The two giant bubbles of viscous matter buried almost 3,000 kilometers away could be proof that a protoplanet collided with Earth 4.5 billion years ago, giving rise to the Moon, a group of scientists indicated on Wednesday.
The leading theory is that the Moon was created when a Mars-sized body collided with the still-forming Earth.
Following the collision with the theoretical protoplanet named Theia, an enormous amount of light materials, such as silicates, was launched into space and in orbit, under the influence of gravity, they agglutinated and formed the Moon.
Theia's denser and heavier core, made of iron and nickel, sank deeper into the Earth, explaining the difference in density between the planet and its satellite.
Despite decades of efforts, scientists have been unable to find any evidence of Theia.
But now an investigation led by scientists from the United States and published in the journal Nature suggests that the evidence is the two bubbles, made of material different from their environment, buried 2,900 kilometers deep, whose existence has been known for four decades but that no one had been able to explain.
These very flattened, tear-shaped bubbles, each the size of a continent, are located on the boundary between the mantle and the Earth's core, one under Africa and the other under the Pacific Ocean.
Scientists determined that the bubbles are much hotter and denser than the surrounding rock, but almost everything about them remains a mystery.
New research suggests that both are "buried relics" of Theia.
Qian Yuan, a geodynamics researcher at the California Institute of Technology and lead author of the work, told AFP that it was "very strange" that no evidence of Theia's impact had been found.
– Eureka! -It was during a class taught by a planetary scientist about that mystery that Yuan first had a glimpse of an answer: «Where is the impactor? My answer is: it's on Earth," she said.
Since then, research has required experts in often separate fields, such as astronomy and geology, to join forces.
Yuan recalled that the collision theory states that Theia crashed into the proto-Earth at more than 35,000 kilometers per hour and that the densest materials melted due to the heat of the impact and sank "very deep into the lower mantle."
Over the years, this material accumulated in two bubbles, located at the antipodes.
The scientist admitted that testing a theory that dates back so far in time, and with possible evidence so deeply buried, is incredibly difficult, which is why his model could not be "100 percent" certain.
But if true, the implications would be immense.
The Theia collision, believed to be Earth's last major accretion event, significantly changed the planet's composition in just 24 hours, Yuan said.
"My feeling is that this initial condition is the reason why the Earth is unique, why it is different from other rocky planets" in the solar system, he said.
The bubbles have been observed sending plumes of magma toward the surface and have also been linked to the evolution of supercontinents, which scientists link to the evolution of life.
Theia "left something on Earth and that played a role in the next 4.5 billion years of evolution," Yuan said.
Christian Schroeder, an expert in Earth sciences and planetary exploration at the University of Stirling in Scotland, told AFP that the theory "fits with several pieces of evidence."
"It's a very significant finding," said Schroeder, who was not involved in the research.
He also highlighted that the mystery of the Moon's formation has not been solved, but this research gives more weight to the Theia impact theory and at the same time provides "a credible explanation for these anomalies at the boundary between the core and the mantle." ».
The remains of Theia "may be responsible for important processes on Earth that continue to this day," Schroeder added.