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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... ... Reunite Gondwanaland! --- Blue Wave/Max v2.12 * Origin: A Little Corner in Time BBS (1:106/113.0)

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