Scientists find oxidized iron deep within the Earth's interior (Update)

January 23, 2018 by Katie Willis, University of Alberta
Diamonds with garnet inclusions can form at depths down to 550 kilometres below the surface. Image: Jeff W. Harris, University of Glasgow. Credit: Jeff W. Harris, University of Glasgow.

Scientists studying the Earth's mantle recently made an unexpected discovery. Five hundred and fifty kilometres below the Earth's surface, they found highly oxidized iron, similar to the rust we see on our planet's surface, within garnets found within diamonds.

The result surprised geoscientists around the globe because there is little opportunity for iron to become so highly oxidized deep below the Earth's surface.

Surprising discovery

"On Earth's surface, where oxygen is plentiful, iron will oxidize to rust," explained Thomas Stachel, professor in the Department of Earth and Atmospheric Sciences at the University of Alberta, who co-authored the study. "In the Earth's deep mantle, we should find iron in its less oxidized form, known as ferrous iron, or in its metal form. But what we found was the exact opposite—the deeper we go, the more oxidized iron we found."

This discovery suggests that something oxidized the rocks in which the superdeep diamonds were founds. The scientists suspect that it was molten carbonate, carried to these great depths in sinking slabs of ancient sea floor.

"It's exciting to find evidence of such profound oxidation taking place deep inside the Earth," said Stachel, Canada Research Chair in diamonds.

Carbon cycle

The study also has implications for understanding the that involves the transport of surface carbon back into the Earth's mantle.

"We know lots about the carbon cycle on Earth's surface, but what about in the mantle?" explained Stachel. "Our study suggests that surface carbon goes down as carbonates to at least 550 kilometres below the . There, these carbonates may melt and react with the surrounding rocks, eventually crystallizing into . Diamonds can then be taken down even deeper in the mantle."

The study shows that the extends deep into mantle, possibly all the way down to the core-mantle boundary, with billion year storage times.

Explore further: Iron carbonates in Earth's mantle help form diamonds

More information: Ekaterina S. Kiseeva et al, Oxidized iron in garnets from the mantle transition zone, Nature Geoscience (2018). DOI: 10.1038/s41561-017-0055-7

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7 comments

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grandpa
1 / 5 (5) Jan 23, 2018
Is this fake news. How in the earth, would they be able to dig that deep?
RealScience
5 / 5 (6) Jan 23, 2018
Is this fake news. How in the earth, would they be able to dig that deep?


They don't have to dig that deep. Diamonds can be brought up from the depths in rising magma, and then reach the surface through volcanoes. Check out Kimberlite volcanic pipes and diamond mining...
grandpa
1 / 5 (2) Jan 24, 2018
They said they were digging down that deep.
Ensign_nemo
5 / 5 (6) Jan 24, 2018
"Scientists digging deep into the Earth's mantle recently made an unexpected discovery.

Five hundred and fifty kilometres below the Earth's surface, they found highly oxidized iron, similar to the rust we see on our planet's surface, within garnets found within diamonds."

The language in the article appears to be using "digging deep" as a metaphor rather than literally digging over half a thousand kilometers.

I believe that it's impossible to do that literally, as the mantle is tremendously hot and under huge pressure that would melt or crush any materials that could be mass-produced to make a 550 km long drilling shaft. One source gives the estimated temperature that deep at above 1500 Celsius:

"The temperature would increase from about 1400°C to 1600°C over the depths interval 350 between 655 km."

http://onlinelibr...abstract
BEGINNING
1.7 / 5 (6) Jan 24, 2018
It is the recent global flood with its catastrophic plate tectnonics...
RealScience
5 / 5 (6) Jan 24, 2018
They said they were digging down that deep.

Scientists digging deep...


That is a description, probably written by a non-scientist, about the work.

There is a difference between a non-scientist-writer's tag-line and the contents of the article, and also between a news article about a paper and the contents of the paper itself.

My guess is that Ensign_nemo is correct and the article writer was trying to be clever, using 'digging deep' in the metaphorical sense of 'digging deep into the mystery' rather than literally digging to the ground. But the tag-line writer could also have been misled by the paper author saying "the deeper we go" (meaning the deeper we analyze samples from).

In any case, there is no way we can currently dig anywhere near that deep. I think that the Kola super-deep borehole still holds the record at about 12 km (which is only a few percent depths discussed in the article).
Captain Stumpy
not rated yet Jan 30, 2018
They said they were digging down that deep.
@grandpa
I mentioned in another thread that you should get your information from the source

The above is a news article written by someone who is not a scientist - but if you actually open the referenced study it explains this
Natural samples from the deep (>200 km) mantle are extremely rare, and are usually only found as inclusions in diamonds. Here we use synchrotron Mössbauer source spectroscopy complemented by single-crystal X-ray diffraction to measure the oxidation state of Fe in inclusions of ultra-high pressure majoritic garnet in diamond.
digging deep is often referred to as "colour" and adds to the readability of the article, as RealScience and Ensign_nemo point out

this is similar to the colour used in phrases like: "it's raining cats and dogs" - you're not going to see said mamalian missiles plummeting from the sky

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