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Swift
2015-Feb-10, 09:19 PM
From R&D magazine (http://www.rdmag.com/news/2015/02/earth%E2%80%99s-surprise-inside?et_cid=4408471&et_rid=54636800&type=cta)


Seismic waves are helping scientists to plumb the world’s deepest mystery: the planet’s inner core.

Thanks to a novel application of earthquake-reading technology, a research team at the Univ. of Illinois and colleagues at Nanjing Univ. in China have found that the Earth’s inner core has an inner core of its own, which has surprising properties that could reveal information about our planet.

Led by Xiaodong Song, a professor of geology at the U. of I., and visiting postdoctoral researcher Tao Wang, the team published its work in Nature Geoscience.

“Even though the inner core is small—smaller than the moon—it has some really interesting features,” said Song. “It may tell us about how our planet formed, its history, and other dynamic processes of the Earth. It shapes our understanding of what’s going on deep inside the Earth.”


The inner core, once thought to be a solid ball of iron, has some complex structural properties. The team found a distinct inner-inner core, about half the diameter of the whole inner core. The iron crystals in the outer layer of the inner core are aligned directionally, north-south. However, in the inner-inner core, the iron crystals point roughly east-west.

Not only are the iron crystals in the inner-inner core aligned differently, they behave differently from their counterparts in the outer-inner core. This means that the inner-inner core could be made of a different type of crystal, or a different phase.


Link to a Univ. of Illinois webpage about the work (http://news.illinois.edu/news/15/0209innercore_XiaodongSong.html)

Link to the abstract in Nature Geoscience (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2354.html)


The Earth’s solid inner core exhibits strong anisotropy1, 2, 3, 4, 5, with wave velocity dependent on the direction of propagation due to the preferential alignment of iron crystals6. Variations in the anisotropic structure, laterally and with depth7, 8, 9, 10, 11, provide markers for measuring inner-core rotation12 and offer clues into the formation and dynamics of the inner core13, 14. Previous anisotropy models of the inner core have assumed a cylindrical anisotropy in which the symmetry axis is parallel to the Earth’s spin axis. An inner part of the inner core with a distinct form of anisotropy has been suggested15, but there is considerable uncertainty regarding its existence and characteristics16, 17, 18, 19. Here we analyse the autocorrelation of earthquake coda measured by global broadband seismic arrays between 1992 and 2012, and find that the differential travel times of two types of core-penetrating waves vary at low latitudes by up to 10 s. Our findings are consistent with seismic anisotropy in the innermost inner core that has a fast axis near the equatorial plane through Central America and Southeast Asia, in contrast to the north–south alignment of anisotropy in the outer inner core. The different orientations and forms of anisotropy may represent a shift in the evolution of the inner core.

Ara Pacis
2015-Feb-12, 04:15 AM
Waiting for the pseudo-scientists to use this to promote special power vortices at those locations.

Or did Captain Jack Harkness beat them to it?

malaidas
2015-Feb-12, 10:18 AM
A truly scientific question here, would this have any major effect on the dynamo effect, or would the outer N/S alignment shield the outer core and mantle from the E/W alignment at the centre? I am assuming that there must be some effect of course as we have detected it.

Swift
2015-Feb-12, 01:47 PM
A truly scientific question here, would this have any major effect on the dynamo effect, or would the outer N/S alignment shield the outer core and mantle from the E/W alignment at the centre? I am assuming that there must be some effect of course as we have detected it.
Good question, and I don't know the answer. When you say "I am assuming that there must be some effect of course as we have detected it.", I'm not sure what you mean. This inner-most core was not detected by its magnetic effects, but its effects on the propogation of seismic waves.

My speculation is that it has to have some effect on the generation of the magnetic field. If the inner-most core has a different crystal structure or is a different phase, it might have very different magnetic properties (or might even be diamagnetic). If it is diamagnetic, that means the Earth's field is generated in just the outer-inner-core (that's a weird expression ;)).

I wonder if the magnetic interactions between the inner-most and outer-inner core is what leads to the movement of the poles and the flips of the magnetic field?

I think we are too early in this work to know any of that. I suspect that others are just trying to replicate their results - it seems to be a significant shift in thinking, and I suspect there are geologists who are skeptical about the findings.

CJSF
2015-Feb-12, 02:52 PM
It it bears out, do you think it could be a remnant from the hypothetical "Mars-sized" impactor that is speculated to have generated the Moon and Earth's comparatively thin crust, &tc?

CJSF

P.S. Google Chrome's word-list ("dictionary") doesn't seem to have the word impactor in it.

Ara Pacis
2015-Feb-13, 04:34 AM
I was wondering about that too. Could the impact dynamics have affected the outer part of the core but not the center? Maybe remelting and later crystalization of the outer-inner core aligned differently due to a new rotation direction or something.

If I understand correctly, as long as the inner-inner and outer-inner core turn at the same rate, it wouldn't create a separate dynamo system between them. IIRC, you can magnetize a steel bar regardless of it's crystal alignments, but I could be wrong or maybe the pressure & temperature regime changes that.

Eclogite
2015-Feb-21, 11:40 AM
If I understand correctly, as long as the inner-inner and outer-inner core turn at the same rate, it wouldn't create a separate dynamo system between them. IIRC, you can magnetize a steel bar regardless of it's crystal alignments, but I could be wrong or maybe the pressure & temperature regime changes that.Since the magnetic field is generated by circulation within the outer core I do not follow why you appear to be mentioning dynamos within the solid inner core. Would you clarify please.

Ara Pacis
2015-Feb-21, 05:49 PM
Since the magnetic field is generated by circulation within the outer core I do not follow why you appear to be mentioning dynamos within the solid inner core. Would you clarify please.

Because Swift wondered about magnetic fields.

malaidas
2015-Feb-22, 10:04 AM
This stems from my question, and it's a question of whether the magnetic field of the inner core had any effect on the magnetic field we experience generated by the outer core etc and if so what effect this discovery might infer.

publiusr
2015-Feb-22, 09:05 PM
I've heard of Epsilon iron before and how it may exhibit antiferromagnetism:
http://en.wikipedia.org/wiki/Hexaferrum
http://en.wikipedia.org/wiki/Antiferromagnetism

grapes
2015-Feb-23, 05:56 AM
My speculation is that it has to have some effect on the generation of the magnetic field. If the inner-most core has a different crystal structure or is a different phase, it might have very different magnetic properties (or might even be diamagnetic). If it is diamagnetic, that means the Earth's field is generated in just the outer-inner-core (that's a weird expression ;)).

I'm pretty sure that the earth's magnetic field primarily originates in the outer core, not the inner core.

But hey I was wrong about eggs and cholesterol

ETA: wikipedia still says that it is generated by convection in the core. The inner core can't convect, because it's solid.
http://en.m.wikipedia.org/wiki/Earth's_magnetic_field

malaidas
2015-Feb-23, 09:28 AM
But would not the static field of the inner core interact with the magnetic field generated by convection in the outer core.

grapes
2015-Feb-23, 11:11 AM
There may not be an inner static field, because of the extreme temperatures. What extreme pressure does, I dunno.

malaidas
2015-Feb-23, 11:47 AM
OK I equally don;t know here, but the fact the article talks about N/S and E/W alignment suggests to me that the model proposes there is one.

grapes
2015-Feb-23, 03:47 PM
OK I equally don;t know here, but the fact the article talks about N/S and E/W alignment suggests to me that the model proposes there is one.
The alignments are of crystal structure. An "easy axis" for a crystal may have multiple magnetic domains pointing in opposite directions, resulting in no magnetic field for the crystal.