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Re: Uranium Dating & South African Sites?
pete (VINCENT@REG.TRIUMF.CA)
13 Nov 1995 11:24:35 GMT
cc3265@CNSVAX.ALBANY.EDU sez:
`Hi all!
`Can anyone tell me if Uranium series dating has ever been used on those
`troublesome South African sites, and, if not, why? I recently learned
`more about the procedures, that they work on breccia and (at least one
`isotope) has a half-life of 4.5by. So why wouldn't this be appropriate
`for South Africa? Last I read, they were using biostratigraphy to date
`the hominids. Is it because the sites are such a mess to begin with, &
`the Uranium series is so prone to error, that it is thought not to be
`worthwhile to try, or is there another, more technical, reason?
I'd just be guessing, but the likely reason is that 4.5by is too long.
For maximum precision, you want to use an isotope whose half
life is in the same order as the time span you're trying to
measure. Most often you hear about the opposite side of the
problem, with dates older than a few hundred kya being too
long to date with C14. But when too little of your sample
has decayed, you have the same problem. Uranium is a trace
element to start with, and for dates of only two or three
million years, you're talking trying to detect one ten thousandth
of the isotope in your sample (instead of half, at 4.5by).
(Sorry if I'm just repeating the obvious.)
--
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vincent@triumf.ca <== faster % Pete Vincent
vincent@freenet.vancouver.bc.ca % Disclaimer: all I know I
% learned from reading Usenet.
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