Abstract EANA2026-62

The continued search for life on Mars lets humans push the boundaries of our understanding of the limits of life. We use the Earth as an analogue to better grasp our place in the Universe and gain deeper insight into biosignature preservation in ancient environments. In 2024, the Perseverance rover detected mm-scale reaction fronts, termed “leopard spots”, within mudstones in Neretva Vallis, the river channel feeding Jezero crater. These features bear morphological and textural similarities to reduction spots found on Earth. The associated minerals, vivianite and greigite, are known to form in low-temperature water due to iron and sulfur reduction reactions. This similarity in formation process points to a possible biological origin for these features and detailed study of terrestrial reduction spots could help to determine the formational processes of the Martian “leopard spots”, including whether they are biological in origin. On Earth, reduction spots are abundant, macroscopic (mm-cm in diameter) geological features in red-bed sediments. They are identified by the absence of ferric oxide, resulting in a bleached region often surrounding a dark core with reduction-sensitive elements such as V or U. These features have been found in vastly different geological eras, from the Cretaceous period (~100 Mya) to the Proterozoic (~1 Gya), demonstrating their ubiquity over time. Their proposed origin is microbial, making them extremely important to study, especially since similar features (“leopard spots”) are found on Mars. Samples containing reduction spots have been obtained from two localities: 1) Stoer, Scotland, a Mesoproterozoic red bed; and 2) Dingwall, Scotland, where sandstones host reduction spots, specifically uraniferous hydrocarbon nodules.

Current characterization by SEM-EDS is being carried out on thin sections from each locality, including samples containing the core, halo, and host rock in order to determine their elemental compositions. µXCT on samples, from both locality, has also been performed to determine differences in X-ray attenuation to study three-dimensional microstructure and phase distribution in more detail. Ongoing analyses include optical microscopy,  Raman spectroscopy, FTIR spectroscopy, stable isotopes (specifically organic C, N, and S, and potentially metals), µXRF, pyrolysis-GC-MS, and loss on ignition values. This research presents a critical example of mineralogy that can be studied on both Earth and Mars and helps to identify biosignatures on Mars. Identifying a biological process for the formation of these reduction spots would have fundamental importance for justifying a Sample Return Mission.