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Triassic-Jurassic boundary changes
My story for New Scientist is up on the web at
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....
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
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