Scientists have made a groundbreaking discovery regarding the mysterious large low velocity provinces (LLVPs) located deep within Earth's mantle. These colossal blobs, found beneath the Pacific Ocean and Africa, might be remnants of Earth's crust that sank into the mantle over the last billion years.

Traditionally, LLVPs have puzzled researchers who knew that seismic waves—waves produced by earthquakes—travel significantly slower—by about 1% to 3%—in these regions compared to other parts of the mantle. This unique characteristic leads scientists to believe that LLVPs play a significant role in influencing the planet's magnetic field and heat flow emanating from the Earth's core.

For years, there has been an ongoing debate about the composition and origins of these LLVPs. Some theories posited that these blobs consist of primordial material dating back to the early formation of the Earth, including remnants from the massive asteroid impact that led to the formation of the moon 4.5 billion years ago. Other hypotheses suggested that they were vast portions of oceanic crust pushed into the mantle due to subduction, a geological process where one tectonic plate slides beneath another.

A recent study led by geodynamicist James Panton from Cardiff University added significant evidence to the subduction theory. Published in Scientific Reports, this groundbreaking research utilized advanced computer modeling to trace the paths of subducted oceanic crust entering the mantle over the past billion years. Remarkably, the findings demonstrated that the recycling of this oceanic crust is enough to form LLVP-like structures without needing an ancient dense layer at the base of the mantle.

Panton remarked, 'Our research indicates that these LLVPs are evolving on their own through the ongoing process of oceanic crust subduction.' This suggests that these peculiar regions are younger than previously thought, potentially dating back to when subduction processes first began on Earth. However, there's a possibility that a thin layer of ancient material still plays a role in the composition of these blobs.

Interestingly, the research highlights a difference between the two LLVPs. The LLVP beneath Africa is older and has a more uniform mix with surrounding crust, featuring less dense volcanic rock known as basalt. In contrast, the Pacific LLVP receives far more crustal material from the Pacific Ring of Fire—a horseshoe-shaped subduction zone that encircles the Pacific Ocean. This increased material flow might explain why the LLVP beneath Africa extends an impressive 342 miles (550 kilometers) higher in the mantle than its Pacific counterpart.

Looking ahead, one intriguing area of study for scientists is how mantle plumes—hot regions within the mantle that rise to create volcanic hotspots—might influence the processes of subduction and the behavior of these LLVPs. Such plumes extend from the mantle's depths to the Earth's surface, impacting areas far from the boundaries of tectonic plates.

This discovery sheds light not just on the structure and dynamics of Earth's interior but also raises questions about our planet's geological history and how these processes have shaped the world we live in today. Why are we only uncovering these mysteries now? Prepare for a thrilling exploration into the unseen forces that have been evolving right beneath our feet!