New evidence for oceans of water deep in the Earth

Jun 12, 2014
Photograph of a diamond-anvil cell (approximately 5 mm across). Between the tips of these gem diamonds, heating experiments on deep-mantle minerals were carried out at conditions of 660 km depth, or about 400 miles below the surface. The experiments revealed a dehydration reaction of the mineral ringwoodite, which can cause melting of the rock deep in the mantle. Evidence for that reaction was then observed in seismic waves passing through 660 km beneath North America, implying that a large amount of water (in the form of hydrated minerals) can reach these great depths through plate tectonics. Credit: Steve Jacobsen / Northwestern University

Researchers from Northwestern University and the University of New Mexico report evidence for potentially oceans worth of water deep beneath the United States. Though not in the familiar liquid form—the ingredients for water are bound up in rock deep in the Earth's mantle—the discovery may represent the planet's largest water reservoir.

The presence of liquid on the surface is what makes our "blue planet" habitable, and scientists have long been trying to figure out just how much water may be cycling between Earth's surface and interior reservoirs through plate tectonics.

Northwestern geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma located about 400 miles beneath North America, a likely signature of the presence of water at these depths. The discovery suggests water from the Earth's surface can be driven to such great depths by plate tectonics, eventually causing partial melting of the rocks found deep in the mantle.

The findings, to be published June 13 in the journal Science, will aid scientists in understanding how the Earth formed, what its current composition and inner workings are and how much water is trapped in .

"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," said Jacobsen, a co-author of the paper. "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 speculated that water is trapped in a rocky layer of the Earth's mantle located between the and upper mantle, at depths between 250 miles and 410 miles. Jacobsen and Schmandt are the first to provide direct evidence that there may be water in this area of the mantle, known as the "transition zone," on a regional scale. The region extends across most of the interior of the United States.

Schmandt, an assistant professor of geophysics at the University of New Mexico, uses seismic waves from earthquakes to investigate the structure of the deep crust and mantle. Jacobsen, an associate professor of Earth and planetary sciences at Northwestern's Weinberg College of Arts and Sciences, uses observations in the laboratory to make predictions about geophysical processes occurring far beyond our direct observation.

The study combined Jacobsen's lab experiments in which he studies mantle rock under the simulated high pressures of 400 miles below the Earth's surface with Schmandt's observations using vast amounts of seismic data from the USArray, a dense network of more than 2,000 seismometers across the United States.

Jacobsen's and Schmandt's findings converged to produce evidence that melting may occur about 400 miles deep in the Earth. H2O stored in mantle rocks, such as those containing the mineral ringwoodite, likely is the key to the process, the researchers said.

Fragments of the blue-colored mineral called ringwoodite, synthesized in the laboratory. This mineral is thought to exist in the mantle at depths between about 500 and 700 km depth. The laboratory-grown material can include a significant amount of water in its crystal structure (i.e. not in liquid form), but it was unknown whether or not water in the form of hydrated minerals such as ringwoodite can persist to 700 km depth. New evidence from experiments and from analysis of seismic waves passing through 700 km reveal that the layer of the Earth’s mantle from 410 to 660 km depth, which geophysicists call the transition zone, may contain a significant amount of H2O in the form of hydrated ringwoodite. Credit: Steve Jacobsen / Northwestern University

"Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles," said Schmandt, a co-author of the paper. "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."

If just one percent of the weight of mantle rock located in the transition zone is H2O, that would be equivalent to nearly three times the amount of water in our oceans, the researchers said.

This water is not in a form familiar to us—it is not liquid, ice or vapor. This fourth form is water trapped inside the molecular structure of the minerals in the mantle rock. The weight of 250 miles of solid rock creates such high pressure, along with temperatures above 2,000 degrees Fahrenheit, that a water molecule splits to form a hydroxyl radical (OH), which can be bound into a mineral's crystal structure.

Schmandt and Jacobsen's findings build on a discovery reported in March in the journal Nature in which scientists discovered a piece of the mineral ringwoodite inside a diamond brought up from a depth of 400 miles by a volcano in Brazil. That tiny piece of ringwoodite—the only sample in existence from within the Earth—contained a surprising amount of water bound in solid form in the mineral.

"Whether or not this unique sample is representative of the Earth's interior composition is not known, however," Jacobsen said. "Now we have found evidence for extensive melting beneath North America at the same depths corresponding to the dehydration of ringwoodite, which is exactly what has been happening in my experiments."

For years, Jacobsen has been synthesizing ringwoodite, colored sapphire-like blue, in his Northwestern lab by reacting the green mineral olivine with water at high-pressure conditions. (The Earth's is rich in olivine.) He found that more than one percent of the weight of the ringwoodite's crystal structure can consist of water—roughly the same amount of water as was found in the sample reported in the Nature paper.

"The ringwoodite is like a sponge, soaking up water," Jacobsen said. "There is something very special about the of ringwoodite that allows it to attract hydrogen and trap water. This mineral can contain a lot of water under conditions of the ."

For the study reported in Science, Jacobsen subjected his synthesized ringwoodite to conditions around 400 miles below the Earth's surface and found it forms small amounts of partial melt when pushed to these conditions. He detected the melt in experiments conducted at the Advanced Photon Source of Argonne National Laboratory and at the National Synchrotron Light Source of Brookhaven National Laboratory.

An EarthScope map illustrates the location of seismometers throughout North America. The EarthScope scientific community conducts multidisciplinary research across the Earth sciences utilizing freely available data from instruments that measure motions of the Earth's surface, record seismic waves, and recover rock samples from depths at which earthquakes originate.

Jacobsen uses small gem diamonds as hard anvils to compress minerals to deep-Earth conditions. "Because the diamond windows are transparent, we can look into the high-pressure device and watch reactions occurring at conditions of the deep mantle," he said. "We used intense beams of X-rays, electrons and infrared light to study the chemical reactions taking place in the diamond cell."

Jacobsen's findings produced the same evidence of partial melt, or magma, that Schmandt detected beneath North America using seismic waves. Because the deep mantle is beyond the direct observation of scientists, they use seismic waves—sound waves at different speeds—to image the interior of the Earth.

"Seismic data from the USArray are giving us a clearer picture than ever before of the Earth's internal structure beneath North America," Schmandt said. "The melting we see appears to be driven by subduction—the downwelling of mantle material from the surface."

The melting the researchers have detected is called dehydration melting. Rocks in the transition zone can hold a lot of H2O, but rocks in the top of the lower mantle can hold almost none. The water contained within ringwoodite in the transition zone is forced out when it goes deeper (into the lower mantle) and forms a higher-pressure mineral called silicate perovskite, which cannot absorb the water. This causes the rock at the boundary between the transition zone and lower mantle to partially melt.

"When a rock with a lot of H2O moves from the transition zone to the lower mantle it needs to get rid of the H2O somehow, so it melts a little bit," Schmandt said. "This is called dehydration melting."

"Once the water is released, much of it may become trapped there in the ," Jacobsen added.

Just a little bit of melt, about one percent, is detectible with the new array of seismometers aimed at this region of the because the melt slows the speed of seismic waves, Schmandt said.

Explore further: Is there an ocean beneath our feet?

More information: Dehydration melting at the top of the lower mantle, Science, 2014. www.sciencemag.org/lookup/doi/… 1126/science.1253358

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betterexists
1 / 5 (12) Jun 12, 2014
How come a Camera was not sent in?
A Video on Youtube could be worthless.
Investment will not be wasted, if I am correct.
betterexists
Jun 12, 2014
This comment has been removed by a moderator.
Wolf358
5 / 5 (10) Jun 12, 2014
Too deep, too hot to reach; camera would melt. Drilling equipment would melt. Pressure would crush all of it. It might be there, but we can't reach it.
RonJohn63
5 / 5 (9) Jun 12, 2014
{How come a Camera was not sent in?}

"at depths between 250 miles and 410 miles."

The deepest humans have ever drilled is 7.6 miles.
Nik_2213
4.4 / 5 (5) Jun 13, 2014
"Though not in the familiar liquid form..."

Nothing to see, folks. No underground floods, lakes or contiguous water features. Just slightly more of certain hydrated minerals than expected. Can't even get the water out without roasting a sample-- If we could drill that deep. But, that modest H2O content lowers the melting point, like Cryolite flux in Aluminium production...
PhotonX
3 / 5 (2) Jun 13, 2014
I came here expecting to see a Creationist Noah's Ark flame war starting (whatever happened to kevintrs, anyway?) though I suppose there would be far more than five answers in that case, found only a camera faux pas, and ended up confused on the following point. I freely admit to being uneducated in geology and Earth science.
"Melting of rock at this depth is remarkable because most melting in the mantle occurs much shallower, in the upper 50 miles,"
My admittedly simplistic understanding was that only Earth's crust is solid, with the remainder being molten or at least plastic, depending on depth. So why would melting at 'only' 400 miles be considered remarkable, when melting at 50 miles is not? Is it because most matter at this depth is only plastic and not molten, and is happening in these spots because of the presence of H2O, or some other reason?
Mathview
5 / 5 (2) Jun 14, 2014
RE: The mineral Ringwoodite: Ringwoodite is a polymorph of olivine, with a spinel structure. Ringwoodite can have deep blue, red, violet, or colourless (pure Mg2(SiO4)) appearance.

This info from Wikipedia. Posted because this article seems to have neglected the chemical formula for the mineral Ringwoodite. A shocking oversight! Well, maybe not shocking.
ryggesogn2
3 / 5 (2) Jun 14, 2014
What is the transport mechanism for surface water to ringwoodite and back to the surface?
Does this regulate the amount of water on the surface?
TheGhostofOtto1923
3.7 / 5 (3) Jun 15, 2014
I came here expecting to see a Creationist Noah's Ark flame war starting
Well verily because The Lord said specifically in his book:

"11 In the six hundredth year of Noah's life, on the seventeenth day of the second month—on that day all the springs of the great deep burst forth" gen7

-And from a creationist website entitled
'Physics and the Bible:
The Terrible Flood of Noah
by Lambert Dolphin'

-we find

"During the formation of the earth on the second and third days of creation, large quantities of water were evidently placed between the earth's crust and mantle in what might be called giant subterranean reservoirs. This water was probably under high pressure to begin with (causing artesian springs and geysers to abound"

-And so we can expect religionists to be rejoicing at the news that god has again described what science has subsequently verified.

It doesn't matter to them that this water is chemically bound the way that H2 and O are similarly bound. God doesnt quibble.
Nik_2213
5 / 5 (2) Jun 15, 2014
There's 'primordial' water from the Earth's formation plus 'Big Splat', and there's the subducted stuff. IIRC, much of North America is underlain by descending fragments of the Farallon oceanic plate...
Stevepidge
1 / 5 (2) Jun 19, 2014
I came here expecting to see a Creationist Noah's Ark flame war starting
Well verily because The Lord said specifically in his book:

"11 In the six hundredth year of Noah's life, on the seventeenth day of the second month—on that day all the springs of the great deep burst forth" gen7

"During the formation of the earth on the second and third days of creation, large quantities of water were evidently placed between the earth's crust and mantle in what might be called giant subterranean reservoirs. This water was probably under high pressure to begin with (causing artesian springs and geysers to abound"

So... you are saying earth's vast oceans and bodies of water came from comets?
It seems to me, and the researchers at Northwestern and Univ. New Mexico are saying otherwise.
TheGhostofOtto1923
4.3 / 5 (6) Jun 19, 2014
It seems to me, and the researchers at Northwestern and Univ. New Mexico are saying otherwise.
The article says nothing about where it came from, only how it got into the mantle.

"The discovery suggests water from the Earth's surface can be driven to such great depths by plate tectonics, eventually causing partial melting of the rocks found deep in the mantle."

-Did you read it?
rockwolf1000
5 / 5 (4) Jun 19, 2014
@ryggysoggy

What is the transport mechanism for surface water to ringwoodite and back to the surface?


AGWites and socialists.

Does this regulate the amount of water on the surface?


No because socialism is evil.

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