Search

The Mars 2020 Perseverance Rover imaged diagenetic textural features in four separate sedimentary units in its exploration of the 25‐m‐thick Shenandoah formation at Jezero Crater, Mars, that we interpreted as probable concretions. These concretions were most abundant in the Hogwallow Flats member of the Shenandoah formation and were restricted to the light‐toned, platy, sulfur‐cemented bedrock at outcrop surfaces, whereas the finely laminated, darker toned, mottled and deformed strata lack concretions. The concretions also had a wide range of morphologies including concentric, oblate, urn, and spheroidal shaped forms that were not clustered, and ranged in size from ∼1 to 16 mm with a median of 2.65 mm. The elemental composition of the concretions compared to the bedrock had greater abundance of magnesium and calcium salts, silicates, and possibly hematite. We compared these Jezero Crater concretions to the geochemistry of concretions from previously published studies and from two new terrestrial analog sites (Gallup Formation, New Mexico and Torrey Pines, California). In addition, we measured organic carbon content of three terrestrial sedimentary analogs of increasing age that contain concretions (Torrey Pines (Pleistocene), Gallup Formation (∼89 Ma), and Moodies Group (∼3.2 Ga)). All measured concretions contained significant concentrations of organic carbon with the maximum organic carbon content (∼2 wt. % Total organic carbon) found in the Moodies Group concretions. Organic carbon abundances in terrestrial concretions was controlled more by the formation mechanism and relative timing of concretion development rather than deposit age. These findings suggested that concretions at Jezero Crater reflect local sites of enhanced biosignature preservation potential. Plain Language Summary: The Perseverance Rover discovered concretions in its exploration of the rock packages at Jezero Crater, Mars and one of the sample return cores was collected from concretion‐rich bedrock. Concretions are resistant cement in the rock that are found in many shapes (usually spherical or oblate) and range from millimeter to meter size scales on Earth; they can be formed through inorganic water‐rock reactions or facilitated by microbial metabolisms. We documented the abundance, size, composition, and shape of the concretions to understand how these features were formed. We found that the concretions are mixtures of salts, clay minerals, and iron oxides. We compared these results to terrestrial concretions with similar mineral compositions and measured the organic carbon in four terrestrial analogs. Comparisons with terrestrial concretions in this study and the literature suggested that the concretion composition in Jezero Crater could have high organic preservation potential. Thus, the concretions in Jezero Crater may retain organic carbon and other biosignatures and might therefore be considered as high priority samples of astrobiological interest out of the current sample suite for return to Earth. Key Points: Jezero Crater concretions are variably enriched in Si, Ca, and Mg salts, and Fe oxidesTerrestrial concretions of similar mineralogy analyzed in this study contain significant organic carbon phasesBased on terrestrial analogs, Jezero Crater concretions may represent sites of enhanced biosignature preservation potential [ABSTRACT FROM AUTHOR]

Mars has many well‐exposed fluvial ridges and fluvio‐deltaic basins; in two of these locations, the Curiosity and Perseverance rovers are currently searching for signs of habitability. The distribution of organic carbon that might persist in ancient fluvial deposits present on Mars is not well understood. In this study, we set out to assess the preservation potential of organic carbon in a hyperarid fluvial environment with observations and analyses of the Amargosa River in Death Valley, California (United States). The lower reaches of the Amargosa River in Badwater Basin are nearly devoid of plants and contain low gradient, meandering channels, making them a valuable terrestrial analog for early martian fluvial systems. We analyzed sediment taken from fluvial deposits exposed in cutbanks of two bends of a meandering channel. We found total organic carbon abundances that were on average 0.15% up to a meter below the surface. X‐ray diffraction and electron microscopy analyses revealed a suite of high redox potential mineral phases (including iron and manganese oxides) mixed with detrital and authigenic silicates, carbonate, and sulfate salts at or close to redox equilibrium with pore fluids in contact with the atmosphere. This finding highlighted that organic carbon can persist in fluvial deposits at low abundance despite oxidizing conditions and saturated sediments and suggested that ancient fluvial deposits on Mars may retain traces of organics in fine‐grained deposits if they are present during deposition. Plain Language Summary: The Curiosity and Perseverance rovers are currently searching for signs of past life on Mars in two ancient river deposits. Since carbon on the surface of Mars could originate from meteorites and chemical reactions in addition to potential Martian life forms, it is valuable to identify sedimentary environments that best preserve biospheric organic carbon. The distribution of organic carbon that might persist in ancient river deposits on Mars is not well understood, yet this understanding is crucial to detecting evidence of past life on Mars. In this study, we set out to determine the preservation potential of organic carbon in an arid, fluvial environment. The Amargosa River (Death Valley, California, United States) hosts a low gradient single threaded river, running through a catchment with little vegetation and making it a valuable terrestrial analog for early Martian fluvial systems. We found that organic carbon can persist in fine‐grained river sediments at low abundance despite oxidizing conditions in the subsurface. Our results suggested that fine‐grained ancient river deposits on Mars are the most promising sampling targets for the Perseverance rover to detect traces of potential life on Mars. Key Points: The hyper‐arid deposits of the ephemeral, alluvial Amargosa River are a useful process analog for ancient Martian river depositsX‐ray diffraction and electron microscopy analyses revealed that the subsurface remains highly oxidizing despite saturated sedimentsFluvial deposits had low abundances of organic carbon in fine‐grained sediment; mudstones are the most promising targets for sampling on Mars [ABSTRACT FROM AUTHOR]

Manganese has been observed on Mars by the NASA Curiosity rover in a variety of contexts and is an important indicator of redox processes in hydrologic systems on Earth. Within the Murray formation, an ancient primarily fine‐grained lacustrine sedimentary deposit in Gale crater, Mars, have observed up to 45× enrichment in manganese and up to 1.5× enrichment in iron within coarser grained bedrock targets compared to the mean Murray sediment composition. This enrichment in manganese coincides with the transition between two stratigraphic units within the Murray: Sutton Island, interpreted as a lake margin environment, and Blunts Point, interpreted as a lake environment. On Earth, lacustrine environments are common locations of manganese precipitation due to highly oxidizing conditions in the lakes. Here, we explore three mechanisms for ferromanganese oxide precipitation at this location: authigenic precipitation from lake water along a lake shore, authigenic precipitation from reduced groundwater discharging through porous sands along a lake shore, and early diagenetic precipitation from groundwater through porous sands. All three scenarios require highly oxidizing conditions and we discuss oxidants that may be responsible for the oxidation and precipitation of manganese oxides. This work has important implications for the habitability of Mars to microbes that could have used Mn redox reactions, owing to its multiple redox states, as an energy source for metabolism. Plain Language Summary: In May 2017, the NASA Curiosity rover observed higher than usual amounts of manganese in the lakebed rocks within Gale crater, Mars. These sedimentary rocks have larger grain sizes than what is typical for the lakebed rocks in Gale crater. This may indicate that the original sediments were formed in a river, delta, or near the shoreline in the ancient lake. In this paper, we discuss how manganese could have been enriched in these rocks—for example, by percolation of groundwater through the original sediments or through the rock afterward—and what oxidant could be responsible for the precipitation of manganese in the rocks. On Earth, manganese becomes enriched because of oxygen in the atmosphere and this process is often sped up by the presence of microbes. Microbes on Earth can use the many oxidation states of manganese as energy for metabolism; if life was present on ancient Mars, the increased amounts of manganese in these rocks along the lake shore would be a helpful energy source for life. Key Points: Enrichments of MnO are observed in bedrock and diagenetic features near a stratigraphic boundary between possible lake margin and lake sedimentsManganese precipitation may have occurred along a lake shoreline via authigenic or early diagenetic scenariosAll alteration scenarios require persistent water and highly oxidizing conditions in what would have been a habitable environment [ABSTRACT FROM AUTHOR]

Carbonate rocks provide unique and valuable sedimentary archives for secular changes in Earth’s physical, chemical, and biological processes. However, reading the stratigraphic record produces overlapping, nonunique interpretations that stem from the difficulty in directly comparing competing biological, physical, or chemical mechanisms within a common quantitative framework. We built a mathematical model that decomposes these processes and casts the marine carbonate record in terms of energy fluxes across the sediment–water interface. Results showed that physical, chemical, and biological energy terms across the seafloor are subequal and that the energetic dominance of different processes varies both as a function of environment (e.g., onshore vs. offshore) as well as with time-varying changes in seawater chemistry and with evolutionary changes in animal abundance and behavior. We applied our model to observations from the end-Permian mass extinction—a massive upheaval in ocean chemistry and biology—revealing an energetic equivalence between two hypothesized drivers of changing carbonate environments: a reduction in physical bioturbation increased carbonate saturation states in the oceans. Early Triassic occurrences of ‘anachronistic’ carbonates—facies largely absent from marine environments after the Early Paleozoic—were likely driven more by reduction in animal biomass than by repeated perturbations to seawater chemistry. This analysis highlighted the importance of animals and their evolutionary history in physically shaping patterns in the sedimentary record via their impact on the energetics of marine environments. [ABSTRACT FROM AUTHOR]

Phosphorus is essential for cell biology, yet scarce in modern marine environments wherein free phosphate is consumed by life or titrated by calcium to form apatite minerals. The environmental conditions under which the early biosphere emerged and phosphorus was integrated throughout biochemistry is yet unknown. We measured the phosphate concentrations of 2.8–2.5 Ga shallow marine carbonate facies across six Neoarchean shelf‐ramp environments. We found that the P/Ca ratios of Neoarchean stromatolites, micrites, and crystal fans were >4‐fold to 12‐fold more enriched in carbonate‐associated phosphate than modern marine coral skeletons and abiotic Phanerozoic carbonates. Our results support the view that Archean productivity was limited by the availability of electrons rather than phosphate or other nutrients, and help explain why phosphorus is so central to the molecules, metabolisms, and bioenergetics observed in cells. Plain Language Summary: Phosphorus is an essential element for life processes. Today, phosphorus is negligible in the surface oceans and exists in very low concentrations in the deep oceans, and thus is the primary limitation on net primary productivity. This circumstance sets up the paradox of why phosphorus plays a key role in the structures and processes of cell biology. Were phosphorus concentrations higher in the Archean oceans early in the evolutionary history of cell biology? In this work, we compared phosphate concentrations in shallow marine carbonates from the Neoarchean (2.8–2.5 billion years ago) and the Phanerozoic (<550 million years ago). We found that primary carbonate structures and fabrics from the Neoarchean yielded significantly higher phosphate concentrations than in the Phanerozoic, and interpreted this to mean that Archean seawater was more enriched in phosphorus than modern oceans. Key Points: P/Ca is higher in Neoarchean shallow marine carbonates than Phanerozoic and modern shallow marine carbonatesHigher phosphate concentrations in Neoarchean than modern seawater indicates that early marine life was not phosphate‐limited [ABSTRACT FROM AUTHOR]

The deposition of marine carbonate rocks is influenced by climate and seawater chemistry. Carbonate platforms usually keep pace with subsidence and sea level rise but "platform drowning" occurs when carbonate sedimentation slows or when siliciclastics replace carbonates. Identifying specific mechanism(s) behind platform drowning is critical for understanding global environmental changes such as Ocean Anoxic Events (OAEs). We developed a model for OAEs which couples ocean basin redox processes to rates of carbonate sedimentation. Well‐oxygenated oceans have steep gradients in saturation state such that deep‐ocean dissolution is balanced by carbonate "overproduction" in shallow water. Through anaerobic metabolisms, deep‐ocean anoxia reduces both dissolution and overproduction, leading to slower accumulation rates in shallow‐water environments. This quasi‐steady state response links carbonate sedimentation with longer timescales associated with redox changes. Redox‐based drowning may have acted alongside other mechanisms to create spatially diverse patterns of platform drowning during Mesozoic OAEs and other Phanerozoic hyperthermal events. Plain Language Summary: Carbonate minerals precipitate from ions dissolved in water. Thick packages of carbonate rocks often form in shallow, tropical waters, and their accumulation rate depends on the availability of ions as well as biological agents that catalyze carbonate deposition such as animals and microbes. Geologic patterns in carbonate rocks are sensitive to these controls on accumulation rates, tying them to Earth's surface chemistry and ecosystems. Sometimes chemical changes in the oceans cause far‐reaching effects that influence patterns observed in carbonate rocks. During the Mesozoic Era, episodes of lowered dissolved oxygen in the world's oceans often coincided with a phenomenon known as "platform drowning". Platform drowning occurs when carbonate platforms—sites of carbonate deposition like the modern Bahamian Islands—experienced slower sedimentation rates and sank into deeper water. Interestingly, there are several chemical pathways that could cause platform drowning, and unraveling the underlying drivers is key for understanding the nature of past environmental changes. Here we present a concept for platform drowning that emphasizes the role of microbes and their effects on global ocean chemistry. This idea helps explain the long timescales of platform drowning and may explain similar patterns during other low‐oxygen episodes in Earth's past. Key Points: A model for carbonate platform drowning was developed based on changing patterns of carbonate production and dissolutionOcean anoxia reduces both carbonate dissolution and the amount of carbonate "overproduction" in the surface oceansLinking carbonate chemistry to ocean redox conditions allowed slower sedimentation over long (105–106 year) timescales [ABSTRACT FROM AUTHOR]

The deposition of marine carbonate rocks is influenced by climate and seawater chemistry. Carbonate platforms usually keep pace with subsidence and sea level rise but "platform drowning" occurs when carbonate sedimentation slows or when siliciclastics replace carbonates. Identifying specific mechanism(s) behind platform drowning is critical for understanding global environmental changes such as Ocean Anoxic Events (OAEs). We developed a model for OAEs which couples ocean basin redox processes to rates of carbonate sedimentation. Well‐oxygenated oceans have steep gradients in saturation state such that deep‐ocean dissolution is balanced by carbonate "overproduction" in shallow water. Through anaerobic metabolisms, deep‐ocean anoxia reduces both dissolution and overproduction, leading to slower accumulation rates in shallow‐water environments. This quasi‐steady state response links carbonate sedimentation with longer timescales associated with redox changes. Redox‐based drowning may have acted alongside other mechanisms to create spatially diverse patterns of platform drowning during Mesozoic OAEs and other Phanerozoic hyperthermal events. Plain Language Summary: Carbonate minerals precipitate from ions dissolved in water. Thick packages of carbonate rocks often form in shallow, tropical waters, and their accumulation rate depends on the availability of ions as well as biological agents that catalyze carbonate deposition such as animals and microbes. Geologic patterns in carbonate rocks are sensitive to these controls on accumulation rates, tying them to Earth's surface chemistry and ecosystems. Sometimes chemical changes in the oceans cause far‐reaching effects that influence patterns observed in carbonate rocks. During the Mesozoic Era, episodes of lowered dissolved oxygen in the world's oceans often coincided with a phenomenon known as "platform drowning". Platform drowning occurs when carbonate platforms—sites of carbonate deposition like the modern Bahamian Islands—experienced slower sedimentation rates and sank into deeper water. Interestingly, there are several chemical pathways that could cause platform drowning, and unraveling the underlying drivers is key for understanding the nature of past environmental changes. Here we present a concept for platform drowning that emphasizes the role of microbes and their effects on global ocean chemistry. This idea helps explain the long timescales of platform drowning and may explain similar patterns during other low‐oxygen episodes in Earth's past. Key Points: A model for carbonate platform drowning was developed based on changing patterns of carbonate production and dissolutionOcean anoxia reduces both carbonate dissolution and the amount of carbonate "overproduction" in the surface oceansLinking carbonate chemistry to ocean redox conditions allowed slower sedimentation over long (105–106 year) timescales [ABSTRACT FROM AUTHOR]

In carbonate‐forming environments, authigenic minerals can cement surface sediments into centimeter‐sized intraclasts that are later reworked into "flat‐pebble" or "edgewise" conglomerates. Flat‐pebble conglomerates comprise only a small portion of facies in modern marine environments but are common in ancient strata, implying that seafloor cements were more widespread in the past. Flat‐pebble conglomerates nearly disappeared after the Ordovician radiation, yet it is unclear if this decline was due to changing seawater chemistry or if increased infaunalization and bioturbation simply worked to break down nascent clasts. We discovered a process analog that produces flat‐pebble conglomerates around the Great Salt Lake, Utah, USA, and studied these facies using field observations, wave models, satellite imagery, petrography, and microanalytic chemical data. Clasts were sourced from wave‐rippled grainstone that cemented in situ in offshore environments. Lake floor cements formed under aragonite saturation states that are lower than modern marine settings, suggesting that physical processes are at least as important as chemical ones. Results from our wave models showed that coarse sediments near the field site experience quiescent periods of up to 6 months between suspension events, allowing isopachous cements to form. Using a simple mathematical framework, we show that the main difference between Great Salt Lake and modern, low‐energy marine settings is that the latter has enough bioturbating organisms to break up clasts. Observations from Great Salt Lake demonstrate how geologic trends in flat‐pebble abundance could largely reflect changes in total infaunal biomass and ecology without requiring regional‐to‐global changes in seawater chemistry. Plain Language Summary: Calcium carbonate is a common sedimentary mineral that precipitates quickly under Earth surface conditions. If carbonate sediments are at rest for long periods of time, they may solidify via cementation into flat, pebble‐sized clasts. Geologic trends show that flat pebbles are anticorrelated with burrows, suggesting they may tell us about animal evolution and ecology. However, it was unknown if animals disrupt clasts through chemical means, leading to slower rates of mineral growth, or if they physically push sediments apart, breaking up nascent cements. We studied flat pebbles forming in Great Salt Lake, Utah, where the water is too salty for burrowing animals. The composition of lake water should lead to slower growth rates for carbonate minerals, yet clasts still form. We conclude that pebbles form during quiescent intervals with little physical energy to move grains, either from waves or from burrowing organisms. As a result, ancient flat pebbles are probably not unique markers for seawater chemistry. Key Points: Sediment cohesion within carbonate environments depends on both physical and chemical energy near the sediment‐water interfaceIf sediment transport is infrequent, burrowing animals provide a significant source of physical energySubstrate cohesion may record physical changes related to the number and behavior of animals rather than geochemical conditions [ABSTRACT FROM AUTHOR]

Aims. We aim to characterize the outflow properties of a sample of early Class 0 phase low-mass protostars in Orion, which were first identified by the Herschel Space Observatory. We also look for signatures of infall in key molecular lines. Methods. Maps of CO J = 3–2 and J = 4–3 toward 16 very young Class 0 protostars were obtained using the Atacama Pathfinder EXperiment (APEX) telescope. We searched the data for line wings indicative of outflows and calculated masses, velocities, and dynamical times for the outflows. We used additional HCO+, H13CO+, and NH3 lines to look for infall signatures toward the protostars. Results. We estimate the outflow masses, forces, and mass-loss rates based on the CO J = 3–2 and J = 4–3 line intensities for eight sources with detected outflows. We derive upper limits for the outflow masses and forces of sources without clear outflow detections. The total outflow masses for the sources with clear outflow detections are in the range between 0.03 and 0.16 M⊙ for CO J = 3–2 and between 0.02 and 0.10 M⊙ for CO J = 4–3. The outflow forces are in the range between 1.57 × 10−4 and 1.16 × 10−3M⊙ km s−1 yr−1 for CO J = 3–2 and between 1.14 × 10−4 and 6.92 × 10−4M⊙ km s−1 yr−1 for CO J = 4–3. Nine protostars in our sample show asymmetric line profiles indicative of infall in HCO+, compared to H13CO+ or NH3. Conclusions. The outflow forces of the protostars in our sample show no correlation with the bolometric luminosity, unlike those found by some earlier studies for other Class 0 protostars. The derived outflow forces for the sources with detected outflows are similar to those found for other, more evolved, Class 0 protostars, suggesting that outflows develop quickly in the Class 0 phase. [ABSTRACT FROM AUTHOR]

Manganese-bearing minerals in ancient strata provide a particularly informative record of the redox potentials of ancient Earth surface environments due to the high specificity of species that can oxidize Mn(II). However, little is known about how this sedimentary archive might have been altered by processes occurring long after lithification, including the effects of metamorphism, fluid mobilization, and metasomatism. We investigated Mn mineralization across known metamorphic gradients in the Kaapvaal craton, South Africa, in Archean and early Paleoproterozoic age carbonate-, shale-, and iron formation-bearing marine strata. We sampled contemporaneous strata that record the drowning of the Campbellrand-Malmani carbonate platform and a transition to iron formation deposition in a range of localities, from two metamorphosed (greenschist and above, affected by the intrusion of the Bushveld igneous complex) and four better-preserved (sub-greenschist) deep subsurface drill cores. To evaluate the geochemistry and mineralization tied directly to petrographic textures and cross-cutting relationships, we combined bulk geochemistry with light and electron microscopy and synchrotron microprobe X-ray absorption spectroscopy and imaging to produce Mn speciation maps at the requisite micrometer length scales for these textures. Samples with lesser degrees of post-depositional transformation contained minor amounts of Mn(II) in early diagenetic marine carbonate cements and detrital carbonate grains, while metamorphosed samples typically contained Mn concentrated into a combination of coarse-grained and vein-filling carbonate phases (ankerite, siderite, and rhodochrosite), garnet and amphibole. Chemical imaging analyses of these more metamorphosed samples show that Mn is held by phases and textures that mineralized post-deposition and lithification, demonstrating that Mn was mobilized - at least locally - by metasomatic fluids, although it is difficult to distinguish whether this Mn was original to these strata or was introduced secondarily. Our results confirm that Mn can be mobilized and therefore caution should be applied when interpreting Mn enrichments in sedimentary rocks, especially when Mn enrichment is not geographically extensive and coincides with metamorphic processes. [ABSTRACT FROM AUTHOR]

Copyright of Der Unfallchirurg is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The Mars Science Laboratory rover Curiosity visited two active wind‐blown sand dunes within Gale crater, Mars, which provided the first ground‐based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial‐like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were present on all dune slopes and had a size and shape similar to their terrestrial counterpart. Grainfall and grainflow occurred on dune and large‐ripple lee slopes. Lee slopes were ~29° where grainflows were present and ~33° where grainfall was present. These slopes are interpreted as the dynamic and static angles of repose, respectively. Grain size measured on an undisturbed impact ripple ranges between 50 μm and 350 μm with an intermediate axis mean size of 113 μm (median: 103 μm). Dissimilar to dune eolian processes on Earth, large, meter‐scale ripples were present on all dune slopes. Large ripples had nearly symmetric to strongly asymmetric topographic profiles and heights ranging between 12 cm and 28 cm. The composite observations of the modern sedimentary processes highlight that the Martian eolian rock record is likely different from its terrestrial counterpart because of the large ripples, which are expected to engender a unique scale of cross stratification. More broadly, however, in the Bagnold Dune Field as on Earth, dune‐field pattern dynamics and basin‐scale boundary conditions will dictate the style and distribution of sedimentary processes. [ABSTRACT FROM AUTHOR]

Banded iron formations ( BIFs) are rock deposits common in the Archean and Paleoproterozoic (and regionally Neoproterozoic) sedimentary successions. Multiple hypotheses for their deposition exist, principally invoking the precipitation of iron via the metabolic activities of oxygenic, photoferrotrophic, and/or aerobic iron-oxidizing bacteria. Some isolated environments support chemistry and mineralogy analogous to processes involved in BIF deposition, and their study can aid in untangling the factors that lead to iron precipitation. One such process analog system occurs at Okuoku-hachikurou ( OHK) Onsen in Akita Prefecture, Japan. OHK is an iron- and CO2-rich, circumneutral hot spring that produces a range of precipitated mineral textures containing fine laminae of aragonite and iron oxides that resemble BIF fabrics. Here, we have performed 16S rRNA gene amplicon sequencing of microbial communities across the range of microenvironments in OHK to describe the microbial diversity present and to gain insight into the cycling of iron, oxygen, and carbon in this ecosystem. These analyses suggest that productivity at OHK is based on aerobic iron-oxidizing Gallionellaceae. In contrast to other BIF analog sites, Cyanobacteria, anoxygenic phototrophs, and iron-reducing micro-organisms are present at only low abundances. These observations support a hypothesis where low growth yields and the high stoichiometry of iron oxidized per carbon fixed by aerobic iron-oxidizing chemoautotrophs like Gallionellaceae result in accumulation of iron oxide phases without stoichiometric buildup of organic matter. This system supports little dissimilatory iron reduction, further setting OHK apart from other process analog sites where iron oxidation is primarily driven by phototrophic organisms. This positions OHK as a study area where the controls on primary productivity in iron-rich environments can be further elucidated. When compared with geological data, the metabolisms and mineralogy at OHK are most similar to specific BIF occurrences deposited after the Great Oxygenation Event, and generally discordant with those that accumulated before it. [ABSTRACT FROM AUTHOR]

The rise of oxygen ca. 2.3 billion years ago (Ga) is the most distinct environmental transition in Earth history. This event was enabled by the evolution of oxygenic photosynthesis in the ancestors of Cyanobacteria. However, long-standing questions concern the evolutionary timing of this metabolism, with conflicting answers spanning more than one billion years. Recently, knowledge of the Cyanobacteria phylum has expanded with the discovery of non-photosynthetic members, including a closely related sister group termed Melainabacteria, with the known oxygenic phototrophs restricted to a clade recently designated Oxyphotobacteria. By integrating genomic data from the Melainabacteria, cross-calibrated Bayesian relaxed molecular clock analyses show that crown group Oxyphotobacteria evolved ca. 2.0 billion years ago (Ga), well after the rise of atmospheric dioxygen. We further estimate the divergence between Oxyphotobacteria and Melainabacteria ca. 2.5-2.6 Ga, which-if oxygenic photosynthesis is an evolutionary synapomorphy of the Oxyphotobacteria-marks an upper limit for the origin of oxygenic photosynthesis. Together, these results are consistent with the hypothesis that oxygenic photosynthesis evolved relatively close in time to the rise of oxygen. [ABSTRACT FROM AUTHOR]

A new experiment is described to detect a permanent electric dipole moment of the proton with a sensitivity of 10-29 e . cm by using polarized "magic" momentum 0.7 GeV/c protons in an all-electric storage ring. Systematic errors relevant to the experiment are discussed and techniques to address them are presented. The measurement is sensitive to new physics beyond the standard model at the scale of 3000 TeV. [ABSTRACT FROM AUTHOR]

We present a far-IR survey of the entire Mon R2 giant molecular cloud (GMC) with Herschel- Spectral and Photometric Imaging REceiver cross-calibrated with Planck-High Frequency Instrument data. We fit the spectral energy distributions of each pixel with a greybody function and an optimal beta value of 1.8. We find that mid-range column densities obtained from far-IR dust emission and near-IR extinction are consistent. For the entire GMC, we find that the column density histogram, or column density probability distribution function (N-PDF), is lognormal below ~1021 cm-2. Above this value, the distribution takes a power law form with an index of -2.15. We analyse the gas geometry, N-PDF shape, and young stellar object (YSO) content of a selection of subregions in the cloud. We find no regions with pure lognormal N-PDFs. The regions with a combination of lognormal and one power-law N-PDF have a YSO cluster and a corresponding centrally concentrated gas clump. The regions with a combination of lognormal and two power-law N-PDF have significant numbers of typically younger YSOs but no prominent YSO cluster. These regions are composed of an aggregate of closely spaced gas filaments with no concentrated dense gas clump. We find that for our fixed scale regions, the YSO count roughly correlates with the N-PDF power-law index. The correlation appears steeper for single power-law regions relative to two power-law regions with a high column density cut-off, as a greater dense gas mass fraction is achieved in the former. A stronger correlation is found between embedded YSO count and the dense gas mass among our regions. [ABSTRACT FROM AUTHOR]

A novel robotic plasma magnetron mole with a 50 cm long cathode was designed, fabricated, and operated. The reason for this endeavor is to alleviate the problems of unacceptable resistive heating of stainless steel vacuum tubes in the BNL Relativistic Heavy Ion Collider (RHIC). The magnetron mole was successfully operated to copper coat an assembly containing a full-size, stainless steel, cold bore, RHIC magnet tubing connected to two types of RHIC bellows, to which two additional pipes made of RHIC tubing were connected. To increase the cathode lifetime, a movable magnet package was developed, and the thickest possible cathode was made, with a rather challenging target to substrate (de facto anode) distance of less than 1.5 cm. Achieving reliable steady state magnetron discharges at such a short cathode to anode gap was rather challenging, when compared to commercial coating equipment, where the target to substrate distance is 10's cm; 6.3cm is the lowest experimental target to substrate distance found in the literature. Additionally, the magnetron developed during this project provides unique omni-directional uniform coating. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system is driven by a motorized spool. Excellent coating adhesion was achieved. Measurements indicated that well-scrubbed copper coating reduced secondary electron yield to 1, i.e., the problem of electron clouds can be eliminated. Room temperature RF resistivity measurement indicated that a 10 µm copper coated stainless steel RHIC tube has a conductivity close to that of pure copper tubing. Excellent coating adhesion was achieved. The device details and experimental results are described. [ABSTRACT FROM AUTHOR]

In view of spacecraft re-entry applications into planetary atmospheres, hybrid thermal protection systems based on layered composites of ablative materials and ceramic matrix composites are investigated. Joints of ASTERM™ lightweight ablative material with C/SiC (SICARBON™) were fabricated using commercial high temperature inorganic adhesives. Sound joints without defects are produced and very good bonding of the adhesive with both base materials is observed. Mechanical shear tests under ambient conditions and in liquid nitrogen show that mechanical failure always takes place inside the ablative material with no decohesion of the interface of the adhesive layer with the bonded materials. Surface treatment of the ablative surface prior to bonding enhances both the shear strength and the ultimate shear strain by up to about 60%. [ABSTRACT FROM AUTHOR]

Introduction: The short-acting narcotic propofol is used for sedation during electroconvulsive therapy (ECT). It remains unclear whether patients develop tolerance to propofol after repeated administration. Therefore, we studied whether propofol dosage had to be increased during a course of ECT. Methods: This retrospective study evaluated records of 39 in- and outpatients at a Swiss psychiatric hospital who underwent 10-21 ECT sessions for affective disorder over 4-28 weeks in 2011-2013. We examined the dose of propofol required to achieve deep sedation at the first and last ECT sessions. Results: 13/39 patients (33.3 %) needed a slightly higher propofol dose at the last ECT session than at the first (Group 1), 12 patients (30.8 %) needed the same dose at the first and last sessions (Group 2) and 14 patients (35.9 %) needed a lower final dose (Group 3). Conclusions: In our study patients did not appear to develop tolerance to propofol after repeated administration. Although the lack of a systematic dosing scheme in our study limits the conclusions that can be drawn, recent studies in animal models indicate that tolerance development is rather unlikely with propofol. Further studies are required to clarify the question of whether repeated use of propofol leads to tolerance. [ABSTRACT FROM AUTHOR]