I can't find anything about the 43% number. It seems way too high. Most of the research on atomspheric oxygen's contribution to fire seems to focus on the 15 to

I can't find anything about the 43% number. It seems way too high. Most of the research on atomspheric oxygen's contribution to fire seems to focus on the 15 to 30% range, as 30% seems to be the upper limit where fires are too common and spread too much. "Belcher’s team’s work indicates that while there is not a firm upper limit to the fire window, 30 percent is a practical limit. Burn prevalence increases only slightly between 23 and 30 percent oxygen, and fuel moisture plays an important role too. It would only be possible to have periods with atmospheric oxygen concentrations approaching 30 percent (and preserve terrestrial vegetation) if Earth were much wetter than today." [1] [1]https://www.earthmagazine.org/article/flammable-planet-fire-finds-its-place-earth-history https://www.earthmagazine.org/article/flammable-planet-fire-... [2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3012516/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3012516/