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Author Topic: Are radioactive elements in the Earth's mantle evenly distributed?  (Read 4822 times)

Offline Bill S

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The decay of radsioactive elements in the mantle contributes to its heating.  What evidence do we have regarding the distribution of these elements?  Is their distribution even or patchy?  How do wew know?
« Last Edit: 09/07/2012 00:30:56 by Geezer »


 

Offline Bill S

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Just spotted my interesting spelling of ele(w)ments; marks for originality?
 

Offline RD

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... What evidence do we have regarding the distribution of these elements?  Is their distribution even or patchy?  How do wew know?

GeoNeutrinos ? ... http://www.nature.com/nature/journal/v436/n7050/full/436467a.html
http://kamland.stanford.edu/GeoNeutrinos/geoNeutrinos.html

Just spotted my interesting spelling of ele(w)ments; marks for originality?

It is possible for you to edit the title of a thread you started.
« Last Edit: 09/07/2012 00:18:16 by RD »
 

Offline JimBob

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I doubt that sicience really knows. I try to stay current - going to the geo. library and forcing myself to read hard rock journal such as Geochimica et Cosmochimica Acta (In English, NOT French) falling asleep half way through articles. What the hell is Abiogenic Carbon anyway??? A little erudite for my taste.



It is possible for you to edit the title of a thread you started.



Si, Hombre.
 

Offline Geezer

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YEAH!!
 
JimBob must be feeling a bit better. Glad to see you are back. Just don't go posting any of your whacky theories!
 

Offline evan_au

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Since the earth appears to be cooling from a once-molten state, we can generally assume that the elements are roughly distributed by density, with the densest ones at the core, and lighter ones towards the outside.

Since the naturally radioactive elements with a half life > 109 years tend to have a high density, we can assume that there is more of these heavy minerals like Uranium, Radium and Thorium closer to the center of the earth, inside the iron core. One exception is Potassium, which is radioactive, but fairly light, and found in silicate minerals.

Radioactive minerals do occur in scattered deposits on the surface of the Earth, from igneous rocks and meteorites. These are often sorted into ore beds because of the melting temperatures of their minerals, their chemical properties, or because of sorting on the basis of density (like mineral sands).
 

Offline Bill S

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we can assume that there is more of these heavy minerals like Uranium, Radium and Thorium closer to the center of the earth, inside the iron core.

Is there any evidence for the presence of radioactive elements in the core?
 

Offline evan_au

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Since we have not really drilled any deeper than the crust, there is no direct evidence at this time.

Indirect evidence comes from models of earth's cooling rate, which would be slowed by the ongoing decay of radioactive elements in the core and the insulation of the crust.

Here are the results of some neutrino observations from within the earth. It suggests that half of the earth's heat comes from uranium & thorium decay. It mentions the current theory that only iron-soluble elements would be in the core - but with the small sample size (111 neutrinos so far), it will take a while for this new technique to narrow down the geographical distribution within the earth. http://physicsworld.com/cws/article/news/2011/jul/19/radioactive-decay-accounts-for-half-of-earths-heat

I guess we could go looking for radioactive materials within differentiated meteorites - to see whether radioactive minerals are enhanced or depleted in iron meteorites vs stony meteorites.
 

Offline Bill S

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The most popular model of radioactive heating is based on the bulk silicate Earth (BSE) model, which assumes that radioactive materials, such as uranium and thorium, are found in the Earth's lithosphere and mantle – but not in its iron core.

Thanks for the link, Evan_au.  I knew I had got the idea from somewhere, but I'd forgotten where it came from.

 

Offline evan_au

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I just found this: The Goldschmidt classification scheme suggests that Uranium & Thorium easily react with oxygen, and will stay in the crust (lithophiles), while others are soluble in iron and will remain in the core (siderophiles).

http://en.wikipedia.org/wiki/Goldschmidt_classification
 

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