A suite of green and carbonaceous black chert interbedded with submarine volcanic rocks from several stratigraphic levels of the Onverwacht Group of the Barberton greenstone belt, from the top of the ~3.48 Ga Komati Formation to the base of the ~3.26 Ga Fig Tree Group have been investigated petrologically and geochemically. Provenance analysis was undertaken using immobile trace element ratios in comparison with potential source rocks from the Barberton granitoid-greenstone terrain. Raman spectroscopy was used to better characterise carbonaceous matter in different chert varieties. Green cherts consist predominantly of silicified mafic to ultramafic volcaniclastic material. Black cherts contain volcaniclastic and/or epiclastic material of ultramafic to felsic composition, admixed with carbonaceous matter. In several cases, the clastic sediment is compositionally distinct to the volcanic substrate, suggesting that it represents volcanic material of relatively distal sources. Soon after settling out of the water column, lithification due to silicification took place. It gave rise to excellent textural preservation, but strongly modified the mineralogical and chemical composition of the seafloor sediments. Zircon, Cr-spinel and rare phosphate minerals are the only primary minerals remaining, while clastic grains have been largely replaced by a fine intergrowth of microquartz, Ti-oxide and K-bearing mica. Chemical changes are similar to those reported previously for silicification of volcanic rocks from the Barberton belt and are consistent with low-temperature hydrothermal processes common to the Palaeoarchaean seafloor environment.

We constrained the origin and genetic environment of modern iron ooids (sand-sized grains with a core and external cortex of concentric laminae) providing new tools for the interpretation of their fossil counterparts as well as the analogous particles discovered on Mars. Here, we report an exceptional, unique finding of a still active deposit of submillimetric iron ooids, under formation at the seabed at a depth of 80 m over an area characterized by intense hydrothermal activity off Panarea, a volcanic island north of Sicily (Italy). An integrated analysis, carried out by X-ray Powder Diffraction, Environmental Scanning Electron Microscopy, X-ray Fluorescence and Raman spectroscopy reveals that Panarea ooids are deposited at the seafloor as concentric laminae of primary goethite around existing nuclei. The process is rapid, and driven by hydrothermal fluids as iron source. A sub-spherical, laminated structure resulted from constant agitation and by degassing of CO₂-dominated fluids through seafloor sediments. Our investigations point the hydrothermal processes as responsible for the generation of the Panarea ooids, which are neither diagenetic nor reworked. The presence of ooids at the seawater-sediments interface, in fact, highlights how their development and growth is still ongoing. The proposed results show a new process responsible for ooids formation and gain a new insight into the genesis of iron ooids deposits that are distributed at global scale in both modern and past sediments.

The exclusive presence of β-D-ribofuranose in nucleic acids is still a conundrum in prebiotic chemistry, given that pyranose species are substantially more stable at equilibrium. However, a precise characterisation of the relative furanose/pyranose fraction at temperatures higher than about 50 °C is still lacking. Here, we employ a combination of NMR measurements and statistical mechanics modelling to predict a population inversion between furanose and pyranose at equilibrium at high temperatures. More importantly, we show that a steady temperature gradient may steer an open isomerisation network into a non-equilibrium steady state where furanose is boosted beyond the limits set by equilibrium thermodynamics. Moreover, we demonstrate that nonequilibrium selection of furanose is maximum at optimal dissipation, as gauged by the temperature gradient and energy barriers for isomerisation. The predicted optimum is compatible with temperature drops found in hydrothermal vents associated with extremely fresh lava flows on the seafloor.

Two rover missions to Mars aim to detect biomolecules as a sign of extinct or extant life with, among other instruments, Raman spectrometers. However, there are many unknowns about the stability of Raman-detectable biomolecules in the martian environment, clouding the interpretation of the results. To quantify Raman-detectable biomolecule stability, we exposed seven biomolecules for 469 days to a simulated martian environment outside the International Space Station. Ultraviolet radiation (UVR) strongly changed the Raman spectra signals, but only minor change was observed when samples were shielded from UVR. These findings provide support for Mars mission operations searching for biosignatures in the subsurface. This experiment demonstrates the detectability of biomolecules by Raman spectroscopy in Mars regolith analogs after space exposure and lays the groundwork for a consolidated space-proven database of spectroscopy biosignatures in targeted environments.