Deep underground, water, water everywhere but not a drop to drink

WASHINGTON Fri Jun 13, 2014 7:57pm EDT

A Schematic cross section of the Earth’s interior is pictured in this undated handout illustration obtained by Reuters on June 13, 2014.   REUTERS/Steve Jacobsen/Handout via Reuters

A Schematic cross section of the Earth’s interior is pictured in this undated handout illustration obtained by Reuters on June 13, 2014.

Credit: Reuters/Steve Jacobsen/Handout via Reuters

Related Topics

WASHINGTON (Reuters) - 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 on Friday said massive amounts of water appear to exist deep beneath the planet's surface, trapped in a rocky layer of the mantle at depths between 250 miles and 410 miles (410 km to 660 km).

But do not expect to quench your thirst down there. The water is not liquid - or any other familiar form like ice or vapor. 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," Northwestern University geophysicist Steve Jacobsen said in a telephone interview. "It alters our thoughts about the composition of the Earth."

"It's no longer liquid water that we're talking about at these great depths. The weight of hundreds of kilometers of rock and very high temperatures above 1,000 degrees Celsius (1,832 Fahrenheit) break down water into its components. And it's not accessible. It's not a resource in any way," Jacobsen added.

Jacobsen said water is taken down into the mantle with minerals during the process known as plate tectonics - the slow, inexorable movement of the colossal rock slabs that make up the Earth's surface.

When the minerals containing this water reach certain depths, they break down in a process called dehydration and release the water to form magmas. Such "dehydration melting" is common in the shallow mantle and forms the source for magmas in many volcanoes.

In a study published in the journal Science, the researchers present evidence that this is also occurring much deeper in the mantle in a region called the "transition zone" between Earth's upper and lower mantle.

The study combined lab experiments involving synthetic ringwoodite being exposed to conditions simulating the heat and pressure of the "transition zone" and observations of events in this zone based on seismic data from a network of more than 2,000 seismometers across the United States.

A team led by Jacobsen and University of New Mexico seismologist Brandon Schmandt identified deep pockets of magma, a likely signature of the presence of water at those depths.

"Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles (80 km)," Schmandt said in a statement. "If there is a substantial amount of H2O in the transition zone, then some melting should take place in areas where there is flow into the lower mantle, and that is consistent with what we found."

The research built on another study in March showing that a commercially worthless diamond found in Brazil contained ringwoodite that entrapped water amounting to more than 1 percent of its weight. Ringwoodite has been found in meteorites, but this was the first terrestrial sample because it normally is so deeply buried.

(Reporting by Will Dunham; Editing by Jonathan Oatis)

FILED UNDER:
We welcome comments that advance the story through relevant opinion, anecdotes, links and data. If you see a comment that you believe is irrelevant or inappropriate, you can flag it to our editors by using the report abuse links. Views expressed in the comments do not represent those of Reuters. For more information on our comment policy, see http://blogs.reuters.com/fulldisclosure/2010/09/27/toward-a-more-thoughtful-conversation-on-stories/
Comments (2)
morbas wrote:
Challenges comet source of water hypothesis. The oceans exist because the mantle is not ready to absorb it. Mar oceans may have been absorbed into a cold mantle. The Earth Thea moon fomation may have driven water out of the mantle, I never thought much of comet water source.
morbas

Jun 14, 2014 12:40pm EDT  --  Report as abuse
Mafettig wrote:
Studied this in a previous life…when the water gets so hot it turns back into steam, pockets form, which force the movement of the plates

Jun 18, 2014 5:36pm EDT  --  Report as abuse
This discussion is now closed. We welcome comments on our articles for a limited period after their publication.

Photo

California's historic drought

With reservoirs at record lows, California is in the midst of the worst drought in decades.  Slideshow