Traces of archaebacteria in ancient sediments

After burial in a sediment, organic matter is altered by various diagenetic processes to insoluble, highly polymeric kerogen and a lipid fraction, composed mainly of hydrocarbons. The as yet uninvestigated potential of factor 430, a porphinoid compound, to serve as a marker for methanogenic archaebacteria is mentioned in relation to the petroporphyrins found in petroleums and sediments. The evidence for isoprenoid ethers and alkanes found in the geological record back to 3 billion years is summarized. An attempt is made to relate the findings to potential archaebacteria precursors. The CIB-C26 isoprenoid alkanes found in several facies of the oldest known sediments in the Isua district of W.Greenland are discussed with respect to the apparent metamorphic alterations of the host rock. The evidence indicates that archaebacteria have existed for at least one billion years, possibly even for more than three billion years.