Unknown rocks would have made Earth habitable billions of years ago

I’Hadean is the period in the history of the Earth the most mysterious there is because we have almost no archive preserved in the terrestrial rocks that really tell us about the state of our Blue Planet more than 4 billion years ago. We do not know very well if there were already oceans at that time and even less if life had appeared there. Publications on this subject have followed and contradicted each other for decades..

Unquestionably, in the early Hadean at least, the Earth was for a time covered by an ocean of global magma and although a crust eventually formed, volcanic activity and the bombardment ofasteroids and of comets were to make our planet a hell worthy of that of Hades, the Greek god, for at least a hundred million years.

The theory of the formation of Solar system also tells us that theatmosphere of the Earth must have been rich in gas carbonic and devoid of biogenic oxygen. So there must have been a strong greenhouse effect and our Blue Planet must then have looked a lot like Venus. Something must have happened around this time that removed massive amounts of CO from the atmosphere.₂ to trap it in the form of rocks.

Two researchers from Yale and Caltech universities in the United States, Jun Korenaga and Yoshinori Miyazaki, have just published in the famous newspaper Nature an interesting article on modelization of the global transformation of the primitive Earth, which made it pass from a ball of fire at a planet almost ocean over a period of about 500 million years. Their work brings a new perspective on the sequestration of carbon dioxide and the fact that the Earth has become a habitable and inhabited planet, which is not the case today, unless one believes the arguments put forward. about a possible detection of phosphine molecules in the upper cloud layers of the atmosphere of Venus.

Disappearing exotic pyroxenites

Korenaga and Miyazaki now argue that during the Hadean, rocks that no longer exist today reacted with water liquid according to geochemical processes when the Earth’s atmosphere was 100,000 times richer in carbon dioxide than today.

The laws of thermodynamicsfluid mechanics and those of physical and some chemistry of the atmospheres of the interior of the Earth in the modeling of the Hadean, constructed with equations by the two geologists, indeed seem to imply that what saved the Earth from hell with a surface temperature exceeding 200°C were rocks particularly rich in minerals belonging to the large family of pyroxenes – from the Greek πυρ (fire) and ξενος (stranger): “stranger to the fire” -, silicates which are common components of igneous rocks and metamorphic species present on Earth today.

These exotic rocks, which no longer exist, were particularly rich in magnesium and should cover our planet, giving it a dark green appearance according to the researchers who add that this kind of rock (pyroxenites) should react with CO₂ giving carbonates.

The idea that the formation of carbonates has made it possible to remove massive doses of carbon dioxide from the atmosphere, which is found in the form of limestone deposited just after the Hadean, in the archaean oceansis not new and geologists have been considering it for a long time.

But in Korenaga and Miyazaki’s new model, the coat warmer and convective of the Hadean andArchean in combination with these exotic pyroxenites would have sequestered carbon dioxide 10 times faster than in previous models of the Earth’s mantle and crust. It would have taken only 160 million years.

As a bonus, as mentioned in a press release from Yale University, the interactions of the water of the first oceans with the pyroxenites which have now disappeared would have been similar to those observed today at the level of the famous hydrothermal vents of The Lost City (The lost city) in the middle of the Atlantic.

There are reactions abiotic between sea water and peridotite of the upper mantle by a process known as serpentinization. This results in fluids rich in hydrogen and methane, all of these processes being relevant for certain theories of the origin of life on earth.