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Response to David Marjanovic's post of Thu, 08 Jan 2004 12:08:43
(below the dashed line).
Perceptive questions, David, and I'll do my best to respond to them.
The longer I research the K-T extinctions, the more I despair that
much of anything will be "proven" concerning cause of the extinctions
for long into the future. The reason is that nearly every aspect of
the K-T geobiological record is controversial. Many new
multidisciplinary data, and interpretations that most scientists
agree upon, are requisite to meaningful progress in discovering the
actual cause(s) of the extinctions.
Your point on transport of iridium is one such controversial topic. I
recall how at the first Snowbird I extinctions conference in 1981,
the impactors claimed that iridium was refractory. Later, they had
iridium migrating to where it best served their purposes. So,
individual multiple "spikes" in place, or enrichments via migration
of the iridium? Based on my communications with other scientists down
through the years, I prefer to think of individual spikes in place.
But, others feel differently.
Just because scientific papers are several years old does not
invalidate them unless they have been shown to be incorrect. Nor,
does it excuse scientists for ignoring the data and interpretations
In fact, multiple iridium spikes do occur at localities other than China.
Hm. These are still rather few -- though the wide geographic distribution
could mean something --, so that, without knowing the local sedimentologies,
I wonder if some bioturbation and groundwater percolation could have
multiplied the peaks or at least smeared them out. It's also interesting
that all 3 papers are quite old. Is there a reason why this topic has
seemingly disappeared from the literature?