1
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de Kock MO, Malatji I, Wabo H, Mukhopadhyay J, Banerjee A, Maré LP. High-latitude platform carbonate deposition constitutes a climate conundrum at the terminal Mesoproterozoic. Nat Commun 2024; 15:2024. [PMID: 38448467 PMCID: PMC10918070 DOI: 10.1038/s41467-024-46390-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 02/26/2024] [Indexed: 03/08/2024] Open
Abstract
During the Mesoproterozoic Era, 1600 to 1000 million years ago, global climate was warm with very little evidence of glaciation. Substantial greenhouse warming would have been required to sustain this ice-free state given 5-18% lower solar luminosity. Paleomagnetic data reported here place voluminous ca. 1.2 Ga shallow marine carbonate deposits from India at an unexpectedly high latitude of around 70° from the equator. Previous studies noted high latitudes, but their implication was never considered. Here, we evaluate the temporal-latitudinal distribution of neritic carbonate deposits across the Proterozoic and identify similar deposits from North China that together with those from India are seemingly unique to the late Mesoproterozoic. A uniformitarian interpretation implies that this is cold-water carbonate deposition, but facies similarity with low-latitude neritic deposits rather suggests a hotter climate and elevated polar ocean temperatures of 15-20° or higher. This interpretation represents a climate conundrum that would require much greater greenhouse warming than documented for the Mesoproterozoic.
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Affiliation(s)
- Michiel O de Kock
- Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, South Africa.
| | - Ingrit Malatji
- Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, South Africa
| | - Herve Wabo
- Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, South Africa
| | - Joydip Mukhopadhyay
- Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, South Africa
- Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research, Odisha, Berhampur, India
| | - Amlan Banerjee
- Geological Studies Unit, Indian Statistical Institute, 203 B. T. Road, Kolkata, West Bengal, India
| | - L P Maré
- Council for Geoscience, Private Bag X112, Pretoria, South Africa
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2
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Cooke GJ, Marsh DR, Walsh C, Black B, Lamarque JF. A revised lower estimate of ozone columns during Earth's oxygenated history. ROYAL SOCIETY OPEN SCIENCE 2022; 9:211165. [PMID: 35070343 PMCID: PMC8728182 DOI: 10.1098/rsos.211165] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 11/25/2021] [Indexed: 05/17/2023]
Abstract
The history of molecular oxygen (O2) in Earth's atmosphere is still debated; however, geological evidence supports at least two major episodes where O2 increased by an order of magnitude or more: the Great Oxidation Event (GOE) and the Neoproterozoic Oxidation Event. O2 concentrations have likely fluctuated (between 10-3 and 1.5 times the present atmospheric level) since the GOE ∼2.4 Gyr ago, resulting in a time-varying ozone (O3) layer. Using a three-dimensional chemistry-climate model, we simulate changes in O3 in Earth's atmosphere since the GOE and consider the implications for surface habitability, and glaciation during the Mesoproterozoic. We find lower O3 columns (reduced by up to 4.68 times for a given O2 level) compared to previous work; hence, higher fluxes of biologically harmful UV radiation would have reached the surface. Reduced O3 leads to enhanced tropospheric production of the hydroxyl radical (OH) which then substantially reduces the lifetime of methane (CH4). We show that a CH4 supported greenhouse effect during the Mesoproterozoic is highly unlikely. The reduced O3 columns we simulate have important implications for astrobiological and terrestrial habitability, demonstrating the relevance of three-dimensional chemistry-climate simulations when assessing paleoclimates and the habitability of faraway worlds.
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Affiliation(s)
- G. J. Cooke
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - D. R. Marsh
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
- National Center for Atmospheric Research, Boulder, CO 80301, USA
| | - C. Walsh
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - B. Black
- Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA
- Department of Earth and Atmospheric Sciences, CUNY City College, New York, NY, USA
| | - J.-F. Lamarque
- National Center for Atmospheric Research, Boulder, CO 80301, USA
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3
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Triple oxygen isotope constraints on atmospheric O 2 and biological productivity during the mid-Proterozoic. Proc Natl Acad Sci U S A 2021; 118:2105074118. [PMID: 34911756 PMCID: PMC8713798 DOI: 10.1073/pnas.2105074118] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/02/2021] [Indexed: 12/16/2022] Open
Abstract
Reconstructing the history of biological productivity and atmospheric oxygen partial pressure (pO2) is a fundamental goal of geobiology. Recently, the mass-independent fractionation of oxygen isotopes (O-MIF) has been used as a tool for estimating pO2 and productivity during the Proterozoic. O-MIF, reported as Δ'17O, is produced during the formation of ozone and destroyed by isotopic exchange with water by biological and chemical processes. Atmospheric O-MIF can be preserved in the geologic record when pyrite (FeS2) is oxidized during weathering, and the sulfur is redeposited as sulfate. Here, sedimentary sulfates from the ∼1.4-Ga Sibley Formation are reanalyzed using a detailed one-dimensional photochemical model that includes physical constraints on air-sea gas exchange. Previous analyses of these data concluded that pO2 at that time was <1% PAL (times the present atmospheric level). Our model shows that the upper limit on pO2 is essentially unconstrained by these data. Indeed, pO2 levels below 0.8% PAL are possible only if atmospheric methane was more abundant than today (so that pCO2 could have been lower) or if the Sibley O-MIF data were diluted by reprocessing before the sulfates were deposited. Our model also shows that, contrary to previous assertions, marine productivity cannot be reliably constrained by the O-MIF data because the exchange of molecular oxygen (O2) between the atmosphere and surface ocean is controlled more by air-sea gas transfer rates than by biological productivity. Improved estimates of pCO2 and/or improved proxies for Δ'17O of atmospheric O2 would allow tighter constraints to be placed on mid-Proterozoic pO2.
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4
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Roland FAE, Borges AV, Darchambeau F, Llirós M, Descy JP, Morana C. The possible occurrence of iron-dependent anaerobic methane oxidation in an Archean Ocean analogue. Sci Rep 2021; 11:1597. [PMID: 33452366 PMCID: PMC7810693 DOI: 10.1038/s41598-021-81210-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Accepted: 01/05/2021] [Indexed: 11/24/2022] Open
Abstract
In the ferruginous and anoxic early Earth oceans, photoferrotrophy drove most of the biological production before the advent of oxygenic photosynthesis, but its association with ferric iron (Fe3+) dependent anaerobic methane (CH4) oxidation (AOM) has been poorly investigated. We studied AOM in Kabuno Bay, a modern analogue to the Archean Ocean (anoxic bottom waters and dissolved Fe concentrations > 600 µmol L-1). Aerobic and anaerobic CH4 oxidation rates up to 0.12 ± 0.03 and 51 ± 1 µmol L-1 d-1, respectively, were put in evidence. In the Fe oxidation-reduction zone, we observed high concentration of Bacteriochlorophyll e (biomarker of the anoxygenic photoautotrophs), which co-occurred with the maximum CH4 oxidation peaks, and a high abundance of Candidatus Methanoperedens, which can couple AOM to Fe3+ reduction. In addition, comparison of measured CH4 oxidation rates with electron acceptor fluxes suggest that AOM could mainly rely on Fe3+ produced by photoferrotrophs. Further experiments specifically targeted to investigate the interactions between photoferrotrophs and AOM would be of considerable interest. Indeed, ferric Fe3+-driven AOM has been poorly envisaged as a possible metabolic process in the Archean ocean, but this can potentially change the conceptualization and modelling of metabolic and geochemical processes controlling climate conditions in the Early Earth.
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Affiliation(s)
- Fleur A E Roland
- Chemical Oceanography Unit, Université de Liège, Liège, Belgium.
| | | | | | - Marc Llirós
- Department of Genetics and Microbiology, Universitat Autònoma de Barcelona, Barcelona, Spain
- Girona Biomedical Research Institute, Salt, Catalunya, Spain
| | | | - Cédric Morana
- Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven (KU Leuven), Leuven, Belgium
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5
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Parsons C, Stüeken EE, Rosen CJ, Mateos K, Anderson RE. Radiation of nitrogen-metabolizing enzymes across the tree of life tracks environmental transitions in Earth history. GEOBIOLOGY 2021; 19:18-34. [PMID: 33108025 PMCID: PMC7894544 DOI: 10.1111/gbi.12419] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Revised: 09/28/2020] [Accepted: 10/05/2020] [Indexed: 05/03/2023]
Abstract
Nitrogen is an essential element to life and exerts a strong control on global biological productivity. The rise and spread of nitrogen-utilizing microbial metabolisms profoundly shaped the biosphere on the early Earth. Here, we reconciled gene and species trees to identify birth and horizontal gene transfer events for key nitrogen-cycling genes, dated with a time-calibrated tree of life, in order to examine the timing of the proliferation of these metabolisms across the tree of life. Our results provide new insights into the evolution of the early nitrogen cycle that expand on geochemical reconstructions. We observed widespread horizontal gene transfer of molybdenum-based nitrogenase back to the Archean, minor horizontal transfer of genes for nitrate reduction in the Archean, and an increase in the proliferation of genes metabolizing nitrite around the time of the Mesoproterozoic (~1.5 Ga). The latter coincides with recent geochemical evidence for a mid-Proterozoic rise in oxygen levels. Geochemical evidence of biological nitrate utilization in the Archean and early Proterozoic may reflect at least some contribution of dissimilatory nitrate reduction to ammonium (DNRA) rather than pure denitrification to N2 . Our results thus help unravel the relative dominance of two metabolic pathways that are not distinguishable with current geochemical tools. Overall, our findings thus provide novel constraints for understanding the evolution of the nitrogen cycle over time and provide insights into the bioavailability of various nitrogen sources in the early Earth with possible implications for the emergence of eukaryotic life.
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Affiliation(s)
- Chris Parsons
- Carleton CollegeNorthfieldMNUSA
- Massachusetts Institute of TechnologyCambridgeMAUSA
| | | | | | | | - Rika E. Anderson
- Carleton CollegeNorthfieldMNUSA
- NASA NExSS Virtual Planetary LaboratoryUniversity of WashingtonSeattleWAUSA
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6
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Fuchsman CA, Stüeken EE. Using modern low-oxygen marine ecosystems to understand the nitrogen cycle of the Paleo- and Mesoproterozoic oceans. Environ Microbiol 2020; 23:2801-2822. [PMID: 32869502 DOI: 10.1111/1462-2920.15220] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 08/25/2020] [Accepted: 08/27/2020] [Indexed: 11/29/2022]
Abstract
During the productive Paleoproterozoic (2.4-1.8 Ga) and less productive Mesoproterozoic (1.8-1.0 Ga), the ocean was suboxic to anoxic and multicellular organisms had not yet evolved. Here, we link geologic information about the Proterozoic ocean to microbial processes in modern low-oxygen systems. High iron concentrations and rates of Fe cycling in the Proterozoic are the largest differences from modern oxygen-deficient zones. In anoxic waters, which composed most of the Paleoproterozoic and ~40% of the Mesoproterozoic ocean, nitrogen cycling dominated. Rates of N2 production by denitrification and anammox were likely linked to sinking organic matter fluxes and in situ primary productivity under anoxic conditions. Additionally autotrophic denitrifiers could have used reduced iron or methane. 50% of the Mesoproterozoic ocean may have been suboxic, promoting nitrification and metal oxidation in the suboxic water and N2 O and N2 production by partial and complete denitrification in anoxic zones in organic aggregates. Sulfidic conditions may have composed ~10% of the Mesoproterozoic ocean focused along continental margins. Due to low nitrate concentrations in offshore regions, anammox bacteria likely dominated N2 production immediately above sulfidic zones, but in coastal regions, higher nitrate concentrations probably promoted complete S-oxidizing autotrophic denitrification at the sulfide interface.
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Affiliation(s)
- Clara A Fuchsman
- Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, MD, 21613, USA
| | - Eva E Stüeken
- School of Earth & Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL, Scotland, UK
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7
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Stanton CL, Reinhard CT, Kasting JF, Ostrom NE, Haslun JA, Lyons TW, Glass JB. Nitrous oxide from chemodenitrification: A possible missing link in the Proterozoic greenhouse and the evolution of aerobic respiration. GEOBIOLOGY 2018; 16:597-609. [PMID: 30133143 DOI: 10.1111/gbi.12311] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 06/23/2018] [Accepted: 07/02/2018] [Indexed: 05/26/2023]
Abstract
The potent greenhouse gas nitrous oxide (N2 O) may have been an important constituent of Earth's atmosphere during Proterozoic (~2.5-0.5 Ga). Here, we tested the hypothesis that chemodenitrification, the rapid reduction of nitric oxide by ferrous iron, would have enhanced the flux of N2 O from ferruginous Proterozoic seas. We empirically derived a rate law, d N 2 O d t = 7.2 × 10 - 5 [ Fe 2 + ] 0.3 [ NO ] 1 , and measured an isotopic site preference of +16‰ for the reaction. Using this empirical rate law, and integrating across an oceanwide oxycline, we found that low nM NO and μM-low mM Fe2+ concentrations could have sustained a sea-air flux of 100-200 Tg N2 O-N year-1 , if N2 fixation rates were near-modern and all fixed N2 was emitted as N2 O. A 1D photochemical model was used to obtain steady-state atmospheric N2 O concentrations as a function of sea-air N2 O flux across the wide range of possible pO2 values (0.001-1 PAL). At 100-200 Tg N2 O-N year-1 and >0.1 PAL O2 , this model yielded low-ppmv N2 O, which would produce several degrees of greenhouse warming at 1.6 ppmv CH4 and 320 ppmv CO2 . These results suggest that enhanced N2 O production in ferruginous seawater via a previously unconsidered chemodenitrification pathway may have helped to fill a Proterozoic "greenhouse gap," reconciling an ice-free Mesoproterozoic Earth with a less luminous early Sun. A particularly notable result was that high N2 O fluxes at intermediate O2 concentrations (0.01-0.1 PAL) would have enhanced ozone screening of solar UV radiation. Due to rapid photolysis in the absence of an ozone shield, N2 O is unlikely to have been an important greenhouse gas if Mesoproterozoic O2 was 0.001 PAL. At low O2 , N2 O might have played a more important role as life's primary terminal electron acceptor during the transition from an anoxic to oxic surface Earth, and correspondingly, from anaerobic to aerobic metabolisms.
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Affiliation(s)
- Chloe L Stanton
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
- Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania
| | - Christopher T Reinhard
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - James F Kasting
- Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania
| | - Nathaniel E Ostrom
- Department of Integrative Biology, Michigan State University, East Lansing, Michigan
- DOE Great Lakes Bioenergy Research Institute, Michigan State University, East Lansing, Michigan
| | - Joshua A Haslun
- Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan
| | - Timothy W Lyons
- Department of Earth Sciences, University of California, Riverside, California
| | - Jennifer B Glass
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
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8
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Schwieterman EW, Kiang NY, Parenteau MN, Harman CE, DasSarma S, Fisher TM, Arney GN, Hartnett HE, Reinhard CT, Olson SL, Meadows VS, Cockell CS, Walker SI, Grenfell JL, Hegde S, Rugheimer S, Hu R, Lyons TW. Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life. ASTROBIOLOGY 2018; 18:663-708. [PMID: 29727196 PMCID: PMC6016574 DOI: 10.1089/ast.2017.1729] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Accepted: 12/10/2017] [Indexed: 05/04/2023]
Abstract
In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward. Key Words: Exoplanets-Biosignatures-Habitability markers-Photosynthesis-Planetary surfaces-Atmospheres-Spectroscopy-Cryptic biospheres-False positives. Astrobiology 18, 663-708.
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Affiliation(s)
- Edward W. Schwieterman
- Department of Earth Sciences, University of California, Riverside, California
- NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
- Blue Marble Space Institute of Science, Seattle, Washington
| | - Nancy Y. Kiang
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Goddard Institute for Space Studies, New York, New York
| | - Mary N. Parenteau
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Ames Research Center, Exobiology Branch, Mountain View, California
| | - Chester E. Harman
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Goddard Institute for Space Studies, New York, New York
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York
| | - Shiladitya DasSarma
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland
- Institute of Marine and Environmental Technology, University System of Maryland, Baltimore, Maryland
| | - Theresa M. Fisher
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona
| | - Giada N. Arney
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Hilairy E. Hartnett
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona
- School of Molecular Sciences, Arizona State University, Tempe, Arizona
| | - Christopher T. Reinhard
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
| | - Stephanie L. Olson
- Department of Earth Sciences, University of California, Riverside, California
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
| | - Victoria S. Meadows
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- Astronomy Department, University of Washington, Seattle, Washington
| | - Charles S. Cockell
- University of Edinburgh School of Physics and Astronomy, Edinburgh, United Kingdom
- UK Centre for Astrobiology, Edinburgh, United Kingdom
| | - Sara I. Walker
- Blue Marble Space Institute of Science, Seattle, Washington
- School of Earth and Space Exploration, Arizona State University, Tempe, Arizona
- Beyond Center for Fundamental Concepts in Science, Arizona State University, Tempe, Arizona
- ASU-Santa Fe Institute Center for Biosocial Complex Systems, Arizona State University, Tempe, Arizona
| | - John Lee Grenfell
- Institut für Planetenforschung (PF), Deutsches Zentrum für Luft und Raumfahrt (DLR), Berlin, Germany
| | - Siddharth Hegde
- Carl Sagan Institute, Cornell University, Ithaca, New York
- Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, New York
| | - Sarah Rugheimer
- Department of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, United Kingdom
| | - Renyu Hu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California
| | - Timothy W. Lyons
- Department of Earth Sciences, University of California, Riverside, California
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
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9
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Meadows VS, Reinhard CT, Arney GN, Parenteau MN, Schwieterman EW, Domagal-Goldman SD, Lincowski AP, Stapelfeldt KR, Rauer H, DasSarma S, Hegde S, Narita N, Deitrick R, Lustig-Yaeger J, Lyons TW, Siegler N, Grenfell JL. Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment. ASTROBIOLOGY 2018; 18:630-662. [PMID: 29746149 PMCID: PMC6014580 DOI: 10.1089/ast.2017.1727] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Accepted: 12/15/2017] [Indexed: 05/04/2023]
Abstract
We describe how environmental context can help determine whether oxygen (O2) detected in extrasolar planetary observations is more likely to have a biological source. Here we provide an in-depth, interdisciplinary example of O2 biosignature identification and observation, which serves as the prototype for the development of a general framework for biosignature assessment. Photosynthetically generated O2 is a potentially strong biosignature, and at high abundance, it was originally thought to be an unambiguous indicator for life. However, as a biosignature, O2 faces two major challenges: (1) it was only present at high abundance for a relatively short period of Earth's history and (2) we now know of several potential planetary mechanisms that can generate abundant O2 without life being present. Consequently, our ability to interpret both the presence and absence of O2 in an exoplanetary spectrum relies on understanding the environmental context. Here we examine the coevolution of life with the early Earth's environment to identify how the interplay of sources and sinks may have suppressed O2 release into the atmosphere for several billion years, producing a false negative for biologically generated O2. These studies suggest that planetary characteristics that may enhance false negatives should be considered when selecting targets for biosignature searches. We review the most recent knowledge of false positives for O2, planetary processes that may generate abundant atmospheric O2 without a biosphere. We provide examples of how future photometric, spectroscopic, and time-dependent observations of O2 and other aspects of the planetary environment can be used to rule out false positives and thereby increase our confidence that any observed O2 is indeed a biosignature. These insights will guide and inform the development of future exoplanet characterization missions. Key Words: Biosignatures-Oxygenic photosynthesis-Exoplanets-Planetary atmospheres. Astrobiology 18, 630-662.
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Affiliation(s)
- Victoria S. Meadows
- Department of Astronomy, University of Washington, Seattle, Washington
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
| | - Christopher T. Reinhard
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
| | - Giada N. Arney
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Mary N. Parenteau
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Ames Research Center, Exobiology Branch, Mountain View, California
| | - Edward W. Schwieterman
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
- Department of Earth Sciences, University of California, Riverside, California
- NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland
- Blue Marble Space Institute of Science, Seattle, Washington
| | - Shawn D. Domagal-Goldman
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Andrew P. Lincowski
- Department of Astronomy, University of Washington, Seattle, Washington
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
| | - Karl R. Stapelfeldt
- NASA Exoplanet Exploration Program, Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California
| | - Heike Rauer
- German Aerospace Center, Institute of Planetary Research, Extrasolar Planets and Atmospheres, Berlin, Germany
| | - Shiladitya DasSarma
- Department of Microbiology and Immunology, School of Medicine, University of Maryland, Baltimore, Maryland
- Institute of Marine and Environmental Technology, University System of Baltimore, Maryland
| | - Siddharth Hegde
- Carl Sagan Institute, Cornell University, Ithaca, New York
- Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, New York
| | - Norio Narita
- Department of Astronomy, The University of Tokyo, Tokyo, Japan
- Astrobiology Center, NINS, Tokyo, Japan
- National Astronomical Observatory of Japan, NINS, Tokyo, Japan
| | - Russell Deitrick
- Department of Astronomy, University of Washington, Seattle, Washington
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
| | - Jacob Lustig-Yaeger
- Department of Astronomy, University of Washington, Seattle, Washington
- NASA Astrobiology Institute, Virtual Planetary Laboratory Team, Seattle, Washington
| | - Timothy W. Lyons
- NASA Astrobiology Institute, Alternative Earths Team, Riverside, California
- Department of Earth Sciences, University of California, Riverside, California
| | - Nicholas Siegler
- NASA Exoplanet Exploration Program, Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California
| | - J. Lee Grenfell
- German Aerospace Center, Institute of Planetary Research, Extrasolar Planets and Atmospheres, Berlin, Germany
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10
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Meadows VS, Arney GN, Schwieterman EW, Lustig-Yaeger J, Lincowski AP, Robinson T, Domagal-Goldman SD, Deitrick R, Barnes RK, Fleming DP, Luger R, Driscoll PE, Quinn TR, Crisp D. The Habitability of Proxima Centauri b: Environmental States and Observational Discriminants. ASTROBIOLOGY 2018; 18:133-189. [PMID: 29431479 PMCID: PMC5820795 DOI: 10.1089/ast.2016.1589] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 09/04/2017] [Indexed: 05/21/2023]
Abstract
Proxima Centauri b provides an unprecedented opportunity to understand the evolution and nature of terrestrial planets orbiting M dwarfs. Although Proxima Cen b orbits within its star's habitable zone, multiple plausible evolutionary paths could have generated different environments that may or may not be habitable. Here, we use 1-D coupled climate-photochemical models to generate self-consistent atmospheres for several evolutionary scenarios, including high-O2, high-CO2, and more Earth-like atmospheres, with both oxic and anoxic compositions. We show that these modeled environments can be habitable or uninhabitable at Proxima Cen b's position in the habitable zone. We use radiative transfer models to generate synthetic spectra and thermal phase curves for these simulated environments, and use instrument models to explore our ability to discriminate between possible planetary states. These results are applicable not only to Proxima Cen b but to other terrestrial planets orbiting M dwarfs. Thermal phase curves may provide the first constraint on the existence of an atmosphere. We find that James Webb Space Telescope (JWST) observations longward of 10 μm could characterize atmospheric heat transport and molecular composition. Detection of ocean glint is unlikely with JWST but may be within the reach of larger-aperture telescopes. Direct imaging spectra may detect O4 absorption, which is diagnostic of massive water loss and O2 retention, rather than a photosynthetic biosphere. Similarly, strong CO2 and CO bands at wavelengths shortward of 2.5 μm would indicate a CO2-dominated atmosphere. If the planet is habitable and volatile-rich, direct imaging will be the best means of detecting habitability. Earth-like planets with microbial biospheres may be identified by the presence of CH4-which has a longer atmospheric lifetime under Proxima Centauri's incident UV-and either photosynthetically produced O2 or a hydrocarbon haze layer. Key Words: Planetary habitability and biosignatures-Planetary atmospheres-Exoplanets-Spectroscopic biosignatures-Planetary science-Proxima Centauri b. Astrobiology 18, 133-189.
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Affiliation(s)
- Victoria S. Meadows
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Giada N. Arney
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Edward W. Schwieterman
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland
- Department of Earth Sciences, University of California at Riverside, Riverside, California
| | - Jacob Lustig-Yaeger
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Andrew P. Lincowski
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Tyler Robinson
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, California
| | - Shawn D. Domagal-Goldman
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Russell Deitrick
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Rory K. Barnes
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - David P. Fleming
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Rodrigo Luger
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - Peter E. Driscoll
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC
| | - Thomas R. Quinn
- Astronomy Department, University of Washington, Seattle, Washington
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
| | - David Crisp
- NASA Astrobiology Institute—Virtual Planetary Laboratory Lead Team, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
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Krissansen-Totton J, Olson S, Catling DC. Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life. SCIENCE ADVANCES 2018; 4:eaao5747. [PMID: 29387792 PMCID: PMC5787383 DOI: 10.1126/sciadv.aao5747] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2017] [Accepted: 12/19/2017] [Indexed: 05/04/2023]
Abstract
Chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. Among solar system planets with substantial atmospheres, the modern Earth has the largest thermodynamic chemical disequilibrium due to the presence of life. However, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic Archean or less oxic Proterozoic eons are unknown. We calculate the atmosphere-ocean disequilibrium in the Precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions. We omit crustal solids because subsurface composition is not detectable on exoplanets, unlike above-surface volatiles. We find that (i) disequilibrium increased through time in step with the rise of oxygen; (ii) both the Proterozoic and Phanerozoic may have had remotely detectable biogenic disequilibria due to the coexistence of O2, N2, and liquid water; and (iii) the Archean had a biogenic disequilibrium caused by the coexistence of N2, CH4, CO2, and liquid water, which, for an exoplanet twin, may be remotely detectable. On the basis of this disequilibrium, we argue that the simultaneous detection of abundant CH4 and CO2 in a habitable exoplanet's atmosphere is a potential biosignature. Specifically, we show that methane mixing ratios greater than 10-3 are potentially biogenic, whereas those exceeding 10-2 are likely biogenic due to the difficulty in maintaining large abiotic methane fluxes to support high methane levels in anoxic atmospheres. Biogenicity would be strengthened by the absence of abundant CO, which should not coexist in a biological scenario.
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Affiliation(s)
- Joshua Krissansen-Totton
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington, Seattle, WA 98195, USA
- Virtual Planetary Laboratory, University of Washington, Seattle, WA 98195, USA
| | - Stephanie Olson
- Department of Earth Sciences and NASA Astrobiology Institute, University of California, Riverside, Riverside, CA 92521, USA
| | - David C. Catling
- Department of Earth and Space Sciences/Astrobiology Program, University of Washington, Seattle, WA 98195, USA
- Virtual Planetary Laboratory, University of Washington, Seattle, WA 98195, USA
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Abstract
AbstractOur Sun, a magnetically mild star, exhibits space weather in the form of magnetically driven solar explosive events (SEE) including solar flares, coronal mass ejections and energetic particle events. We use Kepler data and reconstruction of X-ray and UV emission from young solar-like stars to recover the frequency and energy fluxes from extreme events from active stars including the young Sun. Extreme SEEs from a magnetically active young Sun could significantly perturb the young Earth's magnetosphere, cause strong geomagnetic storms, initiate escape and introduce chemical changes in its lower atmosphere. I present our recent simulations results based on multi-dimensional multi-fluid hydrodynamic and magnetohydrodynamic models of interactions of extreme CME and SEP events with magnetospheres and lower atmospheres of early Earth and exoplanets around active stars. We also discuss the implications of the impact of these effects on evolving habitability conditions of the early Earth and prebiotic chemistry introduced by space weather events at the early phase of evolution of our Sun.
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Bray MS, Wu J, Reed BC, Kretz CB, Belli KM, Simister RL, Henny C, Stewart FJ, DiChristina TJ, Brandes JA, Fowle DA, Crowe SA, Glass JB. Shifting microbial communities sustain multiyear iron reduction and methanogenesis in ferruginous sediment incubations. GEOBIOLOGY 2017; 15:678-689. [PMID: 28419718 PMCID: PMC7780294 DOI: 10.1111/gbi.12239] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 03/17/2017] [Indexed: 05/16/2023]
Abstract
Reactive Fe(III) minerals can influence methane (CH4 ) emissions by inhibiting microbial methanogenesis or by stimulating anaerobic CH4 oxidation. The balance between Fe(III) reduction, methanogenesis, and CH4 oxidation in ferruginous Archean and Paleoproterozoic oceans would have controlled CH4 fluxes to the atmosphere, thereby regulating the capacity for CH4 to warm the early Earth under the Faint Young Sun. We studied CH4 and Fe cycling in anoxic incubations of ferruginous sediment from the ancient ocean analogue Lake Matano, Indonesia, over three successive transfers (500 days in total). Iron reduction, methanogenesis, CH4 oxidation, and microbial taxonomy were monitored in treatments amended with ferrihydrite or goethite. After three dilutions, Fe(III) reduction persisted only in bottles with ferrihydrite. Enhanced CH4 production was observed in the presence of goethite, highlighting the potential for reactive Fe(III) oxides to inhibit methanogenesis. Supplementing the media with hydrogen, nickel and selenium did not stimulate methanogenesis. There was limited evidence for Fe(III)-dependent CH4 oxidation, although some incubations displayed CH4 -stimulated Fe(III) reduction. 16S rRNA profiles continuously changed over the course of enrichment, with ultimate dominance of unclassified members of the order Desulfuromonadales in all treatments. Microbial diversity decreased markedly over the course of incubation, with subtle differences between ferrihydrite and goethite amendments. These results suggest that Fe(III) oxide mineralogy and availability of electron donors could have led to spatial separation of Fe(III)-reducing and methanogenic microbial communities in ferruginous marine sediments, potentially explaining the persistence of CH4 as a greenhouse gas throughout the first half of Earth history.
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Affiliation(s)
- M. S. Bray
- School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
| | - J. Wu
- School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
| | - B. C. Reed
- School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
| | - C. B. Kretz
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - K. M. Belli
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - R. L. Simister
- Departments of Microbiology & Immunology and Earth, Ocean, & Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
| | - C. Henny
- Research Center for Limnology, Indonesian Institute of Sciences, Cibinong, Indonesia
| | - F. J. Stewart
- School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - T. J. DiChristina
- School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - J. A. Brandes
- Skidaway Institute of Oceanography, Savannah, GA, USA
| | - D. A. Fowle
- Department of Geology, University of Kansas, Lawrence, KS, USA
| | - S. A. Crowe
- Departments of Microbiology & Immunology and Earth, Ocean, & Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
| | - J. B. Glass
- School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
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14
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Halevy I, Bachan A. The geologic history of seawater pH. Science 2017; 355:1069-1071. [DOI: 10.1126/science.aal4151] [Citation(s) in RCA: 161] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 02/14/2017] [Indexed: 11/02/2022]
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15
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Gebauer S, Grenfell JL, Stock JW, Lehmann R, Godolt M, von Paris P, Rauer H. Evolution of Earth-like Extrasolar Planetary Atmospheres: Assessing the Atmospheres and Biospheres of Early Earth Analog Planets with a Coupled Atmosphere Biogeochemical Model. ASTROBIOLOGY 2017; 17:27-54. [PMID: 28103105 DOI: 10.1089/ast.2015.1384] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Understanding the evolution of Earth and potentially habitable Earth-like worlds is essential to fathom our origin in the Universe. The search for Earth-like planets in the habitable zone and investigation of their atmospheres with climate and photochemical models is a central focus in exoplanetary science. Taking the evolution of Earth as a reference for Earth-like planets, a central scientific goal is to understand what the interactions were between atmosphere, geology, and biology on early Earth. The Great Oxidation Event in Earth's history was certainly caused by their interplay, but the origin and controlling processes of this occurrence are not well understood, the study of which will require interdisciplinary, coupled models. In this work, we present results from our newly developed Coupled Atmosphere Biogeochemistry model in which atmospheric O2 concentrations are fixed to values inferred by geological evidence. Applying a unique tool (Pathway Analysis Program), ours is the first quantitative analysis of catalytic cycles that governed O2 in early Earth's atmosphere near the Great Oxidation Event. Complicated oxidation pathways play a key role in destroying O2, whereas in the upper atmosphere, most O2 is formed abiotically via CO2 photolysis. The O2 bistability found by Goldblatt et al. ( 2006 ) is not observed in our calculations likely due to our detailed CH4 oxidation scheme. We calculate increased CH4 with increasing O2 during the Great Oxidation Event. For a given atmospheric surface flux, different atmospheric states are possible; however, the net primary productivity of the biosphere that produces O2 is unique. Mixing, CH4 fluxes, ocean solubility, and mantle/crust properties strongly affect net primary productivity and surface O2 fluxes. Regarding exoplanets, different "states" of O2 could exist for similar biomass output. Strong geological activity could lead to false negatives for life (since our analysis suggests that reducing gases remove O2 that masks its biosphere over a wide range of conditions). Key Words: Early Earth-Proterozoic-Archean-Oxygen-Atmosphere-Biogeochemistry-Photochemistry-Biosignatures-Earth-like planets. Astrobiology 16, 27-54.
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Affiliation(s)
- S Gebauer
- 1 Zentrum für Astronomie und Astrophysik (ZAA), Technische Universität Berlin (TUB) , Berlin, Germany
- 2 Institut für Planetenforschung (PF) , Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
| | - J L Grenfell
- 2 Institut für Planetenforschung (PF) , Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
| | - J W Stock
- 3 Instituto de Astrofísica de Andalucía-CSIC , Granada, Spain
| | - R Lehmann
- 4 Alfred-Wegener Institut Helmholtz-Zentrum für Polar- und Meeresforschung , Potsdam, Germany
| | - M Godolt
- 2 Institut für Planetenforschung (PF) , Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
| | - P von Paris
- 5 Université de Bordeaux , LAB, UMR 5804, Floirac, France
- 6 CNRS, LAB , UMR 5804, Floirac, France
| | - H Rauer
- 1 Zentrum für Astronomie und Astrophysik (ZAA), Technische Universität Berlin (TUB) , Berlin, Germany
- 2 Institut für Planetenforschung (PF) , Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany
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16
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Abstract
Pervasive anoxia in the subsurface ocean during the Proterozoic may have allowed large fluxes of biogenic CH4 to the atmosphere, enhancing the climatic significance of CH4 early in Earth's history. Indeed, the assumption of elevated pCH4 during the Proterozoic underlies most models for both anomalous climatic stasis during the mid-Proterozoic and extreme climate perturbation during the Neoproterozoic; however, the geologic record cannot directly constrain atmospheric CH4 levels and attendant radiative forcing. Here, we revisit the role of CH4 in Earth's climate system during Proterozoic time. We use an Earth system model to quantify CH4 fluxes from the marine biosphere and to examine the capacity of biogenic CH4 to compensate for the faint young Sun during the "boring billion" years before the emergence of metazoan life. Our calculations demonstrate that anaerobic oxidation of CH4 coupled to SO42- reduction is a highly effective obstacle to CH4 accumulation in the atmosphere, possibly limiting atmospheric pCH4 to less than 10 ppm by volume for the second half of Earth history regardless of atmospheric pO2 If recent pO2 constraints from Cr isotopes are correct, we predict that reduced UV shielding by O3 should further limit pCH4 to very low levels similar to those seen today. Thus, our model results likely limit the potential climate warming by CH4 for the majority of Earth history-possibly reviving the faint young Sun paradox during Proterozoic time and challenging existing models for the initiation of low-latitude glaciation that depend on the oxidative collapse of a steady-state CH4 greenhouse.
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