Melt: Scientists discover a new molten layer under Earth's crust

Here is something new from Earth's interiors.
Rupendra Brahambhatt
Earth core structure stock image.
Earth core structure stock image.


A team of researchers at the University of Texas at Austin (UTA) has found a new layer under Earth’s crust called "melt," according to a press release. It comprises hot molten rocks and reveals useful insights about our planet's tectonic plate activity. 

Tectonic plates are giant subterranean rocks that form the Earth’s crust and upper mantle. So basically, all the landmass we see around us is built upon tectonic plates. Currently, there are seven major tectonic plates on Earth that keep the seven continents intact.

Interestingly, these plates are constantly moving, and their movement is linked to the occurrence of earthquakes, tsunamis, and volcanic eruptions. Moreover, tectonic motion is so powerful; that it could also lead to the formation of new mountain ranges and even new continents. 

Therefore, it becomes very important to study and know the various factors that do and don’t affect Earth’s tectonic plate activity. 

Not everything that melts affects tectonic plates

Melt: Scientists discover a new molten layer under Earth's crust
Diagram depicting Earth's interiors.

The newly discovered layer melt is located 100 miles (161 km) under the Earth’s surface and is a part of the asthenosphere (the ductile layer beneath the lithosphere at 49 to 248 miles [80 to 400 km] depth from the surface). 

According to UTA researchers, the asthenosphere comprises hot molten rocks and functions as a “soft boundary,” allowing smooth movement of tectonic plates via the mantle (the region between Earth’s core and crust). However, what’s surprising is that melt – which is among the many layers of the asthenosphere doesn’t play any role in this.

“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,” explained Junlin Hua, lead researcher and postdoctoral fellow at UTA, in the press release.

Melt: Scientists discover a new molten layer under Earth's crust
Melt layer (dotted red region) in the asthenosphere.

Since tectonic plates move by the heat produced by Earth’s core and molten mass assist in their movement, scientists tend to associate layers like melt with tectonic plate activity. 

Every time this is done without much consideration, it adds many variables in the calculations that aim at modeling and studying our planet’s interiors. Making the models complex and inaccurate. 

However, these new findings suggest that not everything that contains molten rocks is supposed to be linked to plate tectonics. For instance, melt is found to have no influence on mantle flow, and therefore, it doesn’t affect tectonic motion. 

What does melt do?

Although some previous studies have also reported signs of melt. This is the first time scientists have confirmed the existence of this new layer beneath the Earth’s crust. 

Study author Hua found melt as an anomaly in the asthenosphere. He and his team were studying seismic images of the asthenosphere and discovered a unique molten region whose seismic readings were not at all in relation to the tectonic plate movement. 

They observed the same anomaly on a global scale and were astonished by the seismic properties of this molten region, which they called melt. They argue that just because the new layer doesn’t affect plate tectonics, it doesn’t imply, it’s of no importance. 

The fact it is unrelated to things we know means that maybe it serves an unexplored purpose beneath the Earth’s crust. “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,” said Karen Fischer, one of the study authors and an esteemed American seismologist. 

Hopefully, melt will help us understand various unknown aspects of the asthenosphere and other parts of Earth’s interiors in the future.

The study is published in the journal Nature Geoscience.

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