F or many years there has been great interest in the origin of fossil fuels such as coal and petroleum. In the oceans, there is a constant “snow” of procaryotic membranes and other organic matter that settles on the bottom sediments. Fossil fuel formation begins when organic matter is buried before it can be oxidized to carbon dioxide by microorganisms. When organic matter is buried deeply and subjected to increasing temperature under anaerobic conditions, petroleum and coal are often formed. The quantities involved in these processes are enormous. It has been estimated that the earth contains about 1016 tons of carbon in its sediments. There is increasing evidence that much of the organic material in sediments is bacterial in origin. About 90% of this material is in the form of insoluble kerogen, an organic precursor of petroleum. Recently the hopanoid bacteriohopanetetrol (figure 3.6b) was isolated from kerogen, and evidence is accumulating that kerogen arises from bacterial activity. We may owe our supply of fossil fuels largely to bacteria that serve as the final degraders of the organic material in dead organisms.Video