Using high-resolution imaging of the interiors of our planet, geologists have found something that hasn’t been discovered before—a layer between the core and the mantle that is likely to be a thin but dense sunken ocean floor. Nearly 3,000 kilometres beneath our planet’s surface, its rocky mantle meets the molten metallic outer core. According to the University of Alabama, the changes in physical properties between the outer core and the mantle is greater than that between the surface of the Earth and the air above it. For the new research published in the peer-reviewed journal Science Advances, the geologists deployed a seismic network and collected data during four trips to Antarctica over three years. They used 15 stations buried in Antarctica to measure seismic waves created by earthquakes from around the globe. Later, they used this data to create an image of the Earth, similar to how medical scans are used to create an image of the human body. Like this, they probed a large portion of the southern hemisphere using a detailed method that examines sound wave echoes from the core-mantle boundary. The researchers discovered an unexpected signal that arrived within several seconds of the wave reflected by the boundary. Using these subtle signals, they mapped a previously undiscovered variable layer of material that is “pencil-thing” in geological terms. It measured in the tens of kilometres, which is minuscule when compared to the thickness of Earth’s other layers. According to the researchers, this anomaly is well explained by former ocean seafloors that sunk to the core-mantle boundary. Material from the ocean floor could be carried into the interior of the planet through the locations where two tectonic plates meet. This “subducted” oceanic material could collect along the core-mantle boundary where it can be pushed by the slowly flowing rock in the mantle over time. “Analyzing thousand of seismic recordings from Antarctica, our high-definition imaging method found thin anomalous zones of material at the boundary everywhere we probed. The material’s thickness varies from a few kilometres to tens of kilometres. This suggests we are seeing mountains on the core, in some places up to 5 times taller than Mt. Everest,” said Edward Garnero, co-author of the research, in a press statement. Garnero is a professor at the School Of Earth and Space Exploration at the University of Alabama. These underground “mountains” could play an important role in how heat escapes from the core. These materials from ancient ocean floors can also get caught up in mantle plumes, travelling back to the surface through volcanic eruptions.
