Terre a pu maintenir vie grâce à roches particulières

Earth was able to sustain life thanks to the very special rocks that have now disappeared

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The emergence of life on Earth is perhaps one of the most unusual events the universe has known. Soon after its formation, this rocky and igneous mass that was our planet experienced the birth of life, about 3.5 billion years ago. Very specific conditions were met in time for the land to become habitable, unlike its forge neighbours. If our geological archives have allowed today to chronicle these great moments in our history, then the conditions that allowed the Earth to become a planet capable of sustaining life are still partly unclear. A collaborative study by Yale and Caltech recently put forward the theory that very special rocks that are now extinct suck up a lot of carbon from the atmosphere and interact with seawater in precisely the right way to form biological matter. These rocks, enriched with pyroxene and magnesium, will be the key to Earth’s biological “hospitality.”

4.5 billion years ago, Earth was a very young, very active planet, with a mantle still in the process of fusion and a surface almost entirely covered in magma. Its atmosphere was filled with carbon dioxide (more than 100,000 times the current level) and the temperature at the surface had exceeded 204 degrees Celsius. According to experts, extreme conditions that cannot support life and are very similar to those of Venus today. Why and how might the Earth evolve differently?

Several geological records indicate that by the middle age (the first geological epoch between 4.5 and 4 billion years ago), the Earth’s surface environment was already similar to that of today. It was therefore necessary to fulfill very specific conditions in order for this surface environment to be able to transform from hostile to life to habitable.

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Published in natureThe new study by US researchers attempts to explain and cover the first 500 million years of Earth’s life. ” This period is the most mysterious in Earth’s history ‘, he explains in communication Jun Korenaga, Professor of Earth and Planetary Sciences at Yale University and co-author of the study.

CO2 sequestration2 ten times faster

To imagine the possibility of life emerging in the hostile “magma ball” that was our planet, American researchers suggested that a significant portion of the carbon in the atmosphere must be removed very quickly. ” Somehow a huge amount of carbon in the atmosphere had to be removed Yoshinori Miyazaki, the study’s lead author says.

Since there is no preserved rock sample from the primordial Earth, the team of researchers imagined and designed an entirely experimental model, in order to verify their theory. They then applied precise parameters of thermodynamics, fluid mechanics and atmospheric physics to simulate the conditions of our mid-epoch.

Moreover, they suggested that the Earth at that time was covered with a certain rock that no longer exists today. These rocks would have played a major role in the formation of biological molecules, in particular by absorbing atmospheric carbon from “young” Earth. In fact, from mainly molten materials, they could have been enriched with pyroxenes. In appearance, they were definitely “dark green”. It was also very rich in magnesium, at concentration levels rarely seen in modern rocks. Thus they can react with carbon dioxide2 To produce carbonates, a very effective ability to sequester carbon in the atmosphere.

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The researchers also suggest that as the molten Earth began to cool and solidify, the mantle, which had been moistened by flowing water, underwent strong convection movements. The combination of the wet mantle and higher magnesium peroxinate significantly accelerated the CO2 extraction process.2 from the atmosphere. This phenomenon would have lasted only 160 million years (ten times faster than the traditional rocky mantle).

This chemically heterogeneous mantle is also the source of oceanic crust rich in olivine (the first mineral to crystallize when magma cools), which reacts with seawater and promotes sweating. ” As a bonus, these strange rocks from early Earth could have easily reacted with sea water to generate a large flow of hydrogen. The latter is widely considered essential for the creation of biomolecules Korenaga explains.

Such conditions and thermochemical reactions can currently be observed in the open ocean, particularly in the hydrothermal field of the Lost City in the Atlantic Ocean. The abiotic production of hydrogen and methane that occurs there has made it a favorite place to study the origin of life on Earth. According to the study’s authors, these “fields” could have existed on a global scale, at the bottom of the Hadian Sea. ” Our theory can explain not only how the Earth became habitable, but also why life arose on it. Korenaga concludes.

source: nature

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