New Discovery: Water Exists Far Deeper in the Earth Than Previously Thought

Scientists found a mineral that may offer clues to how much water is stored deep in the Earth.

In a paper published in the Proceedings of the National Academy of Sciences (PNAS), two scientists discussed their findings of a high-pressure phase of a mineral far below the Earth's surface - about 400 to 600 kilometers into the mantle - that could store water.

According to Mainak Mookherjee, assistant professor of geology at Florida State University and Andreas Hermann of University of Edinburgh, water is stored and transported through a high-pressure polymorph of the mineral brucite, saying that the discovery "opens up a Pandora's Box."

Scientists previously thought that brucite was not thermodynamically stable so far down below the Earth. But the find offers more valuable insight about the planet's interior.

"We didn't think water could be stored by hydrous minerals such as brucite," Mookherjee said in a statement. "But now that we know it's there, we need to figure out how much water could be effectively stored inside it."

Based on high-pressure experimental studies, scientists know that minerals capable of transporting water - such as brucite - had limited stability, especially far beneath the Earth where they typically decompose. As they decompose, the minerals release the water, which is recycled back to the surface through volcanic activity.

However, the discovery of a high-pressure phase of brucite could mean that water may be efficiently transported to far deeper into the Earth without decomposing.

"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."

Mookherjee emphasized that water deep in the Earth plays a critical role in sustaining geological activity below the planet's surface. If the planet dries up on the inside, geodynamic activity ceases and this could lead to the Earth's death.

The researchers are planning to follow up on their paper and conduct more simulations to understand the physical properties of brucite deep in the Earth and determine how much water is potentially stored below.