Study of diamonds reveals that water exists in Earth’s mantle

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Diamonds are a geoscientist’s best friend — this is especially true for a group of researchers who recently found hard evidence that water exists deep within Earth’s mantle by examining diamonds from around the world.

The 11 authors of the study come from a variety of institutions and were led by Oliver Tschauner, a research professor of geoscience at the University of Nevada, Las Vegas. Each author had different roles in the experiment. According to George Rossman, a California Institute of Technology professor of mineralogy in the division of geological and planetary sciences and a contributor to the experiment, the experiment involved collecting diamonds from deep within Earth’s mantle and putting them underneath a high-intensity X-ray machine called a synchrotron.

According to Shichun Huang, an igneous petrologist and another researcher on the experiment, the study was a national effort and included labs such as the Lawrence Berkeley National Laboratory and the Argonne National Laboratory.

“Oliver, who was the first author on the paper … found that these diamonds don’t just have a trace of water, they actually have microscopic inclusions of water. But the water is in so much pressure in the diamonds that it is converted into ice,” Rossman said. “It is not the type of ice that you have in your refrigerator. It is a result of pressure (and is) known as ice-VII.”

According to Rossman, Tschauner was not initially looking for water in the Earth’s mantle when he started the experiment, but he had set out to find high pressure forms of dry ice.

Rossman said the idea that there had been water in the mantle has always been speculated about, but now they have direct evidence that it is there. Vitali Prakapenka, a beamline scientist and research professor at University of Chicago and a researcher involved in the study, said the discovery was important because of the information it gives about the chemical composition of the mantle.

“(The) most important part of this study is that … it basically tells us that there is water in the mantle that will change our understanding of … Earth’s formation,” Prakapenka said.

In the future, Huang said they will continue to gather diamonds to examine and study.

“We are here to get a better idea of where the ice-VII comes from. Another project is to look at the diamonds around the world,” Huang said. “So far in this type we have looked at 13 diamonds, and we are looking to look at more. We are collecting more diamonds around the world.”

Contact Sabrina Dong at [email protected] and follow her on Twitter at @Sabrina_Dong_.

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