> I think Glenn got it slightly wrong. Using multiple rocks is fine, *if*
> you have good reason to believe that they were formed at the same time.
> A geologist should normally be able to determine if that is the case.
I am happy with this - we are talking the same language here.
> Austin is apparently using rocks that are "demonstrably not cogenetic"
> (the words of Brent Dalrymple, a radio-dating expert). That violates
> the assumptions of isochron dating, and means that any resulting date is
> meaningless.
If the basalts come from different primary sources, the isochrons
are indeed suspect. I don't know enough about Austin's work to
confirm or challenge Dalrymple's assertion - but would be very
interested to hear how he justifies the words "demonstrably not
cogenetic".
>Using non-cogenetic rocks should cause data points not to fit on a
line.
> But Austin apparently was able to get a line *by throwing away points that
> did not fit on it*. That is also a violation of the way isochron dating
> should be done.
Again, this seems to be an important assertion and I would like
to know more. If there's no further feedback on this, I write to
Steve Austin for his comments.
Thanks Jim,
Best wishes,
*** From David J. Tyler, CDT Department, Hollings Faculty,
Manchester Metropolitan University, UK.
Telephone: 0161-247-2636 ***