Drilling thousands of miles into the Earth to study our planet’s inner layers — its thin crust, rigid mantle, liquid outer core, and solid inner core — simply isn’t feasible given technological limitations.
Instead, geologists typically use clever tricks to explore our planet’s interior, like probing seismic activity triggered by the dynamics of these shifting layers to plumb their mysteries.
And much like these layers, that picture continues to evolve. As detailed in a new study published in the Journal of Geophysical Research: Solid Earth, researchers at the Chinese Academy of Sciences analyzed data from over two million earthquakes across the planet that took place between 1990 and 2024, using a machine learning algorithm to identify structures lurking several thousand miles below the surface.
They identified almost 175,000 “PKP precursors,” mysterious seismic signals that arrive at earthquake detectors before the main event, which can allow scientists to map the Earth’s innermost structures. More specifically, scientists believe the precursors are triggered by “small heterogeneities” just above the region where the Earth’s solid mantle meets its liquid iron core, roughly 1,800 miles below the surface.
While identifying these precursors has “traditionally required painstaking manual screening, a slow and laborious process,” the researchers noted, the new algorithm allowed them to identify “roughly ten times more” PKP precursors “than all previous studies combined.”
With this data in hand, the scientists set out to create what they claim to be the “most complete global map to date of potential small-scale heterogeneities in the Earth’s deep interior,” which includes six new areas that “host significant heterogeneities that had never been documented before.”
“Whereas previous studies could only identify sparse, isolated patches sampled by precursors, our results reveal that these potential heterogeneities may extend across broad regions in the form of continuous bands,” the researchers concluded.
The scientists suggest that these ancient structures — six larger groups spread out across the interior of the globe, as seen in the image above — could be related to subduction zones, where material that gets dragged deep below the surface is chemically altered by the extreme pressure and temperature of the core-mantle boundary. As Science Alert points out, this can spur the material take on vastly different physical properties.
The data could help us identify the time or severity of future seismic activity — and bring us one small step closer in unraveling the mysteries surrounding the formation of the Earth’s various layers and how tectonic plates formed.
More on the Earth’s layers: Scientists Say They Detected Something Huge Shifting Inside the Earth
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