Path: utzoo!mnetor!uunet!husc6!purdue!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: sci.misc
Subject: Re: radiation dating
Message-ID: <11009@mimsy.UUCP>
Date: 11 Apr 88 08:52:33 GMT
References: <5236@uwmcsd1.UUCP> <1138@PT.CS.CMU.EDU> <5250@uwmcsd1.UUCP> <116@slu70.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 38

>>In article <4006@cup.portal.com> roger_warren_tang@cup.portal.com writes:
>>>"Radiation counts used to date things before a supposed catastrophe cannot
[be trusted etc; I never saw the original, only mangled quotations]

>In article <5300@uwmcsd1.UUCP> markh@csd4.milw.wisc.edu (Mark
>William Hopkins) writes:
>>Because the catastrophe itself may be a large source of radiation.

In article <116@slu70.UUCP> guy@slu70.UUCP (Guy M. Smith) writes:
>External radiation is irrelevant to radiometric dating.

Right.  The key to understanding this is that the dating is based on
*ratios* of particular isotopes:

>The technique involves measuring the amounts of specific radioactive
>isotopes (e.g., Rb^87) and their stable daughter products (Sr^87 in
>this case). Crudely, the Rb/Sr ratio is controlled by the age of the
>rock as Rb converts to Sr at a known rate. External radiation has no
>influence on the rate of decay.

If I may say so, markh has the right idea but the wrong details,
something he seems to do all too often.  In this case the details are
the important part.  The point is not that the event (`catastrophe')
may be a source of radiation, but rather that it may be a source of the
isotopes used in dating.  This changes the whole focus of the argument.

If the absolute counts of either Rubidium-87 or Strontium-87 were
influenced by the event, the ratio function [Rb/Sr](t) might have a
sudden discontinuity.  This can be checked, however, by choosing two
more isotopes; as the number of isotopes checked goes up, the
probability of error goes down.  Moreover, there may be an independent
means of verifying that the event did not affect the isotope ratio.
Whether this is in fact the case I cannot say, although I doubt that
anyone doing such dating would not anticipate this line of argument
and have countered it before it even began.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris