Atmosphere layers

The air completely surrounds the Earth and literally wraps it up in a shroud that, under the effect of gravity and centrifugal force caused by the Earth’s rotation, takes a spheroid shape (think of the shape of an egg), flatter at the poles and bulging at the Equator. This is why, even if its boundaries with the interplanetary spaces cannot be accurately identified, it has been called atmosphere (from the Greek atmòs = steam, and sfaira = sphere). A number of layers (spheres) can be identified in the atmosphere; these layers are concentric with the Earth and have different temperatures and chemical properties. Starting from the Earth’s surface (the soil) and going up, we find: the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.
The troposphere
It is the first layer of the atmosphere, the one we live on. The heat that comes from the Earth’s surface warms this layer up and therefore the temperature diminishes when it goes upwards. In the troposphere the air always moves. The troposphere is characterized by atmospheric phenomena like the wind, cloud formation, precipitations, etc. Immediately above it, at a height that varies from the 8 km above the Poles and 18 km above the Equator, there is the tropopause, that represents that passage to the stratosphere.
The stratosphere
In this layer there is no phenomena determined by atmospheric turbulences, as it happens in all the next layers. Here the temperature increases as the height increases, since the ozone layer that is present in this area directly absorbs a part of solar radiations. The stratopause is the border with the mesosphere and it is located at 50 km of height.
The mesosphere
In this layer the temperature diminishes as the height increases. In fact the heat arrives from the Earth’s surface, which is quite far. At around 100 km of height, there is the thermal minimum temperature. The mesopause is located here, representing the passage to the thermosphere.
The thermosphere
The temperature in this layer increases as the height increases. The density of the gases diminished when they go up.
Exosphere
This is the most external layer of the atmosphere. It is also the least known. Researches have calculated that its temperature even exceeds 2000 °C.

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