Oddbean

Well... Kind of. But that's because combustion requires an oxygen rich atmosphere. Life as we know it depends on oxygen but that doesn't mean fire requires life. We've found planets with O and C in their atmospheres so fire is definitively not exclusive to earth.

Agree, gotta reach at least 20% O to have an ignition via either abiotic or biotic means. Venus is a great example. Latest research points to both been a lot more rare than what we once thought. Very interesting distinction between life (no fire) and civilized life (barbecue 😎). Balbi, Amedeo, and Adam Frank. “The Oxygen Bottleneck for Technospheres.” arXiv preprint arXiv:2308.01160 (2023).

I recently learned of a very interesting (though almost certainly not true) theory that the early universe teemed with life because there was a brief (some number of the millions of years, I believe) period where the space of the universe itself was at standard temperature and pressure.

One-click link to the paper: https://arxiv.org/pdf/2308.01160.pdf Very interesting, and a valid point. All technology (and all life) requires a metastable energy gradient, and combustion would have to be the easiest to bootstrap. Our technological toolkit is very dependent on oxygen combustion, an important engineering barrier to space resource development. The authors point out that paper cannot be ignited below 18.5% molar fraction of O2 at standard temperature and pressure. Not mentioned is that this proportion is largely independent of pressure, which is not intuitive at all (and why high-oxygen low-pressure spacecraft atmospheres are so dangerous e.g. Apollo 1). Also not mentioned is the importance of atmospheric nitrogen in supporting combustion. Combustion needs a fuel (reductant), an oxidiser, and heat, as most of you know. Nitrogen (78% of air by volume) is far more than a spectator - it has a low specific heat compared to most fuels (so it doesn't take away too much heat) but a low kinematic viscosity (so when it does gain heat it moves away violently, mixing fresh oxygen in close to the fuel). Nitrogen is also extremely inert chemically, so it doesn't interfere with the complex chain of reactions that comprise combustion. If Earth had a different buffer gas instead of so much nitrogen, combustion could be much more challenging, and require much higher proportions of oxygen for sustainment. CO2 has a much higher specific heat, and water vapor a higher viscosity. Chlorofluorocarbons are both, plus they break down and quench the free radicals on the fuel surface. I used to work with a guy whose doctorate was in combustion chemistry, next time I see him I'll annoy him with questions about this :-p