A mysterious layer lies beneath Earth’s massive tectonic plates.
Sandwiched between two rock layers — the rigid lithosphere and the more pliable asthenosphere— this thin boundary is like the jelly in a peanut butter sandwich. Scientists think it could be very wet rock, or even partially melted rock, but no one knows for sure.
“There have been a lot on conflicting studies,” said Kerry Key, a seismologist at the Scripps Institution of Oceanography in San Diego.
Understanding the nature of the boundary layer and its role in plate tectonics is one of the grand challenges in seismology, according a list assembled by the Incorporated Research Institutions for Seismology in 2009.
Now, a new study co-authored by Key appears to confirm the boundary zone is molten magma, at least under the ocean floor. Off the coast of Nicaragua, beneath the Cocos tectonic plate, researchers discovered a 15-mile-thick (25 kilometers) layer of partially melted rock at the bottom of the lithosphere. The results are published today (March 20) in the journal Nature.