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Asteroid Impact Ended The Triassic



http://story.news.yahoo.com/news?tmpl=story&u=/nm/20020516/sc_nm/science_dinosaurs_dc_1&e=1&ncid=585

WASHINGTON (Reuters) - An asteroid may have wiped out the dinosaurs 65
million years ago, but an earlier one probably allowed the rise of the
giant creatures, who dominated the planet for 135 million years,
scientists said on Thursday.

Piecing together evidence from footprints, fossils and a dusting of a rare
metal found in asteroids, the experts said they had concluded that a huge
impact wiped out most of the plants and crocodilian creatures that ruled
the world during the Triassic era.
...
"Our research adds to the speculation that there was a comet or asteroid
impact about 200 million years ago, followed relatively quickly by the
rising dominance of dinosaur populations of the Jurassic period," said
Dennis Kent, a geology professor at Rutgers University in New Jersey.
...
Looking at footprints and fossilized bones from nearly 80 different sites,
Olsen's team concluded that it only took about 50,000 years for dinosaurs
to start growing big -- really big.
...
The team used a high-resolution mass spectrometer at the lab of Christian
Koeberl of the University of Vienna in Austria to find iridium traces from
geologic layers dating back 200 million years, to the boundary between the
Triassic (248 to 208 million years ago) and the Jurassic (208 to 146
million years ago).

Still to be found is what would be a vast crater, said Olsen, although
there are candidates in Canada and Australia. "We don't actually have an
impact structure yet," he said -- but pointed out it took 15 years to find
the 65 million-year-old crater in the Yucatan.