An international team of scientists led by Graham Pearson, Canada Excellence Research Chair in Arctic Resources at the University of Alberta, has discovered the first sample of a mineral called ringwoodite.
The sample was found within a three‑millimetre‑wide brown diamond, the least valuable type of diamond. Analysis of the mineral has revealed a significant amount of water—1.5 per cent of its weight. This stunning discovery, published in Nature magazine on March 13, 2014, has helped Pearson and his team confirm scientific theories about vast volumes of water trapped 410 to 660 kilometres beneath the Earth, between the upper and lower mantles.
“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.”
Ringwoodite is a form of the mineral peridot, which is believed to exist in large quantities under high pressures in the transition zone. Ringwoodite has been found in meteorites but, until now, no terrestrial sample had been unearthed because scientists have been unable to conduct fieldwork at extreme depths.
Pearson’s sample was found in 2008 in Brazil, where artisan miners unearthed the host diamond from shallow river gravel. The diamond had been brought to the Earth’s surface by a volcanic rock known as kimberlite—the volcanic rock found deepest in the Earth.
Pearson said the discovery was almost accidental in that his team had been looking for another mineral when they purchased the host diamond. The ringwoodite is invisible to the naked eye and buried beneath the surface of the sample.
For Pearson, one of the world’s leading authorities in the study of deep Earth diamond host rocks, the discovery ranks among the most significant of his career, confirming about 50 years of theoretical and experimental work by geophysicists, seismologists and other scientists trying to understand the makeup of the Earth’s interior.
Find out more about Pearson’s discovery.