On Tues, Mar 28 2000 (06:29:13 EST) Richard wrote:
>Good point. But, continuing to play the Devil's advocate.... ;-)
>
>Perhaps there is some underlying reason for a correlation between the
>half-life of an isotope and its original concentration. Do we know enough
>about the physics of half-lives and isotope formation to rule out such a
>correlation? (I would agree that such a correlation sounds unlikely, but it
>would be helpful to your argument if you could rule it out altogether.)
I can't answer your question based on my limited knowledge of physics and
atomic theory. However, I believe that if such a correlation existed then
we would be able to see evidence of that relationship in the data for
isotopes that do exist. I have compiled a short partial table of the
current abundances of radioisotopes and elements. Looking at just the raw
data I don't see any interesting patterns suggesting a correlation. One
could do more with the data but I'm not really interested in pursuing it.
You are welcome to try it for yourself. I'd suggest re-checking the data
in a newer version of the CRC Handbook if you're serious.
Isotope .... Half-Life .... % Nat. Abund* .... Elemental Abund.**
---------------------------------------------------------------
Te-123 .. 12,000,000 M.Y. ...... 0.87% .......... 0.0000002%
Pt-190 ..... 690,000 M.Y. ...... 0.0127% ........ 0.0000005%
La-138 ..... 112,000 M.Y. ...... 0.089% ......... 0.003%
Sm-147 ..... 106,000 M.Y. ..... 14.97% .......... 0.0006%
Rb-87 ....... 48,800 M.Y. ..... 27.85% .......... 0.015%
Re-187 ...... 43,000 M.Y. ..... 62.5% ........... 0.00000007%
Lu-176 ...... 35,000 M.Y. ...... 2.59% .......... 0.00008%
Th-232 ...... 14,000 M.Y. ...... No data for Th . 0.001%
U-238 ....... 4,470 M.Y. ...... No data for U .. 0.00025%
K-40 ........ 1,250 M.Y. ...... 0.00118% ....... 2.59%
U-235 ......... 704 M.Y. ...... No data for U .. 0.00025%
-------------
Sm-146 .......... 70 M.Y. ...... 0.00% .......... 0.0006%
Pb-205 .......... 30 M.Y. ...... 0.00% .......... 0.0015%
* Percent Natural Abundance of Isotope. Data from CRC Handbook of
Physics and Chemistry, 57th ed., 1976, CRC Press.
** Estimated Abundance of Element in the Earth's Crust. Data from
Parker, R.L., 1967, Composition of the Earth's Crust, _in_
Fleischer, Michael, ed., Data of Geochemistry, Sixth Edition:
U.S. Geological Survey Professional Paper 440-D, p. D1-D19.
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BTW, I can't take credit for this argument. Others have used it
before - and probably much better than I have. (For example, see
Dalrymple, G.B., 1991, Age of the earth: Stanford University
Press, Stanford, California, 474 p.)
Steve
[Opinions expressed here are my own
and are not to be attributed to my employer.]
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Steven M. Smith, Geologist Office: (303)236-1192
U.S. Geological Survey Fax: (303)236-3200
Box 25046, M.S. 973, DFC smsmith@usgs.gov
Denver, CO 80225
--The USGS National Geochemical Database NURE HSSR Data Web Site--
http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-97-0492/
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