Characterization and critical testing of potential microfossils from the early Earth: the Apex ‘microfossil debate’ and its lessons for Mars sample return

Abstract

The importance of the search for life within the universe underpins many of the objectives of ESA and NASA. Fundamental to this objective is the recognition and understanding of the early fossil record on planet Earth. The history of study of ‘microfossils’ from the 3465 Ma Apex cherts of the Warrawoona Group in Western Australia is reviewed, as are the criteria put forward to test for for biogenicity of early microfossils. We propose that the null hypothesis of an abiotic or prebiotic origin of ancient microscopical artefacts is sustained until mutually supporting, contextural morphological and geochemical evidence for a biological origin is presented and an abiotic origin is falsified.