For decades, scientists have puzzled over two colossal, dense regions lurking deep inside Earth—massive structures known as Large Low-Shear-Velocity Provinces (LLSVPs). These enigmatic formations, one under Africa and the other beneath the Pacific Ocean, have resisted easy explanation. Now, new research suggests their origin lies not in ancient collisions or cooling magma, but in a slow, primordial leak from Earth’s core itself.
The Long-Standing Mystery
Discovered in the 1980s through seismic data, the LLSVPs are areas where earthquake waves travel significantly slower, indicating a distinct composition from surrounding mantle rock. Theories abounded: remnants of ancient tectonic plates, lingering effects from Earth’s early molten state, or even debris from the giant impact that formed the Moon. However, none fully explained the blobs’ stability and peculiar placement.
These aren’t just random anomalies; they are clues to Earth’s earliest history. Yoshinori Miyazaki of Rutgers University emphasizes that understanding these structures is crucial to unraveling how our planet formed and became habitable.
A Leaky Core?
The latest models propose that lighter elements—magnesium oxide and silicon dioxide—gradually seeped out of Earth’s core as it cooled billions of years ago. These elements, less dense than iron, migrated upwards into the surrounding magma ocean, altering its chemistry and ultimately contributing to the formation of the LLSVPs.
This process isn’t a sudden event but a slow, continuous leak that occurred over millions of years. The key is that different elements crystallize at different rates under immense pressure. The lighter components floated upwards, dissolving into the magma ocean and shifting its composition toward silicate-rich materials.
The Evidence and Remaining Questions
The persistence of these structures over 4.5 billion years—despite intense heat and pressure—supports the idea of a stable, long-term process rather than a chaotic, one-time event. The presence of Ultra-Low Velocity Zones (ULVZs) at the core-mantle boundary, where seismic waves slow to a crawl, further reinforces this theory.
While the magma ocean theory initially faced contradictions—particularly the unexpectedly low levels of ferropericlase—the new models reconcile these discrepancies by accounting for the core leakage. The research suggests that the amount of ferropericlase present is consistent with the observed composition, given the introduction of lighter elements from the core.
Why This Matters
The existence of LLSVPs may have influenced the formation of Earth’s tectonic plates, a critical factor in the planet’s habitability. The African LLSVP has even been linked to weakening of Earth’s magnetic field over the Atlantic. Understanding these deep-Earth processes can provide insights into the evolution of other planets as well.
If we can understand how Earth evolved, we can better understand why it’s so special. Miyazaki concludes that this study provides a more coherent narrative for Earth’s formation, bringing scientists closer to a complete picture of our planet’s complex history.
