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

Table 1

ICP-MS results for U and Th concentrations in DSDP 418A basaltic glass.

Sample name	Sample grain size; # grains	Sample description	Sample weight (mg)	Th (ppm)	U (ppm)	Th/U
DSDP-418A-75-3-[120–123]-ICP–MS #1	~0.3–1.0 mm; 13	(a)	5.3	0.097	0.037	2.66
DSDP-418A-75-3-[120–123]-ICP–MS #2	~0.3–1.0 mm; 42	(a)	10.4	0.129	0.037	3.51
DSDP-418A-75-3-[120–123]-ICP–MS #3	~1.5 × 3 × 4 mm; 1	(a)	17.8	0.164	0.053	3.10
DSDP-418A-75-3-[120–123]-ICP–MS #4	~1 × 1 × 1 mm; 1	(a)	1.6	0.112	0.038	2.97
DSDP-418A-75-3-[120–123]-ICP–MS #5	~1 × 1 × 1 mm; 1	(a)	1.1	0.107	0.040	2.67
DSDP-418A-75-3-[120–123]-ICP–MS #6	~50–300 m; 266	(b)	0.9	0.132	0.042	3.16
DSDP-418A-75-3-[120–123]-ICP–MS #7	~50–300 m; 263	(b)	0.9	0.117	0.035	3.31
DSDP-418A-75-3-[120–123]-ICP–MS #8	~50–300 m; 298	(b)	1.2	0.108	0.032	3.35

For Th and U determinations (ppm), the external reproducibility is 5–10% (2 level) of the quoted abundances.
Sample descriptions:
(a) Test fractions: they comprise predominantly fresh basaltic glass, which also contains numerous small (<100 m) vesicles and their inclusions (e.g., vesicles commonly contain numerous ~1 m sized Fe-sulfide spherules) and possibly some small domains (~a few % by volume) that comprise altered (palagonitized/devitrified) zones and/or phenocryst inclusions such as clinopyroxene and plagioclase.
(b) Pristine, fresh basaltic glass, devoid of alteration, inclusions, or vesicles: the shards of glass are transparent and light tan brown (thinnest shards) to dark brown (thickest shards) in colour. Surfaces invariably show a vitreous luster and comprise curviplanar to conchoidal fractures that impart a myriad of shapes to the grains. All of these grains were found to be isotropic when viewed under petrographic microscope with crossed nicols.
values used for theoretical modelling of alpha-recoil track (Figures 10(h), 10(i), 15(c), and 15(f)) and fission track (Figures 10(g), 15(g), and 15(h)) areal densities in DSDP 418A basaltic glass in this study.