Water crystals found inside diamonds that formed deep below the Earth's surface provide the first evidence that there is liquid water deep in the Earth's mantle.

Ice VII

University of Nevada mineralogist Oliver Tschauner and colleagues analyzed diamonds belched from hundreds of kilometers below the Earth's surface and found crystallized water called ice VII, which forms under high pressure.

The diamonds, which were unearthed from several sites in China and southern Africa, were analyzed using the Advanced Photon Source at Argonne National Laboratory in Illinois. X-rays that bounced off of the rocks revealed that more than a dozen of the diamonds have ice VII.

Recognized As A New Mineral

This particular water crystal is formed in laboratories under high pressure but the ice described in the new study published in the journal Science is the first known natural sample. It is now recognized as a new mineral by the International Mineralogical Association.

Liquid Water Exists Deep In The Mantle

Researchers said that the presence of ice inside the diamonds suggests that pockets of watery fluids exist deep in the mantle, the Earth's layer that is sandwiched between the crust and the core and is made up mostly of solid and very hot rock under immense pressure. The Earth's mantle makes up most of the Earth's volume.

Tschauner said that the water in is free-floating and remains liquid despite the high temperatures in the mantle. Analyses suggest that some of the diamonds that the researchers studied formed at great depths of 610 to 800 kilometers below the Earth's surface.

How Ice Vii Formed Inside Diamonds

During the formation of these diamonds, they must have encapsulated liquid water from around the mantle's transition zone, which is located between the lower mantle and the upper mantle. The high temperatures here prevented the water from crystallizing under high pressure. As the diamonds moved to the surface due to geologic activities, however, the temperature dropped causing the water inside the diamonds to freeze into ice-VII.

"We show that ice-VII occurs as inclusions in natural diamond and serves as an indicator for such water-rich regions," the researchers wrote in their study. "In particular, ice-VII in diamonds points toward fluid-rich locations in the upper transition zone and around the 660-kilometer boundary."

Although the study provided the direct evidence of unbonded water at extreme depths, the researchers were not able to determine how large these water pockets are and how common they are.