Evidence of 'oceans worth' of water in Earth's mantle detected

Schematic cross section of the Earth’s interior highlighting the transition zone layer (light blue, 410-660 km depth), which has an anomalously high water storage capacity. 

The study by Schmandt and Jacobsen used seismic waves to detect magma generated near the top of the lower mantle at about 700 km depth.

Dehydration melting at those conditions, also observed in the study’s high-pressure experiments, suggests the transition zone may be nearly saturated with H2O dissolved in high-pressure rock. 

Credit: Steve Jacobsen/Northwestern University

Researchers have found evidence of a potential "ocean's worth" of water deep beneath the United States.

Although not present in a familiar form, the building blocks of water are bound up in rock located deep in the Earth's mantle, and in quantities large enough to represent the largest water reservoir on the planet, according to the research.

For many years, scientists have attempted to establish exactly how much water may be cycling between the Earth's surface and interior reservoirs through the action of plate tectonics.

Northwestern University geophysicist Steve Jacobsen and University of New Mexico seismologist Brandon Schmandt have found deep pockets of magma around 400 miles beneath North America, a strong indicator of the presence of H₂O stored in the crystal structure of high-pressure minerals at these depths.

"The total H₂O content of the planet has long been among the most poorly constrained 'geochemical parameters' in Earth science. Our study has found evidence for widespread hydration of the mantle transition zone," says Jacobsen.

For at least 20 years geologists have known from laboratory experiments that the Earth's transition zone, a rocky layer of the Earth's mantle located between the lower mantle and upper mantle, at depths between 250 and 410 miles, can, in theory, hold about 1 percent of its total weight as H₂O, bound up in minerals called wadsleyite and ringwoodite.

However, as Schmandt explains, up until now it has been difficult to figure out whether that potential water reservoir is empty, as many have suggested, or not.

If there does turn out to be a substantial amount of H₂O in the transition zone, then recent laboratory experiments conducted by Jacobsen indicate there should be large quantities of what he calls "partial melt" in areas where mantle flows downward out of the zone.

This water-rich silicate melt is molten rock that occurs at grain boundaries between solid mineral crystals and may account for about 1 percent of the volume of rocks.

"Melting occurs because hydrated rocks are carried from the transition zone, where the rocks can hold lots of H₂O, downward into the lower mantle, where the rocks cannot hold as much H₂O."

"Melting is the way to get rid of the H₂O that won't fit in the crystal structure present in the lower mantle," says Jacobsen.

He adds:
"When a rock starts to melt, whatever H₂O is bound in the rock will go into the melt right away. So the melt would have much higher H₂O concentration than the remaining solid. We're not sure how it got there."

"Maybe it's been stuck there since early in Earth's history or maybe it's constantly being recycled by plate tectonics."

Seismic Waves
Melt strongly affects the speed of seismic waves, the acoustic-like waves of energy that travel through the Earth's layers as a result of an earthquake or explosion.

This is because stiff rocks, like the silicate-rich ones present in the mantle, propagate seismic waves very quickly.

According to Schmandt, if just a little melt, even 1 percent or less, is added between the crystal grains of such a rock it causes it to become less stiff, meaning that elastic waves propagate more slowly.

"We were able to analyse seismic waves from earthquakes to look for melt in the mantle just beneath the transition zone," says Schmandt.

Brandon Schmandt (University of New Mexico, left) and Steve Jacobsen (Northwestern University, right) combined seismic observations from the US-Array with laboratory experiments to detect dehydration melting of hydrous mantle material beneath North America at depths of 700-800 km. 

Credit: University of New Mexico/Northwestern University

"What we found beneath the U.S. is consistent with partial melt being present in areas of downward flow out of the transition zone."

"Without the presence of H₂O, it is very difficult to explain melting at these depths. This is a good hint that the transition zone H₂O reservoir is not empty, and even if it's only partially filled that could correspond to about the same mass of H₂O as in Earth's oceans," he adds.

Jacobsen and Schmandt hope that their findings, published in the June issue of the journal Science, will help other scientists to understand how the Earth formed and what its current composition and inner workings are, as well as establish how much water is trapped in mantle rock.

"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," says Jacobsen

Schematic representation of seismometers placed in the US-Array between 2004 and 2014 and used in the study by Schmandt and Jacobsen to detect dehydration melting at the top of the lower mantle beneath North America. 

Credit: NSF-Earthscope

Crystals of laboratory-grown hydrous ringwoodite, a high-pressure polymorph of olivine that is stable from about 520-660 km depth in the Earth’s mantle. 

The ringwoodite pictured here contains around one weight percent of H2O, similar to what was inferred in the seismic observations made by Schmandt and Jacobsen. 

Credit: Steve Jacobsen/Northwestern University

Scientists detect the deep roots of potential catastrophe

This map shows Earth's surface superimposed on a depiction of what a new University of Utah study indicates is happening 1,800 miles deep at the boundary between Earth's warm, rocky mantle and its liquid outer core.

Using seismic waves the probe Earth's deep interior, seismologist Michael Thorne found evidence that two continent-sized piles of rock are colliding as they move atop the core.

The merger process isn't yet complete, so there is a depression or hole between the merging piles. But in that hole, a Florida-sized blob of partly molten rock - called a "mega ultra low velocity zone" - is forming from the collision of smaller blobs on the edges of the continent-sized piles.

Thorne believe this process is the beginning stage of massive volcanic eruptions that won't occur for another 100 million to 2100 million years.

Credit: Michael S. Thorne, University of Utah.

A University of Utah seismologist analysed seismic waves that bombarded Earth's core, and believes he got a look at the earliest roots of Earth's most cataclysmic kind of volcanic eruption. But don't panic. He says it won't happen for perhaps 200 million years.

"What we may be detecting is the start of one of these large eruptive events that - if it ever happens - could cause very massive destruction on Earth," says seismologist Michael Thorne, the study's principal author and an assistant professor of geology and geophysics at the University of Utah.

But disaster is "not imminent," he adds, "This is the type of mechanism that may generate massive plume eruptions, but on the timescale of 100 million to 200 million years from now. So don't cancel your cruises."

The new study, set for publication this week in the journal Earth and Planetary Science Letters, indicates that two or more continent-sized "piles" of rock are colliding as they move at the bottom of Earth's thick mantle and atop the thicker core some 1,800 miles beneath the Pacific.

That is creating a Florida-sized zone of partly molten rock that may be the root of either of two kinds of massive eruptions far in the future:

• Hotspot plume supervolcano eruptions like those during the past 2 million years at Wyoming's Yellowstone caldera, which covered North America with volcanic ash.
• Gargantuan flood basalt eruptions that created "large igneous provinces" like the Pacific Northwest's Columbia River basalts 17 million to 15 million years ago, India's Deccan Traps some 65 million years ago and the Pacific's huge Ontong Java Plateau basalts, which buried an Alaska-sized area 125 million to 199 million years ago.

"These very large, massive eruptions may be tied to some extinction events," Thorne says. The Ontong eruptions have been blamed for oxygen loss in the oceans and a mass die-off of sea life.

Since the early 1990s, scientists have known of the existence of two continent-sized "thermochemical piles" sitting atop Earth's core and beneath most of Earth's volcanic hotspots - one under much of the South Pacific and extending up to 20 degrees north latitude, and the other under volcanically active Africa.

Using the highest-resolution method yet to make seismic images of the core-mantle boundary, Thorne and colleagues found evidence the pile under the Pacific actually is the result of an ongoing collision between two or more piles. Where they are merging is a spongy blob of partly molten rock the size of Florida, Wisconsin or Missouri beneath the volcanically active Samoan hotspot.

The study's computer simulations "show that when these piles merge together, they may trigger the earliest stages of a massive plume eruption," Thorne says.

Thorne conducted the new study with Allen McNamara and Edward Garnero of Arizona State University, and Gunnar Jahnke and Heiner Igel of the University of Munich. The National Science Foundation funded the research.

Scientists Discover Planet with Diamond Mantle - Twice The Size Of Our Sun

Scientists have announced the discovery of a planet made almost entirely of diamonds.

The planet, called 55 Cancri e, is located in a solar system inside the constellation of Cancer, reports NBC News.

It was discovered in 2004, and scientists have been working since then to determine its mass and radius, as well as study its host star’s composition.

The planet is called a “super-Earth,” and scientists believe that the rocky world is composed mostly of carbon (in the form of either graphite or diamond). It also includes iron, silicon carbide, and possibly silicates.

Scientists also believe, based on their research, that at least one-third of the planet’s mass is pure diamond. Lead researcher Nikku Madhusudhan of Yale University stated:

“This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth. The surface of this planet is likely covered in graphite and diamond rather than water and granite.”

While worlds like the “diamond planet” of 55 Cancri e have been theorized before, and at least one has been discovered before now, it is the first of its kind to be identified orbiting around a sun-like star.

Madhusudhan’s study on the planet was published in the journal Astrophysical Journal Letters.

Princeton University astronomer David Spergel stated that it is relatively easy to find out a star’s basic structure and history once its age and mass have been discovered. He added:

“Planets are much more complex. This ‘diamond-rich super-Earth’ is likely just one example of the rich sets of discoveries that await us as we begin to explore planets around nearby stars.”

The Earth’s Core: An Enigma 1,800 Miles Below Our Feet

Geologists have long known that Earth’s core, some 1,800 miles beneath our feet, is a dense, chemically doped ball of iron roughly the size of Mars and every bit as alien. 

It’s a place where pressures bear down with the weight of 3.5 million atmospheres, like 3.5 million skies falling at once on your head, and where temperatures reach 10,000 degrees Fahrenheit — as hot as the surface of the Sun. 

It’s a place where the term “ironclad agreement” has no meaning, since iron can’t even agree with itself on what form to take. It’s a fluid, it’s a solid, it’s twisting and spiraling like liquid confetti.

Researchers have also known that Earth’s inner Martian makes its outer portions look and feel like home. The core’s heat helps animate the giant jigsaw puzzle of tectonic plates floating far above it, to build up mountains and gouge out seabeds. 

At the same time, the jostling of core iron generates Earth’ magnetic field, which blocks dangerous cosmic radiation, guides terrestrial wanderers and brightens northern skies with scarves of auroral lights.

Now it turns out that existing models of the core, for all their drama, may not be dramatic enough. Reporting recently in the journal Nature, Dario Alfè of University College London and his colleagues presented evidence that iron in the outer layers of the core is frittering away heat through the wasteful process called conduction at two to three times the rate of previous estimates. 

The theoretical consequences of this discrepancy are far-reaching. The scientists say something else must be going on in Earth’s depths to account for the missing thermal energy in their calculations. 

They and others offer these possibilities:

• The core holds a much bigger stash of radioactive material than anyone had suspected, and its decay is giving off heat.
• The iron of the innermost core is solidifying at a startlingly fast clip and releasing the latent heat of crystallization in the process.
• The chemical interactions among the iron alloys of the core and the rocky silicates of the overlying mantle are much fiercer and more energetic than previously believed.
• Or something novel and bizarre is going on, as yet undetermined.

“From what I can tell, people are excited” by the report, Dr. Alfè said. “They see there might be a new mechanism going on they didn’t think about before.”

Researchers elsewhere have discovered a host of other anomalies and surprises. They’ve found indications that the inner core is rotating slightly faster than the rest of the planet, although geologists disagree on the size of that rotational difference and on how, exactly, the core manages to resist being gravitationally locked to the surrounding mantle.

Miaki Ishii and her colleagues at Harvard have proposed that the core is more of a Matryoshka doll than standard two-part renderings would have it. 

Not only is there an outer core of liquid iron encircling a Moon-size inner core of solidified iron, Dr. Ishii said, but seismic data indicate that nested within the inner core is another distinct layer they call the innermost core: a structure some 375 miles in diameter that may well be almost pure iron, with other elements squeezed out. 

Against this giant jewel even Jules Verne’s middle-Earth mastodons and ichthyosaurs would be pretty thin gruel.

Core researchers acknowledge that their elusive subject can be challenging, and they might be tempted to throw tantrums save for the fact that the Earth does it for them. Most of what is known about the core comes from studying seismic waves generated by earthquakes.

As John Vidale of the University of Washington explained, most earthquakes originate in the upper 30 miles of the globe (as do many volcanoes), and no seismic source has been detected below 500 miles. But the quakes’ energy waves radiate across the planet, detectably passing through the core.

Granted, some temblors are more revealing than others. “I prefer deep earthquakes when I’m doing a study,” Dr. Ishii said. “The waves from deep earthquakes are typically sharper and cleaner.”

Read more of this article here: Earth’s Core - The Enigma 1,800 Miles Below Us

Seafloor Mountain Expedition Studied Crust's Deepest Layer

A topographical map of the Atlantis Massif, which also shows the location of its Lost City hydrothermal vents.

CREDIT: NOAA.

Scientists recently returned from an expedition to an unusual seafloor mountain, where they conducted what may be the first-ever on-site study of a type of rock that makes up a huge amount of our planet, but is largely out of reach.

Researchers aboard the research vessel JOIDES Resolution sent instruments to the Atlantis Massif, a seamount that lies near the Mid-Atlantic Ridge, a long volcanic rift bisecting the Atlantic Ocean, where two tectonic plates are being slowly shoved apart and fresh oceanic crust is created.

Seamounts are essentially a mountain that doesn't rise above the ocean's surface.

Unlike most seamounts, which are typically made of volcanic rock, geological forces essentially yanked the Atlantis Massif from the Earth's gabbroic layer — the deepest layer of the Earth's crust, which rests directly on the planet's ever-shifting mantle.

High-Res Show Crust-Mantle Boundary - Moho, Where Is Earth's Mantle?

This map shows the global Mohorovičić discontinuity, better known as Moho, based on data from the GOCE satellite.

CREDIT: GEMMA project

Beneath the Earth's crust, the outermost hard shell that makes up just 1 percent of the volume of the planet, lies a hot, viscous layer of rock called the mantle.

Together, the crust and upper portion of the mantle. called the lithosphere, are where most important geological processes occur, such as mountain-building, earthquakes and the source of volcanoes.

The slow churning and overturning of the mantle is what drives the movements of Earth's tectonic plates.

New methods of observation using satellites are helping scientists learn more about this important layer of the Earth's inner and outer layers and where it begins under different regions of the planet.

Andrija Mohorovičić
Until just a century ago, we didn’t know Earth has a crust. In 1909, Croatian seismologist Andrija Mohorovičić found that at about 50 km underground there is a sudden change in seismic speed.

Ever since, that boundary between Earth’s crust and underlying mantle has been known as the Mohorovičić discontinuity, or Moho.

Even today, almost all we know about Earth’s deep layers comes from two methods: seismic and gravimetric.

Seismic methods are based on observing changes in the propagation velocity of seismic waves between the crust and mantle.

Gravimetry looks at the gravitational effect due to the density difference caused by the changing composition of crust and mantle.

But the Moho models based on seismic or gravity data are usually limited by poor data coverage or data being only available along single profiles.

GEMMA Project

GEMMA’s Moho map is based on the inversion of homogenous well-distributed gravimetric data.

For the first time, it is possible to estimate the Moho depth worldwide with unprecedented resolution, as well as in areas where ground data are not available.

This will offer new clues for understanding the dynamics of Earth’s interior, unmasking the gravitational signal produced by unknown and irregular subsurface density distribution.

GEMMA is being carried out by Italian scientist Daniele Sampietro and is funded by the Politecnico di Milano and ESA’s Support To Science Element under the Changing Earth Science Network initiative.

This initiative supports young scientists at post-doctoral level in ESA Member States to advance our knowledge in Earth system science by exploiting the observational capacity of ESA missions

Read more at the ESA Goce website

Hip! Hip! USArray

Probably the most ambitious seismological project ever conducted is taking place in the heartland of America. Its name is USArray and its aim is to run what amounts to an ultrasound scan over the 48 contiguous states of the US. Through the seismic shudders and murmurs that rack Earth's innards, it will build up an unprecedented 3D picture of what lies beneath North America.

It is a mammoth undertaking, during which USArray's scanner - a set of 400 transportable seismometers - will sweep all the way from the Pacific to the Atlantic. Having started off in California in 2004, it is now just east of the Rockies, covering a north-south swathe stretching from Montana's border with Canada down past El Paso on the Texas-Mexico border. By 2013, it should have reached the north-east coast, and its mission end.

Though not yet at the halfway stage, the project is already bringing the rocky underbelly of the US into unprecedented focus. Geologists are using this rich source of information to gain new understanding of the continent's tumultuous past - and what its future holds.