
Heart of Earth's inner core revealed - GotAnyMegadeth
http://www.bbc.co.uk/news/science-environment-31322817
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kens
As for what the east-west axis means... According to the paper, they use a
cylindrical anisotropy model and the best-fit axis is located at (9° N, 89° W)
or its antipode at (9° S, 91° E). In other words, the crystals point along an
axis near the equatorial plane through Central America and Southeast Asia.

The paper is pretty vague about why this would occur: "may represent a
tectonic evolution of the inner core and thus our finding may indeed offer
‘clues about the inner-core history: its age, thermal process, and possibly an
early convective event’."

Paper is available at
[http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo23...](http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2354.html)

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tjradcliffe
But the core doesn't rotate at the same rate as the crust:
[http://news.harvard.edu/gazette/1996/08.15/PuttingaNewSpin.h...](http://news.harvard.edu/gazette/1996/08.15/PuttingaNewSpin.html)
(or has this been proven wrong?)

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kens
That's very interesting. If the inner core rotates 3 degrees a year and the
earthquake data covers 20 years, that would be a 60 degree shift from start to
end of the data set. I looked over the paper again, and they don't mention
this at all.

Edit: I emailed the author of the paper (Xiaodong Song). He says that more
recent work suggests 0.3-0.5 deg/year for core rotation. (This would make the
rotation much less important.)

[http://www.geology.illinois.edu/people/xsong/Sites/papers/zh...](http://www.geology.illinois.edu/people/xsong/Sites/papers/zhangetal05_science.pdf)
[http://www.geology.illinois.edu/people/xsong/Sites/papers/li...](http://www.geology.illinois.edu/people/xsong/Sites/papers/lindner_etal10_jgr.pdf)

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JoeAltmaier
What does it mean for the crystals of the 'inner inner core' to be aligned in
an 'east-west direction'? Its a sphere. Does that mean they are aligned in a
ring, like the grooves in an lp (or the dots on a CD/DVD)? Why doesn't the
graphic reflect that?

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ChuckMcM
Iron crystallizes at high pressure, while the iron is molten it aligns itself
with any magnetic field, then as it crystallizes it can no longer change
direction as the field changes.

This paper suggests that as the inner part of the core was solidifying, the
earth had east/west magnetic poles rather than north/south magnetic poles. And
then something "big" happened to switch the poles north/south. That "big"
thing happened in a fairly short period of time (geologically) if the boundry
between east/west alignment and north/south alignment in the crystals is thin.
They also mention the core is solidifying at a rate of .5mm per year. Which is
how they hope to "date" the event that occurred. Although it is unclear to me
if they consider the process to be dependent on the surface volume or not.

Does that help?

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JoeAltmaier
Not a bit. There's no such thing as an east pole or west pole, like there is a
north pole.

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bdamm
I think the implication is that magnetic North was on the equator, rather than
at the geologic pole.

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ChuckMcM
exactly this. If you had a compass and were on the planet while those crystals
were forming, the 'north' part of the compass would point you to a point along
the equator rather than in the upper latitudes as it does now.

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DiabloD3
9N 89W is off the coast of Costa Rica, 9S 91E is off the coast of Singapore,
which both locations seem to be kind of close to areas prone to earthquakes
and tsunamis.

Also, it says it could have changed half a billion years ago. The current
estimate of the formation of the moon is around 4.5 billion years ago, maybe
these are related and they got their dating wrong?

The only thing I can find that happened half a billion years ago was the end
of the the Neoproterozoic Era (the end of the Proterozoic Eon), which saw the
first multi-celled life and the end of the Marinoan galciation, which could
have subsided through global release of methane from equatorial permafrost.

