? Wegener attempted to explain this by suggesting that the continents moved due to differences in density, and that the less dense continents slid like a carpet across a room. This was rejected because of the enormous force of friction that exists.

Plate tectonics theory

The theory of plate tectonics was proposed in 1968 by the scientific community, based on a compilation of all the available data. According to this theory, the lithosphere is the Earth's rigid outer layer (crust and outer mantle) and is divided into fragments called plates that are in motion. The plates change size and shape and can even disappear. The continents sit atop these plates, and the plates themselves are moved by convection currents in the Earth's mantle . To understand how mountains are formed, you can visit the article on [topic missing].

Plate boundaries are where seismic activity and geological processes occur. The lower boundary of a plate is thermal. Plate collisions generate folds, faults, and earthquakes. For more information about earthquakes, you can consult the article on the Naples earthquake . Several theories have been proposed to explain plate movement. As plates move, three types of stress can occur at their boundaries, resulting in three different types of plate boundaries.

  • Divergent edges or construction limits: They are areas in which there are tensile stresses that tend to separate the plates. The area of ​​the construction limits are the ocean ridges. The ocean floor expands between 5 and 20 cm a year and there is an internal heat flow. Seismic activity occurs at a depth of about 70 km.
  • Converging edges or destructive boundaries: They occur between plates facing each other by compression forces. The thinner and denser plate dips under the other and enters the mantle. They are called subduction zones. As a result of this, orogens and island arches are formed. There are several types of converging edges depending on the activity of the plates:
    • Collision between oceanic and continental lithosphere: The oceanic plate is the one that subducts under the continental one. When this happens, the formation of an oceanic trench occurs, a great seismic activity, a great thermal activity and the formation of new orogenic chains.
    • Collision between oceanic and oceanic lithosphere: When this situation occurs, an oceanic trench and underwater volcanic activity are generated.
    • Collision between continental and continental lithosphere: This caused the ocean that separated them to close and a large orogenic mountain range to form. This is how the Himalayas formed. For more on this process, visit how the Himalayas originated.
  • Neutral edges or shear stresses: They are areas in which the relationship between two plates occurs due to shear stress due to lateral displacements between them. Therefore neither lithosphere is created nor destroyed. Transforming faults are related to shear stresses in which plates move in opposite directions and produce large series of earthquakes.

Constructive or divergent, destructive or convergent edges of plate tectonics

Source: http://www.slideshare.net/aimorales/lmites-12537872?smtNoRedir=1

There is a driving force caused by the heat stored in the Earth's interior. The thermal energy of this stored heat is converted into mechanical energy by convection currents in the mantle. The mantle is capable of flowing at slow speeds (1 cm/year). Therefore, the movement of the continents is barely noticeable on a human scale.

Lithospheric plates on Earth

Eurasian plate

Region east of the Atlantic Ridge. It covers the seabed east of the Atlantic Ridge, Europe and most of Asia to the archipelago of Japan. In its oceanic zone it has a divergent contact with the North American plate, while to the south it collides with the African plate (as a consequence, the Alps were formed), and to the east, with the Pacific and Philippine plates. This area, due to its great activity, is part of the Pacific ring of fire.

Coconuts and Caribbean Plates

These two small oceanic plates are located between North America and South America.

Peaceful plate

It is a huge oceanic plate that contacts eight others. Destructive boundaries are located on its margins that form the Pacific ring of fire.

Indica plate

Includes India, New Zealand, Australia, and the corresponding ocean portion. Its collision with the Eurasian plate produced the rise of the Himalayas.

Antarctic plate

Large plate that forms divergent boundaries with which it contacts.

South American plate

Large plate with a convergent limit in its western zone, very seismically and volcanically active.

Nazca Plate

Oceanic. Its collision with the South American plate originated the Andes.

Philippine license plate

It is oceanic and one of the smallest. It is surrounded by convergent boundaries, associated with subduction waves, with oceanic trenches and island arcs.

North American plate

In its western zone it contacts the Pacific plate. It is related to the famous San Andrés fault (California), a transforming fault that is also considered part of the fire belt.

African plate

Mixed plate. In its western limit the expansion of the ocean takes place. In the north it formed the Mediterranean and the Alps by colliding with the Eurasian plate. In it there is a gradual opening of a rift that will divide Africa into two sections.

Arabic plate

Small plate at the western limit of which the newest ocean, the Red Sea, is opening.

Lithospheric plates

Source: https://biogeo-entretodos.wikispaces.com/Tect%C3%B3nica+de+placas

Planet Earth
Related article:
The structure of the Earth

Add as preferred source in Google