Coal, oil & gas tends to get thought about and described in accordance with the use human beings have lately had for them. Therefore we call them fossil fuels or just simply resources. This is like calling trees timber or animals meat. It does nothing to describe their function or role in the natural environment. We know the earth operates as a holistic system, everything in the system fulfills a function that is vital to the whole system. So, not thinking, for the moment, about the effects of burning all this "fuel", what part does unburnt coal, oil & gas play in the natural environment?