The Value of Panspermia
We have seen that Hoover’s claim to have found fossils of extraterrestrial cyanobacteria in meteorites does not really show that terrestrial life did not originate in our own planet. Even if those structures are indeed extraterrestrial fossils, such an admittedly extraordinary finding would only support the view that alien life has existed. The reasons are simple:
1. Fossils are dead things. Those meteorites did not bring living things to this planet.
2. Even if they had brought living things to this planet, and no one suggests they did, Hoover went to pains to argue that those structures were too different from terrestrial life, so they had to be extraterrestrial (e.g. only 8 amino acids in common out of 20, although for some reason some of the comments in the Journal of Cosmology referred to 8 out of 22). That is, Hoover gives no evidence that terrestrial life came from elsewhere.
We have also seen that the value of panspermia as an explanation for the origin of terrestrial life is quite low.
1. The motivation for the “impossibility proofs” against the idea that life could originate on Earth is often based on misunderstandings of biology, either of evolutionary biology, or genetics, or both.
2. By pointing to panspermia we have not explained the conditions under which life originate at all. That is, by saying that life must have started somewhere else we still have not explained the origins of life.
3. When this problem has been addressed by the advocates of panspermia, they have ultimately grounded their views on absurdities, either non-scientific fictions (e.g. Hoyle’s “superior beings”) or patently false claims (e.g. Klyce’s notion that life has always existed).
This is not to say that the idea of panspermia should not be entertained at all. We do not know yet how life originated. By elaborating different scenarios we challenge our imagination and our understanding. And we prepare ourselves for the fruitful exploration of other worlds where life might exist, or at least might have existed. Having trained our biological thinking on a variety of scenarios, for example, we will be better able to deal with the surprises such exploration is likely to offer.
Even the idea that living things might hitch rides inside meteorites or comets is not completely implausible. Spores can survive for long times. Extremophiles can withstand, it seems, extreme temperatures or radiation, and in addition to bacteria and lichens, even a very small animal, the Tardigrade, has been shown to survive in the vacuum of space!  Of course, as we have also seen in this blog, that life can survive in extreme conditions does not imply that life can originate in those extreme conditions. Nor should we infer either that those extreme conditions may persist for millions, let alone billions of years, as the interstellar journeys envisioned by some panspermia advocates would require, without destroying the extremophile voyagers.
A plurality of views may also help us determine what new types of observations and experimental investigations might be worth undertaking. All in all, the idea of panspermia might still prove useful as we search for life in the universe.