Through the most of Earth’s history, life had existed in microbial form. Only about half a billion years ago complex multi-cellular life appeared, leading to the evolution of higher organisms we see today. This could happen because Earth was in its habitable zone all this time. If it wasn’t, complex life would not have time to evolve. Gros proposes that if we seed other planets, even if they are only transiently habitable, life will have the chance to evolve to complex forms there, because it will start off from the “Cambiran explosion”.
Gros proposes that we will seed other planets in about 50-100 years using probes with artificial intelligence (AI) needed to synthesize microbes adapted for a particular planet that the probe approaches. In our view, this scenario is too optimistic. Even if AI will be at hand in 50-100 years, it may not help. The space journey would take many thousands (if not millions) of years. The more elaborate the technology involved, the more chances are that something will go wrong with it if left unattended during such periods of time. To be fail-safe, the space probes should be as simple as possible.
A more realistic project is to seed star-forming regions rather than planets, as proposed by Michael Mautner back in 1997 (it is surprising, by the way, that Gros never mentions Mautner, who has been persuing the program of planetary seeding for more than 30 years). No AI is required in this case, and, furthermore, it may in fact turn out to be more efficient, as star-forming regions produce up to a few thousand stars (with their planetary systems), so, with the same effort, you may end up with several seeded planets, instead of just one.