WASHINGTON: Water exists far deeper in the Earth - about 400 to 600 kilometres into the mantle - than previously believed, researchers including one of Indian origin have found.
A mineral far below the surface of the Earth may hold the key to how much water is stored in our planet, researchers said.
Mainak Mookherjee, Assistant Professor at Florida State University in the US and Andreas Hermann from the University of Edinburgh in the UK estimate that in the deep Earth - roughly 400 to 600 kilometres into the mantle - water is stored and transported through a high-pressure polymorph of the mineral brucite.
Previously, scientists thought brucite was not thermodynamically stable that deep in the Earth.
"This opens up a Pandora's Box for us. We did not think water could be stored by hydrous minerals such as brucite. But now that we know it is there, we need to figure out how much water could be effectively stored inside it," Mookherjee said.
Based on high-pressure experimental studies, scientists knew minerals that transported water - such as brucite - had limited stability and that these minerals decomposed in the deep Earth.
As they decomposed, they released the water, which is recycled back to surface via volcanic activity.
However, this discovery of a new high-pressure phase of brucite indicates that water could be efficiently transported to far deeper realms without decomposition.
"We had to do quantum-mechanical calculations on thousands of potential structures until we found the one we now reported," Hermann said.
"It really is remarkable that such a well-studied mineral as brucite has something so surprising to offer," he said.
Water plays a critical role in sustaining geological activity below the Earth's surface. Scientists have been working for years to quantify the oceans' worth of water that lay hidden in the crust and mantle.
"For the activity of the planet, deep Earth water is equally important to water on the surface," Mookherjee said.
"My goal is to understand how much water is stored in the deep Earth. If the planet becomes dry on the inside, the planet dies because geodynamic activity within the planet ceases," he said.
The research was published in the journal PNAS.