You Already Know Three Times All The Oceans Are Locked In The Mantle...,

earth  |  Scientists from the University of Alabama have discovered a dense layer of ocean floor material that covers the boundary between the Earth’s core and mantle, according to a study published in the journal Science Advances. 

This layer of ancient ocean floor was likely subducted underground as the Earth’s plates shifted, making it denser than the rest of the deep mantle, and it slows seismic waves reverberating beneath the surface. This ultra-low velocity zone (ULVZ) was previously seen only in isolated patches but has now been found to exist across a large region.

“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 study lead author Dr. Samantha Hansen. “Our research provides important connections between shallow and deep Earth structure and the overall processes driving our planet.”

The layer is only tens of kilometers thick, compared to the thickness of the Earth’s dominant layers. This thin layer was detected through high-resolution imaging of seismic signals, which were used to map a variable layer of material across the study region. The properties of the anomalous core-mantle boundary coating include strong wave speed reductions, leading to the name of ultra-low velocity zone.

“Analyzing 1000’s 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 Dr. Edward Garnero, a geophysicist at Arizona State University who co-led the research. “The material’s thickness varies from a few kilometers to 10’s of kilometers. This suggests we are seeing mountains on the core, in some places up to 5 times taller than Mt. Everest.”

These underground “mountains” are thought to be former oceanic seafloors that have sunk to the core-mantle boundary. They may play an important role in how heat escapes from the core, which powers the magnetic field. Additionally, material from the ancient ocean floors can also become entrained in mantle plumes or hot spots, which travel back to the surface through volcanic eruptions.

The discovery of this layer provides important insights into the structure and processes of our planet, and it underscores the importance of continued exploration and study of the Earth’s interior. 

“This is a really exciting result, and it provides a critical piece of information for understanding how the Earth works,” said Dr. Garnero. “It’s fascinating to think that we can learn so much about our planet just by listening to the echoes of earthquakes.”

The core-mantle boundary, located approximately 2,000 miles below Earth’s surface, is coated with an ultra-low velocity zone (ULVZ) that ranges from a few kilometers to tens of kilometers thick. This coating was discovered through a seismic network that collected data over three years during four trips to Antarctica.

The team, which included students and researchers from various countries, used 15 stations in the network buried in Antarctica that used seismic waves created by earthquakes from around the world to create an image of the Earth’s interior. The technique is similar to a medical scan of the body. The team was able to probe a large portion of the southern hemisphere in high resolution for the first time using this method.

“We found thin anomalous zones of material at the CMB (core-mantle boundary) everywhere we probed,” said Dr. Garnero. “The material’s thickness varies from a few kilometers to tens of kilometers. This suggests we are seeing mountains on the core, in some places up to 5 times taller than Mt. Everest.”

The ULVZs are thought to be former oceanic seafloors that sank to the core-mantle boundary. Oceanic material is carried into the interior of the planet where two tectonic plates meet and one dives beneath the other, known as subduction zones. 

Accumulations of subducted oceanic material collect along the core-mantle boundary and are pushed by the slowly flowing rock in the mantle over geologic time. The distribution and variability of such material explains the range of observed ULVZ properties.

The ULVZs are comparable to mountains along the core-mantle boundary, with heights ranging from less than about 3 miles to more than 25 miles. The team believes that these underground “mountains” may play an important role in how heat escapes from the core, the portion of the planet that powers the magnetic field. Material from the ancient ocean floors can also become entrained in mantle plumes, or hot spots, that travel back to the surface through volcanic eruptions.

The discovery of the ULVZs and their potential implications for Earth’s heat and magnetic fields provides new insights into the planet’s inner workings, and underscores the importance of continued research in this field.