Re: Extinction

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>Sir, you seem to have missed my point entirely.  I am suggesting that the
>date of the Chixculub impact can be dated directly from the fossil record at
>any place on the globe.  An impact creating a 120 mile crater would devastate
>life everywhere on earth, and if it were to occur 8 million years prior to
>the KT boundary, as you pose as a possibility, a mass extinction would have
>occurred there, but as you probably know T rex and others not only flourished
>during this time period but actually evolved.

No, it is you who missed my point entirely.  Actually, T. rex evolved
several million years after the impact, if the Meyerhoff dates are correct
(which is still a possibility).  If the dating is correct, than it would
show that an impact which generates a 120 mi crate would be sufficient to
kill off large groups of animals, "back-of-the-envelope" equations
notwithstanding.

The Manson crater is dated very securly at the early part of the late
Campanian, the same age Meyerhoff et al. claim the Chixculub is dated at.
If so, than multiple large impacts would immediately precede the epoch with
the highest known dinosaurian diversity in the Mesozoic.

[Not that I necessarily believe the Meyerhoff et al. work, but it has not
yet been sufficiently challenged in the scientific press.]

>Futhermore, I do not claim that the Mexican impact was the sole impact -- I
>expect the object fragmented from tidal forces in a fashion similar to the
>recent comet strike of Jupiter -- but I do believe, as I feel is obvious,
>that the object that generated the Chixculub crater and any sister impacts
>exterminated the dinosaurs.

You "believe", and it "feels obvious".  I prefer to take the position that
the impact extinction hyopthesis is sound, but is far from secure.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.