They are among the largest and strangest structures on Earth: huge, mysterious patches of dense rock that hide in the lower parts of the mantle of our planet.
There are two of these gigantic masses, called the Great Low-Cutting Provinces (LLSVP), with one buried beneath Africa and the other beneath the Pacific Ocean.
These anomalies are so massive that they in turn generate their own perturbations, such as the large phenomenon that is currently evolving within and weakening the Earth’s magnetic field, known as the South Atlantic anomaly.
As to how and why LLSVPs came to exist like this within the mantle, scientists have many ideas, but little to the test.
What is known, however, is that these giant spots have existed for a long time, and many think they may have been a part of the Earth since before the giant impact that the Moon was born: ancient traces of the collision between Earth and Earth. hypothetical planet Theia.
Artist’s impression of a planetary collision. (NASA / JPL-Caltech)
According to this widespread argument, the Mars-sized Theia impacted the Earth very early about 4.5 billion years ago, with a huge portion of Theia and / or possibly the Earth fragmenting and becoming the Earth. Moon we know today in orbit around the Earth.
As for what happened to the rest of Theia, it’s uncertain. Was it destroyed or simply rejected into the eternity of space? We do not know.
Some researchers have suggested that the nuclei of these two primordial planets may have fused into one, and that the chemical exchanges produced by this epic fusion are the ones that allowed life itself to prosper in the resulting world.
Now, scientists have returned to these monumental issues with a new proposal, and it’s an idea that reconciles the mysterious LLSVP blobs as well, weaving them into the Terra / Theia hybrid hypothesis.
According to a new modeling by researchers at Arizona State University (ASU), LLSVPs may represent ancient fragments of Theia’s iron-rich, highly dense mantle, which sank deep into Earth’s own mantle when the two developing worlds they were united and buried there. for billions of years.
“The giant impact hypothesis is one of the most examined models for the formation of the Moon, but direct evidence indicating the existence of the Theia impact remains elusive,” said the researchers, led by the first author. Qian Yuan, a PhD student studying mantle dynamics at ASU. , explain in a summary of their findings presented last week at the Conference of Lunar and Planetary Sciences.
“We show that Theia’s mantle can be intrinsically denser than Earth’s mantle, allowing materials in Theia’s mantle to sink to Earth’s lower mantle and accumulate in thermochemical cells that can cause LLSVPs. seismically observed “.
Although it has been speculated for years that LLSVPs could be an alien memory implanted by Theia, the new research seems to be the most comprehensive formulation to date. The results are currently under review, prior to their future publication in Geophysical research letters.
Beyond mantle modeling, the results are also consistent with previous research suggesting that certain chemical signatures linked to LLSVPs are at least as primitive as Theia’s impact.
“Therefore, primitive materials can [originate] of the LLSVPs, which is well explained if the LLSVPs retain materials from Theia mantle that are older than the Giant Impact, ”write Yuan and his co-authors.
We’ll have to see how the rest of the scientific community responds to the team’s findings, but at least we now have another advantage over what these mysterious anomalies may be, and that’s literally the farthest explanation.
“This crazy idea is at least possible,” Yuan said Science.
The findings were presented at the 52nd Lunar and Planetary Science Conference, held as a virtual event last week.