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NASA researchers: Comet shower triggered life on Earth


April 17, 1997
Web posted at: 7:00 p.m. EDT

From Correspondent Don Knapp

SAN FRANCISCO (CNN) -- It's one of the amazing, puzzling questions about the origin of life on Earth: What was the trigger that led to the formation of those primitive life forms that crawled out of the primordial soup many eons ago?

Two NASA researchers now say we may have some distant comet cousins of Hale-Bopp to thank for life itself.

Comets crashing into the Earth brought water, nitrogen and carbon dioxide that make up our atmosphere. But researchers Chris McKay and Bill Borucki have demonstrated that the crashing itself may have been a key event in the origin of organisms.


McKay and Borucki created a vial of gas simulating the best guess of scientists as to the composition of the early atmosphere. They then mimicked a collision of a comet and Earth by aiming a laser blast at the primitive mix.

What they found was that the powerful shock waves from this "micro" blast created temperature and pressure changes that altered the molecular composition of the pseudo-atmosphere.

"Those new molecules, when mixed in with water, form amino acids. They're the start, the first step toward life," Borucki says.

Comet strikes common in Earth's formative years

Today, comet sightings such as Hale-Bopp and Halley are rare. That's because, through the ages, the planets themselves attracted most of the comets in the universe, leaving but a few to roam loose through the skies.


But 3.9 billion years ago, in the late formative period of the Earth, scientists believe comets were decidedly more common. Crater evidence shows they were then bombarding the moon -- an indication that they were also probably striking the Earth.

"Just think what it must have been like 3.9 billion years ago when the sky literally would have millions of such [comet] images, and thousands of them would be slamming into the surface, creating quite a havoc here on Earth -- but also creating the stuff that might have led to life," McKay says.

Many ancient civilizations regarded comet sightings to be significant events. It may turn out that comets were perhaps more significant than even the ancients thought.


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