How sterile is "sterile"? We can reduce microbiota to so many parts per billion, but afaik they can never be fully removed from an environment. Won't any contam

How sterile is "sterile"? We can reduce microbiota to so many parts per billion, but afaik they can never be fully removed from an environment. Won't any contamination from microbiota dramatically effect such an experiment. It may very well be that the conditions for the abiogenesis required no other life to be present.