What if Earth harbors pieces of another planet?
Are there two scientific mysteries about to be solved? Scientists proposed a new theory on Wednesday that could reveal more about the moon and the interior of our planet.
The first mystery is the origin of the Moon, and the most widely accepted theory is that it appeared after a forming planet collided with the future Earth 4.5 billion years ago. A collision with Theia, a Mars-sized protoplanet, would have propelled enough material into space to form the Moon.
The remains of Thea remained to be found. By looking not in the air, but under the ground, according to the study published in nature By a team of scientists from mainly American institutions.
Two “points” under Africa and in the Pacific Ocean
At a depth of 2,900 kilometers below the surface, two large “spots” have intrigued scientists since they were discovered using seismic waves in the 1980s. These blocks are located deep in the Earth’s mantle, the layer that separates the Earth’s core from its crust, and each one is the size of a sphere. The continent, located under Africa and the Pacific.
They are warmer and denser than their surrounding environment. Computer simulations conducted by the researchers indicate that these masses are “buried traces” of the planet Theia, which entered Earth at the time of the collision.
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Qian Yuan, a geodynamics researcher at the California Institute of Technology (CalTech) and first author of the study, told AFP that this collision was “the most violent event the Earth has ever suffered” in its history. Which makes it “very, very strange” that no visible trace remains, he said. What made him think: “Where is the impactor?” My answer: underground. »
Space and geology
The research led experts from two very distinct disciplines, space and geology, to collaborate. During its formation, Theia collided with the Earth at more than 36,000 kilometers per hour, fast enough for part of the impact body to penetrate “a great depth into the Earth’s lower mantle.”
These pieces of essentially molten rock, several tens of kilometers across, cool and solidify, descending to the boundaries of the mantle and the Earth’s core. This was helped by the presence of a greater percentage of iron oxide than found in the terrestrial environment, which made it heavier.
It has accumulated into two distinct masses, each larger than the Moon, according to Qian Yuan, who also insists that these conclusions remain the product of necessarily incomplete models and simulations.
“An important discovery”
An expert in Earth sciences and planetary exploration at the University of Stirling in Scotland told AFP that the theory put forward by Qian Yuan “is consistent with many existing pieces of evidence.” “This is an important result,” said Christian Schroeder, who was not involved in the study.
Even if this theory does not solve, in his opinion, the question of the origin of the Moon, it provides “a reliable explanation for the anomalies observed at the boundary between the mantle and the core.” As for Theia’s remains, they could be “responsible for important ongoing processes on Earth.”
It is known that the blocks carry columns of mantle, and magma rises, to the surface of the Earth’s crust. It is a phenomenon linked to volcanic eruptions and also to the development of supercontinents.
For Qianyuan, Theia’s impact “played a role in Earth’s evolution over 4.5 billion years.” This is what makes it, according to him, “unique (…) different from other rocky planets.”
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