It’s a common elemental theme we see across stories, fantasies, etc. It seems like it is an element that should be part of that pantheon but maybe there is a scientific explanation of why it isn’t? Or is it simply, they did not have enough understanding of it at the time those 4 were suggested.
I think it was lumped into fire. Since lightening does cause fire in nature. Moreover, I think fire stood for heat as well since fire is pretty much the only way to naturally heat something
Friction can just get fucked.
Duh. Rubbing things together releases their own internal fire