These processes have been considered as a source of prebiotic organic matter. However, some lipids may also be formed in-situ via abiotic Fischer-Tropsch-type (FTT) reactions. Lipid biomarkers are commonly used for tracking life through Earth’s history and are also gaining in importance in the search for extraterrestrial life. Formations observed in the dried lake beds of Gale Crater bear a statistically significant, nearly identical resemblance to eukaryotic fossils from the Ediacaran and Cambrian era on Earth but no statistical morphological similarity to pseudo-fossils. In addition, a quantitative statistical morphological analysis was performed comparing these Martian specimens with analog fossils and two pseudo-fossils from Earth. To assist in determining if these Martian specimens are abiogenic geological formations with a superficial resemblance to fossils, a terrestrial-pseudo-fossil image search was conducted employing all relevant key words, and no formations on Earth similar to those on Mars were found, other than genuine fossils. Formations resembling the fossilized remains of "Namacalathus," "Lophophorates," "Kimberella" and ichnofossils of burrowing "tube worms" (priapulids) were found. A detailed search of NASA's Gale Crater image-data-base was conducted with a focus on specific areas and days (sols) in which fossilized impressions of what may be metazoans have been observed. Formations resembling fossilized stromatolites, algae, acritarchs and metazoans have been previously observed and reported in peer reviewed scientific periodicals. The dried lake beds of Gale Crater have been identified by NASA's rover crews as a likely source of fossils. For example, Häntzschel (1975) has identified precambrian pseudofossils formed by curling and desiccation that resemble burrowing tube worm/ priapulid ichnofossils ( Figure 5), whereas Pettijohn (1957) identified a tapering conical formation as a likely pseudo-fossil ( Figure 5). 2011 Pettijohn 1957 Pickerill and Harris 1979 Wacey et al. 2011 Gutstad 1979 Häntzschel 1975 Marshall et al. However, the presence of water would also contribute to erosion and weathering, thereby creating shapes that might superficially resemble fossils, including, as is well known on Earth, concretions that are sinuous, oval or round (De Gregorio et al. 2020a,b) were all observed in the dried lake beds of Gale Crater which may have periodically filled with water (Frydenvang et al., 2017 Hausrath et al., 2018 Rampe et al. It is noteworthy that colleagues (2014, 2015) have identified Gale Crater as a likely source of fossils and that the fossilized formations resembling Ediacaran and metazoan fossils (Baucon et al. Biogenic material could be preserved within an ancient hydrothermal system either through gravitational influx of microbial material from the surface or transport of carbonaceous matter from a deeper sediment. Although it is possible that FTT material could mature into an abiotic kerogen-like material with similar characteristics, it is more likely that the Apex and Strelley Pool carbonaceous matter formed from biological processes. FTT samples were chemically distinct, containing abundant carboxyl functional groups and lacking polyaromatic domains. Electron energy-loss near-edge structure spectroscopy (ELNES) and X-ray absorption near-edge structure spectroscopy (XANES) indicate Apex and Strelley carbonaceous matter contains a complex microstructure with abundant aromatic domains and oxygenated organic functional groups similar to that observed in Gunflint kerogen. In situ scanning-transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM) reveal the presence of ∼100 nm carbonaceous films along quartz grain boundaries in the chert samples, which may be separated from the quartz grains in ultramicrotomed sections.
Carbon-rich black chert dike samples were obtained from the Apex and Strelley Pool localities for comparison with kerogen from the 1.9 Ga Gunflint Formation and laboratory-derived FTT carbonaceous matter. Controversial microfossils from the 3.458–3.465 Ga Apex Basalt and stromatolites from the 3.350–3.458 Ga Strelley Pool Chert are associated with hydrothermal activity, leading to the suggestion that the carbonaceous matter comprising these features is derived from abiotic FTT synthesis rather than biological processes.
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