Asteroid or Comet triggered life on Earth?

[FLO]

Thanks to Mike Godfrey for finding this one:

Asteroid or comet triggered death of most species 250 million years ago

Earth's most severe mass extinction - an event 250 million years ago that wiped out 90 percent of all marine species and 70 percent of land vertebrates - was triggered by a collision with a comet or asteroid, according to new findings by a team led by a University of Washington scientist.

The collision wasn't directly responsible for the extinction but rather triggered a series of events, such as massive volcanism and changes in ocean oxygen, sea level and climate. Those in turn led to species extinction on a wholesale level, said Luann Becker, UW acting assistant professor of Earth and Space Sciences.

"If the species cannot adjust, they perish. It's a survival-of-the-fittest sort of thing," Becker said. "To knock out 90 percent of organisms, you've got to attack them on more than one front."

... While the findings illustrate that impact with large space bodies can be detrimental to life on Earth, Becker noted that there also is evidence they might have been key to life starting here in the first place. Some scientists believe the first life-forming chemicals were deposited on Earth in collisions with comets or asteroids, and some believe comets carried virtually all of the water that exists on the planet today

http://tinyurl.com/fe5s6

[The Warthog]

I still have a little problem with theories that involve life being imported to Earth. It only pushes back the question of how life got started. If life could start somewhere else, why not on Earth? If the chemical compounds needed could be formed on comets, why not on Earth, and so on? Sometimes I think there's a scientific inferiority complex about Earth. The extinction theory is intriguing, though.

[Jamie]

I can see your point WH but the compounds chemical or

otherwise still had to get here somehow didn't they?