When studying ancient microfossils left behind by life on the early Earth, it is essential that scientists prove that the fossils are indeed biological in origin. A number of traits have been used to classify bonafide biological microfossils, including physical structures (cellular elaboration, hollow sheaths or cell walls) and the presence of kerogen.

A recent study has reaffirmed these criteria by examining inorganic filaments preserved in rocks of the Pilbara region in Western Australia. The ‘pseudofossils’ resemble kerogen and other aspects that could have been left behind by living organisms. However, the filaments a made of manganese oxide and lack characteristics like cellular elaboration, hollow sheaths, or cell walls. The pseudofossils from Australia do resemble some filamentous fossils, and highlight why robust criteria must be used to identify true microfossils from ancient organisms.

The study, “Manganese Oxides Resembling Microbial Fabrics and Their Implications for Recognizing Inorganically Preserved Microfossils,” was published in the journal Astrobiology. The work was supported by NASA Astrobiology through the Exobiology Program.