[qubex]

To be perfectly honest, you’ve drawn my attention to an ambiguity I had never before noticed: does panspermia’s hypothesis that “life” came from space require that life arrive fully formed and functional, or does it advocate that complex organic chemicals arrived from space and assembled on earth into a working configuration?

I have always found the idea of panspermia to be a bit of a cop-out as it totally sidesteps the problem of abiogenesis: it’s all fine and well to say “life came from space” but you still need to explain how life arose in space to begin with.

[AnimalMuppet]

I'm not an expert, but I think that there are different flavors of panspermia. Some would say that we got at least single-celled organisms from space; others would say that we just got complex chemicals.

[svachalek]

It's only a cop-out if you try to use it to explain the origin of life in general, not just on Earth.

Life arose very quickly on Earth, almost as soon as it was capable of surviving, so it raises the interesting question: were we just lucky, or is it easy to spawn life, or did it come from elsewhere? The answer creates very different pictures for what Earth-like planets elsewhere in the galaxy actually look like.

[JoeAltmaier]

I'm always confused by that. So there's only one form of life possible? Otherwise life may have arisen before, been wiped out when Earth changed, and life arose again. We may be just the latest in a long series of life forms.

[qubex]

Good point. It might be that the kind of life that arises on a planet depends on what it is bombarded with and which of those various candidate life-forms ‘takes’ on the specific environment.

[dekhn]

theoretically possible but there is no evidence to suggest this. Weighing the various hypotheses, most people would suggest the "simpler" (fewer wipeout/arise events) hypothesis, given the assumption that life arising is considered very rare.

[JoeAltmaier]

Because the earth remade itself several times. Any previous life would have surely been erased. The assertion was that life arose just once. That's hard to prove.

[westmeal]

From what I've read there are people on both ends of the debate. Most people I've seen talking about the idea tend to lean towards amino acid and simple proteins making it down here - not fully functional lifeforms that are able to replicate.

[andrewflnr]

A panspermia theory that involved non-living chemicals coming to Earth would be pretty useless. There's no real doubt that it's possible to generate those chemicals on Earth, and AFAIK it's still believed to be easier to make them on Earth than in space. Organic chemicals from space would just mix with all the ones that were already here.

[lovemenot]

>> it's still believed to be easier to make them on Earth than in space

I don't mean to be glib, but space is very large and time before our planet was formed is very long.

I assume that if it was easy here in those first few hundred million years, it had already been even easier in many elsewhere places. Any one, or multiples of which could have seeded us with as yet locally unavailable precursors and possibly even life.

[undersuit]

I think a complex molecule could accepted. We don't know why our biological systems settled on their chirality, but maybe it was from a massive bump of molecules with all the same chirality from an extra-solar source.

https://en.wikipedia.org/wiki/Chirality_(chemistry)#In_bioch...