[biorxiv.org] Identification of early microfossils relies on morphological and chemical criteria assumed to be unique to life, but whether abiotic microstructures can satisfy these criteria has not been rigorously tested.
Hydrothermal environments preserve microfossils but are also efficient geochemical reactors for abiotic reactions. Protocells form in hydrothermal conditions and represent a plausible abiotic analogue to early microfossils.
Here we show that protocells form from simple organic molecules in low-temperature, alkaline hydrothermal conditions in the presence of silica and produce spheres, filaments, and lenticular structures that strongly resemble the morphology of purported microfossils in Archaean silica cherts.
FTIR spectroscopy provides overlapping chemical signatures across protocells, microorganisms, and geologic microstructures. In addition, the FTIR R3/2 ratio, a chemometric index often used to discriminate domains and determine biogenicity, identifies eight different protocell systems as either bacterial, archaeal, or eukaryotic.
These data suggest that protocells preserved in ancient hydrothermal deposits can satisfy current biogenicity criteria, undermining the reliability of interpretations of the early fossil record.
As life detection is the primary objective for current space exploration endeavours, robust biogenicity protocols that account for abiotic signatures are essential.
Comparison of carbonaceous structures found in putative Archaean microfossils and morphologies of protocells formed in the context of this study. Lettering in white font over black background indicates biomorphs produced in this study, while lettering in black font over white background are published purported microfossils. (a-e) Spheroidal structures. — biorxiv.org
Protocells reproduce morphological and chemical signatures of early microfossils, biorxiv.org
Astrobiology,
