Buried deep below Earth’s surface, about 1,800 miles down, are two giant structures known as large low shear velocity provinces (LLSVPs). These are found beneath Africa and the Pacific Ocean. Scientists have puzzled over these formations for years because they are hotter and denser than the surrounding rock, and their origin remains a mystery.
Recent research led by Yoshinori Miyazaki from Rutgers University and Jie Deng from Princeton suggests these LLSVPs may be remnants from Earth’s early days. According to their study in Nature Geoscience, these structures might have formed during a time when the planet was covered by a vast magma ocean. This study proposes a link between the deep mantle and chemical interactions with Earth’s core during its formation, offering new insights into what made our planet habitable.
The researchers believe that materials from the core slowly leaked into the magma ocean, altering its composition. This process could explain why there are noticeable seismic anomalies and unique chemical signatures in certain volcanic rocks.
Understanding LLSVPs
Scientists first discovered LLSVPs using seismic tomography, a method that visualizes what’s beneath the surface by analyzing earthquake waves. These waves slow down significantly when they pass through the LLSVPs, which can span thousands of kilometers and have complex internal structures. Surrounding these areas are ultra-low velocity zones (ULVZs), where waves slow down even more, suggesting unique material properties.
Current models can’t fully explain the massive size and longevity of LLSVPs or their chemical uniqueness. Past theories, including links to subducted oceanic crust, have fallen short. For instance, the presence of rare helium-3 and tungsten isotopes in volcanic hotspots like Hawaii hinted at a deep reservoir, but how that reservoir remained stable was unclear.
A New Perspective
The new model introduces a revised view of Earth’s formative years, when a global magma ocean was dominant. As Earth’s core cooled, lighter elements began to rise into the magma, changing its composition. This created a “basal exsolution contaminated magma ocean” (BECMO) where the core acted as a slow source of crucial materials like silica.
Instead of a simple, dense iron shell, this model suggests that a more varied layer rich in silicate minerals formed, eventually creating the LLSVPs. These dense structures are stable yet dynamic, influenced by mantle convection and capable of interacting with rising mantle plumes.
Chemical Signatures and Their Implications
Certain volcanic rocks reveal chemical characteristics hinting at a deep reservoir. For example, some basalts show unusual ratios and anomalies that don’t fit with known shallow mantle processes. The BECMO model offers a route for these signals to rise to the surface, suggesting that as materials moved up from the core, they carried with them trace amounts of elements like helium and tungsten.
While this model doesn’t answer every question, it provides a stronger narrative linking seismic data, geodynamic simulations, and chemical insights about Earth’s interior. According to Miyazaki, this new framework helps us better understand how Earth has evolved over billions of years.
Overall, these findings emphasize the deep connections within our planet and enhance our understanding of its history and composition. As research continues, scientists are hopeful that more discoveries will shed light on Earth’s mysterious deep layers.
