There’s a lot we still don’t know about our planet’s core, which lies about 1,800 miles beneath our feet.
Now, a new study has revealed a discovery that could help researchers piece together its mysterious inner workings.
The research suggests that Earth’s core could be encased in an ancient ocean floor that features giant mountains five times the size of Mount Everest.
Researchers made the discovery after creating the most detailed map yet of the geology beneath our planet’s southern hemisphere.
This “recycled ocean floor” would almost act like a blanket that kept heat trapped in the core if confirmed. Samantha Hansen is the lead author of the study and a geological sciences professor at the University of Alabama. She told Insider via email.
Earth is like a giant recycling plant
Scientists have long been confused by the boundary between the mantle and the core.
About 2,000 miles under the Earth’s surface, conditions shift dramatically: temperatures shoot up drastically, and the rock composition changes abruptly from a solid bulk of rock in the mantle to gooey iron sludge inside the core.
To learn more about the boundary between Earth’s mantle and core, scientists studied seismic waves that come from earthquakes. These waves, which propagate from the epicenter through our planet’s interior as they spread outwards from the earthquake, provide valuable information.
“Admittedly, to most people, seismic data is probably not that interesting to look at. The line is constantly changing. But that wiggly line contains an amazing amount of information!” Hansen told Insider.
Scientists had previously spotted areas of so-called ultra-low velocity zones (ULVZ) — areas where the seismic waves unexpectedly slow down — near the core-mantle boundary.
But they had only found patches of this unknown structure.
Hansen’s team headed for Antarctica in order to determine how far ULVZ can go. They placed seismic equipment at 15 stations on the continent and collected data for three years.
They found the ULVZ was much more widespread than previously thought. Indeed, it was present “over a significant portion of the southern hemisphere,” suggesting this layer coats the entirety of the core, said Hansen.
The layer may come from recycled bits of ancient ocean floor
Hansen and her team used modeling to understand how this layer may have appeared.
For them, the answer was clear: the layer was likely bits of ancient ocean floor, gobbled up over the ages from the surface as tectonic plates stretched and squished together.
“The results of the seismic and geodynamic modelling were compared, which was exciting.
“Together, they make a compelling case for subducted oceanic materials being the main source of ULVZs,” she said.
The ocean floor, Hansen explained, is the perfect candidate to form this layer due to its composition. The ocean floor is very dense and heavy, so it can sink into the mantle. As it is under intense pressure, the core may also become heat resistant.
This may explain the drastic changes at the border between the core of the Earth and its mantle.
“By having this additional layer blanketing the core, the heat won’t be able to escape as easily/readily,” Hansen said.
It is important to know how heat escapes from the core. The core’s temperature variations control “where we have mantle plumes,” the pools of lava that create archipelagos like Hawaii, for instance, said Hansen.
It also influences the Earth’s magnetic field, she said.
Before we can add this new layer to science books, more research will be needed to rule out other explanations.
Some have suggested that the ULVZ could be due to another, completely unknown, material, generated by the unique chemical reactions that could be happening at the boundary. Hansen said that some people believe the strange seismic data at the boundary could be due to an unknown state of melting.
If Hansen’s group is right, it could add a whole new chapter in the history of Earth formation.
“If ULVZs are associated with these subduction materials, they could help us get a better understanding of how the overall plate tectonics cycle works and how our planet has evolved through time,” said Hansen.
The findings were published in the peer-reviewed journal Science Advance in April.
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