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Comment by jimmytucson | Hacker News Reader

I'd add when any life began:

    single-celled life (3.8-4.3bya)

...which is notably close to when the Solar System formed (4.6bya)

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... 4.6bya - a good chunk of how long the universe even existed.

One might assume then that life is inevitable. Seems like too much if a coincidence (although I appreciate the tautology of that thought).

The alternative explanation is that seeds from a previous evolution started colonizing the planet as soon as the medium became viable. But that's like cheating.

Panspermia is not cheating. If we believe abiogenesis to be vanshingingly unlikely on any one planet, panspermia paralelises discovery of a solution.

You surely knew I was half joking. Anyway, I'll explain a little further. I said cheating because panspermia, as I understand it, has a very narrow window of usefulness.

If surface abiogenesis is unlikely, panspermia is more unlikely because it needs the former, plus a way for the spores to survive in space, the travel of interplanetary, maybe interstellar distances, atmosphere re-entry and developement in a new environment.

Another factor is that, if we accept the current estimations for the age of Universe and the fact that some elements only are present in second or third generation star systems (because they were formed inside novas), we could be one of the first guests to the party. Panspermia would place abiogenesis even further in the past.

The only scenario in which panspermia would be more likely is that some components that are needed for life can only appear in space and develop on the surface.

That's not to say that panspermia is in itself an absurd idea, actually the fact that some elements need to be created inside stars means that we're somehow children of the stars, it just happens that panspermia isn't a great substitute for abiogenesis. An amplifier, maybe.

Perhaps we understand panspermia differently. I understand it as a possible answer to the question: how did most of the life in the universe arrive where it is presently to be found? Clearly not all life, since as a matter of certainty abiogenesis has occurred at least once.

>> If surface abiogenesis is unlikely, panspermia is more unlikely because it needs the former, plus ...

That depends. Panspermia gets a huge multiplier from distributing the number of planets and eons on which abiogenesis might have happened just once. So it depends on the relative impacts of very different factors - neither of which have been well quantified.

If panspermia had ever been feasible, it was likely more so in the earlier universe. Personally, I prefer it because it seems to follow the Copernican Principle.

So it depends on the relative impacts of very different factors - neither of which have been well quantified.

Well, that's... correct. I still think that it's less probable, but I have no way to prove it :)

Or that "intelligent" life is very unlikely if you consider that our planet will no longer be inhabitable in roughly the next 10% of its total existence and 7% since it's estimated microbial life appeared.

If human equivalent creatures had taken just 10% longer to appear the sun would have dried up all the water on the earth and wiped its atmosphere before it happened.

The satellites of Saturn and Jupiter will still be chugging along.

Our star is unusual, as well over 90% of stars are smaller (and thus longer lived). Though if you go small enough you start dealing with planets in the habitable zone being tidally locked.

But if a species capable of rocketry had not developed, there is no way complex life would be able to get to those satellites.

The increased likelihood of being tidally locked is not the only problem with smaller stars. As a rule, larger stars are more stable and smaller stars are more active. This is made worse by the fact that the habitable zone is closer to the star for smaller stars. Most stars in the universe probably can't support life as we know it because any planet close enough to be warm would get it's atmosphere stripped off by flares.

> But if a species capable of rocketry had not developed, there is no way complex life would be able to get to those satellites.

I'm talking about continuing evolution of the life that may already be there.

Informative points about stars.

It's hard to say for certain that there has never before been an intelligent species. Over hundreds of millions of years even evidence of cities (even assuming that all intelligent species would even make cities) could be entirely wiped away.

Shout out to the Silurian hypothesis. It’s been linked here many times, so I won’t link to it again.

especially true if you consider that if there were hundreds of civilisations scattered across the Universe, the average distances across space and time would still be hundreds of times larger than we could deal with right now, or perhaps ever

for a civilisation with advanced rocketry and telescopes similar to what we have right now, it would still be very unlikely to observe us - firstly because we've only been around at all of a tiny fraction of the time the planet exists, and secondly because despite of all the ruckus we are currently causing in the planet, we'd still be very hard to observe from sufficiently far away

I have all sorts of deluded fantasies regarding U-235 found in gabon.

https://www.iaea.org/newscenter/news/meet-oklo-the-earths-tw...

... and overlapping the the Late Heavy Bombardement.

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

Not really. It's 300-800 million years. That's not nothing. It just looks small by comparison to the time elapsed since then.

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