Saturday, June 21, 2014

Scientists Discover an Ocean 400 miles Deep?

So far this is a nice theory and it obviously makes a great story. Otherwise it happens to be impossible to collect a sample that does not have likely controversial genesis. We do have grain captured in diamond. Thus we know that it is possible for a mineral type to absorb water essentially where it was completely unexpected.

This inability to actually sample at depth except to some degree by proxy makes this type of speculation very questionable. The depths described here are completely explored by inference from seismic waves and perhaps from spectral emissions. Getting ground truth is not possible.
This is mostly a best inference until better data appears and it is hardly conservative. Perhaps they have a grain of gold as well.

Between the upper and lower regions of the Earth Mantle is a layer of wet rock that has three times as much water as all of the oceans

JUNE 12, 2014

The water is hidden inside a blue rock called ringwoodite that lies 700 kilometres underground in the mantle, the layer of hot rock between Earth's surface and its core.

The huge size of the reservoir throws new light on the origin of Earth's water. Some geologists think water arrived in comets as they struck the planet, but the new discovery supports an alternative idea that the oceans gradually oozed out of the interior of the early Earth.

"It's good evidence the Earth's water came from within," says Steven Jacobsen of Northwestern University in Evanston, Illinois. The hidden water could also act as a buffer for the oceans on the surface, explaining why they have stayed the same size for millions of years.

They found signs of wet ringwoodite in the transition zone 700 kilometres down, which divides the upper and lower regions of the mantle. At that depth, the pressures and temperatures are just right to squeeze the water out of the ringwoodite. "It's rock with water along the boundaries between the grains, almost as if they're sweating," says Jacobsen.

The high water storage capacity of minerals in Earth’s mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone. 

2.5% water found in diamond from a volcano

Jacobsen's finding supports a recent study by Graham Pearson of the University of Alberta in Edmonton, Canada. Pearson studied a diamond from the transition zone that had been carried to the surface in a volcano, and found that it contained water-bearing ringwoodite, the first strong evidence that there was lots of water in the transition zone.

The ultimate origin of water in the Earth’s hydrosphere is in the deep Earth—the mantle. Theory1 and experiments have shown that although the water storage capacity of olivine-dominated shallow mantle is limited, the Earth’s transition zone, at depths between 410 and 660  kilometres, could be a major repository for water, owing to the ability of the higher-pressure polymorphs of olivine—wadsleyite and ringwoodite—to host enough water to comprise up to around 2.5 per cent of their weight. A hydrous transition zone may have a key role in terrestrial magmatism and plate tectonics yet despite experimental demonstration of the water-bearing capacity of these phases, geophysical probes such as electrical conductivity have provided conflicting results and the issue of whether the transition zone contains abundant water remains highly controversial11. Here we report X-ray diffraction, Raman and infrared spectroscopic data that provide, to our knowledge, the first evidence for the terrestrial occurrence of any higher-pressure polymorph of olivine: we find ringwoodite included in a diamond from JuĂ­na, Brazil. The water-rich nature of this inclusion, indicated by infrared absorption, along with the preservation of the ringwoodite, is direct evidence that, at least locally, the transition zone is hydrous, to about 1 weight per cent. The finding also indicates that some kimberlites must have their primary sources in this deep mantle region.

Scientists discover an ocean 400 miles beneath our feet that could fill our oceans three times over

By Sebastian Anthony on June 17, 2014 at 9:44 am

After decades of theorizing and searching, scientists are reporting that they’ve finally found a massive reservoir of water in the Earth’s mantle — a reservoir so vast that could fill the Earth’s oceans three times over. This discovery suggests that Earth’s surface water actually came from within, as part of a “whole-Earth water cycle,” rather than the prevailing theory of icy comets striking Earth billions of years ago. As always, the more we understand about how the Earth formed, and how its multitude of interior layers continue to function, the more accurately we can predict the future. Weather, sea levels, climate change — these are all closely linked to the tectonic activity that endlessly churns away beneath our feet.

This new study, authored by a range of geophysicists and scientists from across the US, leverages 
data  from the USArray — an array of hundreds of seismographs located throughout the US that are constantly listening to movements in the Earth’s mantle and core. After listening for a few years, and carrying out lots of complex calculations, the researchers believe that they’ve found a huge reserve of water that’s located in the transition zone between the upper and lower mantle — a region that occupies between 400 and 660 kilometers (250-410 miles) below our feet.

As you can imagine, things are a little complex that far down. We’re not talking about some kind of water reserve that can be reached in the same way as an oil well. The
deepest a human borehole has ever gone is just 12km — about half way through the Earth’s crust — and we had to stop because geothermal energy was melting the drill bit. 660 kilometers is a long, long way down, and weird stuff happens down there.

Basically, t
he new theory is that the Earth’s mantle is full of a mineral called ringwoodite. We know from experiments here on the surface that, under extreme pressure, ringwoodite can trap water. Measurements made by the USArray indicate that as convection pushes ringwoodite deeper into the mantle, the increase in pressure forces the trapped water out (a process known as dehydration melting). That seems to be the extent of the study’s findings. Now they need to try and link together deep-Earth geology with what actually happens on the surface. The Earth is an immensely complex machine that generally moves at a very, very slow pace. It takes years of measurements to get anything even approaching useful data.

With all that said, there could be massive repercussions if this study’s findings are accurate. Even if the ringwoodite only contains around 2.6% water, the volume of the transition zone means this underground reservoir could contain enough water to re-fill our oceans three times over. I’m not saying that this gives us the perfect excuse to continue our abuse of Earth’s fresh water reserves, but it’s definitely something to mull over. This would also seem to discount the prevailing theory that our surface water arrived on Earth via a bunch of icy comets. Finally, here’s a fun thought that should remind us that Earth’s perfect composition and climate is, if you look very closely, rather miraculous. One of the researchers, talking to New Scientist, said that if the water wasn’t stored underground, “it would be on the surface of the Earth, and mountaintops would be the only land poking out.” Maybe if the formation of Earth had be a little different, or if we were marginally closer to the Sun, or if a random asteroid didn’t land here billions of years ago… you probably wouldn’t be sitting here surfing the web.

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