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Every time we assume a limitation like this we've been wrong. If tardigrades can survive floating through space, I think it's reasonable to guess that there might be life that survives at the other extreme.

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throwup238 5 days ago | parent | next [-]

Where do you draw the line for the other "extreme"?

Assuming carbon based life as we know it, 300-400C is the probably a hard limit at which point single carbon bonds begin to break down.

Assuming life on earth as we know it, with ATP universally conserved across the entire evolutionary tree, the limit is really 150C. We've seen incredible survival adaptations like cryptobiosis but no organism exists that doesn't use ATP as its most basic unit of energy storage. That's the theoretical limit, but realistically other highly conserved critical pathways start to break down well before that temperature.

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kergonath 4 days ago | parent | next [-]

> Assuming carbon based life as we know it, 300-400C is the probably a hard limit at which point single carbon bonds begin to break down.

Carbon-Carbon covalent bonds are the strongest we know. 300°C is nothing, carbon melts beyond 3000°C. Some organic molecules in our cells degrade at higher temperatures, but it depends on the availability of other species to react. Otherwise, hydrocarbon chemistry can be done beyond 300°C.

I am not saying that this kind of organisms are likely (I have no clue, it’s not my field). But from a chemical point of view there are 2 factors that could be at play:

- exotic organisms could rely on different chemistries altogether to produce energy and rely on molecules that are unstable under our standard conditions;

- and also chemistry under pressure could be very different from what we are used to on the surface.

	▲	throwup238 4 days ago \| parent [-]
		I don’t know why you think carbon’s melting point or hydrocarbons are relevant to basic biochemistry. The “strongest” bond we know of breaks down starting at 300C (~500C for double iirc). It’s not bulk graphite or under extreme pressure underground. You can fantasize about exotic biochemistries all you want, but what we know about carbon based life here on earth is rather specific in its limits.

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CuriouslyC 5 days ago | parent | prev | next [-]

I don't see why there could't be stabilizing adaptations for phosphate groups, or evolution of alternatives like phosphonates, thiophosphate or imidophosphate. Evolving stable enzymes that still have catalytic activity is also a big lift, but life consistently surprises us.

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5 days ago | parent | prev [-]

[deleted]

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alpaca128 4 days ago | parent | prev [-]

While it’s true and impressive that tardigrades can survive all that, that doesn’t mean they can thrive there. They survive it by entering a stasis, but that’s about as far from living as one can get temporarily.