Abstract EANA2025-124

Early Earth, during the Hadean Eon (4.5-4.0 Ga), was an ocean world with sporadic volcanic landmasses. In parallel, during the Noachian period (4.1-3.7), Mars is believed to have hosted large bodies of liquid water across its surface. At the interface between oceanic crust, water, and geothermal heat, hydrothermal vent systems were likely widespread at the same time on both planets. These environments, rich in organic molecules, minerals, and energy in the form of pH gradients have been proposed as plausible cradles for life’s emergence. Within their porous, mineral-rich walls in a world governed by prebiotic chemistry, specific organic molecules today recognized as the five metabolic precursors (pyruvate, ketoglutarate, acetate, oxalacetate and succinate), could have undergone key transformations that marked the transition from geochemistry to biochemistry.

Today we see remnants of these ancient systems in the geological record. On Earth, Pilbara Craton in Western Australia offers some of the oldest evidence of such environments, while on Mars, Jezero Crater, currently explored by NASA’s Perseverance rover, presents similar potential. These rock archives, often enriched in clays and carbonates, hold chemical and morphological signals that could be either abiotic or biological in origin. Abiotic structures known as biomorphs result from purely chemical processes that can closely mimic biological structures, posing a major challenge for interpretation. In contrast, biological microfossils originate from once-living microorganisms.

Currently, there is no effective method for determining the biogenicity of such structures in samples from the early Earth. As we anticipate the return of Martian samples, developing robust tools and criteria to assess these signals is critical.

We investigated both abiotic and biological scenarios to enable direct comparison between artificial models and real geological samples. Our approach involves generating conditions relevant to early Earth and Mars through clay-carbonate matrices at high temperatures and alkaline pH, mimicking ancient hydrothermal settings. For the abiotic component, we entombed prebiotically plausible molecules within these matrices. In parallel, we simulated the biological structures by entombing Escherichia coli as a model organism in the same matrices.

The samples were analysed morphologically and chemically using epifluorescence microscopy, SEM, micro-FTIR, and GC-MS. These tools allow us to study the characteristics of both abiotic and biological systems and compare them to putative microfossils in the rock record. This comparative analysis enables us to assess the reliability of biogenicity criteria and the likelihood of misinterpreting abiotic signals.

Ultimately, our goal is to develop a robust database to aid in identifying biosignatures, or protobiosignatures, in Martian samples and better understand microfossils and biomorphs on Earth. We aim to redefine how we interpret the earliest traces of life, offering a more rigorous framework for future missions targeting the search for life in our Solar System.