From:    Marty Leipzig
To:      Gary Glunz                             Nov-26-93 09:54:26
Subject: CARL SAGAN AGAIN

Gary Glunz, who told the glacier: up your crevasse, said to Bill Wolff:

 BW> Did the dinosaurs die out for a reason? Why I don't know except
 BW> we now know from air bubbles trapped in amber, that the earth's
 BW> oxygen levels dropped sharply just before they become extinct.

 GG> The current theory is that an impact from a planetesimal ejected

     Ahem. Hypervelocity extraterrestrial bolide, if you please.

 GG> enough debris into the atmosphere so as to block out the sunlight -

     Not quite. Although the impact threw immense amounts of dust,
     etc. into the atmosphere; it was probably smoke and ash from
     the resultant impact-generated fires that caused the
     photosynthetic machinery of the time to shut down.

 GG> thereby inhibiting photosynthesis, and causing oxygen levels to
 GG> drop worldwide.

     As evidenced by 16O/18O data, there was NOT a global O2 drop at
     the K/T boundary. Data shows that since the Riphean, the global
     atmosphere has remained (within limits) rather constant as to
     gas contents; environmentalists notwithstanding.

 GG> But global temperatures also dropped, and since
 GG> dinosaurs were reptiles, they basically froze to death.

     Not really. The Cretaceous biosphere was already experiencing
     all sorts of stress...what with all the tectonic movements,
     the Cretaceous epeiric seaway draining off the continent; not
     to mention that the continental landmasses were being uplifted
     at a fairly rapid rate. Remember, not just the dinosaurs made
     the big exit at the K/T event. It appears that no animal over
     25 kg made it past the boundary; and that scores of microfauna
     (foraminifera, diatoms, tintinnids, calpionellids, etc.) also
     bought it there.

     The Earth and it's biota were under a tremendous amount of
     pressure; it seems that the impact served to kick start the
     entire Cenozoic revolution.

 GG> Not too long ago, Pemex, the Mexican oil company, accedentally
 GG> discovered what is now believed to be the "smoking gun" which
 GG> ended the Mesozoic era.  It is located just north of the Yucatan
 GG> penensula, about 26 miles deep in the earth.

     If I may...It was Amoco, not PEMEX, who first located
     (seismically) the Chixulub Crater. It is a large, oval
     depression (indicating that the angle of impact was not 90
     degrees) with ejecta rims (noted on later, and more intensive
     3-D seismic imagery) and satellite rays. It was not found at a
     depth of 26 miles (that, even by Texas standards, is deep), but
     rather at approximately 16,000'. The reason it generated so
     much interest (apart from the purely scientific) was that
     ancient impact sites are often hosts to accumulations of
     economic minerals. Sudbury, in Canada, is an ancient (Vendian)
     impact site just chock full of bizarre, and economically
     important, FeCoNi minerals. Also, of great interest to us
     industrial scientists in the Awl Bidness, impacts tend to
     bust the hell out of the surrounding country rock; creating
     fractures and fissures which can, when buried at depth, act as
     conduits for the migration, and eventual entrapment, of
     hydrocarbons.

     Hence, the oil company's finding, and subsequent drilling, of
     Chixulub. (Sheesh, I do tend to get rather wordy when I write
     about this stuff...) Anyways, if you would like some further
     info on the results of the inquiry of the impact site; let me
     know. I'll dig it out of my AAPG and GSA archives.

 GG> Scientists estimate
 GG> the time of impact - by the iridium layer in rock strata worldwide -
 GG> to be about 65 or 70 million years ago.

     66.7 MYA (+ or - 2%)....there I go again...


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