[QUOTE]Originally posted by Andor:
I have read somewhere that big sterilizing impacts could have lasted as late as 3,8 billions years ago. Any way, if by 3,5 billion years forms of life as complex as cyanobacteria (stromatolites) were already present, the time for life to evolve seems a little scarce. Here is where the possibility of life surviving underground fits nicely.[/B][/QUOTE]
I read a couple of articles concerning the last big group of impactors, and by big group I mean what are generally called sterilization events, and I remember a range of 3.8 to 4.1 Byr ago. That would have given life (not killed) by the impactors 300 to 600 million years to start. Several of them concerned the generation of organics through the heat of impact, this one is the only reference that I still have Nature 1992, 355: 125-132. If I can find the originals I will post references to them.
------------------
"Chance favors the prepared mind." L. Pasteur
Taz