Impacts would be most catastrophic at the very level of tidal pools where life was most life to form. After all, that's almost the same length of time over which life has gone from its first multicellular specimens through dinosaurs, the development of plants, and up to today's rich abundance. Certainly, a unicell could form in that same length of time. Also, there is no reason to believe that tidal pools were the one and only place where living things could have formed. Given the incredible diversity of bacteria, it would strain credibility to constrain its origin to one environment.
Life origins is a hard problem.
Life's origins might well be a hard problem, but they don't concern evolution theory.