[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: extinction

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.

Dewey McLean