Abstract EANA2026-12

Mars is a key target in the search for extraterrestrial life in the solar system because of the evidence for habitable conditions in the planet’s geological past. As the period of habitable surface conditions ended billions of years ago, any evidence of Martian life is likely to be fossilised. Many ancient putative terrestrial microfossils have been characterised as biogenic based solely on their morphology, and lack further lines of evidence for their biogenicity such as chemical and isotopic biosignatures. Therefore, it can be anticipated that observations of fossilised morphologies may be a critical factor to recognise the existence of past Martian life. Previous studies of contentious terrestrial microfossils demonstrate the pitfalls associated with the evaluation of biogenicity based on morphology alone. Primarily, abiotic structures that resemble biological materials (biomorphs) may be mistaken for microfossils, and so the two must be carefully distinguished when evaluating a potentially biogenic microstructure. Iron-mineralised chemical gardens are an important source of abiotic biomorphs because they resemble ferruginous filamentous microfossils, and could plausibly have formed in early Mars and ancient Earth environments. However, the preservation potential of iron-mineralised chemical gardens has not been established.

We subjected iron-mineralised chemical garden material to artificial maturation experiments under elevated temperatures and pressures. SEM and XRD analyses of the unheated and artificially matured chemical garden filaments demonstrated their high preservation potential relative to the biological materials that they mimic. We found that diagenetic mineralogical transformations were also relatively inhibited, likely due to the close association of silica with the filaments. Overall, these results compel careful scrutiny of putative filamentous microfossils, especially in matured rocks. This is particularly pertinent for Mars exploration missions that may need to evaluate the biogenicity of microstructures found in ancient rocks observed by in situ or returned sample analysis in the future.