Re: Uranium Dating & South African Sites?

13 Nov 1995 22:51:59 GMT

In article <4879tj$>, VINCENT@REG.TRIUMF.CA (pete) writes:
>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.)

Well, yeah, I can see where that could be true for U-238, which is the one
with the 4.5by half-life. However, there are other elements used (don't
know how many) and I read where they are using this technique to date
Neandertal sites in Europe, which are a lot more recent than the SA hominids.
So, that can't be the whole story. Thanks for the reply.