A trove of water may be hiding more than 250 miles (400 kilometers) beneath your feet.
That's where the Earth's mantle meets the crust. Geoscientists had long thought that below this transition zone (starting at 255 miles, or 410 km, deep) a water-filled mineral called brucite was unstable and so decomposed, sending water molecules flowing toward the planet's surface.
But new research suggests that before brucite — which is 50 percent magnesium oxide and 50 percent water — decomposes, it transforms into another, more stable 3D structure. The finding, detailed online Nov. 21 in the journal Proceedings of the National Academy of Sciences, means there's a stash of water located deeper in Earth than was previously thought. [In Photos: Ocean Hidden Beneath Earth's Surface
[This finding] was not entirely expected," said study co-author Andreas Hermann, a lecturer in computational physics at the University of Edinburgh in Scotland. "[That's] because people have studied this material for decades and nobody ever thought of looking whether there would be another phase before it eventually fell apart."
Probing deep Earth
Scientists previously believed that brucite remained stable only as far as the transition zone, a 155-mile-deep (250 km) layer just below the upper mantle. In part, the mineral's structure informed this view. Brucite is a layered material in which the molecules in each layer are strongly bound to each other but weakly connected to other layers. A material like this, if squeezed with enough pressure, must undergo some kind of change. Researchers previously assumed that in response to transition zone pressure, which reaches about 200,000 atmospheres, brucite would crumble. (One atmosphere is approximately is the pressure at sea level).
Unable to probe the deep Earth directly, Hermann and his co-author, Mainak Mookherjee, a professor of geology at Florida State University, used quantum-mechanical calculations, analyzing various possible structures for brucite in deep-Earth conditions.
This is big-data computing," said Hermann. "We create thousands of structures, optimize them all and do calculations accurate enough that if something stands out as more stable than something else, we can reliably say that it is so."
A trove of water may be hiding more than 250 miles (400 kilometers) beneath your feet.