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Re: extinction



> Indeed. How can we say with certainty that the Deccan Traps started
> spewing forth around a million years before the Chicxulub impact (that's
> one figure I've seen), when surely any radiometric dates of both will
> have standard deviations in the order of at least a million years (I
> would expect)?

The standard deviations of the most commonly used methods are considerably
smaller.

> Or are non-radiometric dating methods employed
> to compare the two events (biostratigraphy, etc)?

This, too, is done.

> I've seen one date for Chicxulub of 64.98 +/- 0.05 MYA. Is it possible
> to have such a small standard deviation (just 50,000 years) on a date of
> this age?

Yes -- but not with every method. That method was the U-Pb ratio in zircons.
And it may be miscalibrated so as to be wrong (not imprecise, but incorrect)
by some 500,000 years on a date of this age -- if we trust the, what was it,
K-Ar, I think.