• It is because our planet has partially cooled that it does not burn under the effect of its core, according to our partner The Conversation.

  • In the meantime, the internal heat of the Earth can be used: it is geothermal energy.

    Hot water from the depths is used, for example, for district heating in several cities.

  • The analysis of this phenomenon was carried out by Yaël Nazé, FNRS astronomer at the Institute of Astrophysics and Geophysics of the University of Liège (Belgium).

The heart of the Earth is hot, very hot: around 5400 ° C.

This temperature is close to that found on the surface of the Sun.

On the other hand, it should be noted that the heart of the Sun is much hotter: around 15 million degrees!

In comparison, with a temperature of 1000 to 2000 ° C, most flames are cooler.

Yet despite these high temperatures, neither the heart of the Earth nor the Sun burns.

Burning is a very specific concept, in fact: a chemical reaction called

redox

(usually involving a gas: oxygen) which releases heat.

Very different reactions take place at the heart of the Sun: those of nuclear fusion.

The nuclei of an element called hydrogen combine to form a slightly more complex element: helium.

This reaction also releases energy, which gradually reaches the surface, from where it reaches us thanks to the light.

Although it dissipates the heat produced in this way, the Sun does not cool down because the reactions continue in its heart.

Cross section of the Earth from core to crust © M. Halldin / Chabacano / Wikimedia CC BY-SA 3.0 (French adaptation 20 Minutes)

For Earth, things are a little different: the high temperature comes from the initial heat (the Earth was hot when it formed and has been cooling slowly since) and the decay of the radioactive elements (which are not eternal). .

The heart of the Earth is therefore hot, and the heat is evacuated there too towards the surface.

Our planet has therefore gradually cooled.

So, billions of years ago, the surface got so cold that it solidified - this is the ground you walk on.

Of course, this crust does a bit like a lid on a saucepan and this complicates the cooling, but it continues to happen, especially via volcanic eruptions.

Our “ASTRONOMY” file

An important difference with the Sun is that our planet is gradually cooling down… In the distant future, our Earth will no longer have a hot heart, and this will change the planet: the dynamo that occurs there and generates the magnetic field will stop, the plates of the earth's crust will not move any more… But in the meantime, this internal heat can be used: it is geothermal energy.

Thus, hot water from the depths is used for district heating in several cities ...

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This analysis was written by Yaël Nazé, FNRS astronomer at the Institute of Astrophysics and Geophysics of the University of Liège (Belgium).


The original article was published on The Conversation website.

Declaration of interests

Yaël Nazé does not work, does not advise, does not own shares, does not receive funds from an organization that could benefit from this article, and has not declared any affiliation other than his research organization.

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