I prefer the theory that life is the natural evolution of physical chemical processes given certain conditions. That explains why we think that we’re likely to find life on Neptune. Otherwise it begs the question of why did life start on Mars, and that’s a turtles all the way down kind of situation.

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aurareturn 2 days ago | parent | next [-]

"You start with a random clump of atoms, and if you shine light on it for long enough, it should not be so surprising that you get a plant." -Jeremy England

Life increases entropy and doesn't break 2nd law of thermodynamics.

	▲	mr_mitm 2 days ago \| parent [-]
		Actually it's enough to have a sufficiently large amount of hydrogen. No extra light necessary.

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2 days ago | parent | prev | next [-]

[deleted]

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roncesvalles 2 days ago | parent | prev | next [-]

In addition to one seeding the other, neighboring planets having life also gives support to extra-solar-system panspermia. An advanced civilization could've fired off the "seed" in some vehicles on calculated trajectories to all viable planets, and the Solar System happened to be within the radius of their efforts.

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estimator7292 2 days ago | parent | next [-]

Panspermia is such a juvenile take. It doesn't answer the question at all, just hand-waves it all away with a "because I said so". It's like a religion.

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roncesvalles 2 days ago | parent [-]

I was never attempting to answer where life came from. It's simply that if Mars and Earth both have/had life, the probability that they came from some common cosmic seeding project in our neighborhood becomes a bit more likely.

	▲	vlovich123 2 days ago \| parent [-]
		Vs it’s a natural inevitable process when the conditions support it?

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vlovich123 2 days ago | parent | prev [-]

Where do the turtles start?

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d1sxeyes 2 days ago | parent | prev | next [-]

If that is true, then why does it seem that there has been only a single origin event on Earth?

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rrmm 2 days ago | parent | next [-]

Does it seem that way? It happened at least once (but could have happened many times without "taking over"), and certainly one sort of life seemed to successfully out-compete all others. But none of that says single-origin to me.

Early on I would expect a whole lot of "horizontal gene transfer" sort of things to have taken place. So for example in addition to actual horizontal gene transfer, there are mechanisms like one organism enveloping another to eventually become organelles, co-opting products from each other, etc. All of which would act to homogenize life and make certain process ubiquitous.

Finally, there's an outside chance that "there's only one way to do it".

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d1sxeyes a day ago | parent | next [-]

Absence of evidence is of course not evidence of absence, but all life on earth today seems to be descended from a single organism, 3-4 billion years ago: https://en.m.wikipedia.org/wiki/Last_universal_common_ancest...

This is about a quarter of the lifetime of the universe ago, and we don’t have any evidence at all that life has ever occurred in any other way. We’ve only really been looking for a hundred years or so, but we’ve not found any “fountain of life” where life is being created, we’ve not found evidence of any type of life that isn’t broadly related.

I absolutely agree that it’s not evidence, but I believe that on balance, it makes more sense to take our working hypothesis to be something that fits the evidence we do have, rather than believing the evidence must exist we just don’t have it.

To be clear, I’m not advocating that we don’t investigate both possibilities, and I wouldn’t put much weight behind my own guess here.

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roncesvalles 2 days ago | parent | prev [-]

I think single origin event is highly likely because, for example, it's wholly conceivable that a slightly different variant of AUCG (or just one of the molecules) could've emerged and it would have similar characteristics, but not differentiated enough that one would have a very strong selective advantage over the other.

Diversity could exist in harmony and the lack of any diversity is a pretty strong signal that the only extant version is either very rare or the only to ever emerge.

Everything in nature is diverse except RNA/DNA and this fact alone is a sort of evidence.

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vlovich123 2 days ago | parent [-]

Or the basic life that forms is going to look the same regardless of where it starts on Earth, meaning that you’d never have evidence of two origins.

Or RNA was just a winning virus that infected all other life or killed all competition to make it seem like there was only one origin.

Absence of evidence is not evidence of absence.

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roncesvalles 2 days ago | parent [-]

I'm pretty sure we've checked every lifeform to see if they follow the universal genetic code, and they do. RNA is too fundamental to be a virus infection.

When you should see evidence but don't, "absence of evidence is not evidence of absence" doesn't apply. Otherwise absence becomes unprovable à la Russell's teapot.

	▲	vlovich123 2 days ago \| parent [-]
		Except for that you’d have to have a reasonable belief you know what to look for and where to look. By comparison, we’ve looked nowhere (Earth is big and mostly inaccessible to humans) and don’t know what we should be looking for, since we don’t have any testable models for the origin of life yet. And re RNA I was just giving one example of why all life might have it (ie RNA gave an evolutionary advantage so anything without RNA died). There’s all sorts of reasons why we don’t have evidence of multiple origins, not least of which is that we just haven’t looked in the right place and there could easily be life being created from scratch on this planet without even knowing about it. That’s what the entire field of synthetic biology is even about; just doing it in a lab instead of out in nature so that we can understand the conditions better.

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AngryData 2 days ago | parent | prev | next [-]

Well we aren't sure that it did have a single origin. But also, anything primitive enough to generate randomly is going to be viable food itself for other already existing and more evolved lifeforms, and the conditions for life to start by itself might just be a smorgasbord of energy for existing life forms that could out compete more primitive forms or alter the environmental conditions enough to prevent more life from forming. It might just not be possible for new life forms to arise in a non-sterile environment.

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estimator7292 2 days ago | parent | prev [-]

There is absolutely zero evidence for this either way. We assume this is the case, but there's actually no way to ever know for sure. It's completely possible that life emerged and went extinct on this planet many times. Problem is it was so long ago that any fossil evidence has been either buried so far that we can never reach it, or subducted into the mantle and melted down. Absolutely no way to tell.

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vlovich123 2 days ago | parent [-]

It was so long ago that it would be buried deep under the ocean and we haven’t even explored well the ocean floor. And fossils wouldn’t really tell you whether there was one origin or another.

And you’re right, assuming those fossils even managed to survive in the first place and not get destroyed. And that’s ignoring that early life would have been microscopic and we wouldn’t really see fossils of that.

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d1sxeyes a day ago | parent [-]

Why did it stop?

	▲	vlovich123 a day ago \| parent [-]
		Do we have evidence that it stopped? Or just that we don’t know where to look and what to look for? But even if it did, one clear argument could be that the conditions on Earth when it happened would have been very very different than the earth today. Lots more volcanic activity, lightning storms, and UV radiation. We don’t know the exact conditions needed to create life from inorganic precursors so we don’t have a solid hypothesis of was there multiple origins or a single or is it still happening today. But given we have the beginnings of evidence of life on Mars, Titan, and Triton, and that it would make sense since we know life must arise naturally out of non-life origins (since there was no life at the Big Bang), I would venture to guess that life is both rare and common. Intelligent life also seems common although less common than life overall (other primates, dolphins, Elephants, ravens/crows, and cephalopods are all quite intelligent). Intelligence + tool use is also not uncommon but rarer (we’ve caught animals on tape using tools). Advanced industrial civilization is the only thing so far that we only have a single existence evidence for - is that unique, can there ever only be one on a planet at a time, or can there only be one ever when conditions are right? Eg we wouldn’t have gotten very far if we were on the planet earlier and didn’t have dinosaur bones to power our industry with - the jump from whale oil to nuclear/photovoltaics/wind turbines seems unlikely but maybe it would happen anyway, just longer.

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lawlessone 2 days ago | parent | prev [-]

neptune?

	▲	vlovich123 2 days ago \| parent [-]
		Sorry, I meant a moon of Neptune (Triton). There's also a recent research study suggesting Titan also has life.