Structure of the Earth

Earth in an aquarium

And if we put the Earth in an aquarium?
The Earth has an average radius of 6 371 km, ≈6 378 km at the equator and ≈6 356 km at the poles.
The structure of the Earth is divided into several successive differentiated layers, the atmosphere, the Earth's crust (continental and oceanic crust), mantle (upper and lower) and the core (internal and external).
- The atmosphere is gaseous it contains ≈78% dinitrogen (N₂) and ≈21% of oxygen (O₂).
- The continental crust essentially contains granite (75%), its average thickness is 45 km and its average density is 2.8.
- The oceanic crust essentially contains basalt rock (lava cooled quickly), its thickness is about 5 km and its average density is 3.1.
- The upper mantle essentially contains solid rocks such as peridotite (iron silicate and magnesium silicate SiO 4, Fe and Mg), its thickness is 665 km and its average density is 4.1.
- The lower mantle essentially contains viscous rocks such as perovskite (calcium titanate CaTiO₃), its average thickness is 2,185 km and its average density is 4.6. The mantle remains solid despite the temperature increases when we plunge into its depths, this is due to the pressure on the materials increases more strongly.
- The liquid external core is mainly composed of molten iron, because at these depths the average temperature which is 4000 ° C, taking precedence over the pressure, the average density is then 11.2.
- The solid inner core called in French the "seed", is essentially metallic, the inner core is an alloy of iron (80%) and nickel (20%). Pressure, which is 3.5 million bars (350 GPa), maintains the material in a solid state despite a temperature of about 6000 ° C. The inner core is increasing gradually, by crystallization of the liquid iron of the outer core, which cools slowly. The density in the depths of the Earth is about 13.
All these successive layers are of increasing density. The materials are stacked in the order of their density, iron and nickel in the deepest and iron sulfide, silicates, water, nitrogen, carbon dioxide, ammonia, methane, helium, hydrogen.

This representation is very simplified because these layers can themselves be broken down into sub-layers. To locate these layers, seismologists use seismic waves, when the speed of a seismic wave changes brutally, it is that there is change of medium, so material, so layer. These layers are bounded by discontinuities such as Moho between the crust and the mantle, that of Gutenberg between the mantle and the core.

NB: The Earth formed by accretion of meteorites and the different layers are put in place in accordance with the density of its constituents under the combined action of the internal heat and gravity.

Table: Calculation of the masses in % (right column) of the different layers of the structure of the Earth relative to the mass of the Earth. The masses of the atmospheric layers are insignificant compared to the mass of the Earth, 90% of the mass of the atmosphere is below 16 km altitude in the troposphere and is only 0.0000000003% of the mass of the Earth.

Image: Earth placed in an aquarium. The structure of the Earth is divided into several layers, the atmosphere, the Earth's crust (continental and oceanic crust), mantle (upper and lower) and the core (internal and external). Each layer has a thickness of several tens of kilometers. If one converts each layer of the same density thickness, for example that of water (1) it gives this representation where the earth's crust is insignificant (continental crust in blue sky and oceanic crust in white) and the atmosphere non-existent.
The continental crust on the surface has a thickness of 30 to 65 km (1 blue pixel on the display), the oceanic crust on the surface has a thickness of 1 to 12 km (one white pixel), the viscous upper mantle has a thickness 670 km (≈100 brown pixels), the elastic lower mantle has a thickness of 2180 km (≈230 navy blue pixels), the liquid outer core has a thickness of 2270 km (≈160 green pixels) and the solid inner core has a 1220 km thickness (8 red pixels).