The link between biomineralization and fossilization of bacteria: Insights from field and experimental studies

Fossil biominerals and fossils of microorganisms in ancient rocks contain important biogeochemical signals. Decoding this record may reveal crucial information about the evolution of life on Earth and terrestrial paleoenvironments. However, the identification of traces of life especially in very old rocks is extremely challenging because the morphological and chemical signatures of biominerals and microfossils are subtle, of microscopic size and inevitably altered with aging. In this review, we stress on the fact that biomineralization is often the first step of fossilization and produces particular chemical, structural and morphological features that can be preserved in fossil biominerals or microfossils, with a special focus on Fe-biomineralization. The taphonomic processes affecting biominerals and microfossils and altering their morphology and/or chemical composition over time are then discussed in light of experimental fossilization simulations and field sample analyses. We suggest that taxonomic biases observed in the fossil record may be related to differential abilities of species to trigger biomineralization. This calls for studies of the effective biomineralizing activity and fossilization potential of each species present in highly diverse natural microbial communities. Finally, recent analytical developments leave little doubt that very substantial progress in the study of biomineralization processes and ancient biostructures will be achieved in the near future.