They are among the largest and strangest of all structures on Earth: huge, mysterious blobs of dense rock that lurk deep in the lower parts of our planet’s mantle.
There are two of these gigantic masses – the so-called low shear rate great provinces (LLSVPs) – one buried under Africa, the other under the Pacific Ocean.
These anomalies are so large that they in turn generate their own perturbations, such as the great phenomenon currently evolving within Earth’s magnetic field and weakening it, known as the South Atlantic Anomaly.
As to how and why the LLSVPs originated within the mantle in this way, scientists have many ideas, but little hard evidence.
What is known, however, is that these giant blobs have been around for a long time, and many thought they could have been part of the Earth since before the giant impact that created the moon – ancient traces of the Earth and the hypothetical planet Theia.
Artist’s impression of a planetary collision. (NASA / JPL-Caltech)
According to that widespread argument, the Mars-sized Theia struck very early Earth about 4.5 billion years ago, fragmenting much of Theia and / or possibly Earth, becoming the moon we know today in orbit .
As for what happened to the rest of Theia, it’s uncertain. Was it destroyed or just bounced off into the eternity of space? We do not know.
Some researchers have suggested that the cores of these two primordial planets may have fused into one, and that chemical exchanges brought about by this epic amalgamation allowed life itself to thrive on the resulting world.
Now scientists have returned to these monumental questions with a new proposal, and it’s an idea that also reconciles the mysterious LLSVP blobs and intertwines them with the Earth / Theia hybrid hypothesis.
According to new models by researchers at Arizona State University (ASU), the LLSVPs may represent ancient fragments of Theia’s iron-rich and very dense mantle, which sank deep into Earth’s own mantle when the two developing worlds converged and were buried there. for billions of years.
“The Giant Impact Hypothesis is one of the most researched models for the formation of the moon, but direct evidence indicating the existence of the impactor Theia remains elusive,” said the researchers, led by lead author Qian Yuan, a researcher. PhD student studying mantle dynamics at ASU. , state in a summary of their findings presented at the Lunar and Planetary Science Conference last week.
“We show that Theia’s mantle can be intrinsically several percent denser than Earth’s mantle, allowing materials from Theia’s mantle to sink to the Earth’s lower mantle and accumulate in thermochemical piles containing the seismically observed LLSVPs can cause.”
While there has been speculation for years that the LLSVPs may be an alien souvenir implanted by Theia, the new research appears to be the most comprehensive formulation yet. The findings are currently being reviewed, prior to future publication in Geophysical Research Letters
Aside from the mantle modeling, the results are also consistent with previous research suggesting that certain chemical signatures associated with the LLSVPs are at least as primitive as the Theia impact.
“Therefore, the primitive materials [originate] of the LLSVPs, which is well explained as the LLSVPs preserve Theia mantle materials 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 for now, we’ve got another clue as to what these mysterious anomalies might be – and it’s literally the most distant explanation yet.
“At least this crazy idea is possible,” said Yuan Science
The findings were presented at the 52nd Lunar and Planetary Science Conference, held as a virtual event last week.