When did that get there?
The Earth's interior harbors many secrets, but they can't hide from dogged geologists forever.
In a new study published in the journal Science, researchers who analyzed extensive seismic imaging data from Antarctica have discovered what they believe is material from the ancient floor of an ocean, subsumed by the Earth's interior over untold millions of years to reach where it now resides near the planetary core. The giveaway? A "thin" and noticeably dense layer wedged in the the core-mantle boundary, some 2,000 miles beneath the surface.
"Analyzing thousands of seismic recordings from Antarctica, our high-definition imaging method found thin anomalous zones of material at the CMB everywhere we probed," said study co-author Edward Garnero, a professor in the School of Earth and Space Exploration at Arizona State University, in a press release.
The team's readings traced the resonating seismic waves emitted from earthquakes, which they noticed were drastically slowing down in parts of the CMB. These speed-hindering patches are known as ultra-low velocity zones (ULVZ), which more or less come in the form of mountains protruding from the CMB.
"The material's thickness varies from a few kilometers to tens of kilometers," Garnero said. "This suggests we are seeing mountains on the core, in some places up to fives times taller than Mt. Everest."
From the extent that seismic waves were getting slowed in such a geologically thin layer, the researchers suggest that the ULVZs must be composed of material from an ancient ocean floor, far denser than the surrounding mantle.
Though this has been posited by geologists before, the researchers' data suggests these Everest-dwarfing mountains may surround the entire core — and we're only now beginning to take notice.
And these mountains are far from inconsequential irregularities. The researchers believe that they may play a crucial role in determining how heat escapes from Earth's molten core. In addition, it's likely that this ocean material ends up being reused to form the floor of oceans today, gradually dredged up through volcanic eruptions.
"Seismic investigations, such as ours, provide the highest resolution imaging of the interior structure of our planet, and we are finding that this structure is vastly more complicated than once thought," said lead author Samantha Hansen, a professor of geological sciences at the University of Alabama, in the release. "Our research provides important connections between shallow and deep Earth structure and the overall processes driving our planet."
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