discarding panspermia with insufficient evidence
One of the topics that’s been prominently featured on Weird Things has been panspermia, the hypothesis that life can originate somewhere in the galaxy and spread though asteroid or comet impacts, or even forward contamination by alien spacecraft. We know that amino acids can form all on their own when certain molecules are irradiated, that some creatures can easily survive a trip though space, and there’s evidence that molecules crucial for life here may have a strong link with primordial impacts. Now, true, the theory has been abused by those who either do not understand what it actually entails, or by those who just refuse to keep up with the science and spend most of their time accusing some secret anti-panspermia cabal trying to keep them down, but overall, it’s quite sound which is why it’s still being kept in mind by astrobiologists. Or so you would think unless you go by a Scientific American blog post which says the following…
In some ways the motivation for proposing this kind of cosmic panspermia is a little dated. It comes from a time when we felt that the origin of life of on Earth was such a mystery, and such an unlikely event, that it was convenient to outsource it. Although this didn’t actually solve the real question of life’s origins, it meant that a specific origin ‘event’ could be extremely rare among the 200 billion stars of the Milky Way yet life would still show up in other places.
These days I think our discoveries about the remarkable abundance and diversity of so-called pre-biotic chemistry […] in every nook and cranny of our solar system, and even in the proto-stellar nebula of other stars and the wilds of interstellar space — swings the pendulum back to Earth. Nature seems adept at making all the pieces for life, apparently raising the odds of local bio-genesis.
How are these two thoughts connected again? I’m not exactly sure how life being very adaptable would mean that it raises the odds of Earth being its origin because we’re talking about evolution rather than abiogenesis. Caleb Scharf, the scientist who wrote the post, seems to be making the same kind of mistake many creationists do when trying to ridicule evolutionary theory by asking how life would’ve come from non-life and nothing that evolution fails to answer this question. So it’s little wonder that whatever life gets here or starts here would fill every available nook, cranny, and environmental niche since natural selection would favor their reproduction. But whether the origin of these species is on Earth or in space is more or less a toss-up if we’re considering just how well they adapted to their current environments.
Yes, we could say that it’s more likely that life originated on Earth because space is vast and the odds of enough comets and asteroids hitting the planet at just the right conditions for life to take hold are astronomical, literally, so it makes sense to look for an explanation that makes life more likely to arise here. That explanation may not be right, but we don’t have a complete picture of how it came to be and so we’re still trying to find viable ideas that seem to fit the evidence we’ve observed so far. But an important part of the process is not to discard hypotheses without any evidence that they simply don’t fit with the observations, something that Scharf does with an odd certainty about the habitability of promising places in the solar system by hearty microorganisms that should dominate the universe based on the way natural selection works.
But the problem, and the potential paradox, is that if evolved galactic panspermia is real it’ll be capable of living just about everywhere. There should be [organisms] on the Moon, Mars, Europa, Ganymede, Titan, Enceladus, minor planets and cometary nuclei. Every icy nook and cranny in our solar system should be a veritable paradise for these ultra-tough life forms, honed by natural selection to make the most of [the] appalling conditions. So if galactic panspermia exists why haven’t we noticed it yet?
He then goes on to answer his own question by saying that we probably haven’t looked all that hard in all these places, don’t know for what we’re really looking, or possibly both, and ponders would it would mean if we kept searching and found nothing. You can tell that he’s really pushing for the Earth-centric explanation and again, as elaborated above, I can see why, but his primary reason for pushing it seems to be based on a very strange confusion between abiogenesis and natural selection with no facts to back it up. The argument seems to be: we know more extreme organisms on Earth, natural selection seems to be doing it’s job, we haven’t explored all of the promising candidates for life in our solar system in sufficient detail and we don’t really know what we’re trying to find and how we’ll know we found it, therefore, life arose on Earth. Doesn’t seem like a scientific train of thought to me, especially with all the evidence that there was at least an important role being played by organic matter or microorganisms from space…