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6.2.2. Dynamic model

Dynamic model of the internal structure of the Earth

The plate tectonics is a theory that explains how the expansion of the ocean floor, and distribution occurs earthquakes and volcanoes. To explain the movement of the continents, it was necessary to think of a dynamic model of the interior of the Earth that complements the geochemical model.

The geodynamic model is based on the physical state of the layers and their mechanical properties under the pressures and temperatures at which they are found. Pressure and temperature affect the mechanical behavior, density, and state of materials inside the Earth. Therefore, this model divides the Earth into layers that are not exactly the same as the layers of the geochemical method, which separated them by their chemical composition.

The dynamic model divides the Earth according to the discontinuities provided by seismic studies, distinguishing the following areas with different behavior before pressure and temperature:

Modelo geodinámico del interior de la Tierra

Nanow jesús madrid from es [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Lithosphere

The lithosphere is made up of the crust (continental and oceanic) and the outermost part of the upper mantle. Its thickness varies between 50 and 100 km, depending on whether it is oceanic or continental.

The lithosphere, due to the movements of the sublitospheric mantle, is fragmented forming lithospheric plates, on whose edges endogenous geological phenomena are concentrated, such as magmatism (including volcanism), seismicity or orogenesis. The lithospheric plates are subjected to different movements:

  • Horizontal movements or plate tectonics.
  • Vertical movements or isostatic adjustments.

Beneath the lithosphere, in some places, an area of ​​partially molten rocks called the asthenosphere (over which plates moved) was thought to exist, although today, when it appears, it is called the low-velocity zone for seismic waves.

Mesosphere

The mesosphere comprises the rest of the mantle that is under the lithosphere. It is solid, although it has a plastic behavior that allows it to flow. Convection currents are generated , rising mantle plumes from the D "level and descending cold lithospheric plates from the subduction zones.

The level or zone D", in the lower part of the mesosphere, is partially melted by receiving heat from the outer core. Here the convection currents are generated that cause the movement of the tectonic plates. Sometimes, from the level D" plumes come out thermals, very hot magma that reaches the lithosphere forming hot spots, with a lot of volcanic activity like Hawaii.

Video: What is a Volcanic Hotspot? (Educational).

Endosphere

The endosphere is the innermost part of the Earth, and coincides with the core of the geochemical model. Temperatures are around 4500ºC. Heat is transmitted from the inner core (solid) to the outer core (fluid) and convection currents are generated that propagate the heat outwards accumulating at level D". These convection currents are the cause of the existence of the Earth's magnetic field

Both the geochemical and dynamic models are under continuous review. It must be taken into account that the models are simplifications of reality and that, sometimes, the layers are not continuous or have the same thickness.


         

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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.