For many years, researchers have been intrigued by two massive structures hidden deep beneath the Earth’s surface. These anomalies might possess geochemical characteristics that differ from the surrounding mantle, yet their source remains unclear. Geodynamicist Yoshinori Miyazaki from Rutgers University and his team offer an unexpected explanation regarding these anomalies and their significance in influencing Earth’s capacity to sustain life.
This diagram shows a cross-section that reveals the interior of the early Earth, featuring a hot molten layer situated above the core-mantle boundary. Image credit: Yoshinori Miyazaki/Rutgers University.
The two enigmatic structures, referred to as large low-shear velocity regions and ultra-low velocity regions, lie at the boundary between the Earth’s mantle and core, approximately 2,900 km (1,800 miles) beneath the Earth’s exterior.
Large low-shear velocity regions are vast, continent-sized masses of hot and dense rock.
One of these regions is located beneath Africa, while the other is situated beneath the Pacific Ocean.
The ultra-low velocity zone resembles a thin layer of melt that adheres to the core much like a puddle of molten rock.
Both structures significantly slow seismic waves and display unusual compositions.
“These are not random, odd phenomena,” Dr. Miyazaki, co-author of a related paper published in the journal Nature Earth Science, explained.
“They represent traces of Earth’s primordial history.”
“Understanding their existence could help us unravel how our planet formed and what made it habitable.”
“Billions of years in the past, the Earth was covered by an ocean of magma.”
“While scientists anticipated that as the mantle cooled, it would establish distinctive chemical layers—similar to how frozen juice separates into sweet concentrate and watery ice—seismic surveys have shown otherwise. Instead, large low-shear velocity regions and ultra-low velocity zones appear as irregular accumulations at the Earth’s depths.”
“This contradiction sparked our inquiry. When starting with a magma ocean and performing calculations, the outcome does not match the current observations in the Earth’s mantle. A critical factor was missing.”
The researchers propose that over billions of years, elements such as silicon and magnesium may have leached from the core into the mantle, mixing with it and hindering the development of pronounced chemical layers.
This process could clarify the bizarre structure of the large low-shear velocity and ultra-low velocity regions, potentially visibly representing the solidified remnants of a basal magma ocean tainted by core materials.
“What we hypothesized is that this material could be leaking from the core,” Dr. Miyazaki noted.
“Incorporating core components might account for our current observations.”
“This discovery goes beyond merely understanding the chemistry of the deep Earth.”
“Interactions between the core and mantle may have shaped the Earth’s cooling process, volcanic activity, and atmospheric evolution.”
“This could help clarify why Earth possesses oceans and life, while Venus is a frigid hothouse and Mars a frozen wasteland.”
“Earth has water, life, and a relatively stable atmosphere.”
“In contrast, Venus’ atmosphere is over a hundred times thicker than Earth’s and is mainly carbon dioxide, while Mars’ atmosphere is much thinner.”
“While we do not fully comprehend why this is the case, the processes occurring within the planet—its cooling and layer evolution—could be a significant part of the explanation.”
By synthesizing seismic data, mineral physics, and geodynamic modeling, the authors reaffirm that the extensive low-shear velocity regions and ultra-low velocity zones offer crucial insights into Earth’s formative processes.
These structures may also contribute to volcanic hotspots like those in Hawaii and Iceland, thereby connecting deep Earth dynamics to the planet’s surface.
“This study exemplifies how the integration of planetary science, geodynamics, and mineral physics can aid in unraveling some of Earth’s long-standing enigmas,” said co-author Dr. Jie Deng, a researcher at Princeton University.
“The notion that the deep mantle may still retain the chemical memory of ancient core-mantle interactions provides fresh perspectives on Earth’s unique evolution.”
“Every new piece of evidence contributes to piecing together Earth’s early narrative, transforming scattered hints into a more coherent picture of our planet’s development.”
“Despite the limited clues we have, we are gradually forming a significant narrative,” Dr. Miyazaki remarked.
“With this research, our confidence in understanding Earth’s evolution and its distinctiveness can now be bolstered.”
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J. Deng et al. 2025. Heterogeneity in the deep mantle formed through a basal magma ocean contaminated by core materials. Nature Earth Science 18, 1056-1062; doi: 10.1038/s41561-025-01797-y
Source: www.sci.news
