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Study: Deep beneath the earth, more water than in all the oceans combined

(Source: NASA)

In the remote and forested terrain of Juina in western Brazil, an ugly rock with an uglier name surfaced months ago inside a diamond mine. It was a tiny green crystal, all scars and bumps. It “literally look[ed] like [it had] been to hell and back,” one scientist said in March. But despite the provenance, the ringwoodite stone wasn’t scorched — it was, in fact, sopping wet.

Providing an unparalleled glimpse into the our planet’s innards, the stone rode a violent volcanic eruption to the surface from 325 miles inside the Earth’s mantle. “The eruption … is analogous to dropping a Mentos mint into a bottle of soda,” Graham Pearson, a geochemist at the University of Alberta, told LiveScience. “It’s a very energetic, gas-charged reaction that blasts its way to the Earth’s surface.”

It was one of the first times anyone had seen the sponge-like ringwoodite in anything but a meteorite or a laboratory. Formed only in conditions of extreme pressure, it is composed of 1.5 percent water and appeared to confirm that the Earth’s insides are very, very wet. “It translates into a very, very large mass of water, approaching the sort of mass of water that’s present in all the world’s ocean,” Pearson said.

Actually, according to fresh research published in this issue of Science, it may be substantially more than that. The findings, researchers theorize, tell us what makes our planet blue and suggests how the Earth formed. The oceans weren’t perhaps the product of icy comets as earlier research theorized, but were the result of geological and tectonic activity that drove water to the surface.

Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” co-author Steve Jacobsen of Northwestern University said in a statement. “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”

Scientists have long suspected there was a lot of water beneath our feet, but this may be the first direct evidence that a vast reservoir of water is locked inside the mantle’s “transitional zone.” The significance: If just 1 percent of the “transitional zone” is made up of water, researchers say, it would triple the amount of water on the Earth’s surface.

The study produced laboratory evidence showing that rock melting and shifting inside the transitional zone traps water. “It’s good evidence the Earth’s water came from within,” Jacobsen told New Scientist.

Of course, it’s not the kind you can put in your Brita, nor would it save a desert wanderer. It’s trapped in the molecular structure of the rock.

Researchers got to that conclusion by studying seismic waves produced by North American earthquakes. These afforded a peek into the regional deep crust. Then to corroborate their suspicions, they put ringwoodite into conditions similar to 400 miles below the Earth’s surface, which showed how the water is trapped.

“When a rock with a lot of H20 moves from the transition zone to the lower mantle it needs to get rid of the H20 somehow, so it melts a little bit,” Schmandt said. “This is called dehydration melting.”

Then, “once the water is released,” researcher Jacobsen added, “much of it may become trapped there in the transition zone” about 400 miles deep in the Earth.

And its a good thing, too, Jacobsen told New Scientist: “We should be grateful for this deep reservoir. If it wasn’t there, it would be on the surface of the Earth, and mountain tops would be the only land poking out.” 

Terrence McCoy covers poverty, inequality and social justice. He also writes about solutions to social problems.



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