It's not clear to me that volcanoes don't release both CFCs and HFCs. Do you have a citation? I'm looking at the wiki articles, and then at the related chem ar

It's not clear to me that volcanoes don't release both CFCs and HFCs. Do you have a citation? I'm looking at the wiki articles, and then at the related chem articles about HFC types and synthesis. I'm not a chemist, but a quick look around makes me think the known CFC, fluorocarbon and halomethanes in volcanic gases would suggest the same or similar compounds as in our engineering uses. https://en.wikipedia.org/wiki/Volcanic_gas#Composition https://en.wikipedia.org/wiki/Volcanic_gas#Composition https://en.wikipedia.org/wiki/Halomethane https://en.wikipedia.org/wiki/Halomethane https://en.wikipedia.org/wiki/Hydrofluorocarbon https://en.wikipedia.org/wiki/Hydrofluorocarbon On Hiawatha, agreed it's not yet dated, though it is recent: "The age of the crater is presently unknown, but an impact sometime during the Pleistocene is consistent with presently available geological and geophysical data." - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6235527/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6235527/ They also raise the possibility that some of the radar returns indicate it's still hot in the center of the impact area(!). If so, it's probably one of the YDB impactors. Btw, there's been another one discovered near it: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL078126 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL07.... They say they don't think it's related, though it does still have large features that should have been eroded away if it were really old. We'll see!