Coal and petroleum were found millions of years ago from the degradation of biomass. These are exhaustible nonrenewable resources. Our known petroleum will last for about forty years and coal resources will last for another two hundred years, so we should use them judiciously. When the fossil fuel is burnt, carbon dioxide, oxides of nitrogen and sulfur and water are formed. If combustion takes place in insufficient air carbon monoxide is formed in place of carbon dioxide. These are all poisonous at high concentration.