Triassic-Jurassic boundary changes

[Jeff Hecht <jeff@jeffhecht.com>]

My story for New Scientist is up on the web at 
http://www.newscientist.com/news/news.jsp?id=ns99992290

Although the possible impact has grabbed other headlines (including 
ours), Olsen et al also point out that there were major faunal 
changes at the Triassic-Jurassic boundary, revealed by footprints. 
The biggest was the appearance of the first big theropods in the 
earliest, nearly double the mass of the largest seen just 50,000 
years earlier in the end Triassic. That's a big difference, which 
Olsen attributes to extinction wiping out possible competitors.

I didn't have room to go into details of possible craters. 
Manicouagan is an obvious candidate; Olsen says it has no iridium in 
the melt. There's no shocked quartz, but an oblique impact splatters 
shocked quartz in only one direction. There's also the possibility of 
a deep-ocean impact that would have quite different effects and not 
leave a detectable crater today.

At 7:14 PM -0400 5/16/02, Emma C. Rainforth wrote:
> Likewise Manicouagan (Hodych and Dunning 1992) is supposedly 213 Ma 
> but again the error bars (largely due to difficulties with argon 
> loss) span TENS of millions of years (not to mention those authors 
> had to discard a good third of their results to GET '213'!). But, 
> Manicouagan is being redated as we speak....
>
> emma
>
>
> Hodych, J. P. and G. R. Dunning. 1992. Did the Manicouagan impact 
> trigger end-of-Triassic mass extinction? Geology 20:51-54.

--
Jeff Hecht, science & technology writer
jeff@jeffhecht.com; http://www.jeffhecht.com
Boston Correspondent: New Scientist magazine
Contributing Editor: Laser Focus World,  WDM Solutions
525 Auburn St., Auburndale, MA 02466 USA
v. 617-965-3834; fax 617-332-4760