(Source: Paramount Pictures)
Trapped crystalline water is believed to be enough to fill the Earth's oceans 1 to 3 times over

A freakish find -- a mineralogical surprised tucked inside a dirty, seemingly worthless gemstone -- has shown highly compelling evidence that the Earth's water may have sprung not from space, but from a mantle.  Now mankind is finding out how little it knew about the Earth's innards, as it slowly discovers that sometimes the truth is stranger than fiction.
I. The Core and Geodes
The 2003 disaster bomb The Core depicted a group of intrepid scientists who used a high tech drilling rig that vaguely resembled a Japanese bullet train. The scientists dug through the Earth's mantle to drop atomic bombs in an attempt to restart the Earth's core, which had been stopped by U.S. weapons experiments.
One of the most often snickered about parts of the movie by scientists is the infamous "geode" scene, which shows the drilling rig get stuck inside a pocket of empty space -- a geode made of amethyst, a kind of purple quartz.  As Movie Mistakes summarizes:
The geodes occurring in the mantle during the film are impossible in two ways. Firstly, there are no gaps at those depths. The pressure is approximately 3.5 million times surface pressure, and it is not feasible that such structures could form, let alone be maintained. Secondly, the crystals inside the geodes are described as amethysts. Amethysts are a purple variety of quartz, and as any undergrad geology student could tell you, there is no quartz in the mantle, it simply is not stable at such high temperatures.
The Core Geode
The Core's infamous "geodes" scene [Image Source: Paramount Pictures]

While the possibility of finding quartz crystals, particularly hollow ones, in the core is still an outlandish thought, researchers over the last decade have discovered an almost equally unlikely find which likely abounds in the mantle -- water.
II. Trailblazers Slowly Unraveled Mystery of Incredible Pressurized Crystal
Now a pair of papers has offered new insight, taking that a novel hypothesis much closer to being proven scientific fact.
The first paper was published in March, and detailed how a mantle-derived sample the material that houses the water in the mantle was found on the Earth's surface for the first time.  The work of an international team of geology, gemology, geophysics, and geochemistry experts Professor Graham Pearson, Canada Excellence Research Chair in Arctic Resources at the University of Alberta, the study found trapped in side a brown 3 millimeter diamond worth around $20 USD, a piece of a mineral called "Ringwoodite".
This special crystal inside the diamond is a high-pressure polymorph of olivine, which has been theorized to be abundant in the crust, but trapped in a belt of the mantle known as the "transition mantle".

Blue Ringwoodite
A Ringwoodite sample [Image Source: Wikimedia Commons]
Ringwoodite is made by mixture of Silicon, oxygen, iron, and magnesium, the crystal's formula is (Mg, Fe)2SiO4 and it has a spinel structure.  The crystal is named in honor of Australian scientist Ted Ringwood, who formulated much of the key components of mankind's modern understanding of the Earth's mantle (although Ringwood himself did not predict Ringwoodite).
To date the only known samples of ringwoodite had been made in the lab or found in meteorites.  The first samples were harvested in 1969 from meteors that showered down on Tenham Station in Australia.  A paper was published in the prestigious peer-reviewed journal Nature, giving the world its first glimpse at this unusual blue crystal with the world.
The discovered crystal was highly unstable, but geologists quickly identified it as olivine crystal and discovered it was stabilized by radically high pressures.  They speculated it might be stable at pressures similar to the 410-660 kilometer (255-410 mile) deep region of the mantle -- 18 to 23 GigaPascals.  That hypothesis was later confirmed by lab-made samples.
In 1996, using an exotic high pressure construct UMN Professor David C. Rubie discovered something extraordinary -- in hot, super-pressurized conditions, Ringwoodite stored up to 2.6 percent of its weight in ionized water (hydroxide).  At the time Professor Rubie's peers were already speculating that a sea of olivine lay in the transition mantle, with much of its crystallized as Ringwoodite.  Could those deposits hold secrets oceans within the mantle?
A 2003 paper further expanded upon this work, suggesting that so-called "hydrous olivine" may be the Earth's biggest reservoir of water, containing the equivalent of one to three times the Earth's entire oceans, trapped in a crystalline phase inside the mantle.
III. The First Mantle-Derived Ringwoodite Sample Has Lots of Water in It
All that was left to observe was to find actual water inside a Ringwoodite sample from the mantle itself.  The new study published in March did exactly that, on a fluke.  The researchers were buying cheap, unattractive diamonds, examining them for another mineral, when they found an incredible find in one of the tiny, rough stones -- tiny entrapped Ringwoodite crystals.
Ringwoodite in diamond
Professor Graham Pearson [Image Source: Richard Siemens]

The find is incredibly rare because typically diamonds don't form in the "domain" of Ringwoodite.  Olivine (and Ringwoodite) was predicted to be found in the transition zone lies between the upper and lower mantles.  The upper mantle is relatively slow moving layer of molten rock.  It consists of an estimated 75 percent dunite rock, which in turn is typically around 75 percent olivine.  
By contrast, diamonds typically form in the upper mantle.  A diamond that forms on the edge of the transition zone, as deep as 300 km or more may be relatively worthless to gemologists but is incredibly rare from a research perspective. The diamond was harvest in 2008 from the kimberlite gravel-filled river in the Juina area of Mato Grosso, Brazil.  Kimberlite is among the deepest derived of volcanic rocks. 
Ringwoodite infographic
[Image Source: U of Alberta]
The tiny piece of Ringwoodite was painstakingly extracted at the University of Alberta -- a university known for having the world's largest diamond research group.  After the extraction came the critical test -- did it have water?
Analyzing the extracted crystal with high precision infrared spectroscopes and X-ray imagers, the researchers not only found water, but an abundance of it -- roughly 1.5 percent of the crystal's weight was water, indicating roughly it to be loaded to about 60 percent of its theoretical capacity.
Professor Pearson remarked on the find:
This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area.  That particular zone in the Earth, the transition zone, might have as much water as all the world’s oceans put together.[The stone was] so small, this inclusion, it’s extremely difficult to find, never mind work on, so it was a bit of a piece of luck, this discovery, as are many scientific discoveries.
One of the reasons the Earth is such a dynamic planet is because of the presence of some water in its interior.  Water changes everything about the way a planet works.
Ringwoodite Diamond
The diamond sample that contained Ringwoodite [Image Source: U of Alberta]

His study on the work was published in perhaps science's most prestigious peer-reviewed journal, Nature.  A pair of co-authors from Ghent University in the Netherlands -- Professor Laszlo Vincze and Professor Bart Vekemans -- received senior author credits on the study.

IV. Wet Mantle Drives Unique Mantle Seismic Activity
The second paper, just proposed, is perhaps equally important.  It has proposed a model for how the transition zone of the mantle works, in a sense.
Researchers at the University of New Mexico (UNM), Northwestern University (NWU), University of Southern California (USC), the Carnegie Institution of Washington, and the University of Wyoming (UW) compared data harvested from seismic P-to-S conversions recorded by a dense seismic array in North America called USArray.

US Array
U.S. Arrray in the Alaskan tundra [Image Source: USGS]

USArray has migrated around the country, collecting high-accuracy seismic readings.  It currently resides in Alaska.  The observed data was compared to the output from numeric models and high-pressure laboratory experiments on olivine.
U.S. Array
A diagram of a U.S. Array seismography station [Image Source: USGS]

The study's findings indicate that the mantle's transition zone undergoes an exotic rheological process called "dehydration melting", where currents of hydrous ringwoodite transform into perovskite and the trapped water is expelled back into the transition zone, forming more high-pressure Ringwoodite.
Water is a key part of this process.
Researchers at the University of New Mexico (UNM), Northwestern University (NWU), University of Southern California (USC), the Carnegie Institution of Washington, and the University of Wyoming (UW) were responsible for this new model, which is the only known model able to explain newly observed effects spotted in the latest round of high-accuracy seismology data.
V. Strange Earth
Professor Steve Jacobsen, a study coauthor from Northwestern University comments:
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.  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.
Ringwoodite here is key.  Its crystal-like structure makes it act like a sponge and draw in hydrogen and trap water.
The study also suggests that if the mounting evidence is accurate, it would indicate a vast amount of water in the mantle, offering intriguing proof that the Earth's abundant supply of water came primarily not from collisions with asteroids and meteorites in Earth's early days, but from inside the cooling molten shell that was created as solar debris gravitationally collapsed into planets.

The mantle may be the source of most of the Earth's surface water.
[Image Source: Deposit Photos]
A paper has been published in science's other most prestigious peer-reviewed journal -- Science.  The study's firth author is UNM geophysics Professor Brandon Schmandt, while UW geology Professor Ken Dueker is its senior author.
More work still needs to be done.  New drilling techniques could one day offer mankind's first direct observations of the mantle, allowing direct tests of the composition of the upper mantle -- and perhaps eventually the transition mantle and the faster, flowing lower mantle.
What's next -- a material that gets stronger the more pressure it's exposed to?  Who knows, but one thing is for sure.  Science is often as strange and unbelievable as the best and worst works of fiction.

Sources: Nature [journal paper], Science [journal paper], University of Alberta [press release], The Guardian

"Young lady, in this house we obey the laws of thermodynamics!" -- Homer Simpson

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