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dating with dna

I would like to challenge the dna researchers on this list who feel that 
they can date things like the splitting of taxonomic lines with dna.
You have not carefully examined your underlying assumptions when you make
such statements as "dinos split from mammals 230 Ma".  That is a statement
which can NOT be defended scientifically unless you have the dna from the
animal where the split actually occurs.  Let me explain.

You are erroneously assuming that all dna changes at a constant rate,
which the fossil record clearly demonstrates is not reasonable. 
why should change in dna occur at a static rate.  would it not be reasonable
to assume that some changes morphology, habits, and hence the underlying
biochemistry of the animal would require numerous changes rapidly, rather
than at a set rate.

for geochronologists, we never believe any date unless we can verify it by
two independent methods, that themselves have been calibrated against
verifiable methods.  chemically based dating methods (i.e., amino acid
racemization, methods used for desert varnish, obsidian hydration, etc.)
are notoriously dependent upon geochemical conditions.  similarly dna must
depend on biochemical conditions in the body.  i'll believe dna dates
like that when they have been corroborated by recognized geochronological 

Bonnie Blackwell,                               bonn@qcvaxa.acc.qc.edu
Dept of Geology,                                (718) 997-3332
Queens College, City University of New York,    fax:  997-3349
Flushing, NY 11367-1597