MILAN - In what seems like a chapter from "Journey to the Centre of the Earth", the chemical composition of a small and extremely rare gem has led some researchers to think that there might be some oceans hundreds of kilometres under the surface of the Earth.
A special mineral
The mineral in question is ringwoodite, which forms when olivine, an extremely common material of the Earth's mantle, is exposed to high pressure. When it is exposed to a less pressurised environment, it returns being olivine. Graham Pearson, a diamond expert at the University of Alberta, stumbled upon a small and apparently useless 3 mm piece of brown diamond in Mato Grosso, Brazil, while he was looking for another type of mineral. Within that diamond, he and his team found some ringwoodite and discovered that 1.5% of the weight of this ringwoodite was formed by trapped water. The data have been published on Nature.
Thanks to the analysis of the depth at which this mineral has been found and to the composition of the water that it contains, Pearson thinks there might be water in the depths of the surface of the Earth. The discovery confirms the estimates of some experiments performed at high pressure in the laboratory, which suggested that a water reserve equal in size to the combined mass of all the oceans is found under the Earth's mantle. This is also suggested by an analysis performed by Hans Keppler, of Beyreuth University, in Germany. The Earth's crust, including all the deepest parts of the oceans, is around 100 kilometres in depth. From there, the higher part of the mantle spans around 300 kilometres. Between the higher and lower parts of the mantel lies the section of origin of ringwoodite, an area that is found between 410 and 660 kilometres under the Earth's surface, known as "transition zone".
In another article we reported that a study revealed how around 400 miles under the Earth's mantle of North America there might be a hidden water reserve trapped in this mineral. The discovery can help explain how the Earth's water supply works and how underground water might influence the movement of the Earth's crust.
di Alessandro Conte