[eloff]

Citation needed?

We have a sample size of just one (our solar system). But we already know that life on Earth began very soon after it cooled enough to have liquid water - that gives us some confidence that it can't be that hard for life to start.

We know life's been around on Earth for ~4 billion years, surviving multiple insane climate swings from subtropical vegetation and species living in the Arctic to the entire planet freezing over, multiple massive impacts from space, insane volcanism that people today just would not even recognize as volcanism. Hopefully that means life's somewhat durable.

[cmrdporcupine]

If what you mean by 'life' is bacterium, sure. That's all that was here for 3 billion years. I don't think we'd find that very exciting.

Eukaryotes are basically a fluke. The symbiosis event that created Eukaryotes from a random combination of Archaea and Bacteria appears to have happened only _once_ in the entire history of the earth.

It's arrogant to assume that life as we know it is both inevitable and inevitably complex in a manner similar to our complexity.

A practically infinite universe means potentially infinite diversity, including phenomenon that may not recognize as life at all to us, but should be equally interesting.

[Balgair]

> The symbiosis event that created Eukaryotes from a random combination of Archaea and Bacteria appears to have happened only _once_ in the entire history of the earth.

That story is very much in flux still. We're not very certain on how that occurred, let alone how many times over those billions of years.It's linked to the Great Oxygenation Event, likely, but we're still in the very early stages of understanding that era.

> A practically infinite universe means potentially infinite diversity, including phenomenon that may not recognize as life at all to us, but should be equally interesting.

As is usual in science, it depends. If you are dealing with matter like us, then there are only a few universal solvents (5? I can't find the citation). In those solvents, there are a countable amount of ways that the chemistry will allow for 'life' to 'evolve'. The ways that the life can then evolve are really complicated and diverse, but there does seem to be a evolution/development trade-off, where you have to go through developmental 'keyholes' to get to a new level of complexity. Is that infinite? I've no idea, but it feels like a different ordinal of infinity.

https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...

[perl4ever]

"Eukaryotes are basically a fluke. The symbiosis event that created Eukaryotes from a random combination of Archaea and Bacteria appears to have happened only _once_ in the entire history of the earth."

Isn't it possible that once it happened, it filled a niche that prevented something similar from happening again? Thus, the fact it only happened once doesn't tell you how probable it was to happen at all.

I have the impression other similar things may have happened as well. Recent articles about a viral-like protein that may be crucial to how long term memory works suggest that chance combinations of life that melded may be a theme.

[bduerst]

>Isn't it possible that once it happened, it filled a niche that prevented something similar from happening again?

Except it did happen again. Chloroplasts and mitochondria organelles are so different they are considered to have been generated from separate events.

Assuming that there are niches though is dangerous, because it assumes the evolution is guided, which it isn't. It's entirely possible that this has happened many times throughout history, but the resulting new organisms couldn't compete and died off without a leaving a trace.

That's why assuming it only happened twice is survivor bias.

[perl4ever]

"Assuming that there are niches though is dangerous, because it assumes the evolution is guided, which it isn't"

No, I wasn't suggesting that evolution is guided. If something evolves, and it ends up in the way of anything evolving similarly, it's not purposeful. It just is, as long as some catastrophe doesn't clear the way.

Edit: your comment "It's entirely possible that this has happened many times throughout history, but the resulting new organisms couldn't compete and died off without a leaving a trace." is a distinction without a difference to me. That's what I meant by it not happening, and the existing organisms occupying a niche.

[jrd259]

I think finding life on any other world would be very exciting even if uni-cellular. While we know which organic compounds are common in the nearby universe, we have no idea what other "architectures" are feasible, even granted an environment (temperature, pressure, solar spectrum) roughly like ours (including extremophiles). Life optimizes, but it's also path-dependent. Surely Earth's genetic code is accidental and path-dependent, but how constrained is the protein design space? For example, given a star like ours, do we have optimum chlorophyll? Or if you make your living as a sulfate reducing prokaryote, how many different ways can you do that?

No telescope will tell us what the ribosomes of Barnard b look like, of course.

But if only macroscopic life excites you, is it clear that you need eukaryotes for complex (multi-cellular) life? And how can you know it happened only once? It could also be that it happened multiple times, but one strain outcompeted (or just ate) every other. There could be undiscovered alternate "eukaryotes" if they remained single-cellular, too.

[millstone]

Why fixate on life at all? Would inorganic intelligent robots be a boring discovery?

[adrianN]

I think most people would classify most things as life if they reproduce and have a metabolism.

[andrewflnr]

Actually, cell-level endosymbiosis seems to have happened a bunch of times. Chloroplasts in plants are basically the same deal. The amoeboid paulinella chromatophora seems to have an independent lineage of chloroplasts. The Wikipedia page on endosymbiosis has more examples. It's starting to look pretty common.

Also, complex multicellularity (IIRC defined as differentiated cells) has evolved (according to the latest theory) six times. So that looks pretty likely to happen eventually, as well.

Human-level technological civilization, yeah, that looks like a one-time thing so far.

Edit: check out this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3910982/ They just casually mention "diatom-derived plastids", which are basically organelles that used to be diatoms, eukaryotic organisms in themselves!

[craftyguy]

> I don't think we'd find that very exciting.

Uh, that would be absolutely, positively very exciting to find microbes that originated someplace other than Earth. If you expect we'll find little green humanoid-looking things, you're going to be highly disappointed for likely centuries.

[dev_north_east]

> microbes that originated someplace other than Earth

Well we could never be sure of that without real samples. Who's to say it's not all the result of panspermia?

[dotancohen]

> bacterium, sure... I don't think we'd find that very exciting.

I think that most people, be them scientists, religious leaders, politicians, or even laymen, will have their lives changed forever. For the religious, discovery of extra-terrestrial bacteria will upend most of the interpretations of their holy books. Those books are the foundation of modern Western society (Do not kill, do not steal, do not take another man's wife, etc). By upending the basis of society we have no idea how humanity will end up. Will we throw everything based on the bible away? Reinterpret them? Will the Jews and Muslims reconcile? Will the Christians set out on another crusade? Will that crusade be to the extra-terrestrial bacteria to sterilize them?

> event that created Eukaryotes ... happened only once.

The insemination event which led to your birth also happened only once. However, it is does happen often enough in systems that have the right conditions. And there are trillions of available planets, right here in the Milky Way.

[dev_north_east]

> I think that most people, be them scientists, religious leaders, politicians, or even laymen, will have their lives changed forever.

Scientists yes, the rest won't care that much. It'll make the news sure but it'll be out of the headlines within a week. Maybe I'm a cynic but I'd put money on that being the case.

Additionally speaking as a religious person, it wouldn't change any of my beliefs. And I'm struggling to see how it would for others of my faith really.

[bduerst]

Except the universe isn't infinite.

It's true the universe is very large and feels infinite, but we know that it's about 25 billion galaxies (the size of the Milky Way) and that it has finite mass.

Sure, these numbers are incredibly large, but like you said, we're dealing with probabilities that are also incredibly small. There should be a cutoff somewhere for the observable universe as to what it is probable or improbable of producing.

[hndamien]

The universe and the observable universe are different things. As far as we can measure, the universe appears to be flat (by measuring the observable universe). With finite mass, but expanding space, how is it not infinite?

[bduerst]

You just said it yourself - infinite space but finite mass. "Life" by most definitions is made of mass, not space.

Claiming infinite space has infinite possibilities for life is quite literally a Celestial Teapot argument.

[hndamien]

I didn't make any claim about life. I just wanted to challenge the statement about the universe being finite. I also agree with the other commenter that I'm not sure we can even be sure the mass is finite, but also happy to be enlightened.

[bduerst]

The context of this conversation is probability of generating life. Debating theories on dark energy isn't relevant since it's not dense enough to generate life.

[eloff]

Is it that simple? Empty space has energy (dark energy) and E=MC^2 means energy and mass are interchangeable. Hence infinite space does imply infinite mass.

Not a physicist, so I'm probably dead wrong. But I would like to be enlightened.

[bduerst]

It is that simple, unless you think dark energy is dense enough to create a single celled organism (it's not).

[eloff]

We were talking about life, I didn't presume to say anything about intelligent or multi-cellular life. I agree with what you're saying though.

[dwaltrip]

If it were the case that is incredibly unlikely for life to get started in general, we would still be making those observations, give that we are here. This is the problem with only having one poorly understood data point that we ourselves are part of.

I'm optimistic that there is life out there. And if so, we should be able to get hard evidence by studying exoplanet atmospheres in the next few decades. Until then, it is very difficult to assess.

[kosievdmerwe]

Essentially "The Anthropic Principle" if people want to read more about it.

[eloff]

Agreed that a sample size of 1 doesn't tell us much - but it does tell us something, which is my point.

[rbanffy]

> it can't be that hard for life to start.

We have a selection bias happening here. We observe life because if life didn't appear as soon as the Earth was cool enough, the odds of us being here and able to reason about that would be small. We shouldn't consider it particularly abundant until we find a separate biosphere where life developed independently.

I personally think it's really easy to get molecules making copies of themselves, but we don't have enough data to claim that.

[eloff]

No, we can actually gain some statistical confidence here that life can't be that hard to start. That doesn't mean it's true to reality, just that with the information we have at sample size = 1, we do actually know something.

The fact that we're not on some planet around a red-dwarf a trillion years from now discussing this, but on a relatively young world does in fact tell us something.

[lovemenot]

Further, the speed at which it happened here is very compelling.

This planet is 4.6B years old Life is at least 3.5B years old. Maybe older. And for the first few hundred million, Earth was a fireball. So it happened almost as soon as it was possible to.