Scientists have discovered a hidden layer of the Earth, which is 160 km below the surface and covers at least 44% of the planet, reported “Daily Mail”. This previously unknown region of molten rock is part of the asthenosphere, located beneath the tectonic plates in the upper mantle, which is a soft boundary that allows solid rock plates to move.
While the discovery is significant, it shatters long-held theories that molten rock affects the viscosity of the asthenosphere. Junlin Hua of the University of Texas at Austin said in a statement:
“When we think of something melting, we intuitively think that it must play a big role. But what we found is that even when the fraction of molten matter is quite high, its effect on mantle flow is very small.”
Previous theories suggested that the movement of these tectonic plates was probably due to convection currents in the molten rocks in the Earth’s mantle beneath the crust. This idea would explain how solid rock plates can move smoothly beneath the surface.
However, researchers from the University of Texas at Austin have put an end to this theory. And while that may seem like a blow to the scientific community, co-author Torsten Becker said it means one less complicated variable for computer models of Earth.
We can’t rule out that local melting doesn’t matter, said Becker, who designs geodynamic models of the Earth at the Institute of Geophysics at the University of Texas Jackson School.
“But I think it leads us to look at these observations of melting as a marker of what’s going on in the Earth, not necessarily as actively contributing to something.”
The idea to search for a new layer in the Earth’s interior occurred to Hua while studying seismic images of the mantle beneath Turkey during his doctoral research.
Intrigued by signs of partially molten rock beneath the Earth’s crust, Hua collected similar images from other seismic stations until he had a global map of the asthenosphere.
What he and others thought was an anomaly was common around the world, showing up in seismic readings wherever the asthenosphere was hottest.
The next surprise comes when he compares the map of the earth’s molten crust with seismic measurements of tectonic movements and finds no connection, even though the molten layer covers almost half the planet, bgvoice.bg reported.
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 origin of the causes of its weakness is fundamental to understanding plate tectonics.”
The discovery of the new layer comes less than a month after scientists announced that the rotation of Earth’s inner core is slowing down.
