Scientists have discovered a hidden layer of Earth, which sits 100 miles below the surface and covers at least 44 percent of the planet.
This previously unknown region of molten rock is part of the asthenosphere, located under tectonic plates in the upper mantle, which forms a soft boundary that allows the solid rock slabs to move.
While the discovery is significant, it shatters long-held theories that molten rocks influence the asthenosphere’s viscosity.
Junlin Hua, with the University of Texas, Austin, said in a statement: ‘When we think about something melting, we intuitively think that the melt must play a big role in the material’s viscosity.
‘But what we found is that even where the melt fraction is quite high, its effect on mantle flow is very minor.’
Scientists identified a previously unknown layer of Earth. The newly discovered region of molten rock sits 100 miles below the crust
Previous theories have suggested that the movement of these tectonic plates is likely caused by convection currents in the molten rock in Earth’s mantle below the crust.
This idea would explain how the solid rock slabs can move seamlessly under the surface.
However, the University of Texas, Austin researchers have put this theory to rest.
And while it may seem like a blow to the scientific community, coauthor Thorsten Becker said this means one less tricky variable for computer models of the Earth.
‘We can’t rule out that locally melt doesn’t matter,’ said Becker, who designs geodynamic models of the Earth at the Jackson School’s University of Texas Institute for Geophysics.
‘But I think it drives us to see these observations of melt as a marker of what’s going on in the Earth, and not necessarily an active contribution to anything.’
The molten rock layer covers at least 44 percent of Earth and may play a role in to why the asthenosphere, located under tectonic plates in the upper mantle, is soft
The idea to look for a new layer in Earth’s interior came to Hua while studying seismic images of the mantle beneath Turkey during his doctoral research.
Intrigued by signs of partly molten rock under 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, appearing on seismic readings wherever the asthenosphere was hottest.
The next surprise came when he compared his melt map with seismic measurements of tectonic movement and found no correlation, despite the molten layer encompassing almost half the Earth.
Coauthor 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’s weak is fundamental to understanding plate tectonics.’
The discovery of a new layer comes less than one month after scientists announced that Earth’s inner core rotation is slowing down.
A team from Peking University in China revealed that days on Earth could be increasing in length, thanks to changes in the rotation speed of our planet’s inner core.
