constituents of seawater of primitive Earth. The radiolysis of adenine adsorbed onto montmorillonite was studied. The most important result is that adenine is adsorbed onto montmorillonite, when it is dissolved in artificial seawater 4.0 Ga, and the clay protects adenine against gamma radiation decomposition. However, - 1 desorption of adenine from montmorillonite was possible only with 0.10 mol L of KOH. This result indicates that adenine was strongly bonded to montmorillonite. Fourier transform infrared spectroscopy showed that NH 2 group and electrostatic interactions, between negatively charged montmorillonite and positively charged adenine, are responsible for adsorption of adenine onto montmorillonite. In addition, X-ray diffractograms showed that adenine enters in the interlayer space of montmorillonite.

Baumgartner, R.J., Van Kranendonk, M.J., Pagès, A., Fiorentini, M.L., Wacey, D., Ryan, C., 2020. Accumulation of transition metals and metalloids in sulfidized stromatolites of the 3.48 billion - year - old Dresser Formation, Pilbara Craton. Precambrian Research 337, 105534.

http://www.sciencedirect.com/science/article/pii/S0301926819302591 Stromatolites of the ~3.48 billion - year - old Dresser Formation (Pilbara Craton, Western Australia) provide some of the oldest convincing evidence of life on Earth. Here, we augment previous evidence with a detailed investigation of the concentrations and distributions of various transition metals (Cr, Mn, Co, Ni, Cu, Zn, Mo, Se, Ag, Sn, Au, Hg, and Pb) and metalloids (As, Sb, and Te) in unweathered samples of strongly sulfidized stromatolites from drill cores. High - resolution elemental mapping and in situ compositional analysis of sulfides (pyrite and sphalerite) show that these sedimentary and hydrothermally sourced elements are strongly concentrated in texturally distinctive, nano-porous pyrite enriched in autochthonous organic matter, which forms the major, petrogenetically earliest component of wrinkly laminated and digitate growth fabrics within the stromatolites. Repeated cyclic alternations of various transition metals and metalloids (most importantly Ni and Zn), plus the presence of disconformities and overgrowth relationships between wrinkly stromatolite laminae, suggest that these element accumulations were primarily established by depositional processes during continuous stromatolite formation. Because transition metals and metalloids generally have strong affinities for organic matter, and can play active roles in biochemical processes, we interpret these element accumulations in the Dresser Formation stromatolites to be the result of binding to organic matter of living microbial communities and/or dead biomass, and perhaps also microbial utilization. Collectively, our results show that the precise characterization of transition metal - metalloid concentrations and distributions can unveil element enrichment patterns suggestive of biological activity, e ven in some of Earth's oldest stromatolites.

Behera, P., Mohapatra, M., Kim, J.Y., Rastogi, G., 2020. Benthic archaeal community structure and carbon metabolic profiling of heterotrophic microbial communities in brackish sediments. Science of The Total Environment 706, 135709.

http://www.sciencedirect.com/science/article/pii/S0048969719357043 Archaea Benthic play a crucial role in the biogeochemical cycles and food webs, however, their spatiotemporal distribution and environmental drivers are not well investigated in brackish sediments. The composition and abundances of benthic archaeal communities were examined from a coastal lagoon; Chilika (India) which is experiencing an intense pressure from anthropogenic and natural factors. High-throughput sequencing of 16S n Crenarchaeota rRNA genes revealed that sediment ( = 96) archaeal communities were largely composed of Euryarchaeota Thaumarchaeota Woesearchaeota Pacearchaeota (18.76%), (18.34%), (13.45%), (10.05%), and (4.21%). Archaeal taxa affiliated to methanogens, sulfate-reducers, and ammonia-oxidizers were detected suggesting that carbon, sulfur, and nitrogen cycles might be prominent in benthic sediments. Salinity, total Phragmites karka organic carbon, available nitrogen, available phosphorus, macrophyte ( ) and inter-taxa relationships between community members and with bacterial communities played steering roles in structuring Nitrosopumilus the archaeal communities. Marine sites with mesohaline-polyhaline regime were dominated by Thaumarchaeota and . In contrast, riverine sites with oligohaline regime demonstrated a higher abundance of Thermoprotei Methanomicrobia Methanobacteria . Macrophyte dominated zones were enriched in and in their Nitrosopumilus rhizosphere sediments, whereas, bulk (un-vegetated) sediments were dominated by . Spatial patterns in archaeal communities demonstrated 'distance -d ecay' patterns which were correlated with changes in physicochemical factors over geographical distances. Heterotrophic microbial communities showed much