In 2008, gem hunters in Brazil found a small and seemingly worthless brown diamond, which was later on bought by scientists who were looking for another mineral, for a mere $20. What looked like a commercially-worthless diamond, however, turned out to be a rare and precious find as scientists found it contains evidence that there is water deep inside earth.
Inside the rough diamond was a microscopic trace of ringwoodite, a mineral similar to olivine that only forms under extremely hot and pressurized environment such as deep within the Earth's mantle. Most of the ringwoodite samples found in laboratories came from meteorites and no sample has yet been unearthed from the Earth's surface because scientists have to dig the mineral from extreme depths.
Scientists theorized that the brown diamond may have rocketed out to the earth's surface during a violent volcanic eruption known as kimberlite when it hitchhiked with volcanic rocks. "The eruption of a kimberlite is analogous to dropping a Mentos mint into a bottle of soda," explained Graham Pearson, a professor in the Faculty of Science at the University of Alberta in Edmonton, Canada . "It's a very energetic, gas-charged reaction that blasts its way to Earth's surface."
In the study "Hydrous mantle transition zone indicated by ringwoodite included within diamond" published in the journal nature March 13, Pearson and colleagues analyzed the mineral and found that 1.5 percent of its weight is made up of water molecules, giving hints of large quantities of water trapped 410 to 660 kilometers below the Earth's surface.
"This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area," said Pearson. "That particular zone in the Earth, the transition zone, might have as much water as all the world's oceans put together."
Hans Keppler, a geochemist at the University of Bayreuth in Germany, however, noted that it is possible that not all of the transition-zone layer are as wet as hinted by the ringwoodite and that the volcanic eruption that brought the diamond to the surface may just have brought magma from the water-rich part of the mantle.
"If the source of the magma is an unusual mantle reservoir, there is the possibility that, at other places in the transition zone, ringwoodite contains less water than the sample found by Pearson and colleagues," Keppler said. "However, in light of this sample, models with anhydrous, or water-poor, transition zones seem rather unlikely."
