2023-11-01 22:23:22
Scientists proposed a new theory Wednesday that might solve two mysteries in one fell swoop, one circling the Earth every day and the other concerning the innards of our planet.
The first enigma is the origin of the Moon, for which the most commonly accepted theory is its appearance following the impact of a forming planet with the future Earth 4.5 billion years ago.
The collision with Theia, a protoplanet the size of Mars, would have propelled enough material into space for its agglomeration to form the Moon.
It remained to find remains of Theia. Looking not up into the air, but underground, if we are to believe the study published in Nature by a team of scientists from mainly American institutions.
Hotter and denser masses
Because 2900 km below the surface, two large “blobs” have intrigued scientists since their discovery using seismic waves in the 1980s. Laid at the bottom of the Earth’s mantle, the layer separating the Earth’s core from its crust , these masses, each the size of a continent, are located under Africa and the Pacific Ocean.
They are warmer and denser than the environment surrounding them. And the researchers’ computer simulations suggest that these masses are “buried relics” of Theia, which entered Earth at the time of the collision.
This collision was “the most violent event suffered by the Earth” in its history, said Qian Yuan, a geodynamics researcher at the California Institute of Technology (CalTech) and first author of the study.
Which makes it “very, very strange” that there is no visible trace left, according to him. And what motivated his thinking: “Where is the impactor? My answer: underground”.
An impact at 36,000 km/h
The research led experts from two very distinct specialties, space and geology, to collaborate.
Theia hit the Earth, then in formation, at more than 36,000 km/h, a speed sufficient for part of the impactor to penetrate “very deep into the lower mantle of the Earth”.
These pieces of essentially molten rock, several tens of kilometers wide, cooled and, solidifying, descended to the limit of the mantle and the earth’s core. Helped in this by a greater proportion of iron oxide than that of the terrestrial environment, which made them heavier.
They accumulated into two distinct masses, each of which is larger than the Moon, according to Qian Yuan, who also insists that these conclusions remain the fruit of necessarily imperfect models and simulations.
Existing indices
An expert in earth science and planetary exploration at Scotland’s University of Stirling said the theory put forward by Qian Yuan “agrees with several existing clues.” “This is a significant finding,” according to Christian Schroeder, who did not participate in the study.
Even if, according to him, it does not resolve the question of the origin of the Moon, this theory provides “a credible explanation for the anomalies observed at the boundary between the mantle and the core”.
As for the remains of Theia, they may well “be responsible for important ongoing processes on Earth.” The masses are known to carry plumes from the mantle, rising magma, to the surface of the Earth’s crust. A phenomenon linked to volcanic eruptions but also the evolution of supercontinents.
For Qian Yuan, Theia’s impact “played a role in the evolution of the Earth over 4.5 billion years.” And this is what, according to him, would make it “unique (…) different from other rocky planets”.
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