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chornedsnorkack
2014-May-19, 08:43 AM
Earth core is supposed to be mostly iron because iron meteorites are mostly iron.

But iron meteorites vary widely in composition. The concentration of nickel varies from hexahedrites, which are 5...6% Ni, to ataxites, which are 18...25 % Ni.

What is the Ni content of Earth core?

Romanus
2014-May-20, 05:40 PM
Given that you'll have outliers in any statistical sample, I doubt that the fraction of nickel is much more than the ratio of nickel to iron in the Sun, which is about 1:18 (~6%). Most iron meteorites have a similar percentage of nickel; ataxites are pretty rare.

chornedsnorkack
2014-May-21, 02:57 PM
Given that you'll have outliers in any statistical sample, I doubt that the fraction of nickel is much more than the ratio of nickel to iron in the Sun, which is about 1:18 (~6%).
But the fraction of nickel is much less in Earth crust: about 1:500 or 1:700.

Most iron meteorites have a similar percentage of nickel; ataxites are pretty rare.
Yes, but hexahedrites are also pretty rare.

John Mendenhall
2014-May-21, 03:14 PM
Iron fits what we observe best; unlikely that it's anything else.

Romanus
2014-May-21, 05:48 PM
But the fraction of nickel is much less in Earth crust: about 1:500 or 1:700.

Nickel is a siderophile element; most of it separated out of the Earth's crust during its formation to settle in the core.


Yes, but hexahedrites are also pretty rare.

Ah, but not octahedrites, the most common class.

Let's not run too fine a comb over this, though. The major types of iron meteorites represent perhaps a dozen parent bodies, out of an incalculably large original population, none of which formed in our part of the Solar System. There's no telling how many other metallic bodies are out there that we have no samples of, to say nothing of the planetesimals that went into the Earth's formation. Using the solar ratio (which is close to the chondritic ratio) seems the most parsimonious, though.

Related links:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC34384/
http://www.soest.hawaii.edu/GG/ASK/earths_core.html

Jeff Root
2014-May-22, 09:24 AM
none of which formed in our part of the Solar System.
Can you elaborate on this?



to say nothing of the planetesimals that went into the
Earth's formation.
I don't get what you mean by this. What about them?

-- Jeff, in Minneapolis

Romanus
2014-May-24, 04:40 AM
Can you elaborate on this?

The parent bodies of the iron meteorites probably formed in the asteroid belt, not in the Inner Solar System, where their orbits would have been too unstable. Differentiated meteorites in the Inner Solar System were either accreted by the terrestrial planets, impacted the Sun, or were perturbed outward.



I don't get what you mean by this. What about them?

As in the earlier point, the iron-rich parent planet bodies in the Inner Solar System are no longer with us.

Jeff Root
2014-May-24, 07:15 AM
The major types of iron meteorites represent perhaps a
dozen parent bodies, out of an incalculably large original
population, none of which formed in our part of the Solar
System.



Can you elaborate on this?
The parent bodies of the iron meteorites probably formed
in the asteroid belt, not in the Inner Solar System, where
their orbits would have been too unstable. Differentiated
meteorites in the Inner Solar System were either accreted
by the terrestrial planets, impacted the Sun, or were
perturbed outward.
If they were perturbed outward, then wouldn't many of
them now be in the main belt?

-- Jeff, in Minneapolis

Romanus
2014-May-24, 06:11 PM
^
"Perturbed outward..."

Now that I think about it, I'll correct myself to saying it's not likely. If a hypothetical asteroid were perturbed by Earth from an Earth-crosser to a Mars-crosser (or the reverse case), it would still be in an unstable orbit. The metallic asteroids in the the main belt have probably been there in some form for the lifetime of the Solar System, exactly *because* their orbits don't cross the main planets or fall into unstable Kirkwood Gap resonances.

grapes
2014-May-25, 03:50 AM
Even before my graduate days in geology, I had always heard that the earth's core was five percent nickel.

And ten percent dime

chornedsnorkack
2014-Jul-18, 04:52 PM
Nickel is a siderophile element; most of it separated out of the Earth's crust during its formation to settle in the core.


And iron did not. So should Earth core be enriched in nickel compared to the solar abundance?

korjik
2014-Jul-18, 05:07 PM
And iron did not. So should Earth core be enriched in nickel compared to the solar abundance?

?

Iron did separate out. That is why the core is iron.

Looking at only the core, the Ni content should be a higher percentage than solar abundance, but looking at the whole Earth, it should be fairly close to solar, once you factor for the loss of H and He

Jeff Root
2014-Jul-18, 05:08 PM
Say whaaaat???

Edit: Yeah. What korjik said.

-- Jeff, in Minneapolis

StupendousMan
2014-Jul-18, 07:34 PM
Definition of siderophile, from dictionary.com



sid·er·o·phile
adj.
1. (of a cell or tissue) having an affinity for iron.

2. Geology . (of a chemical element in the earth) having an affinity for metallic iron.

noun
3. a siderophile element, tissue, or cell.

chornedsnorkack
2014-Jul-18, 09:48 PM
?

Iron did separate out. That is why the core is iron.
And yet a lot of iron is found in Earth crust, both in ores and large amount of diffuse ingredients. Iron is the fourth most common element in Earth crust, after oxygen, silicon and aluminum. Unlike nickel, a lot of iron did not go to crust.

So how much iron DID go to core, compared to nickel (which almost all went to core)?


Looking at only the core, the Ni content should be a higher percentage than solar abundance,
Precisely.
Can anyone quantify how much higher?

Jeff Root
2014-Jul-19, 12:49 AM
What makes you think the percentage of nickel that went
to the core was much greater than the percentage of iron?

Iron is believed to be the most common element in the
Earth as as whole, comprising 34.6% by mass. Nickel is
believed to be the fifth most common, at 2.4%.

-- Jeff, in Minneapolis

danscope
2014-Jul-19, 04:59 AM
Imagine if 10% of the very center of the core was gold ? Hot as blazes, incoruptable and pretty heavy. There's a fair bet
that it is. Just saying.

korjik
2014-Jul-19, 07:30 AM
And yet a lot of iron is found in Earth crust, both in ores and large amount of diffuse ingredients. Iron is the fourth most common element in Earth crust, after oxygen, silicon and aluminum. Unlike nickel, a lot of iron did not go to crust.

So how much iron DID go to core, compared to nickel (which almost all went to core)?

Precisely.
Can anyone quantify how much higher?

No. It is not solvable without knowing the exact initial composition and exact thermal history.

geonuc
2014-Jul-19, 08:02 AM
Imagine if 10% of the very center of the core was gold ? Hot as blazes, incoruptable and pretty heavy. There's a fair bet
that it is. Just saying.

Just saying what? That it's a fair bet that the earth's core comprises 10% gold?

danscope
2014-Jul-21, 06:58 PM
Probably so. Not that we will ever get to it, but quite possible.

Hornblower
2014-Jul-21, 09:31 PM
Probably so. Not that we will ever get to it, but quite possible.
Can you give us a technical description of a hypothetical process that could have concentrated that much gold in Earth's core?

danscope
2014-Jul-21, 10:01 PM
Considering that it is so heavy and molten at such low temperatures, that is where it would wind up. Cataclysmic collisions
would have been sufficient to dislodge small amounts , forcing them to the surface , with molten quartz ,leaving trace amounts like we see. It's just a casual theory, speculation , but interesting.

Swift
2014-Jul-22, 12:50 AM
Considering that it is so heavy and molten at such low temperatures, that is where it would wind up. Cataclysmic collisions
would have been sufficient to dislodge small amounts , forcing them to the surface , with molten quartz ,leaving trace amounts like we see. It's just a casual theory, speculation , but interesting.
danscope,

Q&A is not for idle speculation. If you do not know the mainstream explanation for something, you should not be tossing out your own pet ideas in Q&A.

WayneFrancis
2014-Jul-22, 04:54 AM
10% gold? Why would it be that much gold? Why would Earth have a unusually high ratio of gold to other elements?

chornedsnorkack
2014-Jul-22, 06:31 AM
What is the observed range of gold content in iron meteorites? I have not read of any iron meteorite having 10 %, and that despite having an appreciable variability range of nickel content.

Hornblower
2014-Jul-22, 03:06 PM
I have not found any data for gold in iron meteorites, but the following site has data for carbonaceous meteorites, which if I am not mistaken are relatively undifferentiated samples of the precursor dust that formed the rocky planets.
http://www.webelements.com/iron/geology.html

This page is for iron, but you can click on the periodic table icon in the upper left and select gold for the corresponding data.

The carbonaceous meteorites average about 22% iron and a millionth as much gold. My educated guess is that iron meteorites, along with Earth's core, have a similar fraction of gold, perhaps with some enrichment toward the center as a result of the gold's great weight. If we concentrate all of the gold at the center, it might make a nugget on the order of 50 miles in diameter.

Another educated guess is that the amount of nickel in Earth's core is roughly estimated from what is found in iron meteorites, which are believed to be fragments of the cores of differentiated large asteroids that later collided.

danscope
2014-Jul-22, 04:03 PM
No more opinion as per the admin.