THE broken comet now heading for Jupiter suggests a new perspective on an ancient question - how did Earth's magnificent profusion of organic life arise?
Recent views from the now sharp-eyed Hubble space telescope show 20 or more comet fragments. Some are several kilometers across.
Their violent impact next July will be reminiscent of the pummeling that traumatized Earth four billion years ago.
Now it also seems possible that some of the final blows may actually have helped organic life get going.
This new concept, helps origin-of-life scientists resolve a dilemma. What little they have learned about Earth's early environment has made what little they have learned about pre-life chemistry seem impossible.
However, marine chemist Jeffrey Bada of the University of California's Scripps Institution of Oceanography at San Diego says the chemical pessimists don't appreciate what an asteroid punch can do for them when it is delivered at the right time and place.
In the 1950s, many cosmic chemists thought Earth's early atmosphere probably was rich in such compounds as methane and ammonia.
Dr. Bada's colleague Stanley Miller - then at the University of Chicago - ran a now-famous experiment in which an electric spark simulated the action of lightning in such a primeval atmosphere.
Captured in circulating water, chemicals produced by the spark reacted to form amino acids - building blocks of proteins - and other life precursor chemicals.
This became one of the standard scenarios for earthly life's origin. But spoil-sport climatologists noted that the young sun was 20 to 30 percent dimmer than the sun is today.
Earth would have frozen unless the air had enough heat-trapping carbon dioxide to compensate for the dimmer sun. Unfortunately, Miller's kind of pre-life chemistry won't work in a carbon-dioxide-rich atmosphere.
As Bada and Miller explained to reporters during the recent annual meeting of the American Association for the Advancement of Science in San Francisco, this has been a show-stopper for many origin theories. It looked as though Earth was either too frozen for life or the atmosphere had too much carbon dioxide to produce the chemical raw materials needed to fuel pre-life chemistry in the sea.
Now Bada says that a frozen Earth may not have been so bad after all.
His latest studies suggest that only the top few hundred meters of ocean were frozen. Down below, the water would have been at near-freezing temperatures. That would have been ideal for pre-life chemistry.
Sea floor vents, bringing chemicals from beneath the crust, could have supplied some raw materials. Incoming comets and asteroids could have been even more helpful.
Such solar system debris is loaded with organic chemicals. These would have transformed during the impact into new raw materials for life. Melting through the ice, an incoming missile could dump this material into the sea.
Refrozen ice would seal it in while pre-life chemistry proceeded.
No one knows if this actually happened. It's just informed speculation.
But it does show that the kind of pre-life chemistry that Miller and others have demonstrated in the laboratory could have taken place after all.