That's the title to a post in the WSJ:  "Coal, oil and gas are “fossil” fuels, right? They are derived from ancient life-forms and are nonrenewable, stored energy, extracted from prehistoric sunlight. In the case of coal and most oil, this is obviously true: You can find fossil tree trunks and leaves in coal seams and chemicals in oil that come from plankton. *** But there’s increasing doubt about whether all natural gas (which is 90% methane) comes from fermented fossil microbes. Some of it may be made by chemical processes deep within the earth. If so, the implications could be profound for the climate and energy debates."