From: Steven M. Smith <smsmith@helios.cr.usgs.gov>
Date: 27 March 2000 18:27
>On Sat, 25 Mar 2000 (15:41:06 -0000) Richard wrote:
>>Steven, You wrote:
>[Snippage]
>>>But, how do these revelations affect my original point? Actually, if
>>>anything, they improve it. The question still stands. With the
exceptions
>>>noted in my first post (and David Bowman's correction of my
sunlight/cosmic
>>>ray blunder), why are there no naturally-occurring radioactive isotopes
>>>having half-lifes of 70 million or less? This question is valid whether
>>>all Sm-146 (70 M.Y. half life) has decayed or whether it has simply
>>>decayed to the point that we can no longer detect it.
>>
>>To justify that point, you need to show that the original concentrations
>>were well within today's detection limits. That may be obvious to you, but
>>not to a layman like me!
>
>If we were only talking about Sm-146 (known as a rare-earth-element), this
>justification might be important. But let's look at the problem
>statistically. What are the odds that every known isotope in the top half
>of the list provided in my original post had an original concentration high
>enough that we can still detect it today AND every single element (with
>noted exceptions) having a half-life of 70 M.Y. or less did not? Pretty
>slim, I'd predict.
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.)
As you're a geologist and not a physicist, perhaps this is outside your
field.
Richard Wein (Tich)
See my web pages for various games at http://homepages.primex.co.uk/~tich/
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