From: Steven M. Smith <smsmith@helios.cr.usgs.gov>
>Since the average life expectancy of any radiometric isotope is on the
order
>of 10 times the half-life, we can reasonably infer that the elements of
>which our earth is composed were created no less than about 1-7 billion
>years ago.
I don't know anything about radiometric dating, but this sounds odd to me.
What do you mean by the "average life expectancy" of an isotope? After 10
half-lives there should still be one thousandth of the original material
left. Is this too small to detect? And anyway, your argument would give an
*upper* limit of 7 BY.
Shouldn't you be looking at the half-life of Sm-146 (70 MY), the longest
lasting of the elements that *can't* be found? If the Earth is about 4.5 BY
old, this is 64 half-lives, so only about 10^ -20 of the original material
should be left. It sounds plausible that that would be too small to detect.
Have I missed something?
Richard Wein (Tich)
See my web pages for various games at http://homepages.primex.co.uk/~tich/
This archive was generated by hypermail 2b29 : Thu Mar 23 2000 - 14:10:22 EST