If you want to find earth’s vast reservoirs of water, you may have to look beyond the obvious places like the oceans and polar ice caps. Scientists say they have found a vast reservoir of water – enough to fill the world’s oceans three times over – trapped up to 660km beneath the crust of the earth, potentially transforming our understanding of how the planet was formed.
But do not expect to quench your thirst down there. The water is not liquid – or any other familiar form like ice or vapour. It is locked inside the molecular structure of minerals called ringwoodite and wadsleyite in mantle rock that possesses the remarkable ability to absorb water like a sponge.
“It may equal or perhaps be larger than the amount of water in the oceans,” said Northwestern University geophysicist Steve Jacobsen, who co-authored a study in the journal Science. “It alters our thoughts about the composition of the earth.”
He said the finding suggested the earth’s water may have come from within, driven to the surface by geological activity rather than being deposited by icy comets hitting the forming planet.
“I think we are finally seeing evidence for a whole-earth water cycle, which may help explain the vast amount of liquid water on our planet,” he said.
Jacobsen and his colleagues are the first to provide direct evidence that there may be water in an area of the Earth’s mantle known as the transition zone. They based their findings on a study of a vast underground region extending across most of the interior of the United States.
Scientists used data from the USArray – a network of seismometers across the US that measures the vibrations of earthquakes – and a series of laboratory experiments on rocks simulating the high pressures found more than 600km underground.
It produced evidence that the melting and movement of rock in the transition zone led to a process where water could become fused and trapped in the rock.
The discovery is remarkable because most melting in the mantle was previously thought to occur at a much shallower distance, about 80km below the earth’s surface.
“If [the stored water] wasn’t there, it would be on the surface of the earth, and mountaintops would be the only land poking out,” he said.
Additional reporting by Reuters
* An earlier version of this article incorrectly carried the headline 'Vast ocean found under core of the Earth'.