There could be an ocean’s worth of water more than 500km under the Earth’s surface that equals the known water content across the entire planet.
Findings published in the latest issue of the journal Nature show that water was found in a sample of ringwoodite, a stone formed under extreme pressure inside the Earth’s mantle.
“[T]he Earth’s transition zone, at depths between 410 and 660 kilometres, could be a major repository for water,” reads an excerpt from the study’s findings.
The ringwoodite discovery was made by Professor Graham Pearson of the University of Alberta during an excavation in Mato Grosso, Brazil. When Pearson’s team examined a seemingly worthless brown diamond that they had uncovered they found the ringwoodite sample within, which contained about 1.5 percent water.
However, Pearson and his team acknowledge the finding, the first of its kind, does not flatly settle the water theory, noting, “The issue of whether the transition zone contains abundant water remains highly controversial.”
But Pearson himself is now convinced, telling the Edmonton Journal, “What you can definitely say from our finding is that there are oases of water, wet spots, in the deep Earth. Now, if you extrapolate it to the whole of this area we call the transition zone, it means there might be the same mass of water as what’s held in all of the world’s oceans.”
If Pearson is correct, the presence of water deep under the Earth’s surface could help scientists better understand the shifting of tectonic plates, which may be thinned and corroded by the presence of water.
As to the existence of the ringwoodite sample itself, Pearson and his team say it was likely pushed to the Earth’s surface by a volcanic eruption.
So, where did all this water, if it actually exists, come from? Pearson says it may have literally been sucked down beneath the Earth’s surface as tectonic plates shifted. Or, in a scenario out of a science fiction writer’s imagination, it could be primordial water tucked away beneath the planet’s surface dating back to the formation of the Earth itself.
In an accompanying Nature article, University of Bayreuth geochemist Hans Keppler cautions that no firm conclusions can be made based on the single ringwoodite sample. Still, he writes that the most likely scenario does in fact point to large reservoirs of water trapped deep underground.
"If the source of the magma is an unusual mantle reservoir, there is the possibility that, at other places in the transition zone, ringwoodite contains less water than the sample found by Pearson and colleagues," Keppler writes.
"However, in light of this sample, models with anhydrous, or water-poor, transition zones seem rather unlikely."