Molten Rock Boundary Discovered Deep Within Earth's Mantle (Video)

The mystery of what lies beneath our Earth's surface may have been solved--at least partially. A new study seems to confirm that the boundary that lies between the rigid lithosphere and the more pliable asthenosphere is actually made out of molten magma.

The findings, published in the journal Nature, were a surprise even to the researchers. They had intended to try and understand the crustal fluid cycle at the subduction zone. During the course of their research, though, they stumbled upon a partial-melt layer that implied that the "in-between" layer was molten.

The lithosphere is Earth's rigid, outermost layer. Up to 150 miles thick, it's made out of Eath's crust and the uppermost portion of the mantle. It is responsible for forming the continental and oceanic plates that shift around the planet's surface. The asthenosphere, in contrast, is a highly pliable, heated layer located beneath the lithosphere and is involved in plate tectonic movement. Seismic waves pass relatively slowly through the asthenosphere while they pass much faster through the rigid lithosphere. In past decades, it was thought that the boundary layer between the two was likely melt-free and weakened by water-rich minerals.

These new findings prove otherwise. The researchers mapped the molten layer beneath the Cocos plate, located beneath Central America, using a technique that looks for subtle variations in Earth's naturally occurring electric and magnetic fields. The electromagnetic data shows far more sensitivity to features like this and can reveal pockets of liquid, such as oil and gas reservoirs.

In this case, though, the scientists didn't find oil and gas. Instead, they found the boundary.

"The information from the new images confirms the idea that there needs to be some amount of melt in the upper mantle and that's really what's creating this ductile behavior for plates to slide," said Samer Naif, Scripps graduate student, in an interview with UPI.

Learning more about the boundary could allow scientists to better understand earthquakes and other geological processes. The team plans to learn why the magma is there, and what events led to its formation.

Want to see the researchers in action? Check out the amazing lightning storm as they deployed their equipment, courtesy of Scripps Institute of Oceanography.