Re: extinction

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

Response to Jaime Headden's post of Sat, 17 Jan 2004 16:27:53.

Jaime wrote:

"And what if the cataclysmic event that ended the dinos, as it were,
occured before the stratgraphic foundation for the separation of the
Cretaceous and Tertiary? We see Ir-enriched layers both before, well
before, and at the boundary, suggestive that if the layers are all
related, the extinctions may well have been underway thousands of years
before the definition between Eras occured."


Dear Jaime, and other Colleagues,

The general K-T transition biological turnover was underway long 
before K-T boundary time, and persisted into the Tertiary. The notion 
of a catastrophic wipe out of most of earth's life at the K-T 
boundary seems to have gotten into the literature by a physicist who 
knew nothing whatsoever about the K-T paleontological record. One has 
to be careful about imaginary "first principles" to make sure that 
they are supported by the K-T transition geobiological record--which 
is the final arbiter of all that we do in K-T science.

I recall how at the K-TEC II meeting in 1981, Luis Alvarez had looked 
at species range charts across the K-T boundary and interpreted the 
cut off of ranges of many species at the boundary as proof of an 
impact-induced catastrophe.

Paleontologists, on the other hand, know that ranges cut offs at 
specific localities are very likely are the result of a gap in the 
stratigraphic record. Alvarez simply could not understand how 
paleontologists could not see the cut off of ranges as proof of a 
global K-T boundary catastrophe.

We commonly encountered hiatus-controlled cut off of ranges at 
various places in the stratigraphic record in my graduate research 
program on Cretaceous and Tertiary marine phytoplankton along the 
Atlantic Coastal Plain.

I'll have more to say about the generalized K-T biological turnover 
in a later post.

Cordially,
Dewey McLean