The characterisation of the organic material in Ontong Java Plateau tuff as an analogue for the search for fossil life on Earth and Mars

Abstract

Distinctive microtubules in glassy volcaniclastic shards can be observed within tuff from the Ontong Java Plateau (OJP_13), which have been suggested to be putative ichnofossils and could serve as analogues for the types of samples that may be encountered on Mars. Argon cluster ion beam etching and ultraviolet/ozone cleaning were evaluated as methods for decontaminating geological samples prior to analysis. Xray photoelectron spectroscopy (XPS) and gas chromatography/mass spectrometry (GC/MS) were conducted on a sample of OJP_13 tuff. The comparative efficiency of conventional pyrolysis gas chromatography/mass spectrometry (py-GC/MS) and pyGC/MS with tetramethylammonium hydroxide, also called thermal hydrolysis and methylation-GC/MS (THM-GC/MS) to detect and identify the organic material in OJP_13 samples was assessed. Measurements of the carbon and nitrogen chemistry in OJP_13 were made using XPS, and this was compared to the data that was obtained by THMGC/MS. The XPS analysis demonstrated that organic material was concentrated in the perimeter of the glass shards. Time of flight secondary ion mass spectrometry imaging demonstrated that the organic material was associated with micro-fractures in the surrounding matrix and in the devitrified glass textures in the perimeter of the shard. The analysis was conducted on OJP samples from different strata and basalts from other regions, which did not contain the tubular features. This demonstrated that nitrogenous organic material was not specific to the OJP_13 sample that contained the microtubules but appeared to occur throughout the OJP tuff. THM-GC/MS and XPS analyses were conducted on artificially decomposed plant biopolymers. The composition of the organic material in OJP tuff was similar to that of decomposed chitin. It was proposed that a component of the organic material in OJP could be the remnants of a chitinous organism. The presence of chitin implied that fungi could have produced the microtubular textures. Additionally, during this investigation, it was observed that carbonaceous films on the surfaces of minerals are thermally stable and are therefore undetectable by py-GC/MS. These films may be responsible for the non-biological synthesis of complex organic compounds