The Mystery of the Giant Blobs at the Center of the Earth
There is a mystery hidden deep beneath the surface of the Earth. In the 1980s, scientists discovered two large “spots” in the lower mantle surrounding the core that exhibited strange characteristics. These continent-sized masses, one under Africa and the other under the Pacific Ocean, slow down earthquake sound waves passing through them, which is why researchers call them low shear velocity provinces (LLSVP). Oddly enough, they don’t make the waves less powerful.
“No one knew what they were and whether they were just a temporary phenomenon, or whether they had been there for millions or even billions of years,” Arwen Deuss, a seismologist at Utrecht University in the Netherlands who co-authored a 2025 study on LLSVPs, said in a statement.
Although the origins of these continent-sized masses remain unclear, one hypothesis is that they formed from pieces of the Earth’s crust slipped beneath other tectonic plates in the mantle. Once there, they melted and formed a dense mud-like pool of molten rock that did not appear to mix with the rest of the mantle. What lends credence to this theory is a “graveyard” of cooler subduction plates in the area surrounding the mystery blobs.
Comparing 3D computer models of the LLSVPs and the surrounding subduction plate graveyard led Deuss and his colleagues to propose a theory of their composition that could explain their peculiarities. The unusual masses, they proposed, might be made of grains much larger than the surrounding plates, which is why they don’t dampen sound waves even though they slow them down. If true, that would mean these strange spots could be up to half a billion years old.
But this is not the only theory on the genesis of these giant masses. Another more violent hypothesis places their origins billions and billions of years ago, during the first formation of the Earth.
Building on theories that the Moon was created when the first proto-Earth collided with a smaller planet (dubbed Theia), former Cal Tech geophysicist Qian Yuan proposed that the same hypothetical collision was responsible for the LLSVPs. In fact, Qian believes that the mysterious masses are actually remnants of Theia that remained trapped inside the Earth. If true, it could explain both why these areas have unusually high iron content and why we found no Theia debris.
Research into these mysterious structures will continue, but it may be some time before we know whether the LLSVPs are primordial remnants of our own planet or alien blobs from its violent past. If only we could take a trip to the center of the Earth to find out for sure.
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Main image: caltech / YouTube
