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

Figure 12

High resolution SEM (secondary electron) images of alpha-recoil track etch-tunnels (ARTETs) at the glass-palagonite interface (as observed on freshly fractured surfaces of basaltic glass “chip samples” from DSDP-418A-75-3[120–123]). (a–c) Representative close-up images of typical ARTETs found at the glass-palagonite interface. Note the meandering, branching nature of the etch-tunnels and the occurrence of FM within them, and note that tunnel diameters are about the same size as a typical alpha-recoil track (~120 nm pink dots labelled “ART”). Other features include “pockmarks” that represent new side-tunnels (SARTETs), and flare-out voids (interpreted as etch-tunnelling of locally dense regions of ARTs or as ARTETs affected by prolonged “overetching” ± pressure solution). (d) Overview image, showing a typical region of the glass-palagonite interface where abundant ARTETs occur, which are being encroached upon and overprinted by palagonite. (e) Overview of a region where numerous ARTETs, FVs, and SARTETs occur. (f) A region where an ARTET forms an etched-out “loop.” (g) Close-up from (e), highlighting abundant FM lining tunnel walls and draping/bridging across tunnel void spaces. (h) Close-up from (g). For comparison, several hypothetical imogolite filaments are drawn to scale (in blue) (i.e., 20 Å wide, the exact thickness of a single strand of imogolite), some of which also depict the 20 Å thick coating of iridium (magenta). Note the identical thickness of these hypothetical, iridium-coated imogolite filaments and the real nanofilaments imaged by SEM. ART: alpha-recoil track; ARTETs: alpha-recoil track etch-tunnels; Au: granules of gold sputtering; FG: fresh basaltic glass; FM: filamentous material; FV: flare-out voids; Im: imogolite; P: palagonite; SARTETs:“starting” alpha-recoil track etch-tunnels.