RE: Suspicious impact craters and iridium layers

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
>
> > Even the well-studied Chicxulub crater has had its radiometric date
> > changed more than once.
>
> What has happened to the U/Pb-in-zircons date of 64.98 +- 0.05 Ma that's
> mentioned in Night Comes to the Cretaceous? (Especially considering the fact
> that the latest dates for the K-Pg boundary are half a Ma older -- but this
> seems to be a common discrepancy between U/Pb-in-zircons and K/Ar, Ar/Ar and
> the like... ~:-| )
>
Out of date.

Kirk Johnson showed some of the new sites which will pin down the iridium layer 
very well. In one outcrop, there was an ash layer
less than a meter below the iridium spike and a second maybe 30 cm above it. 
Both ashes give statistically the same date.

(Now I have to go and change the dates on all my websites... Grr... 65.0 was 
such a nice round number, too.)

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
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Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
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