Hugh Pickens writes "NASA reports that according to a study by Rebecca Martin and Mario Livio asteroid collisions may have provided a boost to the birth and evolution of complex life on earth delivering water and organic compounds to the early Earth and accelerating the rate of biological evolution with occasional impacts to disrupt a planet's environment to the point where species must try new adaptation strategies. 'Too many asteroids, and you've got an unrelenting cosmic shooting gallery, raining fiery death from above,' writes Fraser Cain. 'Too few asteroids, and complex life might not get the raw material it needs to get rolling. Life never gets that opportunity to really shake things up and evolve into more complex forms.' Martin and Livio suggest that the location of an asteroid belt relative to a Jupiter-like planet is not an accident. The asteroid belt in our solar system, located between Mars and Jupiter, is a region of millions of space rocks that sits near the 'snow line,' which marks the border of a cold region where volatile material such as water ice are far enough from the sun to remain intact. 'To have such ideal conditions you need a giant planet like Jupiter that is just outside the asteroid belt [and] that migrated a little bit, but not through the belt,' Livio explains. 'If a large planet like Jupiter migrates through the belt, it would scatter the material. If, on the other hand, a large planet did not migrate at all, that, too, is not good because the asteroid belt would be too massive. There would be so much bombardment from asteroids that life may never evolve.'"