> Steven Schimmrich wrote:
>
>> Well, if the data form an isochron, it's assumed that the system has been
>> closed since isotopic resetting.
>
> However, Davis Young points out in "Christianity and the age of the earth"
> that there are some physical inspections that can be made to help ensure
> that the rocks being dated have not been contaminated in some way. They
> involved things like looking for cracks and signs of seepage into the rock
> being dated.
Exactly. I think I pointed this out several times in my post where I said
that you have to look at the rocks petrographically (under the microscope) to
look for evidence of alteration, metamorphism, etc. and you can't just grab
a rock and isotopically date it being ignorant of the geologic setting.
- Steve.
-- Steven H. Schimmrich Callsign KB9LCG s-schim@uiuc.edu Department of Geology, University of Illinois at Urbana-Champaign 245 Natural History Building, Urbana, IL 61801 (217) 244-1246 http://www.uiuc.edu/ph/www/s-schim Deus noster refugium