Discovery of Naturally Etched Fission Tracks and Alpha-Recoil Tracks in Submarine Glasses: Reevaluation of a Putative Biosignature for Earth and Mars

Figure 21

Summary of complex “abiotic” microtextures found in DSDP 418A basaltic glass that have the potential to be mistaken for signs of microbial activity (i.e., microbial etchings, groovings, borings, alteration, or remains). (a–c, e, f, h, and i) are from sample DSDP-418A-75-3-[120–123] and (d, g) are from sample DSDP-418A-68-3[40–43]. (a–f) are SEM (secondary electron) images ((a–c, e, and f) are from basaltic glass “chip samples” and (d) is from a polished petrographic section) and (g–i) are transmitted light photomicrographs of polished sections taken in plane polarized light (uncrossed polars). (a) Dendritic nanogrooves on a vesicle wall (close-up image from Figure  1(b) in French and Muehlenbachs [107]) that represent frozen viscous fingers of magmatic fluid injected into the vesicle wall upon quenching of the glass. (b) Alpha-recoil track etch-tunnels (ARTETs). (c) A fission track etch-tunnel. (d) Granular palagonite ART alteration (close-up from Figure 2(b)). (e) ARTETs at the glass-palagonite interface affected by prolonged overetching and/or are “pressure solution enhanced” (from Figure 17 in this study; Figure  1 in French [139])—akin to the tunnels shown in Figures 7(e) and 21(i)—also note that this region (e) occurs along the same glass-palagonite interface that is shown in Figure 11(a) (i.e., in the vicinity of dense concentrations of other bona fide/incipient ARTETs). (f) Authigenic imogolite filaments (close-up from (e); Figure 17; Figure  1 in French [139]). (g) ARTETs at the glass-palagonite interface. (h) Palagonite fingers that have overprinted previously existing ARTETs. (i) ARTETs—most of which have been affected by prolonged overetching and/or are “pressure solution enhanced,” resulting in string-of-pearls texture and elongate wide tunnels (among other forms—see Figure 7(e)).

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