La Terre se refroidit depuis sa formation il y a 4.5 milliards d'années. © 3D motion, Adobe Stock

Earth is cooling faster than previously thought

New thermal conductivity measurements indicate that the Earth is cooling faster than previously thought, suggesting that our planet’s tectonic activity may stop sooner than expected.

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[EN VIDÉO] A billion years summed up in 40 seconds: plate tectonics
Researchers have modeled the motions of plate tectonics over the past billion years.

Since its formation 4.5 billion years ago, The Earth is still giving off heat, and thus to cool down. this is the heat It mainly comes from the radioactive disintegration of the various Earth envelope components. Three other energy sources Can also be cited: gradual crystallization of the outer core, and movements gravity metal crystallizes inside the nucleus liquid, and theenergy Earth’s internal tide. The assembly produces a large heat flux which is necessary to generate pregnancy Mantelik, here Underlies the tectonic and volcanic activity of our planet. It can be said that it is this flow of heat that makes the Earth geologically alive. However, this heat flow will not be eternal.

As the Earth cools, it gradually exhausts its internal heat source. The day will come (too far) when the heat flow will not be enough to support convection in the mantle. It is very likely that at that time, the Earth will become a “dead” planet, and the movement of tectonic plates will cease. Although this long-term evolution is not in doubt, it is still difficult to quantify it. Because we don’t know exactly at the moment Speed The earth cools, or how long it will take to exhaust its reserves.

Bridgmanite, a more conductive mineral than previously thought

To answer these questions, it is necessary to understand how heat travels inside the Earth, to the surface where it is evacuated by volcanic activity, among other things. One of the main areas seems to be the interface between the outer core and Coat. In fact, it is at this level that the liquid crystalline mush of the outer core, consisting of a mixture of Act Based on nickel, in direct contact with mantle rocks. the regression Between these two levels is very high and the heat flow is very high. In this interface, the mantle is mainly formed It is made of a mineral called bridgemanite. Knowing the ability of this mineral to conduct heat will make it possible to better understand the rate of cooling of the Earth. A team of researchers from ETH Zürich and the Carnegie Institution of Washington has reproduced the conditions prevailing in the laboratory at the core/mantle interface level, in order to measure the radiative thermal conductivity of bridgemans at the bridge base level. cloak.

The results showed that the average thermal conductivity at the core/mantle interface would be 1.5 times greater than previously estimated. This new value indicates that the heat flux from the core may be greater than previously thought. To reassess heat flow has two results. First, the convection generated in the mantle must be stronger than assumed. As a result, the mantle cools more efficiently, and therefore faster than previously expected designs.

Towards the acceleration of the Earth’s cooling

This new data may have consequences for Duration The life of some tectonic activity driven by convection in the mantle. Rapid mantle cooling in particular can lead to modifications in the metallic phases at the core/mantle interface. Indeed, when bridgemanite cools, it turns into a new mineral, after perovskite. However, this mineral conducts heat more efficiently than bridgemanite. Thus, the colder the Earth, the more post-perovskite becomes the dominant mineral at the base of the mantle, accelerating heat transfer towards the surface and thus accelerating the cooling process.

The results of the study were published in Earth and Planetary Science Letters Therefore, new horizons are opened about the evolution of the dynamics of the Earth. like Mars and MercureThus the Earth can become inactive much more quickly than we thought. But let’s rest assured, if we have no idea how long it will last, plate tectonic movement still has a good life ahead of it.

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