Scientists have assembled the most accurate map yet of the underlying geology under Earth’s southern hemisphere, revealing something not previously discovered: an ancient ocean floor that may have wrapped around the core.
This thin, dense layer lies about 2,900 kilometers (1,800 miles) below the surface, where the molten metallic outer core means the rocky mantle above it. This is the Primary mantle boundary (CMB).
Understanding exactly what lies beneath our feet—in as much detail as possible—is vital to studying everything from volcanic eruptions to variations in Earth’s magnetic field, which protects us from solar radiation in space.
“Seismic investigations, like ours, provide the highest resolution imaging of the internal structure of our planet, and we are finding that this structure is much more complex than previously thought,” He says Geologist Samantha Hansen of the University of Alabama.
Hansen and her colleagues used 15 monitoring stations buried in the ice of Antarctica to map seismic waves from the earthquakes over a period of three years. The way these waves move and bounce off reveals the composition of the materials inside the Earth. Because sound waves move slower in these regions, they are called ultra-low velocity regions (ULVZs).
Analysis [thousands] From seismic recordings from Antarctica, our high-resolution imaging method found thin, anomalous regions of material in the CMB everywhere we looked,” He says Geophysicist Edward Garnero of Arizona State University.
The thickness of the material varies from a few kilometers to [tens] of kilometres. This suggests that we see mountains in the core, in some places as high as five times Mount Everest. “
According to the researchers, this ULVZ is most likely oceanic crust buried over millions of years.
While the sinking crust is nowhere near recognized subduction zones at the surface — areas where moving tectonic plates push rock down into the Earth — the simulations in the study show how convection currents could have shifted the ancient ocean floor where it is today. .
It’s difficult to make assumptions about rock types and their motion based on the motion of seismic waves, and researchers don’t rule out other options. However, the ocean floor hypothesis seems to be the most likely explanation for these ULVZs at the moment.
There’s also a suggestion that this ancient oceanic crust could have wrapped around the entire core, although it’s so thin it’s hard to know for sure. Future seismic surveys should be able to add more to the overall picture.
One way the discovery could help geologists is to figure out how heat escapes from the hotter, denser core into the mantle. The differences in composition between these two layers are greater than they are between the solid surface rock and the air above them in the part where we live.
“Our research provides important links between shallow and deep Earth structure and the overall processes that drive our planet.” He says Hansen.
Research published in Science advances.
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