How to Search for Life in Martian Chemical Sediments and Their Fluid and Solid Inclusions Using Petrographic and Spectroscopic Methods

Abundant resources and efforts have been employed in the search for life on Mars. Satellites, landers, and rovers have tested atmospheric gases, general sediment and rock compositions, and images of Mars surface in an effort to detect biosignatures left by any possible modern or ancient life. Chloride and sulfate minerals suggestive of past acid saline lakes have been found on Mars. In terrestrial acid brine environments, these minerals trap microorganisms and organic compounds and preserve them within fluid inclusions and as solid inclusions for long geologic time periods. Some cells remain viable, especially in the isolated, microscopic aqueous environments of fluid inclusions. Fluid inclusions in these same saline minerals on Mars have yet to be examined. This paper describes petrographic and geochemical methods that have been used recently to detect and make general identifications of microorganisms and organic compounds preserved in modern and Permian Mars-analog acid saline lake halite and gypsum. It then makes recommendations for how Martian chemical sediments could be examined for these biosignatures, both by rovers and in returned samples. This new protocol for the examination of Martian chemical sediments and sedimentary rocks may provide the next step for detection of any preserved biosignatures on Mars

Early Acidification of Mars and the Potential Implications for Biology

A leading paleoclimate theory for Mars, based on the identification of phyllosilicate minerals in ancient terrains, posits that the first several million years of the planet’s history were dominated by neutral to alkaline pH. However, evidence is mounting for the consideration of an alternate hypothesis: that some smectites on Mars formed under acidic conditions, and that the early surface of Mars may not have been subject to circum-neutral pH conditions, at least not uniformly. Work on shergottitic liquids suggests that up to 2400 ppm of sulfur could have degassed from martian magma, supplying more than enough sulfur for the planet’s sulfate-rich sediments and sedimentary rocks, and isotopic evidence of mass independent fractionation reveals that sulfur in martian meteorites underwent atmospheric reactions. Radiative modeling of sulfur volatiles in the martian atmosphere indicates that SO2 and H2S would have acted as powerful greenhouse gases trapping heat in different wavelength-dependent atmospheric windows than CO2 and H2O, supplying the necessary heat for surface temperatures to rise above freezing. Photochemistry suggests that sulfur would have been removed from the atmosphere through the deposition of sulfur dioxide, oxidized to sulfate at the surfaceatmosphere interface. This, in turn, could have led to the early acidification of the surface, thereby explaining the paucity of carbonates on Mars. This idea is supported by 1) the recent laboratory synthesis of Fe/Mg smectite from an Adirondack basalt simulant in an acidic hydrothermal system, and 2) studies of the mineral composition of terrestrial analogs, particularly at acid salt lakes

Biosignatures in Mars Analog Acid Salt Lakes

Paleolake sites on Mars, particularly buried deposits that have been shielded from surface radiation, serve as intriguing targets for the search for life. Mars-like ephemeral playa lakes here on Earth can offer insights and perspectives on the possibilities for physical, metabolic, and biomolecular biosignature recovery from similar environments on Mars

Report on ICDP Deep Dust workshops: probing continental climate of the late Paleozoic icehouse–greenhouse transition and beyond

Chamberlin and Salisbury's assessment of the Permian a century ago captured the essence of the period: it is an interval of extremes yet one sufficiently recent to have affected a biosphere with near-modern complexity. The events of the Permian - the orogenic episodes, massive biospheric turnovers, both icehouse and greenhouse antitheses, and Mars-analog lithofacies - boggle the imagination and present us with great opportunities to explore Earth system behavior. The ICDP-funded workshops dubbed "Deep Dust," held in Oklahoma (USA) in March 2019 (67 participants from nine countries) and Paris (France) in January 2020 (33 participants from eight countries), focused on clarifying the scientific drivers and key sites for coring continuous sections of Permian continental (loess, lacustrine, and associated) strata that preserve high-resolution records. Combined, the two workshops hosted a total of 91 participants representing 14 countries, with broad expertise. Discussions at Deep Dust 1.0 (USA) focused on the primary research questions of paleoclimate, paleoenvironments, and paleoecology of icehouse collapse and the run-up to the Great Dying and both the modern and Permian deep microbial biosphere. Auxiliary science topics included tectonics, induced seismicity, geothermal energy, and planetary science. Deep Dust 1.0 also addressed site selection as well as scientific approaches, logistical challenges, and broader impacts and included a mid-workshop field trip to view the Permian of Oklahoma. Deep Dust 2.0 focused specifically on honing the European target. The Anadarko Basin (Oklahoma) and Paris Basin (France) represent the most promising initial targets to capture complete or near-complete stratigraphic coverage through continental successions that serve as reference points for western and eastern equatorial Pangaea. © 2020 Copernicus GmbH. All rights reserved

Report on ICDP Deep Dust workshops: probing continental climate of the late Paleozoic icehouse–greenhouse transition and beyond

Chamberlin and Salisbury's assessment of the Permian a century ago captured the essence of the period: it is an interval of extremes yet one sufficiently recent to have affected a biosphere with near-modern complexity. The events of the Permian - the orogenic episodes, massive biospheric turnovers, both icehouse and greenhouse antitheses, and Mars-analog lithofacies - boggle the imagination and present us with great opportunities to explore Earth system behavior. The ICDP-funded workshops dubbed "Deep Dust," held in Oklahoma (USA) in March 2019 (67 participants from nine countries) and Paris (France) in January 2020 (33 participants from eight countries), focused on clarifying the scientific drivers and key sites for coring continuous sections of Permian continental (loess, lacustrine, and associated) strata that preserve high-resolution records. Combined, the two workshops hosted a total of 91 participants representing 14 countries, with broad expertise. Discussions at Deep Dust 1.0 (USA) focused on the primary research questions of paleoclimate, paleoenvironments, and paleoecology of icehouse collapse and the run-up to the Great Dying and both the modern and Permian deep microbial biosphere. Auxiliary science topics included tectonics, induced seismicity, geothermal energy, and planetary science. Deep Dust 1.0 also addressed site selection as well as scientific approaches, logistical challenges, and broader impacts and included a mid-workshop field trip to view the Permian of Oklahoma. Deep Dust 2.0 focused specifically on honing the European target. The Anadarko Basin (Oklahoma) and Paris Basin (France) represent the most promising initial targets to capture complete or near-complete stratigraphic coverage through continental successions that serve as reference points for western and eastern equatorial Pangaea.This research has been supported by the ICDP (DeepDust2019 grant).Ye

Aqueous alteration processes in Jezero crater, Mars—implications for organic geochemistry

The Perseverance rover landed in Jezero crater, Mars, in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep-ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, which probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks and are preserved in minerals related to both aqueous environments

Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial

SummaryBackground Azithromycin has been proposed as a treatment for COVID-19 on the basis of its immunomodulatoryactions. We aimed to evaluate the safety and efficacy of azithromycin in patients admitted to hospital with COVID-19.Methods In this randomised, controlled, open-label, adaptive platform trial (Randomised Evaluation of COVID-19Therapy [RECOVERY]), several possible treatments were compared with usual care in patients admitted to hospitalwith COVID-19 in the UK. The trial is underway at 176 hospitals in the UK. Eligible and consenting patients wererandomly allocated to either usual standard of care alone or usual standard of care plus azithromycin 500 mg once perday by mouth or intravenously for 10 days or until discharge (or allocation to one of the other RECOVERY treatmentgroups). Patients were assigned via web-based simple (unstratified) randomisation with allocation concealment andwere twice as likely to be randomly assigned to usual care than to any of the active treatment groups. Participants andlocal study staff were not masked to the allocated treatment, but all others involved in the trial were masked to theoutcome data during the trial. The primary outcome was 28-day all-cause mortality, assessed in the intention-to-treatpopulation. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.Findings Between April 7 and Nov 27, 2020, of 16 442 patients enrolled in the RECOVERY trial, 9433 (57%) wereeligible and 7763 were included in the assessment of azithromycin. The mean age of these study participants was65·3 years (SD 15·7) and approximately a third were women (2944 [38%] of 7763). 2582 patients were randomlyallocated to receive azithromycin and 5181 patients were randomly allocated to usual care alone. Overall,561 (22%) patients allocated to azithromycin and 1162 (22%) patients allocated to usual care died within 28 days(rate ratio 0·97, 95% CI 0·87–1·07; p=0·50). No significant difference was seen in duration of hospital stay (median10 days [IQR 5 to >28] vs 11 days [5 to >28]) or the proportion of patients discharged from hospital alive within 28 days(rate ratio 1·04, 95% CI 0·98–1·10; p=0·19). Among those not on invasive mechanical ventilation at baseline, nosignificant difference was seen in the proportion meeting the composite endpoint of invasive mechanical ventilationor death (risk ratio 0·95, 95% CI 0·87–1·03; p=0·24).Interpretation In patients admitted to hospital with COVID-19, azithromycin did not improve survival or otherprespecified clinical outcomes. Azithromycin use in patients admitted to hospital with COVID-19 should be restrictedto patients in whom there is a clear antimicrobial indication