Scientists detect a new layer of molten rock hidden under Earth’s tectonic plates

Scientists have discovered a hidden layer of the earth, which is located 100 miles below the surface and covers at least 44% of the planet.

This previously unknown region of molten rock is part of the asthenosphere, located under tectonic plates in the upper mantle, that forms a smooth boundary that allows slabs of solid rock to move.

While the discovery is significant, it shatters long-held theories that molten rock influences the viscosity of the asthenosphere.

Junlin Hua, from the University of Texas, Austin, said in a statement: “When we think of something melting, we intuitively think that melting must play a significant role in the viscosity of the material. But what we found is that even when the melt fraction is quite high, its effect on mantle flow is very small.”

Previous theories have suggested that the movement of these tectonic plates is probably caused by convection currents in the molten rock in the Earth’s mantle below the crust. This idea would explain how slabs of solid rock can move seamlessly below the surface.

However, researchers at the University of Texas, Austin have dismissed this theory. And while it may seem like a blow to the scientific community, co-author Thorsten Becker said that this means a less complicated variable for computer models of Earth.

“We cannot rule out that local melt doesn’t mattersaid Becker, who designs geodynamic models of the Earth at the University of Texas Institute of Geophysics at the Jackson School. “But I think it leads us to view these meltdown observations as a marker of what’s happening on Earth, and not necessarily as an active contribution to anything.”

The idea to search for a new layer in the interior of the Earth occurred to Hua while studying seismic images of the mantle under Turkey during his doctoral research.

Intrigued by the signs of partially molten rock beneath the crust, Hua compiled similar images from other seismic stations until he had a global map of the asthenosphere.

What he and others had taken to be an anomaly was commonplace around the world, showing up in seismic readings where the asthenosphere was hottest.

The next surprise came when he compared his melt map with seismic measurements of tectonic movement and it found no correlation, despite the fact that the melt layer covered almost half of the Earth.

Co-author Karen Fischer, a seismologist and professor at Brown University, said: “This work is important because understanding the properties of the asthenosphere and the origins of why it is weak is critical to understanding plate tectonics.”

The discovery of a new layer comes less than a month after scientists announced that the rotation of Earth’s inner core is slowing.

A team from Peking University in China revealed that days on Earth could be increasing in length, thanks to changes in the rotation rate of our planet’s inner core. (YO)