New insights into molecular fossils: The fate of terpenoids and the origin of gem-dialkylalkanes in the geological environment

Molecular organic geochemists rely heavily upon the accurate identification (structure and absolute stereochemistry) of organic compounds found in sedimentary rocks and petroleum samples. This information not only allows direct connections to be made between natural products found in living organisms and compounds found in the geological record, it also allows inferences to be made about the diagenetic and catagenetic reactions that connect the two. However, the unequivocal identification of molecular fossils is not easily achieved.; This dissertation explores the identification of molecular fossils through laboratory synthesis and through detailed analysis of their geological and environmental occurrences. In particular, geomimetic synthesis---the modification of well defined natural products using chemical treatments intended to simulate natural processes in the sedimentary environment---provides critical insights into the identity and origin of molecular fossils.; Using these strategies, the geological fate of terpenoid natural products specific to land plants and the origin of a new class of molecular fossils, gem-dialkylalkanes, is investigated. Ionic processes sometimes involving complex skeletal rearrangements are shown to be important in controlling the assemblage of geological terpenoids found in rock and petroleum samples. Gem-dialkylalkanes have yet to be linked to particular living organisms, however they are found in Precambrian to Recent samples in contexts consistent with a chemoautotrophic source organism living at redox boundaries in sediments. Their structures are consistent with a bacterial polyketide origin.