These are among the largest and strangest of all structures on Earth: huge and mysterious patches of dense rock that hide deep in the lowest parts of the mantle of our planet.
There are two of these gigantic masses – called the large low-speed provinces (LLSVP) – with one buried under Africa, the other under the Pacific Ocean.
These anomalies are so massive that they in turn generate their own perturbations, such as the widespread phenomenon that is currently evolving and weakening the Earth’s magnetic field, known as the South Atlantic Anomaly.
As to how and why LLSVPs came to exist in this mantle, scientists have a lot of ideas, but little in terms of difficult evidence.
What is known, however, is that these huge spots have existed for a very long time, many believing that they could have been part of the Earth since the huge impact that gave birth to the Moon – ancient traces of the collision between Earth and the hypothetical planet Theia.
The artist’s impression of a planetary collision. (NASA / JPL-Caltech)
According to this widespread argument, Theia the size of Mars hit the Earth very early about 4.5 billion years ago, with a huge chunk of Theia and / or possibly the Earth fragmenting and becoming the Moon we know. today in orbit around the Earth.
As for what happened to Theia’s rest, it’s uncertain. Was it destroyed or simply bounced back into the eternity of space? We do not know.
Some researchers have suggested that the nuclei of these two primordial planets could have merged into one, and that the chemical exchanges made by this epic fusion have allowed life itself to thrive on the resulting world.
Now, scientists have returned to these monumental questions with a new proposal and it is an idea that reconciles the mysterious LLSVP blobs, weaving them into the hypothesis of the hybrid Earth / Theia.
According to new models developed by researchers at Arizona State University (ASU), LLSVPs may represent ancient fragments of Theia’s iron-rich and very dense mantle, which sank deep into the Earth’s mantle as the two worlds in progress. have united and been buried there for billions of years.
“The giant impact hypothesis is one of the most examined models of the Moon’s formation, but the direct evidence indicating the existence of the Theia impactor remains elusive,” the researchers, led by first author Qian Yuan, a doctoral student studying the dynamics of the mantle at ASU, explained in a summary of their findings presented last week at the Lunar and Planetary Science Conference.
“We show that Theia’s mantle can be a few percent intrinsically denser than Earth’s mantle, allowing Theia’s mantle materials to sink into the Earth’s lowest mantle and accumulate in thermochemical piles that can cause seismically observed LLSVPs. “
Although there has been speculation for years that LLSVPs could be an alien souvenir implanted by Theia, the new research seems to be the most comprehensive formulation to date. The findings are currently being reviewed prior to future publication in Geophysical research letters.
Beyond mantle modeling, the results are also consistent with previous research suggesting that certain chemical signatures related to LLSVP are at least as primitive as the impact of Theia.
“Therefore, primitive materials can [originate] from LLSVPs, which is well explained if LLSVPs keep 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 reacts to the team’s findings, but at least for now we have a different perspective on what these mysterious anomalies might be – and that’s literally the farthest explanation so far.
“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.