On Tue, 02 Sep 2008 12:01:51 -0600, Greg Crinklaw
wrote:

It is my understanding that there is a widespread layer of magnetic
spherules marking the end of the Clovis period.

That is not correct. Spherules have been found in a few locations, but
their positioning, as well as mineralogical analysis, are far from
consistent or conclusive. Most meteor and impact specialists remain very
skeptical.

That seems to me to be
somewhat more than "weak and not well supported." I know that there is
no evidence for an impact crater, but there was a thick ice sheet at the
time. The idea that the impact was on the ice seems reasonable, at
least at first glance. Has anyone done any modeling of this sort of
impact?

Most people who study impacts are of the opinion that the North American
ice sheets were not thick enough at this time to prevent an impact from
leaving a scar. Some of those supporting a Holocene impact deal with
this problem by supposing a glancing impact, or some sort of air burst
similar to Tunguska.

Are you aware of a simpler alternative explanations for the
magnetic spherules?

It remains to be seen if there actually are widely spread spherules that
can be linked chemically and temporally to a single event. It is
possible there was a North American impact 12,000 years ago, but
_currently_ the evidence is weak. At this point, those interested in
this possibility should be out collecting evidence, not writing books
trying to explain the extinction of mammoths. Too many conclusions are
being drawn from far too little evidence. IMO that's not good science.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com