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The preservation of organic biosignatures during the Proterozoic Eon required specific taphonomic windows that could entomb organic matter to preserve amorphous kerogen and even microbial body fossils before they could be extensively degraded. Some of the best examples of such preservation are found in early diagenetic chert that formed in peritidal environments. This chert contains discrete domains of amorphous kerogen and sometimes kerogenous microbial mat structures and microbial body fossils. Our understanding of how these exquisite microfossils were preserved and the balance between organic degradation and mineral formation has remained incomplete. Here, we present new insights into organic preservation in Proterozoic peritidal environments facilitated through interactions among organic matter, cations, and silica. Organic matter from Proterozoic peritidal environments is not preserved by micro- or cryptocrystalline quartz alone. Rather, preservation includes cation-rich nanoscopic phases containing magnesium, calcium, silica, and aluminum that pre-date chert emplacement and may provide nucleation sites for silica deposition and enable further chert development. Using scanning electron microscopy and elemental mapping with energy dispersive X-ray spectroscopy, we identify cation enrichment in Proterozoic organic matter and cation-rich nanoscopic phases that pre-date chert. We pair these analyses with precipitation experiments to investigate the role of cations in the precipitation of silica from seawater. Our findings suggest that organic preservation in peritidal environments required rapid formation of nanoscopic mineral phases through the interactions of organic matter with seawater. These organic-cation interactions likely laid the initial foundation for the preservation and entombment of biosignatures, paving the way for the development of the fossiliferous chert that now contains these biosignatures and preserves a record of Proterozoic life.

Nitrogen-containing heterocyclic compounds are fundamental biochemical components of all life on Earth and, presumably, life elsewhere in our solar system. Detection and characterization of these compounds by traditional solvent extraction, chromatographic separation, and GC–MS analysis require more sample mass than will be available from samples returned to Earth from Mars. With its small sample mass requirement, Surface Enhanced Raman Spectroscopy could be an appropriate technique for analysis of returned samples. We have developed a SERS method for the detection of maleimide (2,5-pyrroledione), an N-containing heterocycle with a structure that is widespread in biochemicals. This semi-quantitative methodology accurately determines maleimide concentration in the range from 60 µg/mL to 120 µg/mL. We present a maleimide SERS standard spectrum which will be useful as a reference for future works. The present work demonstrates an easy, accurate, and effective method for the non-destructive qualitative and semi-quantitative study of maleimide as a first step toward developing a method for analysis of related compounds.

Solar system bodies with surface and sub-surface volatiles will show observational evidence of activity when they reach a temperature where those volatiles change from solid to gas and are released. This is most frequently seen in comets, where activity is driven by the sublimation of water, carbon dioxide, or carbon monoxide ices. However, some bodies (notably the asteroid (3200) Phaethon) show initiation of activity at very small heliocentric distances, long after they have reached the sublimation temperatures of these ices. We investigate whether the sodium present in the mineral matrix could act as the volatile element responsible for this activity. We conduct theoretical modeling which indicates that sodium has the potential to sublimate in the conditions that Phaethon experiences, depending on the mineral phase it is held in. To test this, we then exposed samples of the carbonaceous chondrite Allende to varying heating events similar to what would be experienced by low perihelion asteroids. We measured the change in sodium present in each sample, and find that the highest temperature samples show a significant loss of sodium from specific mineral phases over a single heating event, comparable to a day on the surface of Phaethon. Under specific thermal histories possible for Phaethon, this outgassing could be sufficient to explain this object's observed activity. This effect would also be expected to be observed for other low-perihelia asteroids as well, and may act as a critical step in the process of disrupting small low-albedo asteroids., Published in PSJ with interactive figures

The surface of Mars has been well mapped and characterized, yet the subsurface — the most likely place to find signs of extant or extinct life and a repository of useful resources for human exploration — remains unexplored. In the near future this is set to change.

The Khor Al-Adaid sabkha in Qatar is among the rare extreme environments on Earth where it is possible to study the formation of dolomite-a carbonate mineral whose origin remains unclear and has been hypothetically linked to microbial activity. By combining geochemical measurements with microbiological analysis, we have investigated the microbial mats colonizing the intertidal areas of sabhka. The main aim of this study was to identify communities and conditions that are favorable for dolomite formation. We inspected and sampled two locations. The first site was colonized by microbial mats that graded vertically from photo-oxic to anoxic conditions and were dominated by cyanobacteria. The second site, with higher salinity, had mats with an uppermost photo-oxic layer dominated by filamentous anoxygenic photosynthetic bacteria (FAPB), which potentially act as a protective layer against salinity for cyanobacterial species within the deeper layers. Porewater in the uppermost layers of the both investigated microbial mats was supersaturated with respect to dolomite. Corresponding to the variation of the microbial community's vertical structure, a difference in crystallinity and morphology of dolomitic phases was observed: dumbbell-shaped proto-dolomite in the mats dominated by cyanobacteria and rhombohedral ordered-dolomite in the mat dominated by FAPB. This publication was made possible by NPRP Grant 7-443-1-083 from the Qatar National Research Fund (a member of Qatar Foundation). MD was supported by the National Sciences and Engineering Research Council of Canada (NSERC Discovery Grant) and the Canada Foundation for Innovation and Ontario Research Fund (Leaders Opportunity Fund, Grant Number 22404). The statements made herein are solely the responsibility of the authors. The authors would like to acknowledge Oleksandra Kaskun for performing alkalinity measurements, Dr. K. Tait at the Royal Ontario Museum for use of XRD and Sal Boccia at the Ontario Centre for the Characterizations of Advanced Materials (OCCAM) for the assistance with SEM imaging. Scopus

Ooids are accretionary grains commonly reported from turbulent, shallow-water environments. They have long been associated with microbially dominated ecosystems and often occur in close proximity to, or embedded within, stromatolites, yet have historically been thought to form solely through physicochemical processes. Numerous studies have revealed both constructive and destructive roles for microbes colonizing the surfaces of modern calcitic and aragonitic ooids, but there has been little evidence for the operation of these processes during the Archean and Proterozoic, when both ooids and microbially dominated ecosystems were more widespread. Recently described carbonate ooids from the 2.9 Ga Pongola Supergroup, South Africa, include well-preserved examples composed of diagenetic dolomite interpreted to have formed from a high-Mg-calcite precursor. Spatial distributions of organic matter and elements associated with metabolic activity (N, S, and P) were interpreted as evidence for a biologically induced origin. Here, we describe exceptionally well-preserved ooids composed of calcite, collected from Earth's oldest known carbonate lake system, the ~2.72 Ga Meentheena Member (Tumbiana Formation), Fortescue Group, Western Australia. We used optical microscopy, Raman spectroscopy, XRD, SEM-EDS, LA-ICP-MS, EA-IRMS, and a novel micro-XRF instrument to investigate an oolite shoal deposited between stromatolites that preserve abundant evidence for microbial activity. We report an extremely fine, radial-concentric, calcitic microfabric that is similar to the primary and early diagenetic fabrics of calcitic ooids reported from modern temperate lakes. Early diagenetic silica has trapped isotopically light and thermally mature organic matter. The close association of organic matter with mineral phases and microfabrics related to primary and early diagenetic processes suggest incorporation of organic matter occurred during accretion, likely due to the presence of microbial biofilms. We conclude that the oldest known calcitic ooids were likely formed through processes similar to those that mediate the accretion of ooids in similar environments today, including formation within a microbial biosphere.

This paper reports a previously unidentified paleoenvironmental record found in sand dunes of the Atacama Desert, Chile. Long-term aeolian deflation by prevailing onshore winds has resulted in the deposition of sand on the irregular surface of a Miocene-aged anhydrite outcrop. Two deposits ~25 km apart, along the prevailing wind trajectory, were hand excavated then analyzed for vertical (and temporal) changes in physical and chemical composition. Radiocarbon ages of organic matter embedded within the deposits show that rapid accumulation of sediment began at the last glacial maximum and slowed considerably after the Pacific Ocean attained its present post-glacial level. Over this time period, grain sizes are seen to increase while accumulation rates simultaneously decrease, suggesting greater wind speeds and/or a change or decrease in sediment supply. Changes in δ34S values of sulfate in the sediment beginning ~10 ka indicate an increase in marine sources. Similarly, δ2H values from palmitic acid show a steady increase at ~10 ka, likely resulting from aridification of the region during the Holocene. Due to the extreme aridity in the region, these sand dunes retain a well-preserved chemical record that reflects changes in elevation and coastal proximity after the last glacial maximum.

The Cretaceous-Paleogene boundary (KPB) in the Hell Creek area of Montana is recognized in several places by an iridium anomaly, which is typically identified at or very near the lithological contact between the Hell Creek Formation and the Tullock Member of the Fort Union Formation. Previous work in the area has argued that organic carbon isotope (δ13Corg) excursions can be used for chemostratigraphic correlation within these continental depositional environments, most importantly for the identification of the KPB where impact evidence is unavailable. However, it is unclear how modern surficial weathering affects δ13Corg values, particularly in terrestrial depositional settings, and whether standard sampling methods are sufficient to obtain unaltered rock material. We tested the fidelity of the terrestrial δ13Corg record with respect to surficial alteration and contamination through investigation of different field sampling techniques, including hand trenches, a backhoe-excavated trench, and sediment coring. We find that δ13Corg values in hand and backhoe trenched sections are more positive than δ13Corg values in cored sections, implying that modern surficial alteration affects δ13Corg values but not overall trends. A negative δ13Corg excursion associated with the KPB is present in most sections we analyzed, but it does not appear to be unique within our sections. The KPB excursion occurs within a coal layer, and we observe similar excursions within other carbon-rich lithologies. Given that we cannot disentangle local lithological effects from global atmospheric changes, we conclude that a negative δ13Corg excursion is not an unequivocal indicator of the KPB in the Hell Creek area.

Raman spectroscopy has emerged as a powerful, non-contact, non-destructive technique for detection and characterization of in situ organic compounds. Excitation using deep UV wavelengths (

The CanMars Mars Sample Return Analogue Deployment (MSRAD) was a closely simulated, end-to-end Mars Sample Return (MSR) mission scenario, with instrumentation, goals, and constraints modeled on the upcoming NASA Mars 2020 rover mission; this paper reports on the post-mission validation of the exercise. The exercise utilized the CSA Mars Exploration Science Rover (MESR) rover, deployed to Utah, USA, at a Mars-analogue field site. The principal features of the field site located near Green River, Utah are Late Jurassic inverted, fluvial paleochannels, analogous to features on Mars in sites being considered for the ESA ExoMars rover mission and present within the chosen landing site for the Mars 2020 rover mission. The in-simulation (“in-sim”) mission operations team worked remotely from The University of Western Ontario, Canada. A suite of MESR-integrated and hand-held spectrometers was selected to mimic those of the Mars 2020 payload, and a Utah-based, on-site team was tasked with field operations to carry out the data collection and sampling as commanded by the in-sim team. As a validation of the in-sim mission science findings, the field team performed an independent geological assessment. This paper documents the field team's on-site geological assessment and subsequent laboratory and analytical results, then offers a comparison of mission (in-sim) and post-mission (laboratory) science results. The laboratory-based findings were largely consistent with the in-sim rover-derived data and geological interpretations, though some notable exceptions highlight the inherent difficulties in remote science. In some cases, available data was insufficient for lithologic identification given the absence of other important contextual information (e.g., textural information). This study suggests that the in-sim instruments were largely adequate for the Science Team to characterize samples; however, rover-based field work is necessarily hampered by mobility and time constraints with an obvious effect on efficiency but also precision, and to some extent, accuracy of the findings. The data show a dearth of preserved total organic carbon (TOC) – used as a proxy for ancient biosignature preservation potential – in the fluvial-lacustrine system of this field site, suggesting serious consideration with respect to the capabilities and opportunities for addressing the Mars exploration goals. We therefore suggest a thorough characterization of terrestrial sites analogous to those of Mars rover landing sites, and in-depth field studies like CanMars as important, pre-mission strategic exercises.

The pervasiveness of black shale preservation in association with Late Devonian biological crises suggests marine anoxia played a major role in driving ecological perturbations. However, Devonian black shale deposition is still mechanistically poorly understood. We have compiled detailed biomarker lipid chemostratigraphic records for 83 different rock samples using molecular constituents of bitumens of Upper Kellwasser equivalent black shales from two foreland basins: from the low paleolatitude Appalachian Basin (New York State) and from the high paleolatitude Madre de Dios Basin (Bolivia), in order to better understand local environmental conditions and organic source inputs during this depositional event. Despite strong indications from stable nitrogen isotopic signatures for fixed nitrogen nutrient limitation, the biomarker assemblages with consistently low-moderate hopane/sterane ratios ( 28 /C 29 sterane ratios at higher paleolatitude in the more nutrient-replete Madre de Dios Basin suggest prasinophyte microalgae flourished in this setting in accordance with palynological evidence for high contributions of Tasmanites cysts in these strata. All samples contain only very low absolute amounts of aryl isoprenoids (with 2,3,6-trimethyl substitution) and other aromatic carotenoids, up to several orders of magnitude lower than concentrations reported from other Phanerozoic euxinic basins. These data are consistent with local marine paleo-redox models for both basins lacking a persistently shallow sulfidic aquatic zone and demonstrate that temporally persistent or spatially pervasive photic zone euxinia is not necessarily associated with all black shale sequences in the Late Devonian.

The Koonwarra Fossil Beds are widely recognized for their high-fidelity preservation of freshwater/terrestrial vertebrate and invertebrate fossils. A preliminary investigation suggests that organic biomarkers are also exceptionally well preserved and could contribute significantly to understanding the ecology of this ancient lake system. Solvent-extractable organic matter was collected from a single feldspathic siltstone/mudstone sample and analyzed using gas chromatography-mass spectrometry (GC-MS). The distribution of n-alkanes suggests a significant input of terrestrial plant material into the lake. The very low ratio of eukaryotic steranes to bacterial hopanes may reflect the decomposition of abundant plant material in the lake. Polycyclic aromatic hydrocarbons may record wildfire activity in the surrounding watershed.

The Late Devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the Earth's atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems. The biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox-mediated reactions that comprise the marine N cycle. In order to explore the impact of climate change on N biogeochemistry in a Late Devonian epeiric sea, we sampled a core from the Appalachian Basin that spans the interval from the greenhouse climate at the base of the Famennian period to glacial conditions near its conclusion. Based upon stable isotope analysis of N, C, and S as well as elemental analysis of N, C, P, S, and Fe, we contend that two distinct biogeochemical regimes obtained during the contrasting climates. The greenhouse regime featured low seawater O2 and pH that served to significantly curtail the oxidation of ammonia – i.e. nitrification – resulting in an ammonium-dominated water column and low sediment δ15N values. The greenhouse also featured more extensive recycling of C, N, and P. In contrast, the higher seawater O2 and pH of the icehouse regime permitted nitrification in the water column resulting in a nitrate-dominated system and higher sediment δ15N values. We conclude that nitrification was the key component of the N cycle that differentiated the two climate/biogeochemical regimes.

MAGNETIC RESONANCE IMAGING (MRI) is the modality of choice for noninvasive morphologic evaluation of articular cartilage (1). With promising new treatment options available for patients with osteoarthritis and posttraumatic cartilage defects, there is increased need for detecting early morphologic changes of articular cartilage (2-6). Cartilage volume measurements are also an important component of research studies designed to better understand the pathogenesis of osteoarthritis and to evaluate the efficacy of newly developed disease-modifying agents (7,8). For these reasons there has been much recent effort to develop MRI pulse sequences that allow more accurate assessment of cartilage morphology (9). MRI sequences used to evaluate cartilage morphology can be broadly divided into dark fluid and bright fluid sequences, depending on the signal intensity of synovial fluid. Dark fluid cartilage imaging is primarily performed using spoiled gradient recalled-echo (SPGR) sequences. SPGR sequences have been successfully used to evaluate articular cartilage in clinical practice (10,11) and to perform cartilage volume measurements in research studies (12-15). However, the main disadvantage of using these sequences for clinical cartilage imaging is the low signal intensity of synovial fluid, which may decrease the conspicuity of superficial cartilage lesions (16,17). Bright fluid cartilage imaging sequences include T2-weighted and intermediate-weighted fast spin-echo (FSE) (16,18-20), driven equilibrium Fourier transform (DEFT) (21), dual echo in the steady-state (DESS) (22,23), and various steady-state free-precession (SSFP) sequences (24-28). Bright fluid sequences are especially useful for clinical cartilage imaging since the high signal intensity synovial fluid creates an arthrogram-like effect against the intermediate-to-low signal intensity articular cartilage. However, there are disadvantages associated with all currently available bright fluid cartilage imaging sequences. Intermediate-weighted FSE images suffer from blurring due to the acquisition of high spatial frequencies late in the echo train. T2-weighted FSE images have poor contrast between articular cartilage and subchondral bone, which makes it difficult to detect diffuse cartilage thinning and to determine the exact thickness of focal cartilage defects. On DESS images it is often difficult to delineate articular cartilage when synovial fluid is not present within the joint to create an arthrogram-like effect. SSFP images are prone to banding artifact in areas of magnetic susceptibility, which is particularly severe at 3.0T. Gradient refocused acquisition in the steady-state (GRASS) is another sequence that can produce three-dimensional images of the knee with bright synovial fluid due to coherence of transverse magnetization with secondary T2 weighting. GRASS sequences have been previously used to evaluate the articular cartilage of the knee joint (29-31). Suppressing signal from adipose tissue can improve GRASS cartilage assessment by reducing chemical shift artifact and by optimizing the overall dynamic contrast range of the images (32). However, there are no previously published studies on the evaluation of articular cartilage using a fat-suppressed GRASS sequence. This is perhaps secondary to the poor signal-to-noise ratio (SNR) efficiency of currently available fat-suppressed GRASS sequences that prevents them from providing complete anatomic coverage of the knee joint in a reasonable scan time. Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) is a recently developed chemical shift-based technique that may be useful for providing fat-water separation for GRASS cartilage imaging. IDEAL is a three-point fat-water separation method that uses asymmetric echoes and least-squares estimation in order to achieve the maximum possible SNR performance. Echo shifts are optimized to provide the most effective signal averaging at 3.0T (33-36). Signal from the source images is decomposed into separate fat and water signals using a least-squares solution matrix inversion (37). Once fat and water have been separated they can be recombined into in-phase (water+fat) and out-of-phase (water−fat) images after correction for chemical shift artifact in the readout direction (34,35,37). IDEAL fat-water separation has been previously used in SPGR (38) and SSFP (25) cartilage imaging. This study was performed to demonstrate the feasibility of combining IDEAL fat-water separation with a GRASS sequence to produce high-quality 3D images of the knee with bright synovial fluid at 3.0T. This study was also performed to provide a preliminary comparison of the IDEAL-GRASS and IDEAL-SPGR sequences for evaluating articular cartilage and to demonstrate the usefulness of the IDEAL-GRASS sequence for clinical cartilage imaging.