MOLECULAR FOSSILS FOR ARCHEAN BIOTA : FACT OR FICTION?

Organic matter is an important and well accepted indicator of biota, their physiologies and of environmental conditions prevailing during accumulation of sedimentary rocks. We know this because of the extensive record of Phanerozoic and Proterozoic kerogens and associated biomarkers. The record of Archean organic matter is much more fragmentary than in younger sediments and is generally corrupted by exposure to the effects of metamorphism and ionizing radiation over long timescales. Accordingly, occurrences of molecular fossils in Archean rocks are rare and their meaning subject to many uncertainties. Presently, the Pilbara Craton of Western Australia seems to be the only location where well-founded biomarker research has been conducted in rocks as old at 2700 million years. This presentation evaluates the problems associated with analysis and interpretation of Archean organic matter and identifies background knowledge, analytical techniques and sampling methods needed to extend the scope and reliability of molecular fossil studies in sediments older than about 2000 million years.