[Posted and E-mailed]

In general, isotopic dating methods don't apply well to sedimentary
formations (which is where most fossils are found).

That is not really true.  The succession of fauna, ordering of the
geologic column, and even evolution, were all quite well-established
(mid to late 1800s) long before the technology existed to perform
accurate isotope dating (mid 1900s)...  even before scientists were
aware of radioactivity (circa 1890-1900) or the existence of
isotopes (early 1900s).

See, for example:  Dalrymple, G. Brent, 1969.  "40Ar/36Ar Analyses
of Historic Lava Flows" in _Earth and Planetary Science Letters_
vol. 6, pp. 47-55.  It lists argon assessments for 26 samples from
several sources of known age.  I have a reference to another study
but I have not yet obtained the actual paper, so I can't recommend
it.

Uncertainty in a measured age is a function of uncertainty in the
isotope assessments *and* the half-life of the relevant isotope.
Since K-40 has a fairly long half-life (about a billion years),
it's fairly rare to have age uncertainties less than a few tens
of thousands of years.

Measurements on recent samples indicate that the initial conditions
are usually suitable for accurate long-term K-Ar ages, but in most
cases the uncertainty in the assessment of young ages is greater
than the known ages of the samples (because they are all less than
a few thousand years old).

K-Ar dating shows excellent correlations with other long-term
measurements (e.g., isotope ages by Rb/Sr or Sm/Nd isochron dating
as in [1], ordering of the geological column as in [2] or [3],
and continental drift as in [4]).

[1] Dalrymple, G. Brent, 1991.  _The Age of the Earth_.  California:
    Stanford University Press,  ISBN 0-8047-1569-6.  See:  Tables
    5.5 and 5.6 (pp. 230-231, 239) for lists of lunar rocks dated
    by multiple isotopic methods;  Table 6.3 (pp. 287-289) for lists
    of meteorites dated by multiple methods.

[2] Harland, W. Brian, et al., 1990.  _A geologic time scale 1989_.
    Cambridge:  Cambridge University Press, ISBN 0-521-38765-5.
    The entire book details a large database of isotopic ages shows
    their correlation with position in the geologic column.

[3] Dalrymple, G. Brent, 1986.  "Radiometric Dating, Geologic Time,
    and the Age of the Earth",  U.S. Geologic Survey Open-File Report
    86-110.  See pp. 22-24 for a chart and discussion of correlation
    between K-Ar age and stratigraphic position of the Land Mammal
    Ages of the Cenozoic.

[4] Dalrymple, G. Brent, 1986.  (Ref. [3])  See  Figs. 2-3 and p. 25
    for a chart of distance from the Hawaiian mantle plume versus
    K-Ar age.

--
Chris Stassen                          http://www.stassen.com/chris/
NOTE:  The "Reply-To" address of this message is an auto-bounce.
Use "http://www.stassen.com/chris/feedback/submit.html" for private
or offline responses, if you don't know my real E-mail address.