[no subject]

[Michael.Hannah@vuw.ac.nz]

I am new to the list and , like grub from the middle of Texas, I hope that I
am not going over old ground. It seems to me a mistake to consider the K/T
boundary from a dinosaur-centric point of view. The vast majoritory of the
K/T extinctions are marine and any model explaining the event must cover all
these facets.

>From my reading of the palaeontological literature (eg all the micropal data
produced  by Gerta Keller)  plus work done here by my students indicates
that the K/T extinctions are geologicaly almost instantaneous - of the order
of hundreds of thousands of years. However, the fact that there is any time
at all associated with the extinctions to me is very weighty evidence
against an Impact as the sole mechanism for the event. An impact allows no
precursor events in the fossil record. At the same time there is a large
body of physical and chemical evidencethat seems to support the impact (yes
I know that much is equivocal, but I still have trouble with shocked quartz
coming from a volcano and the latest zircon data is very strong). Perhaps
Keller is right and what we are looking at is the meteor (or volcanic
eruption) delivering the coup de gras to a world which had been ecologically
stressed for hundreds of thousands of years. 


Cheers
Mike Hannah
Victoria University of Wellington
New Zealand