Scientists presented a new theory Wednesday that could solve two mysteries in one fell swoop: one that orbits the Earth every day and the other that concerns our planet’s interior.
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The first mystery is the origin of the Moon, whose creation is the most widely accepted theory following the impact of a forming planet on the future Earth 4.5 billion years ago.
The collision with Theia, a protoplanet the size of Mars, would have thrown enough material into space to agglomerate into the moon.
Remains of Theia still remained to be found. By looking not into the air, but underground, says the study published in Nature by a team of scientists from mainly American institutions.
Photo credit: Hernán Cañellas | Nature Journal
Two large “blobs” 2,900 km below the Earth’s surface have fascinated scientists since they were discovered using seismic waves in the 1980s. These masses, each of different sizes, are located at the bottom of the Earth’s mantle, the layer that separates the Earth’s core from the crust of a continent lying beneath Africa and the Pacific Ocean.
They are warmer and denser than the surrounding environment. And the researchers’ computer simulations suggest that these masses are “buried relics” from Theia that came to Earth at the time of the collision.
This collision was “the most violent event Earth has experienced” in its history, Qian Yuan, a geodynamics researcher at the California Institute of Technology (CalTech) and lead author of the study, told AFP.
Which, in his opinion, makes it “very, very strange” that there is no visible trace left. And what motivated him to think: “Where is the impactor?” My answer: underground.
The research resulted in experts from two very different disciplines, space travel and geology, collaborating.
Theia struck Earth, then in formation, at more than 36,000 km/h, a speed sufficient to penetrate part of the impactor “very deep into the lower mantle.”
These pieces of essentially molten rock, tens of kilometers wide, cooled and, solidifying, sank to the edge of the Earth’s mantle and core. The higher proportion of iron oxide compared to the terrestrial environment also contributed to this, which made them heavier.
They accumulated into two distinct masses, each larger than the moon, according to Mr. Yuan, who also insists that these conclusions remain the result of inevitably imperfect models and simulations.
An expert in earth sciences and planetary science at Scotland’s University of Stirling told AFP that the theory put forward by Mr Yuan was “consistent with several existing lines of evidence”. “This is a significant finding,” said Christian Schroeder, who was not involved in the study.
Although, in his opinion, it does not resolve the question of the Moon’s origin, this theory provides “a credible explanation for the anomalies observed at the mantle-core boundary.”
As for Theia’s remains, they may well be “responsible for important ongoing processes on Earth.”
The masses are known to carry clouds from the Earth’s mantle, rising magma, to the surface of the Earth’s crust. A phenomenon that is related to volcanic eruptions but also the development of supercontinents.
For Mr. Yuan, Theia’s influence “played a role in Earth’s evolution over 4.5 billion years.” And that, in his opinion, would make it “unique (…) different from other rocky planets”.