Posted on 08/30/2009 2:39:28 PM PDT by decimon
CORVALLIS, Ore. A team of scientists from Oregon State University has created the first global three-dimensional map of electrical conductivity in the Earth's mantle and their model suggests that that enhanced conductivity in certain areas of the mantle may signal the presence of water.
What is most notable, the scientists say, is those areas of high conductivity coincide with subduction zones where tectonic plates are being subducted beneath the Earth's crust. Subducting plates are comparatively colder than surrounding mantle materials and thus should be less conductive. The answer, the researchers suggest, may be that conductivity in those areas is enhanced by water drawn downward during the subduction process.
Results of their study are being published this week in Nature.
"Many earth scientists have thought that tectonic plates are not likely to carry much if any water deep into the Earth's mantle when they are being subducted," said Adam Schultz, a professor in the College of Oceanic and Atmospheric Sciences at Oregon State and a co-author on the Nature study. "Most evidence suggests that subducting rocks initially hold water within their minerals, but that water is released as the rocks heat up."
"There may be other explanations," he added, "but the model clearly shows a close association between subduction zones and high conductivity and the simplest explanation is water."
The study is important because it provides new insights into the fundamental ways in which the planet works. Despite all of the advances in technology, scientists are still unsure how much water lies beneath the ocean floor and how much of it makes its way into the mantle.
The implications are myriad. Water interacts with minerals differently at different depths, and small amounts of water can change the physical properties of rocks, alter the viscosity of materials in the mantle, assist in the formation of rising plumes of melted rock and ultimately affect what comes out on the surface.
"In fact, we don't really know how much water there is on Earth," said Gary Egbert, also a professor of oceanography at OSU and co-author on the study. "There is some evidence that there is many times more water below the ocean floor than there is in all the oceans of the world combined. Our results may shed some light on this question."
Egbert cautioned that there are other explanations for higher conductivity in the mantle, including elevated iron content or carbon.
There also may be different explanations for how the water if indeed the conductivity is reflecting water got there in the first place, the scientists point out.
"If it isn't being subducted down with the plates," Schultz said, "how did it get there? Is it primordial, down there for four billion years? Or did it indeed come down as the plates slowly subduct, suggesting that the planet may have been much wetter a long time ago? These are fascinating questions, for which we do not yet have answers."
The scientists conducted their study using electromagnetic induction sounding of the Earth's mantle. This electromagnetic imaging method is very sensitive to interconnecting pockets of fluid that may be found within rocks and minerals that enhance conductivity. Using magnetic observations from more than 100 observatories dating back to the 1980s, they were able to create a global three-dimensional map of mantle conductivity.
Anna Kelbert, a post-doctoral research associate at OSU and lead author on the paper, said the imaging doesn't show the water itself, but the level of conductivity and interpreting levels of hydrogen, iron or carbon require additional constraints from mineral physics. She described the study of electrical conductivity as both computationally intensive and requiring years of careful measurements in the international observatories.
"The deeper you want to look into the mantle," Kelbert said, "the longer periods you have to use. This study has required magnetic field recordings collected over decades."
The scientists say the next step is to replicate the experiment with newly available data from both ground observatories and satellites, and then conduct more research to better understand the water cycle and how the interaction with deep-Earth minerals works. Their work is supported by the National Science Foundation and NASA to take the next steps in this research program.
Ultimately, they hope to produce a model quantifying how much water may be in the mantle, locked up within the mineral-bearing rocks.
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Contact:
Adam Schultz Oregon State University 541-737-9832 adam@coas.oregonstate.edu
Heh... Pellucidar... not E. R. Burroughs’ best work, but entertaining enough. :’)
Where can I read about these wierd things?
http://bible.cc/genesis/1-7.htm. The firmament has a few definitions, including the heavens, the air in which birds fly, and is also known as the expanse.
http://en.wikipedia.org/wiki/Supercritical_fluid
It would be more like the atmosphere of Jupiter, which it isnt. Water in the mantle would mean a gaseous core. Which is not the case.
Ping
As water enters the mantle(and it does through subduction zones) it becomes supercritical, meaning in a geseous/liquid state. It would penetrate back up through the mantle rock realizing its liquid state through underwater volcanism and other means. Since the core of the earth is iron and a supercritical liquid is lighter, it will always naturally reenter the most stable state.
Now there’s some science for you.
There’s something to be said for it.
Water does seem to lubricate the action of subduction zones. And consider the planet Venus, which has neither water nor active subduction zones.
Subducted oceanic mud gives up its water gradually, and reluctantly, usually having quite a bit left to vaporize explosively when it finds a volcanic outlet.
It does, especially at slip/strike faults. And some water obviously enters with the subduction. I have taken several geology courses in my studies, and while Im not anything of an expert like other claim to be, there are explanations. That is what is great about science. What doesnt work as a theory is discarded or changed and refined.
Its not a suprise that most of the underwater volcanic activity its located at these zones. Its called the ring of fire for a reason. Supercritical water and superheated water are very explosive at the high pressures.
Amazingly, the earths water is really a miniscule amount | 5/15/2012 | thanks central_va.The Louis Frank keyword:
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