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Re: Crashing Comets Not Likely The Cause Of Earth's Mass Extinctions



B tH wrote:
>
> So, if not an extra-terrestrial impact, what caused the Permian
> extinction?  Dan from "Roseanne" in "When Dinosaurs Roamed North America"
> assured us a comet broke up into five pieces and smushed us way back then.
>
> I trust Dan - he always seemed to know when the kids were going bad.   :-)

The Permian extinction is almost certainly causally related to the
Siberian Traps volcanism, although which of the multitude of catastrophes
generated by it (if ony one) was most significant is unclear. See recent
books by Benton and by Erwin (among others) for good general reviews.

> That and there seems to be very good evidence of super-craters for that
> time period.
>
On if by "good evidence" you mean "essentially no evidence"....

No iridium spike; buckyballs alleged to have extrasolar (!?!) isotopic
composition; a "crater" under glacial ice which is not confirmed by any
real evidence nor dated by any means.

-- 
Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA