It’s a heat magic so you can tell it’s not pressure explosions, it’s combustion, so Fire.
Wood is natural material that comes from plants which grow up from the ground so basically Earth. Earth and vegetation often go hand in hand.
Lightning is generally considered from Fire (see lightning generation from Avatar: The Last Airbender). Lightning also a Plasma so ye.
You could also argue Light is just from Fire sice almost everything associated with Light is also associated with Fire, since Fire emits Light. The Sun, a lantern/torch, a candle, etc. This is especially true in WoM where the only sources of light aside from magic come from fires.
Yeah but that logic kind of applies in reverse. If hotter fires contain Plasma, that suggests Fire is the origin and Plasma is the product, which I say is pretty fair. Yeah it can obviously happen vice versa but you could say the same for Magma.
That being said Plasma doesn’t depend on the existence of Fire but as I tried to say with the Avatar example I think Fire in terms of “the 4 elements” just represents heat, and that hot stuff following this train of thought all descend from Fire. It isn’t really a matter of science more than it is just a way of grouping things.
If it was completely scientific then limiting elements to just being byproducts of other elements is nonsense, there’s a reason why the 4 elements were abandoned and we now use the periodic table. This is especially clear when considering Iron and Gold, which are literal natural elements, not byproducts of Earth. However we consider Metal a byproduct of Earth because Earth is solid like Metal and Metal can come from Earth. Likewise, I have said Plasma is a byproduct of Fire because Fire is hot like Plasma and Plasma can come from Fire, and then applied that to Lightning as it is a Plasma.