March 13, 2014

Could There Be Vast Oceans Of Water Beneath The Earth’s Mantle?

April Flowers for redOrbit.com - Your Universe Online

The first terrestrial sample of a water-rich gem that reveals new evidence about the existence of large volumes of water has been discovered by an international team of scientists which was led by University of Alberta's diamond scientist, Graham Pearson.

Analysis of the gem, called ringwoodite, reveals that it contains a significant amount of water — 1.5 percent of its own weight. These findings, reported in a recent issue of Nature, confirms certain scientific theories that vast volumes of water are trapped 250 to 400 miles underneath the surface of the planet, between the upper and lower mantle.

"This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area," said Pearson, a professor in the Faculty of Science, and Canada Excellence Research Chair in Arctic Resources at the U of A. "That particular zone in the Earth, the transition zone, might have as much water as all the world's oceans put together."

The new gem ringwoodite is a form of the mineral peridot, thought to exist in vast quantities under high pressures in the transition zone. Scientists have found ringwoodite in meteorites before this, but no terrestrial sample has ever been found — mostly because scientists are unable to conduct fieldwork at extreme depths.

The sample identified by Pearson and his team was found in 2008 in the Juina area of Mato Grosso, Brazil. The host diamond, which was unearthed by artisan miners from shallow river gravels, was brought to the surface by a volcanic rock known as kimberlite. Kimberlite is the most deeply derived of all volcanic rocks.

The discovery, according to Pearson, was basically an accident. His team had been looking for another mineral when they purchased the three-millimeter-wide, dirty-looking, commercially worthless brown diamond. Ringwoodlite is impossible to see with the naked eye, and it was buried beneath the surface of the diamond. So its discovery in 2009, by Pearson's graduate student John McNeill, was a fortunate accident.

"It's so small, this inclusion, it's extremely difficult to find, never mind work on," Pearson said, "so it was a bit of a piece of luck, this discovery, as are many scientific discoveries."

Using Raman and infrared spectroscopy and X-ray diffraction, the sample underwent years of analysis before it was officially confirmed as ringwoodite. Pearson's Arctic Resources Geochemistry Laboratory — which forms part of the world-renowned Canadian Centre for Isotopic Microanalysis, also home to the world's largest academic diamond research group — performed the critical water measurements.

The research team included members from the Geoscience Institute at Goethe University, University of Padova, Durham University, University of Vienna, Trigon GeoServices and Ghent University. Pearson, himself one of the world's leading authorities in the study of deep Earth diamond host rocks, ranks this discovery as being among the most significant of his career. According to Pearson, this finding confirms about 50 years of theoretical and experimental work by geophysicists, seismologists and other scientists trying to understand the makeup of the Earth's interior.

There has been a deep divide among scientists about the composition of the transition zone and whether it is full of water, or desert-dry. The discovery that water exists beneath the crust will affect the study of volcanoes and plate tectonics, affecting how rock melts, cools and shifts below the crust.

"One of the reasons the Earth is such a dynamic planet is the presence of some water in its interior," Pearson said. "Water changes everything about the way a planet works."