They are among the largest and strangest structures on Earth – huge and mysterious patches of dense rock that lurk deep in the lower parts of our planet’s mantle.
There are two of these giant masses, called Large Low Shear Speed Provinces (LLSVP), one buried under Africa and the other under the Pacific Ocean.
These anomalies are so massive that, in turn, they generate their own disturbances, such as the great phenomenon that is currently evolving and weakening the Earth’s magnetic field, known as the South Atlantic Anomaly.
As for how and why LLSVPs came to exist like this within the mantle, scientists have many ideas, but little hard evidence.
However, what is known is that these giant blobs have been around for a long time, and many think they could have been part of the Earth since before the giant impact that gave birth to the Moon – ancient traces of the collision between Earth. and hypothetical planet Theia.
Artist’s impression of a planetary collision. (NASA / JPL-Caltech)
According to that widely held argument, Theia, the size of Mars, struck early Earth about 4.5 billion years ago, with much of Theia and / or possibly Earth fragmenting and becoming the Moon we know today in orbit around. from the earth.
As for what happened to the rest of Theia, it is uncertain. Was it destroyed or did it just bounce back into the eternity of space? We do not know.
Some researchers have suggested that the cores of these two primordial planets may have merged into one, and that the chemical exchanges brought about by this epic merger are what allowed life to thrive in the resulting world.
Now, scientists have returned to these monumental questions with a new proposal, and it is an idea that also reconciles the mysterious LLSVP spots, intertwining them with the hybrid Earth / Theia hypothesis.
According to a new model by researchers at Arizona State University (ASU), LLSVPs may represent ancient fragments of Theia’s highly dense and iron-rich mantle, which sank deep into Earth’s own mantle when the two worlds in development came together, and has been buried there. for billions of years.
“The giant impact hypothesis is one of the most scrutinized models for the formation of the Moon, but direct evidence indicating the existence of the Theia impactor remains elusive,” the researchers, led by first author Qian Yuan, a candidate for PhD studying mantle dynamics at ASU. , they explain in a summary of their findings presented last week at the Lunar and Planetary Science Conference.
“We show that the Theia mantle can be intrinsically several percent denser than the Earth’s mantle, allowing materials from the Theia mantle to sink to the lowest mantle on Earth and accumulate in thermochemical piles that can cause the seismically observed LLSVPs. “
While there has been speculation for years that LLSVPs may be an alien memory implanted by Theia, the new research appears to be the most comprehensive formulation yet. The findings are currently under review, prior to 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 the Theia impact.
“Therefore, primitive materials can [originate] of the LLSVPs, which is well explained if the LLSVPs preserve Theia mantle materials 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 for now at least, we have another clue as to what these mysterious anomalies might be, and it’s literally the wildest explanation yet. .
“This crazy idea is at least possible,” Yuan said. Sciences.
The findings were presented at the 52nd Lunar and Planetary Science Conference, held as a virtual event last week.