Study suggests mid-mantle holds as much water as Earth's oceans

June 8, 2017 by Bob Yirka, Phys.org report
TEM images of ringwoodite and bridgmanite before and after annealing. (A) Inverted bright-field image of ringwoodite before annealing (ρi = 11.0/μm2). (B) Inverted bright-field image of ringwoodite after annealing for 12 hours at 2000 K (ρf = 0.87/μm2). (C) Dark-field image of bridgmanite before annealing (ρi = 8.43/μm2). (D) Dark-field image of bridgmanite after annealing for 24 hours at 1600 K (ρf = 4.32/μm2). Rw., ringwoodite; Brg., bridgmanite. Credit: Science Advances  07 Jun 2017: Vol. 3, no. 6, e1603024, DOI: 10.1126/sciadv.1603024

(Phys.org)—A team of researchers affiliated with several institutions in Japan and Germany has found evidence that suggests the middle of Earth's mantle holds as much water as the planet's oceans. In their paper published on the open access site Science Advances, the group describes their theory and their experiments to try to prove them correct.

Scientists are convinced that the uppermost part of the mantle and lower part closest to the core are relatively free. This is because the materials they are made of can't to store water very well. The layer in between (at 410 to 660 kilometers below the surface), however, has been a topic of debate, with some believing it is also nearly water free and others suggesting it could harbor massive amounts of water. This is because the mid-mantle is dominated by the minerals wadsleyite and ringwoodite, which are known to be able to hold a lot of water. In this new effort, the researchers sought to settle the debate by using logic and .

The team notes that prior research has shown that the viscosity of the middle zone of the mantle is lower than that of both the and . To figure out if the middle zone is holding water, the researchers used this information and conducted lab experiments meant to replicate such conditions. They created synthetic ringwoodite to represent the middle mantle and bridgmanite to represent material from the lower mantle. They then used a technique that involved measuring dislocation mobility to infer viscosity and then added water to the ringwoodite. They report that doing so reduced its viscosity and matched measurements taken of the real mantle—this suggests that the real-world middle mantle does, indeed, hold water. By adjusting the amount of water added to their synthetic mantle and calculating changes in , they were able to estimate how waterlogged the real-world minerals are. They then used that information to calculate how much water is in the entire mid-mantle. They report that it is very nearly equal to the amount of water in all of the world's oceans.

More testing will have to be done, of course, but if scientists can prove without doubt that the middle is filled with water, it calls into question theories that suggest water arrived on Earth from comets.

Explore further: Scientists discover why rocks flow slowly in Earth's middle mantle

More information: A nearly water-saturated mantle transition zone inferred from mineral viscosity, Science Advances  07 Jun 2017: Vol. 3, no. 6, e1603024, DOI: 10.1126/sciadv.1603024 , http://advances.sciencemag.org/content/3/6/e1603024.full

Abstract
An open question for solid-earth scientists is the amount of water in Earth's interior. The uppermost mantle and lower mantle contain little water because their dominant minerals, olivine and bridgmanite, have limited water storage capacity. In contrast, the mantle transition zone (MTZ) at a depth of 410 to 660 km is considered to be a potential water reservoir because its dominant minerals, wadsleyite and ringwoodite, can contain large amounts of water [up to 3 weight % (wt %)]. However, the actual amount of water in the MTZ is unknown. Given that water incorporated into mantle minerals can lower their viscosity, we evaluate the water content of the MTZ by measuring dislocation mobility, a property that is inversely proportional to viscosity, as a function of temperature and water content in ringwoodite and bridgmanite. We find that dislocation mobility in bridgmanite is faster by two orders of magnitude than in anhydrous ringwoodite but 1.5 orders of magnitude slower than in water-saturated ringwoodite. To fit the observed mantle viscosity profiles, ringwoodite in the MTZ should contain 1 to 2 wt % water. The MTZ should thus be nearly water-saturated globally.

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12 comments

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tblakely1357
4 / 5 (3) Jun 08, 2017
So places with dried up wells just have to drill a bit deeper.....
Nik_2213
4.3 / 5 (6) Jun 08, 2017
I do hope that's a joke, as you'd have to roast the rock --eg with magma-- to boil off the meagre water content...
willys36
1.7 / 5 (6) Jun 08, 2017
Why in the world would you think he is joking? All someone has to do to replenish water supply under this scenario is drill a 500 mile deep well. And isn't it interesting that science thinks they have identified enuf water on earth to fund a Noahtion Biblical flood?
Nik_2213
4 / 5 (4) Jun 08, 2017
Noachian ?? Australia, beetles, plagiarised from prior 'Epic of Gilgamesh' etc etc...
jonesdave
4.4 / 5 (7) Jun 08, 2017
Why in the world would you think he is joking? All someone has to do to replenish water supply under this scenario is drill a 500 mile deep well. And isn't it interesting that science thinks they have identified enuf water on earth to fund a Noahtion Biblical flood?


There is more than *enough* water to account for the various flood legends, without getting it from the mantle. As the last ice age ended, sea levels rose considerably (~120m, iirc). Some of that may have been sudden. Such as the possible breaching of the barrier between the Black Sea and the Med. If there is anything at all to these flood stories, then it is probably just a folk memory of such events. Over many, many generations of retelling, the stories have taken on a life of their own, and should not be taken literally.
TheGhostofOtto1923
not rated yet Jun 09, 2017
"12And lo, to rid the earth of the vermin that humanity had become, He reached down with his mighty hand and had squeezed the earth so that the waters therein had come forth unto the surface. 13And he had thus held this squeeze unto the earth for 40 days and 40 nights until the verminous plague thereupon had withered and was no more.

14And during the tribulation Noah, and his daughters, and his sons, had cowered aboard the Boat in constant prayer and awe; and even as the terrible grip of the Lord was eased, and the waters were again sucked back into the bosom of the earth, did their faith not waiver.

15So that when the dove returned at last with vegetation in its beak and the Boat had found dry land, was the covenant with god renewed. 16And Noah, and his daughters, and his sons went forth to replenish the land as god had so directed in glorious incestuosity." - Book of God chap 2
koitsu
not rated yet Jun 10, 2017
I always thought the comet hypothesis was asinine anyway.
Darll
1 / 5 (1) Jun 11, 2017
Perhaps we are closing in on the 'hollow earth' theory?
Nik_2213
not rated yet Jun 11, 2017
#k: Which comet hypothesis ?? Links, please.
#D: Check out 'Tomographic Seismology'. Sorry, there's no room down there for a void.
Ozburb
1 / 5 (2) Jun 22, 2017
wiki suggests that the water in the mantle is up to 3 times the amount in our oceans. If all this water were on the surface, it would be enough to cover mt everest. This would explain where all the water went after the 'flood' and the fact that the top of met everest (& other mountains) is made of limestone.
BEGINNING
1 / 5 (1) Jun 23, 2017
"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, and the floodgates of the heavens were opened"

Genesis 7:11
Nik_2213
5 / 5 (1) Jul 26, 2017
#Oz, there's limestone high on Everest because India's continuing collision with Asia crumpled much of the prior sea-bed between them into mega-ruckles and vast 'nappes'...

Tangential: Victorians attributed sea-bed stuff high in Welsh hills to Noachian event. Subsequent analysis of scouring patterns proved such had been 'bulldozed' from Irish Sea's bed by South-spreading ice-cap, and sea-levels had been lower rather than higher...

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