Comment by pncnmnp
Some interesting stuff from the Nature paper> The Perseverance rover has explored and sampled igneous and sedimentary rocks within Jezero Crater to characterize early Martian geological processes and habitability and search for potential biosignatures ..... the organic-carbon-bearing mudstones in the Bright Angel formation contain submillimetre-scale nodules and millimetre-scale reaction fronts enriched in ferrous iron phosphate and sulfide minerals, likely vivianite and greigite, respectively.
> Organic matter was detected in the Bright Angel area mudstone targets Cheyava Falls, Walhalla Glades and Apollo Temple by the SHERLOC instrument ..... A striking feature observed in the Cheyava Falls target (and the corresponding Sapphire Canyon core sample), is distinct spots (informally referred to as ‘leopard spots’ by the Mars 2020 Science Team) that have circular to crenulated dark-toned rims and lighter-toned cores
> PIXL XRF analyses of reaction front rims reveal they are enriched in Fe, P and Zn relative to the mudstone they occur in ..... In the reaction front cores, a phase enriched in S-, Fe-, Ni- and Zn was detected
> Given the potential challenges to the null hypothesis, we consider here an alternative biological pathway for the formation of authigenic nodules and reaction fronts. On Earth, vivianite nodules are known to form in fresh water ..... and marine ..... settings as a by-product of low-temperature microbially mediated Fe-reduction reactions.
> In summary, our analysis leads us to conclude that the Bright Angel formation contains textures, chemical and mineral characteristics, and organic signatures that warrant consideration as ‘potential biosignatures’ that is, “a feature that is consistent with biological processes and that, when encountered, challenges the researcher to attribute it either to inanimate or to biological processes, compelling them to gather more data before reaching a conclusion as to the presence or absence of life .....
I had to look up PIXL XRF from this paper - https://arxiv.org/pdf/2402.01544 - it is:
> The Planetary Instrument for X-ray Lithochemistry (PIXL) is an X-ray fluorescence (XRF) spectrometer mounted on the arm of the National Aeronautics and Space Administration’s (NASA) Mars 2020 Perseverance rover (Allwood et al., 2020; Allwood et al., 2021). PIXL delivers a sub-millimeter focused, raster scannable X-ray beam, capable of determining the fine-scale distribution of elements in martian rock and regolith targets. PIXL was conceived following the work by Allwood et al. (2009) that demonstrated how micro-XRF elemental mapping could reveal the fine-textured chemistry of layered rock structures of ~3,450-million-year-old Archean stromatolitic fossils. Their work not only pushed back the accepted earliest possible window for the beginning of life on Earth, but also demonstrated that significant science return might be possible through XRF mapping. PIXL was proposed, selected, and developed to carry out petrologic exploration that provide the paleoenvironmental context required in the search for biosignatures on Mars, analogous to Allwood et al.’s earlier work.