- Two deep Earth structures, LLSVPs and ULVZs, puzzle scientists for decades
- LLSVPs are dense hot rock regions under Africa and the Pacific Ocean
- ULVZs are thin, partially molten sediment layers above Earth's core
A new study offers a fresh explanation for two mysterious structures hidden nearly 1,800 miles beneath our feet. For decades, scientists have struggled to understand these enormous formations because their size, shape and strange behaviour do not match traditional ideas about how Earth formed. Now, new research published in Nature Geoscience may finally help solve this puzzle and reveal how these deep-Earth processes shaped the planet we live on today, reported Science Daily.
This new understanding comes from a study by a team led by Rutgers University geodynamicist Yoshinori Miyazaki. The research focused on two unique structures at the boundary between Earth's mantle and core, Large Low-Shear-Velocity Provinces (LLSVPs) and Ultra-Low-Velocity Zones (ULVZs).
LLSVPs are vast regions of extremely hot and dense rock, one located beneath Africa and the other beneath the Pacific Ocean. ULVZs, on the other hand, are thin, partially molten layers that appear as small pockets of sediment above the core. Both structures significantly attenuate seismic waves, indicating that they contain materials or conditions different from the surrounding mantle.
According to Miyazaki, these structures are neither coincidental nor anomalous. He said these are like traces of Earth's early history, and understanding them could help explain how Earth formed and became habitable.
Miyazaki explained that Earth was once covered by a vast ocean of molten rock. As this magma ocean cooled, scientists expected clear chemical layers to develop in the mantle, much like the separation of juice's sweet and watery parts when it freezes.
But seismic studies don't reveal such layers. Instead, LLSVPs and ULVZs appear as irregular patches at the bottom of the mantle.
The team believes that the missing element is Earth's core. Their models suggest that over billions of years, elements like silicon and magnesium gradually migrated from the core to the mantle. This mixing prevented the mantle from forming the expected chemical layers.
This same process also shaped the unique structure of LLSVPs and ULVZs. According to the researchers, these structures are the cooled remnants of "basal magma oceans" that were altered by material ejected from the core. Miyazaki says that taking this material into account makes sense for why these structures look the way they do today.
Miyazaki said that these processes between the mantle and core can influence not only the chemical composition but also the Earth's heat flow, volcanic activity, and the evolution of its atmosphere. This could help explain why water and life survived on Earth, while Venus became extremely hot and Mars became cold and lifeless.
They explained that Earth's atmosphere is stable, Venus's atmosphere is very dense and filled primarily with carbon dioxide, while Mars' atmosphere is very thin. The cooling of each planet and the evolution of its internal structures may be a major factor in these differences.
By combining seismic data, mineral physics, and geodynamic modelling, the team demonstrated that deep structures like LLSVPs and ULVZs are important evidence of Earth's formation. The research also indicates that these regions may have played a key role in powering volcanic hotspots like Hawaii and Iceland, providing a direct link between Earth's internal and external processes.
Co-author Ji Deng said this study is an example of how collaboration between different scientific fields can help solve Earth's long-standing mysteries. He added that chemical traces of early core-mantle interactions may still be present in the mantle, opening new avenues for understanding Earth's unique evolution.
Researchers say each new discovery brings them closer to piecing together Earth's early history. Previously disparate clues now appear to form a clearer and more connected story.
