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Comment by ramraj07 | Hacker News Reader

I have very little reason to believe life evolved in Earth or even in Mars for that matter. The more likely scenario is that there’s rocks floating around everywhere that have spores of life throughout the galaxy ready to seed a suitable planet in geologically instantaneous timelines. That will explain the extremely rapid emergence of life on earth initially while it took a few billion years to evolve any further. In which case if Mars had flowing water at some point it likely also harbored at least single cell life.

Source: biologist but not specializing in evolution.

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But you only introduce an unnecessary extra step in the same theory. Life still had to evolve somewhere, just that now it had to embark onto interstellar trip.

But instead of having a single planet generating random molecular combinations to roll for proto-DNA, you have billions or more. Life would have to evolve extremely commonly for it to be more probable to evolve by itself on any specific planet than on literally any planet which then encouters an event causing panspermia.

But alas, that's an external observer viewpoint. It's important to note that it does not say that life is more probable to have evolved somewhere else than Earth (since we have an effective sample size of 1). It only says that the extra step introduced in the panspermia theory does not have a negative probabilistic impact, on the contrary.

Not entirely unnecessary.

It's a big question as to why life started on Earth as soon as it did, pretty much as soon as it was even possible.

That could be because life is very easy to start if conditions are right. In which case it's quite likely to have started on early Mars too, and we should expect to find at least simple life all over the place.

The other possibility is that it didn't start on Earth, and was seeded from somewhere else.

The big question is how local regions of low entropy that exhibit metabolism and replication (ie. life) came into existance out of inanimate matter. Where it happened is secondary.

Yes, that is the biggest question. Understanding where it happened may give us some clues of course.

Why not add more steps? The aliens¹ brought microbial life on an interstellar ship and seeded it. A lot better chance than riding out for a few million years on a piece of rock! See, it's approximately on the same trailing end of unlikely as panspermia, but I fancy this one more.

¹Let's call them Engineers

If living organisms can survive on a meteorite, they can definitely survive on moon/mars, which contradicts our observations.

Nitpick: They'd survive in a meteorite.

They likely would not survive on a meteorite in the sense of active metabolism and replication. We'd be talking about very dormant spores.

That raises 2 problems for me.

1. How exactly are these spores of life getting into asteroids and being pinged around the Universe? The mechanism seems absurd to me. Earth is teeming with life, but outside of our explorations I believe none of it escapes our planet at all.

2. The life that would reach us would be already specialised for whatever environment it came from, and I would imagine would result a lower amout of variety, since it's already a successful species. But on our planet we have a massive amount of variety, which I believe points more to a bootstrapped start where competition was less intense, and odd things could develop, which were later outcompeted (see the Cambrian explosion).

Disclaimer: Not even a biologist, but I'm more willing to accept that life started and evolved here. Of course that might all be cast in doubt if we detect masses of life on asteriods or metoerites, but the first attempt at that seems to have come up with nothing so far.

Collisions? Large enough collisions eject large amounts of rocks into space. A good fraction of rocks ejected from earth would have some viable single cell life inside it, all you need are some cavities in them that don’t reach insane temperatures during this process, which is very possible for big enough rocks.

Remember that while you deal with insane numbers on the space side, viz. it’s emptiness, the number of planets etc., you’re meeting an insane adversary with biology as well. The number of cells in a single piece of sand in this planet is insane. The number of particles we might eject if there’s a catastrophic event from earth is insane. Anyone who worked on biology would know how hard it is to keep things truly sterile. I’m just extending it to outside space as well.

As for the conditions being too specific, while it’s true, I don’t see many outrageous combinations you can commonly observe in planets in the galaxy so I’m not sure if that’s a big deal breaker.

NASA proved in the 70s that some microorganisms survive atmospheric rentry. In fact, they could not possibly be killed by any means known to man, except for some enormous cosmic event with very powerful radiation / cosmic rays. This was done to question the idea of it being "safe" or not to travel in space or other planets, if it is possible to "scrub" our ships clean and avoid bringing germs with us. Apparently thats not 100% possible, some critters survive space and the harshness of re-entry just fine.

What makes you think panspermia is more likely than abiogenesis?

The only data point we have suggests the evolution of eukaryotic cells and multicellular life is simply less likely than abiogenesis. There are plenty of hypothesis to explain why that might be the case.

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