the cooling mentioned most likely is be the first fragment of this comet hitting -
ep --- Ron Baalke <[EMAIL PROTECTED]> wrote: > > > http://www2.dailycamera.com/bdc/environment/article/0,1713,BDC_2434_1677499,00.html > > Asteroid theory gains ground > > Impact probably did in the dinosaurs, new study says > > By Katy Human > Daily Camera > January 16, 2003 > > Dinosaurs probably died because of an asteroid > impact - the dust, dead plants > and global wildfires caused by the giant collision - > and not because of > ancient volcanic eruptions or climate change, > according to a new study by > scientists in Colorado, Pennsylvania and Washington, > D.C. > > Although many paleontologists have come to believe > the asteroid impact theory > in recent years, some remained convinced that > changes in the weather about > 65 million years ago doomed the dinosaurs, said Kirk > Johnson, a paleobotanist > at the Denver Museum of Nature and Science. > > Others simply thought the asteroid theory was too > clean and simple, said Johnson, > co-author of a paper published last week in the > Proceedings of the National > Academy of Sciences. > > "We've shown how complicated the world was back then > ... and even with that, the > asteroid comes out clearly," he said. > > The new study lends more credibility to the asteroid > theory by showing that > climate change did not affect dinosaur survival. > > Pat Holroyd, a vertebrate paleontologist at the > University of California, Berkeley's > Museum of Paleontology and a colleague of Johnson > and his co-authors, said she > thinks the paper is a "very important" one. > > "Time will tell if it helps answer all our > questions," she said. "We'll need to talk > about it in meetings, see if this works worldwide > ... but this sets the standard for > studies elsewhere." > > Johnson and his colleagues - Peter Wilf at > Pennsylvania State University and > Brian Huber at the Smithsonian Institution - studied > fossils of plants and ocean > animals for detailed information about climate > changes in the million years or so > before and after the dinosaurs' demise. > > For the plant-based climate record, Johnson pored > through 22,000 plant fossils > excavated from a North Dakota site known to straddle > the Cretaceous-Tertiary > boundary, when dinosaurs died. Leaf shapes are > directly related to climate, he said. > > Huber looked at the fossils of tiny marine animals > called foraminifera, which record > temperatures in another way. And both scientists > linked their climate data to real > dates with a geological trick related to the > planet's shifting magnetism. Wilf pulled > the data together, Johnson said. > > "The curves matched, and they showed this neat > pattern of climate change," he > said. "A half-million years before the asteroid hit, > we see a strong chug of global > warming, probably linked to volcanic eruptions in > India." > > Volcanoes spew carbon dioxide, a greenhouse gas, > into the atmosphere, he > explained. Some researchers suggest that > volcano-caused climate change killed > the dinosaurs. > > "Then just before the hit, 100,000 years before, > there's a strong cooling, and it (the > temperature) drops back down to the level it was at > before," Johnson said. > > But during the major climate swing, little changed > on land, he said. "There were > still crocodiles in the Arctic ... and we had the > same dinosaur community here in > North America: tyrannosaurus, triceratops, the > duckbills." > > Yet when the giant asteroid struck, every land > animal bigger than a dog died, and > 50 percent to 80 percent of plants - the base of the > food chain on land - > disappeared. > > "This starts to take volcano and climate out of the > argument," Johnson said. > > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list __________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
