For decades, scientists have been baffled by two enormous structures buried deep inside Earth. These anomalies may retain geochemical signatures distinct from the surrounding mantle. Yet, their origin remains enigmatic. Rutgers University geodynamicist Yoshinori Miyazaki and colleagues offer a striking explanation for these anomalies and their role in shaping Earth’s ability to support life.
The illustration shows a cutaway revealing the interior of early Earth with a hot, melted layer above the boundary between the core and mantle. Image credit: Yoshinori Miyazaki / Rutgers University.
The two enigmatic structures, known as large low-shear-velocity provinces and ultra-low-velocity zones, sit at the boundary between Earth’s mantle and its core, nearly 2,900 km (1,800 miles) beneath the surface.
Large low-shear-velocity provinces are continent-sized blobs of dense, hot rock.
One sits beneath Africa; the other is perched under the Pacific Ocean.
Ultra-low velocity zones are thin, molten patches clinging to the core like lava puddles.
Both types of structures slow seismic waves dramatically, signaling unusual composition.
“These are not random oddities,” said Dr. Miyazaki, co-author of a paper published in the journal Nature Geoscience.
“They are fingerprints of Earth’s earliest history.”
“If we can understand why they exist, we can understand how our planet formed and why it became habitable.”
“Billions of years ago, Earth was covered by a global ocean of magma.”
“As it cooled, scientists expected the mantle to form distinct chemical layers, similar to frozen juice separating into sugary concentrate and watery ice.”
“But seismic studies show no such strong layering. Instead, large-low shear velocity provinces and ultra-low velocity zones form irregular piles at the planet’s base.”
“That contradiction was the starting point. If we start from the magma ocean and do the calculations, we don’t get what we see in Earth’s mantle today. Something was missing.”
The team’s model suggests that over billions of years, elements such as silicon and magnesium leaked from the core into the mantle, mixing with it and preventing strong chemical layering.
This infusion could explain the strange composition of large low-shear-velocity provinces and ultra-low-velocity zones, which can be seen as solidified remnants of what the scientists termed a basal magma ocean contaminated by core material.
“What we proposed was that it might be coming from material leaking out from the core,” Dr. Miyazaki said.
“If you add the core component, it could explain what we see right now.”
“The discovery is about more than deep-Earth chemistry.”
“Core-mantle interactions may have influenced how Earth cooled, how volcanic activity unfolded and even how the atmosphere evolved.”
“That could help explain why Earth has oceans and life, while Venus is a scorching greenhouse and Mars is a frozen desert.”
“Earth has water, life and a relatively stable atmosphere.”
“Venus’ atmosphere is 100 times thicker than Earth’s and is mostly carbon dioxide, and Mars has a very thin atmosphere.”
“We don’t fully understand why that is. But what happens inside a planet, that is, how it cools, how its layers evolve, could be a big part of the answer.”
By integrating seismic data, mineral physics and geodynamic modeling, the authors reconceived large low-shear velocity provinces and ultra-low-velocity zones as vital clues to Earth’s formative processes.
The structures may even feed volcanic hotspots such as Hawaii and Iceland, linking the deep Earth to its surface.
“This work is a great example of how combining planetary science, geodynamics and mineral physics can help us solve some of Earth’s oldest mysteries,” said study co-author Dr. Jie Deng, a researcher at Princeton University.
“The idea that the deep mantle could still carry the chemical memory of early core–mantle interactions opens up new ways to understand Earth’s unique evolution.”
“Each new piece of evidence helps fill in gaps in Earth’s early history, turning scattered clues into a clearer picture of its evolution.”
“Even with very few clues, we’re starting to build a story that makes sense,” Dr. Miyazaki said.
“This study gives us a little more certainty about how Earth evolved, and why it’s so special.”
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J. Deng et al. 2025. Deep mantle heterogeneities formed through a basal magma ocean contaminated by core exsolution. Nat. Geosci 18, 1056-1062; doi: 10.1038/s41561-025-01797-y
