Scientists simulate Earth's creation to solve core problem

Nov 19, 2012
Credit: NASA

(Phys.org)—Using computer simulations, researchers from the University of California, Davis, and the Chinese Academy of Sciences in Beijing have helped to solve a mystery that scientists have puzzled over since the early 1950s: What accounts for Earth's core density?

Their discovery: That Earth's core contains 0.1-0.8 percent carbon, the largest reservoir of carbon on the planet.

The findings were published this week in the journal PNAS Early Edition.

"We knew the density of the core, and we knew that metal iron and nickel alone couldn't account for that density," said UC Davis geology professor and study co-author Qing-Zhu Yin. "You need something lighter."

Carbon was one of the major missing light element candidates; others included silicon, oxygen, phosphorus, magnesium, hydrogen and nitrogen. To discover their content in the Earth's core, Yin and co-author Yigang Zhang went to the computer.

"We played with about 260 atoms to try to simulate Earth's formation," Yin said. "We assigned them their basic properties and let the do the work in the computer. Now we know how to account for that density deficit."

An accurate knowledge of carbon's influence will help to increase our understanding of the Earth's age and the exact timing of the core's formation.

"It's about understanding the nature of the Earth," Yin said. "We're able to better understand the physical and involved in Earth's formation."

Explore further: Lava on Hawaii continues moving through vacant lot

More information: www.pnas.org/content/early/201… 826109.full.pdf+html

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User comments : 32

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waremi
2.8 / 5 (6) Nov 19, 2012
OK, I'm lost. How can a QM model of 260 atoms shed light on the dynamics of billions of tons of heavy metals forming the core of a planet?
bigj531
5 / 5 (5) Nov 19, 2012
OK, I'm lost. How can a QM model of 260 atoms shed light on the dynamics of billions of tons of heavy metals forming the core of a planet?


Because it still follows the same laws of physics...
waremi
2.6 / 5 (8) Nov 19, 2012
Because it still follows the same laws of physics...


Last I heard QM and Gravity had not been reconciled, so no, they don't.
Modernmystic
1.6 / 5 (9) Nov 19, 2012
Because it still follows the same laws of physics...


Last I heard QM and Gravity had not been reconciled, so no, they don't.


Because intelligent apes on a blue planet circling a G type star in the arm of one of billions of spiral galaxies can't see how to marry together the math of two of their theoretical frameworks of a concept they call physics doesn't mean that the laws of physics are effected by that "failure"...
rubberman
4.2 / 5 (5) Nov 19, 2012
Because it still follows the same laws of physics...


Last I heard QM and Gravity had not been reconciled, so no, they don't.


It isn't about gravity, it's about density. Although the 2 are directly related which is likely how they were able to determine the percentage of the element that couldn't be iron.
waremi
5 / 5 (2) Nov 19, 2012
It isn't about gravity, it's about density. Although the 2 are directly related which is likely how they were able to determine the percentage of the element that couldn't be iron.


Interesting, what I was getting at is that a planet's core depends on more than simple molecular chemistry. It involves convection transport, and boundary layer conditions across a wider pressure and temperature gradient than I would think could be simulated in a few hundred atoms.
cantdrive85
1.2 / 5 (11) Nov 19, 2012
"We knew the density of the core, and we knew that metal iron and nickel alone couldn't account for that density," said UC Davis geology professor and study co-author Qing-Zhu Yin. "You need something lighter."


Wow, they must have quite the apparatus to achieve the required 'in situ' measurements of the core of the Earth to make such a claim.

A2G
1.8 / 5 (5) Nov 19, 2012
I have to agree with you on that one CD. We need to stop making statements that are presented as factual when we are only assuming something to be true. We really do NOT know for sure what is at the core of the Earth. The professor should have phrased his statement in a way that conveyed that idea. I do see this as an issue in science today. Theories based on theories based on theories. Not a wise branch to climb out on.
waremi
5 / 5 (5) Nov 19, 2012
Wow, they must have quite the apparatus to achieve the required 'in situ' measurements of the core of the Earth to make such a claim.


They used a sonogram. A really big one i.e. seismic pressure waves.
jscroft
1 / 5 (11) Nov 19, 2012
Not a huge surprise. Sort of puts the lie to the notion of "Peak Oil," doesn't it? "Fossil" fuels, my eye.
cantdrive85
1.3 / 5 (13) Nov 19, 2012
Wow, they must have quite the apparatus to achieve the required 'in situ' measurements of the core of the Earth to make such a claim.


They used a sonogram. A really big one i.e. seismic pressure waves.

Still not a direct measurement, extrapolations and assumptions must still be employed.
Modernmystic
4.8 / 5 (10) Nov 19, 2012
Still not a direct measurement, extrapolations and assumptions must still be employed.


Do you think that MRI scans are helpful in diagnosing cancer?
cantdrive85
1.4 / 5 (10) Nov 19, 2012
Not as helpful as a biopsy.
Modernmystic
4.7 / 5 (6) Nov 19, 2012
Not as helpful as a biopsy.


Was that what I asked?

If you see cancer on an MRI, you don't have to employ an assumption...you can look, point, and say there it is. There is no fundamental difference between that and EM radiation entering your eye and being interpreted by your brain...
waremi
4 / 5 (1) Nov 19, 2012
Still not a direct measurement, extrapolations and assumptions must still be employed.


That is true of any number of things we know, and this one does not involve as many assumptions as you might think. Still that is one reason they are currently planning to probe the absolute density of the Earth's core using a neutrino beam.
cantdrive85
1.4 / 5 (10) Nov 19, 2012
Not as helpful as a biopsy.


Was that what I asked?

If you see cancer on an MRI, you don't have to employ an assumption...you can look, point, and say there it is. There is no fundamental difference between that and EM radiation entering your eye and being interpreted by your brain...


You may be able to see the tumor, but does that tell you everything you need to know about it?
waremi
4.4 / 5 (7) Nov 19, 2012
You may be able to see the tumor, but does that tell you everything you need to know about it?


Not everything, but it does tell you its density.
cantdrive85
1.9 / 5 (9) Nov 19, 2012
Does measuring P-waves equate to an MRI? This is a legit question, no devil's advocate here.
CrossMan
4.5 / 5 (2) Nov 19, 2012
QM and GR have not been reconciled, but you can add Newtonian gravity to QM just fine (it's just a potential).

The bulk modeling is important and done separately. It depends on a certain coefficient describing how C behaves in the presence of other atoms. They computed this coefficient, which is then fed back into the bulk modeling to give the C wt%.
waremi
5 / 5 (6) Nov 19, 2012
Does measuring P-waves equate to an MRI? This is a legit question, no devil's advocate here.


Equates more to a sonogram, the reflection and deflection of the waves off the core is dependent on density and governed by Snell's law which is quite well understood, and the imaging produced of the crust is used by the oil industry to plan drilling.
Torbjorn_Larsson_OM
5 / 5 (2) Nov 19, 2012
Ah, very interesting. People have noticed that terrestrials should drown in water and carbon, while our own are very dry and silicidated. The most common asteroids, carbonaceous chondrites, have ~ 10 % water by mass but Earth, Moon and Mars initial mantle had only ~ 0.05 %.

Similarly models of superEarths gets them a ~ 30 % carbon shell, which forms an amorphous diamond crust by pressure.

This is a *huge* problem for astrobiology. Water worlds would be marginally habitable (available metals for cell metabolism rare), carbon worlds would be uninhabitable (no available metals).

But it turns out planetary system formation models naturally keep inner terrestrial dry and silicidated as ours. And since our systems terrestrials has the same generic water content, they should have about the same volatile carbon content too. 0.1 - 0.8 % carbon of Earth core dominating the supply, itself ~ 30 % of Earth mass, would mean an initial mantle content of ~ 0.03 - 0.3 % carbon by mass.

Not bad!
Torbjorn_Larsson_OM
4.8 / 5 (4) Nov 19, 2012
@ waremi: Yes, vague. They are likely looking a handful of atoms as a model system, to understand how carbon behaves in iron under pressure and heat, it is an often used method. The rest of the physics you mention is applied as constraints.

GR and QM is reconcilable (quantized gravity, with gravitons and all), until GR gives out under high energy/large curvature. Blame the effective theory of GR, not the working reconciliation. But that has nothing to do with the model following the same QM (rather chemistry) models under different pressures and temperatures, as commented before me.

@ A2G: The model is generating testable predictions. No more, no less. Being able to do so means we alredy know a lot. Sufficiently much? No, then we wouldn't be asking.

@ Cantdrive85: "not a direct measurement". Define "direct" testably. The physics is in if you can make a testable prediction under constraints. Ultimately we achieve a global unambiguous test (no competing theory).
unknownorgin
1 / 5 (7) Nov 20, 2012
I just can not go with the idea that the earth formed from dust because only large chunks of nickle iron would sink to the core because of convection current stiring so that leaves the remains of a super nova or the earth was the core of a star because that is the only way you get such pure chunks of metal that could be milled into an engine block or made into knifes as the eskimos did.
StarGazer2011
1.9 / 5 (7) Nov 20, 2012
Seems to be a philosophical mistake here. A model is a theory, its a possible explanation given a certain set of assumptions; nothing more. It is never, ever, ever, evidence of anything by itself.
While it may be true that the core contains carbon, it may also be false, we still dont know.
What we need to do is devise a way to test the theory with empirical evidence in a way which will either falsify the theory or support it.
I'm pretty sure theres a name for that process...
rubberman
3.7 / 5 (3) Nov 20, 2012
I just can not go with the idea that the earth formed from dust because only large chunks of nickle iron would sink to the core because of convection current stiring so that leaves the remains of a super nova or the earth was the core of a star because that is the only way you get such pure chunks of metal that could be milled into an engine block or made into knifes as the eskimos did.


If the earth is the core of a star, how do you think the star formed?
Howhot
not rated yet Nov 22, 2012
I'm pretty sure theres a name for that process...

Oooo ooo me first! Ooo me first. Is it the scientific method?
Lurker2358
3.8 / 5 (4) Nov 23, 2012
Ok. Where is all the gold coming from which ends up in hydrothermal vents?

If you say "meteors" that's the Standard Model answer for everything.

Gold is one of the densest natural metals on the planet, and as such should be in it's highest concentration in the core. The same can be said for all of the rare earth's and heavy metals.

In fact, the core should be denser than the average density of Iron, if the Earth is differentiated.

Iron isn't even particularly dense compared to lots of other metals on the Periodic table.

The real question here: "how is it possible for the core to be less dense than iron?"

Perhaps another good question would be, "is the DATA correct?"
tadchem
3 / 5 (2) Nov 23, 2012
@modernmystic:
The mathematics of QM and GR have been unified. It is simply that they are rather awkward for routine use because it requires 'visualizations' of 4-tensors in Minkowski space - curved 4-dimensional space-time. In Minkowski space, a tensor can have projections ("shadows") in regular 3-space with a fixed time rate of flow, or in 4-dimensional quantum space (the 'standard model').
As in all projective geometries, what you see depends on the angles of the viewpoints and the rotations. See the cover of Douglas Hofstadter's "Godel, Escher, and Bach; the Eternal Golden Braid" for an example. http://en.wikiped...over.jpg
rkolter
5 / 5 (1) Nov 23, 2012
I just can not go with the idea that the earth formed from dust because only large chunks of nickle iron would sink to the core because of convection current stiring so that leaves the remains of a super nova or the earth was the core of a star because that is the only way you get such pure chunks of metal that could be milled into an engine block or made into knifes as the eskimos did.


I am resisting the urge to ridicule you. I have to assume that you are trolling, because if you really were this wrong-headed, you would have died long before you learned how to type.

Just for fun though, if we were the core of a star, what kind of star would we be the core of? Stars that are capable of generating iron in their cores have this nasty tendency to detonate and form neutron stars or black holes.
Parsec
not rated yet Nov 24, 2012
Not as helpful as a biopsy.


Was that what I asked?

If you see cancer on an MRI, you don't have to employ an assumption...you can look, point, and say there it is. There is no fundamental difference between that and EM radiation entering your eye and being interpreted by your brain...


This is a very valid point, particularly since the seismic data used for core measurements is processed using the exact same algorithms that a CAT scanner uses to create 3D pictures of the earth. One is Computer Axial Tomography (CAT), the other is Seismic Axial Tomography (SAT).
PhotonX
not rated yet Nov 24, 2012
If you see cancer on an MRI, you don't have to employ an assumption...you can look, point, and say there it is.
You can certainly see that a mass is there. You don't know the composition of that mass, though MRI has a better chance of determining that than CT or US. I've never counted the number of core biopsies and fine needle aspirations I've seen, but it's probably over a thousand, and all of them had imaging procedures done first, which identifies the mass, then the BX/FNA identifies the exact nature of it. So, partial credit to each of you.
PhotonX
not rated yet Nov 24, 2012
This is a very valid point, particularly since the seismic data used for core measurements is processed using the exact same algorithms that a CAT scanner uses to create 3D pictures of the earth. One is Computer Axial Tomography (CAT), the other is Seismic Axial Tomography (SAT).
CT deals strictly with radiation attenuation as the beam passes through the target. I don't know much about SAT, but I think it deals with a large component of refracted waves bouncing back to the surface, which I think would require a somewhat different algorithm, but that's probably nit-picking on my part, certainly the concept is the same.