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

Figure 20

Three examples of “bimodal” distributions of microscopic corrosion features in geological samples—in each case, most likely related to the bimodal “size versus population (i.e., areal density)” distribution of fission tracks versus alpha-recoil tracks. (a) Phase contrast photomicrograph showing one large fission track etch-pit surrounded by a multitude of much smaller alpha-recoil track etch-pits on the experimentally etched cleavage surface of mica (from Huang and Walker [130]—no scale bar available). (b) SEM (secondary electron) image of one large fission track etch-tunnel surrounded by several much smaller alpha-recoil track etch-tunnels in DSDP-418A-75-3-[120–123] basaltic glass (close-up from Figure 11(a)). (c) SEM (BSE) image of several large palagonite granules surrounded by a multitude of much smaller palagonite granules (from Plate 1 in Furnes et al. [50] of sample 148–896A-11R-1, 111–113 cm—from the Costa Rica Rift). The original interpretation is that both varieties of palagonite granules are biogenic in origin (i.e., “produced by the etching of microbes”: Furnes et al. [50]). However, in light of our newly proposed “abiotic” paradigm for interpreting corrosion microtextures in submarine glasses (Figure 19), we reinterpret the bimodal distribution of palagonite granules in (c) to have more likely arisen due to the concomitant, preferential palagonitization of several large fission tracks (granular palagonite “FT” alteration—labelled as “g.p. ‘FT’ alt.?”) and a multitude of tiny alpha-recoil tracks (granular palagonite “ART” alteration—labelled as “g.p. ‘ART’ alt.?”), during infiltration of seawater.

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