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

Figure 10

Petrographic, SEM, and theoretical modelling study of “granular palagonite ART alteration” microtexture in DSDP 418A basaltic glass. (a–c) Thin section photomicrographs (in plane polarized light) of samples DSDP-418A-68-3[40–43] (a, b) and DSDP-418A-75-3[120–123] (c), highlighting “granular palagonite ART alteration.” (d–f) Close-up SEM (BSE) images from (a, b). (g–i) Theoretical plots of model fission track (g) and alpha-recoil track (h, i) areal distributions in DSDP 418A basaltic glass (calculated using (1) and (2); fission tracks are shown in green (g) and alpha-recoil tracks in pink (h, i)). The model track distributions in (g–i) are shown at approximately the same scale as the SEM images in (d–f), respectively—see green and pink arrows. Note that fission tracks are quite sparse (g), but alpha-recoil tracks are quite abundant and correlate very well with the observed pattern of development and areal distribution of ~0.3–1.0 μm palagonite “granules” (i.e., compare (h) and (e), and (i) and (f)), thus indicating that, during corrosion of basaltic glass by seawater, granular palagonite microtextures develop through selective palagonitization of alpha-recoil tracks (and not microbial activity). To emphasize this idea, several hypothetical, previously existing alpha-recoil tracks (120 nm pink dots) are plotted in (f), which would have acted as ideal “point sources” of radiation damage amenable to preferential corrosion/palagonitization. ART: alpha-recoil track; cf: corrosion front; f₁: early fractures associated with palagonite; FG: fresh basaltic glass; GP: granular palagonite ART alteration; P: palagonite; plg: plagioclase.