A University of Alabama-led study has previously been seen as only a hint, but it shows that ancient ocean floors may have spanned the entire core-mantle boundary. If the new earthquake data is correct, we will need to add another layer to our understanding of the Earth. This layer, which fits neatly between the Earth’s mantle and outer core, is thought to be an ancient ocean floor that now reconstructs our view of the core-mantle boundary.
In a study published in the journal Science Advances, led by a team from the University of Alabama, Arizona State University and the University of Leeds, researchers traveled to Antarctica four times to collect three years of seismic data from a network of 15 stations across the continent. The data allowed them to map the seismic waves generated by earthquakes and create a new high-resolution image of the Earth’s interior.
Structure of the Earth. Bulletin of the Earth Sciences Department of the Russian Academy of Sciences
To get the data, researchers literally went underground. Buried stations in Antarctica have provided the first high-resolution view of the Earth’s mantle in the southern hemisphere. Using seismic waves created by earthquakes over three years, the researchers found “unexpected energy” in the data.
They found that geological features previously thought to be isolated formations likely completely cover the Earth, forming an entirely new layer.
“Seismic surveys like ours provide the highest resolution images of our planet’s interior structure, and we are discovering that this structure is much more complex than once thought,” Samantha Hansen, a professor of geological sciences at Alabama and lead author of the study, said in a press release. “Our research reveals important links between Earth’s surface and deep structure and the overall processes that drive our planet.”
The images show that between the mantle and the molten and metallic layer of the outer core is a “dense but seemingly sunken ocean floor.” This has been seen in previous studies, but was thought to be an isolated phenomenon. The researchers say this ancient ocean floor, known as an ultra-low velocity zone, something much denser than the surrounding mantle, covers the entire core-mantle boundary and likely slid deeper underground as Earth’s plates shifted.
The unique seismic data revealed what they call a thin layer of variable thickness, which can range from three miles to more than 25 miles thick. “What this tells us,” said Edward Garnero of Arizona State University in a press release, “is that we are seeing mountains on the core, in some places five times higher than Everest.”
However, the ultra-low velocity zone is best described as ancient ocean floor that has sunk. “Ocean material is transported to the interior of the planet where two tectonic plates meet and one dives under the other, known as subduction zones,” the researchers say. “Packs of subducted ocean material collect along the core-mantle boundary and are pushed out by slowly flowing rock in the mantle over geologic time.”
Another intriguing point about the study is that the location of Earth’s molten layer beneath this newly discovered ocean floor means that underground mountains may play a key role in determining how quickly heat escapes from the core.
