by Antony Ashkenaz
May 06, 2022
been baffled by
the existence of
Now, a new study may
offer insights into the origins of the anomalies, suggesting that
they could be leftovers from a cosmic collision.
Officially known as
Large Low-Shear-Velocity Provinces (LLSVPs),
these blobs are massive, each the size of a continent, and 100 times
taller than Mount Everest.
Until now, scientists have known very little about these blobs, why
they exist, and why they have odd shapes of varying heights.
A team of researchers believe that these anomalies are actually the
Theia, a protoplanet that
struck the Earth 4.5 million years ago, in a collision that resulted
in the formation of the Moon.
These blobs, which sit below West Africa and the Pacific Ocean, have
confounded seismologists for decades.
Sujoy Mukhopadhyay at the University of California Davis,
highlighted the importance of understanding these lumps, saying:
"if these things are
truly ancient, it tells us something about how our planet
According to Qian Yuan,
a PhD student in geodynamics at Arizona State University
(ASU), Tempe, these anomalies are,
"the largest thing in
the Earth's mantle."
While experts have
theorized that these blobs were by crystallizing out of the depths
of Earth's primordial magma ocean, Mr Qian believes that lumps are
actually the remains of Theia itself.
These LLSVPs are much denser than the mantle of the Earth
surrounding them, and as a result, it tends to abruptly slow down
seismic waves to pass through them.
In the study (Giant
Impact Origin for the Large Low Shear Velocity Provinces),
the authors wrote:
"Here, we demonstrate
that Theia's mantle may be several percent intrinsically denser
than Earth's mantle, which enables the Theia mantle materials to
sink to the Earth's lowermost mantle and accumulate into
thermochemical piles that may cause the seismically-observed
Edward Garnero, a
seismologist at ASU Tempe who was not involved in the work,
noted that this is the first time any researcher has made a serious
case for this theory,
"I think it's
completely viable until someone tells me it's not."
This theory, which was
first proposed in the 1970s, also serves to explain why the Moon
is dry and doesn't have a significant iron core.
In a model developed by Mr Qian, he found that after the collision
of Theia, the
protoplanet would have quickly
merged with the Earth.
Previously, Mr Qian and Mingming Li of the School of Earth
and Space Exploration used geodynamic modeling and analysis to
learn more about the two blobs.
The results of their seismic analysis led to a surprising discovery
that the blob under the African continent is about 621 miles
(1,000 km) higher than the blob under the Pacific Ocean.
According to Mr Qian and Mr Li, the best explanation for the vast
height difference between the two is that,
the blob under the
African continent is less dense (and therefore less stable) than
the one under the Pacific Ocean...