10x more U in Earth's core?

  • Thread starter TEFLing
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If the abundance of Uranium in the earth is around 10ppb...

then the total mass of U in earth is around 3e19g

that's around 1e19 moles (virtually all U-238), corresponding to 3e23 decays / second, which would generate at most 2-3TW of power (attributing the entire 52MeV decay chain energy to each decay of U-238

But U-238 supposedly generates up to 20-30TW of power, up to 10x as much

Moreover, the (continental) Crustal abundance of U is 3mg/kg, and the total bulk Crustal abundance of U is 1mg/kg

Given that the Crust masses around 2-3e25g, that already implies 3e19g of U... i

All of earth's U resides in the (continental) Crust alone ?

Doesn't that strongly suggest, that there may well be more U on and in earth, than indicated by the abundances of meteors & solar photosphere ?
 

Astronuc

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It would be helpful if one would cite one's references for various values.

Uranium is a naturally occurring element with an average concentration of 2.8 parts per million in the Earth's crust. Ref: http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/mining-of-uranium/uranium-mining-overview.aspx

 

davenn

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As Astronuc said, you really do need to supply some references for your statements

............... than indicated by the abundances of meteors & solar photosphere ?
Being a meteorite collector and studier there of, I am not aware of any uranium in meteorites.
None of mine are radio active, I have never read or heard of others stating such.
But I am open to information :smile:

And I'm not sure what you think the solar photosphere has to do with the topic ?
Any miniscule anount of uranium that the sun may have would likely to be deep in the core and
would have got there when the solar nebula coalesced to form the sun and the planets.

From all I have read, the sun cannot produce uranium and other heavy elements unless it goes
super nova and for our sun, that isn't the future.
 

Astronuc

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All of earth's U resides in the (continental) Crust alone ?

Doesn't that strongly suggest, that there may well be more U on and in earth, than indicated by the abundances of meteors & solar photosphere ?
It's not clear that all of earth's U is in the crust and mantle.

"Table 1 lists the composition of the solar photosphere from absorption spectroscopy. Abundances are normalized to 1012 hydrogen atoms on a logarithmic scale that is usually used in astronomy." https://par.nsf.gov/servlets/purl/10036398

The abundance of U in the earth's crust is ~3 ppm, while the abundance in the solar atmosphere and meteorites is much less by about 3 orders of magnitude (see NSF report). It means that the distribution of elements, and U in this case, is non-uniform in the solar system, and the distribution on earth is also non-uniform, as is indicated by deposits of REE and refractory alloys.

About 70% of the total heat flux (44 TW) at the Earth surface comes from the radioactive decay of uranium, thorium and potassium [Helffrich and Wood, 2001], with 11 TW accounting for U alone. Uranium is known to be mainly present in the mantle and it is assumed that 50 wt% of total U in the Earth is stored in the lower mantle [Turcotte et al., 2001].
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2006GL027508
 
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using those solar abundances of the elements, and their atomic weights, you can use Excel to determine the mass of each element present in the earth

those calculations yield a total estimated mass of uranium in the entire planet. Which is comparable to the amount of uranium known to exist in earths crust alone

and that total mass of uranium? Only generates at most 2 terabytes from radioactive decay. Whereas we expect. Uranium decay to be generating 5 to 10 times more power than that.

That could require up to an order of magnitude more uranium presence in the planet. Then would be indicated by those solar abundances.

Davenn makes the obvious conclusion that solar abundances of uranium, derived from the Suns surficial photosphere, most likely underestimate the total amount of uranium present in the sun. Much of which Has probably sunk down deep into the interior? Just as on the Earth.
 
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Using Wikipedia solar / solar-system abundances, the calculated present-day radioactive decay power of K-40 is 8 TW, essentially in agreement with the figure above.

However, using the same abundances for Th-232 yields only 2 TW, low by a factor of 4-5. For U-238, only 2.6 TW, low by a factor of 3-4. For U-235, only 0.1 TW, low by a factor of as much as 10 or more.

Naively, such implies that solar abundances, derived as they are from the photospheric surface layers of the sun, underestimate the actual prevalence of super-heavy isotopes by at least a factor of a few or more, as Davenn suggested above -- perhaps on a crude scale-height calculation, mgH ~ kT ? Since Thorium & Uranium mass nearly 8x more than Potassium, their expected scale-heights in the solar envelope would be much reduced, perhaps confined largely to the Sun's radiative core, below the "reach" of convection in its upper envelope ?

FYI, the same abundances imply that earth initially formed amidst approximately 40 earth masses of H and about 10 earth masses of He.
 
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This "solar abundance earth" is only 6% Fe by mass, not the 36% geologists report

So the "solar earth" under-estimates iron & heavier metals by factors of 3-6 or more

To get 36% of earth's mass in Fe would have required ~300 earth masses, or about 1 Jupiter mass, in total original nebular material

which would have included an entire earth mass of C and 3 earth masses of O

Prima facie, there may be notable disagreement between elemental abundances Astronomers report from their observations, and abundances Geologists report from theirs ? This might possibly impact estimates of initial proto-planetary disk mass & distribution thereof also ?
 
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solar abundances suggest earth ought to have much more oxygen, and less iron, than usually stated

iron oxides, under extreme pressure, actually have the right density, electrical conductivity and high spin magnetically ordered ferromagnetism required for the core

if iron oxides are thought to be prevalent in the lower mantle and outer core, it's not a leap to suggest that they reside in the inner core too?



FeO phase space.jpeg wp_ss_20190718_0002.png wp_ss_20190718_0003.png wp_ss_20190718_0004.png wp_ss_20190719_0002.png
 

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