Re: extinction

["Dewey M. McLean" <dmclean@vt.edu>]

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 them.

Cordially,
Dewey McLean

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> >  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?