Researchers confirm Earth's inner core is solid

October 19, 2018, Australian National University
Credit: CC0 Public Domain

A new study by researchers at The Australian National University (ANU) could help us understand how our planet was formed.

Associate Professor Hrvoje Tkalčić and PhD Scholar Than-Son Phạm are confident they now have direct proof the earth's inner core is solid.

They came up with a way to detect shear waves, or "J waves" in the inner core - a type of wave which can only travel through solid objects.

"We found the inner core is indeed solid, but we also found that it's softer than previously thought," Associate Professor Tkalčić said.

"It turns out - if our results are correct - the inner core shares some similar elastic properties with gold and platinum. The inner core is like a time capsule, if we understand it we'll understand how the planet was formed, and how it evolves."

Inner core shear waves are so tiny and feeble they can't be observed directly. In fact, detecting them has been considered the "Holy Grail" of global seismology since scientists first predicted the inner core was solid in the 1930s and 40s.

So the researchers had to come up with a creative approach.

Their so-called correlation wavefield method looks at the similarities between the signals at two receivers after a major earthquake, rather than the direct wave arrivals. A similar technique has been used by the same team to measure the thickness of the ice in Antarctica.

"We're throwing away the first three hours of the and what we're looking at is between three and 10 hours after a large earthquake happens. We want to get rid of the big signals," Dr Tkalčic said.

"Using a global network of stations, we take every single receiver pair and every single large earthquake - that's many combinations - and we measure the similarity between the seismograms. That's called cross correlation, or the measure of similarity. From those similarities we construct a global correlogram - a sort of fingerprint of the earth."

The study shows these results can then be used to demonstrate the existence of J waves and infer the shear wave speed in the inner core.

While this specific information about shear waves is important, Dr Tkalčić says what this research tells us about the inner core is even more exciting.

"For instance we don't know yet what the exact temperature of the inner core is, what the age of the inner core is, or how quickly it solidifies, but with these new advances in global seismology, we are slowly getting there.

"The understanding of the Earth's has direct consequences for the generation and maintenance of the geomagnetic field, and without that geomagnetic field there would be no life on the Earth's surface."

The research has been published in Science.

Explore further: The temperature 3,000 kilometers below the surface of the Earth is much more varied than previously thought

More information: Hrvoje Tkalčić et al. Shear properties of Earth's inner core constrained by a detection of J waves in global correlation wavefield, Science (2018). DOI: 10.1126/science.aau7649

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12 comments

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betterexists
1 / 5 (12) Oct 19, 2018
Most Important is to use Robots to drill a THIN hole from 1 End of this planet to the other end. Make sure that the other end will not get near a ocean, unless the drilling was also STARTED in a Ocean !
It should take Top Priority; We have already used Air with Planes !
antialias_physorg
4.1 / 5 (9) Oct 19, 2018
There was a brilliant xkcd comic a couple days ago regarding mantle geologists...that goes even more so for core geologists:

https://m.xkcd.com/2058/

(don't forget to hover your mouse over the image for the customary additional joke)
betterexists
1 / 5 (5) Oct 19, 2018
Most Important is to use Robots to drill a THIN hole from 1 End of this planet to the other end. Make sure that the other end will not get near a ocean, unless the drilling was also STARTED in a Ocean !
It should take Top Priority; We have already used Air with Planes !

Another way, which is also appropriate. If you look at the sky, you see trillions of Stars(Suns, possibly far more powerful than ours). We are able to fly from continent to continent on earth, but not yet to transport materials (Who knows - Essential Gold, Platinum, Diamonds, rare earth materials etc.,) and trap energy from the universe. Once we get abundant energy and materials...We will have to get back to still deeper study of our body, DNA, Cell etc., to enrich ourselves !
Mayday
5 / 5 (3) Oct 19, 2018
Betterex, have you considered running for office?
rrwillsj
1 / 5 (6) Oct 19, 2018
Oh one considers bettingeffluence appropriate for a position in trumpenella's crime family now infesting the White House.

However, doesn't Acting President John F. Kelly already have enough of a burden as the only adult in the room?

Old_C_Code
3.7 / 5 (3) Oct 19, 2018
rrwilljiz: that post prove's you're insane. They call you guys madmen: angry, unreasonable, delusional.

The article is about Earth's solid core.
guptm
5 / 5 (1) Oct 19, 2018
The detection of the waves closes an 80-year quest to find them and confirms a solid, but soft, inner core. Congratulations to all the geophysicists! This year now goes in the history pages.
Some people would still say: the center of the flat sheet cannot be liquid!
rrwillsj
5 / 5 (2) Oct 20, 2018
old_coot, how cute. As you also failed to comment on this article.
cantdrive85
2 / 5 (4) Oct 20, 2018
The detection of the waves closes an 80-year quest to find them and confirms a solid, but soft, inner core.

It is a correlation at best, don't get too excited.
rrwillsj
5 / 5 (2) Oct 21, 2018
Well cant, I gotta agree with you.

Damn! Who'd ever thought it?

A lot of the problem with comprehending the results of lengthy, complicated research? Is how can the researcher's explain their findings in some manner that is easily understood by the Public?

The terms used in this article. Solid, soft. temperature, shear waves and so on. Really do not mean the same thing to the research scientists as those same words defined by the Public's experience.
FredJose
1 / 5 (6) Oct 22, 2018
Right! Good for the researchers in their creative use of technology!

It does however, raise the issue of just why and how earth got its solid core in the first place.

Currently there exists no plausible naturalistic explanation that shows how that solid core got into place initially.
There's the cooling problem if it started out as molten - taking billions of years too long to solidify.
There's the sinking thru problem - just too many highly implausible auxiliary factors required.

So whilst this research confirms a solid core, the bigger problem just gets even more, well... solid!
antialias_physorg
3 / 5 (2) Oct 22, 2018
Is how can the researcher's explain their findings in some manner that is easily understood by the Public?

Researchers aren't in the business of explaining their research to the public. Their business is research. Which means: when you write a paper you write it for other researchers so that they can build upon it. Other researchers who can make use of your results work in a similar field (so there's no point in starting at Adam and Eve every time you publish a paper)

In then end: What is the public going to do with the findings of researchers? Absolutely nothing. So while it would be nice for researchers to write public-friendly papers it would serve no purpose.

The guys who do write for the public are science journalists. And they write the stuff you find on sites like phys.org and the publicity pages of universities.

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