Table 3.

Supposed mechanisms of preservation/degradation of biomarkers due to the interactions with minerals under mid-UV irradiation.

Mineral	Biomarker	Radiation	Protection/Preservation	Catalysis/Degradation	Supposed Mechanism
Quartz	Adenine	200–300 nm	Under N2	Under O2	Photo-oxidation by O2 (Oro & Holzer 1979).
Quartz	Glycine	200–300 nm	Under N2	Under O2	Photo-oxidation by O2 (Oro & Holzer 1979).
Quartz	Naphthalene	200–300 nm	x	Under O2/N2	Photo-oxidation by O2 (Oro & Holzer 1979).
Murchison meteorite	Indigenous organics	200–300 nm	x	Under O2/N2	Photo-oxidation by O2 (Oro & Holzer 1979).
Palagonite	Glycine	210–710 nm	x	Under Martian-like atmosphere	Photolysis into CH4, C2H6, C2H4 (Stoker & Bullock 1997).
JSC Mars-1 and Salten Skov Martian soil analogs	Indigenous amino acids	190–325 nm	x	Under Martian-like atmosphere	Decomposition induced by radicals produced by photolysis of water condensed onto minerals (Garry et al. 2006).
JSC Mars-1 Martian soil analog	Carboxylic acids α-aminoisobutyric acid (AIB), mellitic acid, phthalic acid, and trimesic acid	Solar radiation > 200 nm	x	Under low Earth orbit conditions	Decomposition induced by radicals/oxidants produced by TiO2–photocatalysis (Stalport et al. 2010).
I-MAR Martian regolith simulant	Amino acids L-Alanine, L-valine, L-aspartic acid, L-glutamic acid, and glycine	210–900 nm	x	Under Martian-like atmosphere	Photolytic oxidation up to UV penetration depth, then decomposition induced by radicals formed from condensed atmospheric water vapor diffused into the regolith (Johnson & Pratt 2011).
Aqueous suspensions of anatase, goethite, and hematite	Carboxylic, hydroxycarboxylic, and aminocarboxylic acids, carboxylated aromatics, amino acids and peptides	355 nm	x	Under N2	Decarboxylation initiated by charge transfer from the metal oxide to the adsorbate. Specifically, anatase, goethite, and hematite feature a similar photocatalytic activity for aromatic, carboxylic, and hydroxycarboxylic acids, while for α-amino acids and peptides hematite has reduced activity (Shkrob et al. 2010).
Aqueous suspensions of anatase, goethite, and hematite	Nucleic acid components	355 nm	Only for double-stranded oligoribonucleotides and DNA	Under N2	Oxidation of purine nucleotides leads to formation of purine radical cations and sugar-phosphate radicals. In the case of pyrimidine nucleotides other than thymine only the sugar-phosphate moiety undergoes oxidation, while deprotonation from the methyl group of the base occurs for thymine derivatives. Single-stranded (ss) oligoribonucleotides and wild-type ss RNA are oxidized at purine sites, while double-stranded (ds) oligoribonucleotides and DNA show high stability against oxidation (Shkrob et al. 2011).
Aqueous suspensions of montmorillonite and kaolinite	DNA	266 nm	Under terrestrial ambient conditions	x	Photoprotection due to specific molecule-mineral interactions; specifically, a change in DNA configuration from B to A when adsorbed on the mineral surface, which is more compact and its binding to the surface sites may take place through electrostatic and/or hydrogen bonds likely stabilizing the molecule (Scappini et al. 2004).
Aqueous suspensions of montmorillonite	RNA molecule ADHR1	254 nm	Under terrestrial ambient conditions	x	Photoprotection due to specific molecule-mineral interactions (Biondi et al. 2007).
Nontronite	Glycine and adenine	190–400 nm	Under N2	x	Photoprotection is not only due to mechanical shielding, but also stabilizing molecule-mineral interactions, such as electrostatic interactions of the molecules in the interlayers and/ or on the edges of nontronite allowing a more efficient energy dissipation and/or easier recombination for the fragments of the photo-dissociated molecules (Poch et al. 2015).
Nontronite	Urea	190–400 nm	x	Under N2	Catalysis in urea photo-oxidation and decomposition, maybe due to chelation with Fe3+ ions (Poch et al. 2015).
Smectites montmorillonite, nontronite and saponite	25 Amino acids	200–400 nm	Under Martian-like conditions	x	Photoprotection by mechanical shielding effect (dos Santos et al. 2016).
Sulfates gypsum and jarosite	25 Amino acids	200–400 nm	Under Martian-like conditions	x	Photoprotection due to low UV absorbance of sulfates or entrapment of amino acids upon recrystallization of partially dissolved sulfate (dos Santos et al. 2016).
Augite, enstatite, hematite and basaltic lava	25 Amino acids	200–400 nm	x	Under Martian-like conditions	Photocatalytic activity due to iron(II) reactions (dos Santos et al. 2016).
Calcite, calcium sulphate, kaolinite, clay-bearing Atacama desert soil + 0.6% NaClO4	Purine, pyrimidine and uracil	200–400 nm	Under Martian-like conditions	x	Photoprotection mechanism not specified (Ertem et al. 2017).
Ferric oxide + 0.6% NaClO4	Purine, pyrimidine and uracil	200–400 nm	x	Under Martian-like conditions	Complete decomposition before UV irradiation (Ertem et al. 2017).
Magnesium oxide and forsterite	Adenine, uracil, cytosine, and hypoxanthine	185–2000 nm	x	Under vacuum	Catalysis likely due to a proximity effect (Fornaro et al. 2013).
Lizardite, antigorite and apatite	AMP and UMP	200–930 nm	Under Martian-like conditions	x	Various photoprotection mechanisms: mechanical shielding/stabilizing molecule-mineral interactions for lizardite and antigorite, photo-luminescence for apatite (Fornaro et al. 2018).
Labradorite, natrolite, hematite, forsterite	AMP and UMP	200–930 nm	x	Under Martian-like conditions	Remarkable catalytic activity of labradorite and natrolite, likely due to photo-ionization phenomena that may occur inside the mineral matrix promoting redox processes. For hematite and forsterite the catalytic activity is not so high, maybe due to the opacity of iron to UV radiation (Fornaro et al. 2018).