Precambrian microbe-like pseudofossils: A promising solution to the problem

Abstract

Of various problems that have hindered progress in documenting the Precambrian history of life, the difficulty in distinguishing between bona fide microbial fossils and nonbiological microscopic pseudofossils has been among the most serious. Though errors in the interpretation of putative Precambrian fossil microbes have diminished greatly over recent years, mistakes continue to be made. We suggest that such errors can be avoided by the use of a multifaceted strategy based on a specified series of biologically definitive characteristics that document the presence of interrelated biological morphology and biologically derived chemistry. To illustrate this promising approach, we use optical microscopy, confocal laser scanning microscopy, and Raman spectroscopy, together, to distinguish between authentic microbial fossils and microscopic “look-alikes,” both coccoidal and filamentous, rock-embedded in five Proterozoic and two Archean geological units: bona fide fossils of the ∼800 Ma Bitter Springs Formation of central Australia and ∼3050 Ma Farrel Quartzite of northwestern Australia; and objects we regard to be pseudofossils from the ∼770 Ma Chanda Limestone of southern India, ∼800 Ma Myrtle Springs Formation of South Australia, ∼1020 Ma Lakhanda Formation of southeastern Siberia, ∼1700 Ma Vempalle Formation of central India, and ∼2629 Ma Marra Mamba Iron Formation of northwestern Australia. The results demonstrate that no single criterion, by itself, is sufficient to establish the biological origin of such objects. Instead, as shown here, this problem appears solvable by the use of an interdisciplinary approach that combines the data and techniques of geology, biology, and chemistry.