This question has biologic, chemical and geophysic elements but the question is for chemical specialists. Hence my choice to post it in "chemistry". There is a consistent idea about fossil fuels - petroleum not being biotic but "mantle derived hydrocarbons". It has most probably been discussed before but: http://www.gasresources.net/ This paper argues: So what would be the current scholar view about the origin of earth oil? Fossil / biotic or abiotic?