By JonThm on YouTube.com Jonathan Thomason
A gas flames turns methan (Or other hydrocarbon) into CO2 and H2O: The H2O is a steam in turbulent flow.
This does molecular nuclear fusion – which is why a gas flame gives off radiation as it liberates γ and X rays, plus loads of heat. Which is why such a flame forms He. For which there is no chemical source.
The deep Earth does molecular nuclear fusion from high pressure water – which is where we get He from! But the deep also forms γ rays and 18O.