University of Alberta scientists have found calcium silicate perovskite at Earth's surface. "Nobody has ever managed to keep this mineral stable at the Earth's surface," said Graham Pearson, a professor in the University of Alberta's Department of Earth and Atmospheric Sciences and Canada Excellence Research Chair Laureate. He explained the mineral is found deep inside Earth's mantle, at 700 kilometers.

"The only possible way of preserving this mineral at the Earth's surface is when it's trapped in an unyielding container like a diamond," he explained. "Based on our findings, there could be as much as zetta tonnes (1021) of this perovskite in deep Earth".

The team found the calcium silicate perovskite within a diamond mined from less than one kilometer beneath Earth's crust, at South Africa's famous Cullinan Mine (best known as the source of two of the largest diamonds in the British Crown Jewels). Pearson explained that the diamonds from the mine are among not only the most commercially valuable in the world, but are also the most scientifically valuable, providing insight into the deepest parts of Earth's core.

The particular diamond in question would have sustained more than 24 billion pascals of pressure, equivalent to 240,000 atmospheres. The diamond originated roughly 700 kilometers below Earth's surface, whereas most diamonds are formed at 150 to 200 kilometers depth.

"Diamonds are really unique ways of seeing what's in the Earth," said Pearson. "And the specific composition of the perovskite inclusion in this particular diamond very clearly indicates the recycling of oceanic crust into Earth's lower mantle. It provides fundamental proof of what happens to the fate of oceanic plates as they descend into the depths of the Earth."

This research saw Pearson team up with colleagues from the University of British Columbia who together lead a program-the Diamond Exploration Research and Training School, part of NSERC's Collaborative Research and Training Experience-to train the next generation of highly qualified diamond explorers.



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