Extremophiles are real world examples of the kind of life that still has some commonality with the rest of us and yet they are already skirting the edges of what's possible and they thrive in what wouldn't even begin to qualify as livable circumstances for others.
They're not going to start a Venusian equivalent of the royal society but they are life and I think it is important to note the fact that life doesn't necessarily have to be intelligent or even multi-cellular to be just as real as we are. And the thresholds for 'life' are probably a lot lower than for 'intelligent life'.
i don't think you can go that far from room temperature with nucleic acids. one thing that casts doubt on my thesis here is that though luca clearly used nucleic acids, surely (?) life didn't start that way. but we haven't found even undersea-vent extremophile life with a silicone-based genome or any other alternative chemistry, even in ecological niches where there would be no competition from carbon-based life. so,
- i could be just wrong;
- abiogenesis might have originally produced carbon-based life and then been unable to escape the shackles of that heritage, even in places like the parts of undersea vents that are too hot for carbon-based extremophiles;
- implausibly, those places do contain non-carbon-based life that nobody has recognized yet; or,
- more provocatively, abiogenesis might have happened somewhere extraterrestrial (venus, mars, europa) and only infected earth after already getting quite close to luca
life on earth does seem to have taken a long time, most of the planet's lifetime in fact, to get to the point of sometimes being able to prove theorems
> we haven't found even undersea-vent extremophile life with a silicon[e!]-based genome
That may simply be because even there carbon has the advantage and would call anything else 'food', so on the timescales that we observe life silicon based life might simply not have time enough to evolve.
It's an interesting question, and if life really revolves around a single atom (Carbon) being present that would in itself be yet another one of those things that makes you wonder what the chances are of life existing at all.
Judging by our own evolutionary timetable it may be that on the 'hot' earth other life forms were possible but as things cooled down they were no longer viable (I'm assuming that 'hot' life would evolve faster and 'cold' life would evolve slower, this may well be a wrong assumption), and as earth cools down further it may well be that things that are not viable right now may become viable. Life seems to have very few pre-requisites, energy and some specific molecules present in non-zero quantities and you're off to the races.
Also: nucleic acids may not be a pre-requisite either: life may well require them for bootstrapping but they may not be a requirement for all forms of life.
i was thinking of silicones because silanes are unstable even at room temperature, let alone at undersea-vent temperatures, while silicones can be stable up to lava temperatures if you don't require them to be organic (the alkali silicates i mentioned upthread, which gradually shade into the kinds of organic-functionalized silane surfactants used to enable organics to bond to phyllosilicate functional fillers). maybe silanes, dissolved in liquid ammonia, could work at low temperatures, but i doubt it
my thought with the undersea vents is that, if there was a diverse hadean or archean ecosystem of non-carbon-based life, some of it should have survived in the parts of the vents that are too hot for carbon-based life. maybe the cells that froze to death in boiling water would become food for carbon-based extremophiles, but the cells in the hotter parts of the rock should be safe
but we don't observe that, and i think that the most likely explanation is that there wasn't any silicone-based life in the hadean
nucleic acids are definitely not a requirement for all forms of life
Extremophiles are real world examples of the kind of life that still has some commonality with the rest of us and yet they are already skirting the edges of what's possible and they thrive in what wouldn't even begin to qualify as livable circumstances for others.
https://en.wikipedia.org/wiki/Extremophile
They're not going to start a Venusian equivalent of the royal society but they are life and I think it is important to note the fact that life doesn't necessarily have to be intelligent or even multi-cellular to be just as real as we are. And the thresholds for 'life' are probably a lot lower than for 'intelligent life'.