Scientists have discovered the first-ever earthly sample of a water-rich mineral they say provides new proof that there are vast oceans of water deep beneath the Earth’s surface.
The team, led by Graham Pearson from Canada’s University of Alberta, found a mineral called ringwoodite in a sample of rock taken from a Brazilian riverbed. Ringwoodite is a form of the gem-quality mineral peridot. Scientists believe there’s a sizable amount of peridot in part of Earth’s mantle called the transition zone, a high-pressure area located between the lower and upper mantle.
While ringwoodite has been found in meteorites, it hadn’t been previously detected in earthen samples. Its color can range from deep blue to red, violet, or it can even be colorless. Scientists have not been able to do the kind of research to locate ringwoodite because of the depths that would be involved in searching for and retrieving the mineral from its theorized location. The sample of ringwoodite found by the research team was designated a water-rich mineral after the scientists conducted an analysis that indicated that 1.5 percent of its total weight is water.
Researchers said the presence of this water confirms the theories that there are vast bodies of water being held somewhere between 410 and 660 kilometers below the surface of the Earth.
“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.”
Pearson said that their discovery almost didn’t happen since he and his team were originally looking for another mineral when they first obtained a little hunk of what they referred to as a “three-millimeter-wide, dirty-looking, commercially worthless brown diamond” in 2009. They didn’t spot the ringwoodite until they happened to dig beneath the diamond’s surface.
“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.”
The brown diamond sample Pearson’s team worked with was found in shallow river gravels by Brazilian miners in 2008. The scientists believe the diamond made it to Earth’s surface via a volcanic rock called kimberlite, which has been known to contain diamonds. Formation of kimberlite takes place deep within the Earth’s mantle and is considered to be one of the deepest of all volcanic rocks.
The research team analyzed their sample of ringwoodite for several years. Among the techniques that were used to confirm the find were Raman and infrared spectroscopy as well as X-ray diffraction. The team measured the water content of the mineral at Pearson’s Arctic Resources Geochemistry Laboratory at the University of Alberta.
Scientists have debated the structure of Earth’s transition zone; some say the region of the mantle is full of water, while others insist is dry.
Pearson and his team say being able to provide some proof that water does exists deep within the Earth will provide insight to those who study volcanism as well as plate tectonics.
“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.”
The Pearson team’s research and findings are featured in Nature.