In seeking an answer to the question posed to this panel—Can we understand the processes of fossilization and inorganic chemistry sufficiently well to differentiate fossils from the artifacts in a sample?—the preceding examples suggest potential directions for future study. Microorganisms mediate a wide variety of natural mineralization processes. To a large extent this appears to be underpinned by the seemingly universal adaptive value of extracellular exopolymers in regulating the biology of microorganisms. The strong tendency of EPS to scavenge a wide variety of metallic cations from the surrounding environment suggests that we may improve our ability to detect biogenic signatures in rocks by searching well-characterized samples for anomalous concentrations of trace metals. In conjunction with other types of chemofossil evidence (e.g., isotopes and organic biomarker compounds), spatial distributions of trace metals that are comparable in pattern and scale to microbial cells and biofilms may provide additional evidence for biogenicity. And through an improved understanding of the varied role(s) played by trace elements in modern microbial processes, we may eventually be able to extract paleobiological information from rocks even where primary organic materials have been completely degraded and lost. The limiting factor is likely to be the survival of trace element biosignatures during diagenesis, a problem that can be addressed through detailed comparisons of modern and ancient analogs.
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