Search

In this issue of I American Mineralogist i , [2] propose that a mineral paragenetic mode can be defined as "a natural process by which a collection of atoms in solid and/or fluid form are reconfigured into one or more new solid forms." Mineral evolution research ([3]), to some extent, has enriched mineral crystal chemistry. Mineral paragenetic association is the product of mineral evolution to an advanced stage, in which one mineral symbiotic assemblage may correspond to one or more natural processes. [Extracted from the article]

Highlights: [•] Semiconducting mineral photocatalysis to evaluate origin and evolution of life. [•] New model on the use of solar energy by non-phototrophic microorganisms. [•] New insights on energy yielding pathway for life on early Earth. [Copyright &y& Elsevier]

Based on the most active hydrosphere on the earth, the interplay between adjacent semiconducting minerals and electrochemically active microorganisms was scientifically researched in the marine euphotic zone of the Yellow Sea, China. Fe and Ti were found in suspended minerals by ICP-MS and EDS, probing the element composition of suspended minerals from macro to micro. Moreover, SR-XRD and Raman indicated that semiconducting minerals of iron and titanium metal oxide in situ such as anatase, rutile, brookite, and goethite consisted in suspended minerals, notably, which retained prominent photo-response property and distinct photoelectric catalytic potential under visible light. 16S rRNA gene systematically emerged that electrochemically active microorganisms, such as Pseudomonas and Paraclostridium, were pivotal in the solution and preponderant on the electrode respectively after a period of cultivation. Whereupon a dual-chamber reactor was established to probe into the mechanism of redox reaction and electron transfer process between microorganisms and suspended minerals. Importantly, compared with a graphite electrode, the maximum power density of the reaction was 2.78 times with the increase of suspended minerals as the electron acceptor under dark conditions, as well as 236.53% promotion with visible light. Experiments gave an index that semiconducting minerals could interact with electroactive microorganisms, effectively promoting the process of extracellular electron transfer in the euphotic zone, which will make a foundation for further research on electron energy transfer based on the interactions of semiconducting minerals and electrochemically active microorganisms, as well as the regulation mechanism of elements cycling. [ABSTRACT FROM AUTHOR]

• Primary Mn, Mo, Ce and Cr minerals evolved periodically after the GOE. • The evolutionary dynamics of high-valent minerals followed Mn>Ce>Mo>Cr. • All minerals kept continuous deposition and active evolution from 1.8 to 0.8 Ga. • There are two depositional discontinuities around the GOE and the NOE. Understanding the co-evolution of redox-sensitive minerals is crucial for unraveling Earth's oxygenation history. In this study, we used a global-scale mineralogical dataset encompassing 12,141 samples of both the primary and secondary minerals containing manganese (Mn), molybdenum (Mo), chromium (Cr) and cerium (Ce), and 18,777 samples of primary phosphorus (P) and carbon (C) minerals. By developing mathematical models of evolutionary dynamics, we quantified the time lag between changes in the atmospheric oxygen level (p O 2) and the corresponding response in the evolution of these minerals. The analysis revealed that the evolutionary time lag sequence of high-valent Mn, Ce, Mo and Cr minerals after 2.4 Ga, aligns with the thermodynamic sequence of oxidation reactions, with Mn and Ce minerals displaying the most rapid dynamic response, followed by Mo and Cr minerals (denoted as MnIV>CeIV>MoVI>CrVI). All minerals maintained active and continuous evolution throughout the period of orogenic quiescence from 1.8 to 0.8 Ga, but have two depositional discontinuities during the Great Oxidation Event (the GOE) and the Neoproterozoic Oxidation Event (the NOE) (C, P minerals had a depositional slowdown at around the NOE). The collective missing of mineralogical records pointed to the rapid evolution of the Earth's internal and external environment, and is possibly caused by a sharp decrease in material input (such as the tectono-magmatic lull or slowdown) or strong secondary alterations at around the GOE and the NOE. The quantitative analysis on the evolutionary dynamics of redox-sensitive minerals may contribute to refining proxies that constrain the evolving redox state of deep-time Earth. [ABSTRACT FROM AUTHOR]

The interplay between electrochemically active microorganisms (EAMs) and adjacent minerals universally occurs in natural environments, in which soil is an extremely typical and active one. We stimulated the extracellular electron transfer (EET) process between the bacterial community and birnessite in red soil (collected from Hainan, China) by constructing a microbial fuel cell equipped with synthetic birnessite cathode. Compared to graphite-cathode, the cell voltage of birnessite-cathode was increased by 22% when loading a 1000 Ω-resistance, indicating the EET between microbes and birnessite. Eleven genera of EAMs in red soil were confirmed through 16S rRNA analysis. Neither palpable novel mineral formation nor change of birnessite crystallinity was observed after reaction by Raman and SEM. As oxygen pumped into cathode chamber was the terminal electron acceptor, birnessite principally performed as an intermediate of holistic electron transfer process to favor the cathodic oxygen reduction. [ABSTRACT FROM AUTHOR]

• Reveal the microorganism-mineral electron transfer in the euphotic zone. • Extracellular electron transfer from P. aeruginosa PAO1 to semiconducting anatase. • Anatase with photoelectric activity promotes extracellular electron transfer. • Both direct and indirect electron transfer appear between anatase and PAO1. • Pyocyanin and pili of PAO1 dominate extracellular electron transfer process. Focusing the marine euphotic zone, which is the pivotal region for interaction of solar light-mineral-microorganism and the elements cycle, we have conducted the research on the mechanism of semiconducting minerals promoting extracellular electron transfer with microorganisms in depth. Therein, anatase which is one of the most representative semiconducting minerals in marine euphotic zone was selected. The mineralogical characterization of anatase was identified by ESEM, AFM, EDS, Raman, XRD, and its semiconducting characteristics was determined by UV–Vis and Mott-Schottky plots. Determined by the electrochemical measurement of I-t curves, the photocurrent density of anatase was more prominent than dark current density. Pseudomonas aeruginosa PAO1 was widely distributed in the euphotic zone, and its mutants of operons deficient in biosynthesis pyocyanin (Δ phz1 Δ phz2) and pili deficient (Δ pilA) were employed in this study. I-t curves indicated that both direct and indirect extracellular electron transfer processes occurred between anatase and PAO1. The indirect electron transfer depending on pyocyanin secreted by PAO1 was the main electron transfer mode. This work demonstrated the light-driven extracellular electron transfer and further revealed the photo-catalyzed mechanisms between anatase and PAO1 in marine euphotic zone. [ABSTRACT FROM AUTHOR]

The Danxia landform is representative of the Cretaceous continental red sediment. The careful identification and potential environmental effects of minerals in Danxia red beds have yet to be clearly reported. In this work, reddish sandstone samples were collected from Lang Mountain Danxia landform in Xinning, Hunan province, China, and their mineral phases, element distribution, microstructure, and the spatial relationship of different minerals were investigated using polarizing optical microscope, environmental scanning electron microscopy, energy-dispersive X-ray analysis, electron probe microanalysis, micro-Raman spectra, micro- X-ray diffraction, X-ray fluorescence spectroscopy, and high-resolution transmission electron microscopy. The results revealed that iron oxide (mainly hematite) and titanium oxide (mainly anatase) were the dominant minerals in Danxia red layers. Microcrystalline hematite was suggested as being the coloring mineral. Anatase, reported here for the first time in Danxia red beds, constituted the content of titanium in the red layer (0.17–0.57%) and was present in a significantly higher amount than the adjacent limestone formation (0.13%). Over 95% of Fe/Ti oxides served as a cementation agent along the framework of coarse-grain minerals (quartz and feldspar). The hematite and anatase were visible-light-responsive semiconductors, with a band gap of 2.01 eV and 3.05 eV, respectively. Photoelectrochemical experiments were performed on synthetic hematite, anatase, and their coupled material. The inactive hematite displayed an enhanced 23-fold photocurrent at 0.8 V (vs. Ag/AgCl) when coupled with anatase. Furthermore, in a photodegradation experiment using methyl orange dye under simulated sunlight, the coupled material showed decolorizing efficiency 2.4 times that of hematite. The anatase, therefore, prominently improved the photocatalytic activities of hematite. It is proposed that these semiconducting minerals in red beds produce oxygen reactive species and have significant environmental effects, which is of great importance. [ABSTRACT FROM AUTHOR]