Asteroids Responsible for Both Rise And Fall of Dinosaurs

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Last updated at: (Beijing Time) Friday, May 17, 2002

Asteroids Responsible for Both Rise And Fall of Dinosaurs

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Massive asteroids hitting the Earth not only helped wipe out the dinosaurs 65 million years ago,but may also be responsible for the species' sudden rise some 135 million years earlier, an international research team said on Thursday.

"Our research adds to the speculation that there was a comet orasteroid impact about 200 million years ago, followed relatively quickly by the rising dominance of dinosaur populations of the Jurassic period," said geologist Dennis Kent from Rutgers University in the United States.

Kent is co-author of the study, which is to be published in theFriday issue of the journal Science.

Their findings suggested that the impact 200 million years ago may have killed off or reduced many competitive species, clearing the way for dinosaurs to adapt and flourish, and allowed a few groups of carnivorous dinosaurs to evolve in size very quickly anddominate the top of the terrestrial food chain globally.

According to Kent, dinosaurs then went on to "dominate for the next 135 million years", until their extinction about 65 million years ago, which is now generally attributed to yet another comet or asteroid impact.

After analyzing dinosaur footprints and other fossils from over70 sites in North America, the team found a quadrupling of iridiumabundance and a "spike" in the concentration of fern spores between the Triassic (248-208 million years ago) and Jurassic (208-146 million years ago).

The identification of the anomaly of iridium and fern spores, both key signatures of an extraterrestrial impact, provides strongevidence that a space object hit the Earth in that time period, the researchers said.

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