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Ghoshal S, Carnegie N, Ezeakunne C, Dangi BB, Kattel S. Deciphering Mg-Surface Interactions with Unsaturated Hydrocarbons: An Integrated Experimental-Theoretical Study. Chemphyschem 2025; 26:e202401061. [PMID: 39887876 DOI: 10.1002/cphc.202401061] [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: 11/22/2024] [Accepted: 01/29/2025] [Indexed: 02/01/2025]
Abstract
Here, we used a combination of laser-induced experiments and density functional theory (DFT) calculations to study the mechanism of growth of carbonaceous species on the Mg surface. Experimental observations revealed that the carbon deposit forms upon laser illumination on the Mg surface, with the deposit being clearer and better structured in the presence of 1,3-butadiene (C4H6) compared to ethylene (C2H4) gas. DFT thermodynamic and kinetic calculations of C2-C4 hydrocarbons interaction on low-index Mg(0001) were used to explain this experimental observation. Our results on Mg(0001) showed that the cis isomer of C4H6 binds more strongly than its trans isomer via a [4+2] cycloaddition mechanism. We also investigated the adsorption of two units of C2H4 and C4H6 molecules, as well as the subsequent dehydrogenation stages that produce radical species responsible for chain growth mechanisms. The results showed that free energy change of dehydrogenation of two units of cis-C4H6 [i. e. cis-C8H12] is lower than the dehydrogenation of trans conformer of C4H6 and C2H4 molecule, indicating that the dehydrogenation of two units of cis-C4H6 facilitates the initiation of growth of carbonaceous species on Mg surfaces. Therefore, the DFT calculations pinpoint the origin of the experimental observation of clearer carbon deposits on the Mg surface.
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Affiliation(s)
- Sourav Ghoshal
- Department of Physics, Florida Agricultural and Mechanical University, Tallahassee, FL, 32307, USA
| | - Nathaniel Carnegie
- Department of Chemistry, Florida Agricultural and Mechanical University, Tallahassee, FL, 32307, USA
| | - Chidozie Ezeakunne
- Department of Physics, University of Central Florida, Orlando, FL, 32816, USA
| | - Beni B Dangi
- Department of Chemistry, Florida Agricultural and Mechanical University, Tallahassee, FL, 32307, USA
| | - Shyam Kattel
- Department of Physics, University of Central Florida, Orlando, FL, 32816, USA
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2
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Liu J, Hardisty DS, Kasting JF, Fakhraee M, Planavsky NJ. Evolution of the iodine cycle and the late stabilization of the Earth's ozone layer. Proc Natl Acad Sci U S A 2025; 122:e2412898121. [PMID: 39761407 PMCID: PMC11745384 DOI: 10.1073/pnas.2412898121] [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: 06/27/2024] [Accepted: 11/27/2024] [Indexed: 01/23/2025] Open
Abstract
The origin of complex life and the evolution of terrestrial ecosystems are fundamental aspects of the natural history on Earth. Here, we present evidence for a protracted stabilization of the Earth's ozone layer. The destruction of atmospheric ozone today is inherently linked to the cycling of marine and atmospheric iodine. Supported by multiple independent lines of geological evidence and examined through an iodine mass balance model, we find that elevated marine iodide content prevailed through most of Earth's history. Since the rise of oxygen ~2.4 billion years ago, high marine iodide concentrations would have led to significant inorganic iodine emissions to the atmosphere, facilitating catalytic ozone destruction and resulting in atmospheric ozone instability with periodic or persistently lower ozone levels. At a global scale, unstable and low ozone levels likely persisted for about two billion years until the early Phanerozoic, roughly 0.5 billion years ago. The delayed stabilization of the Earth's ozone layer holds significant implications for the tempo and direction of the evolution of life, in particular life on land.
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Affiliation(s)
- Jingjun Liu
- Department of Earth and Planetary Sciences, Yale University, New Haven06511
| | - Dalton S. Hardisty
- Department of Earth and Environmental Sciences, Michigan State University, East Lansing48824
| | - James F. Kasting
- Department of Geosciences, The Pennsylvania State University, State College16802
| | - Mojtaba Fakhraee
- Department of Earth and Planetary Sciences, Yale University, New Haven06511
| | - Noah J. Planavsky
- Department of Earth and Planetary Sciences, Yale University, New Haven06511
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3
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Felix JD. Modern analogs for ammonia flux from terrestrial hydrothermal features to the Archean atmosphere. Sci Rep 2024; 14:1544. [PMID: 38233446 PMCID: PMC10794450 DOI: 10.1038/s41598-024-51537-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Accepted: 01/06/2024] [Indexed: 01/19/2024] Open
Abstract
The isotopic composition of nitrogen in the rock record provides valuable evidence of reactive nitrogen sources and processing on early Earth, but the wide range of δ15N values (- 10.2 to + 50.4‰) leads to ambiguity in defining the early Precambrian nitrogen cycle. The high δ15N values have been explained by large fractionation associated with the onset of nitrification and/or fractionation produced by ammonia-ammonium equilibrium and water-air flux in alkaline paleolakes. Previous flux sensitivity studies in modern water bodies report alkaline pH is not a prerequisite and temperature can be the dominate parameter driving water-air flux. Here, I use the chemical and physical components of 1022 modern hydrothermal features to provide evidence that water-air NH3 flux produced a significant source of fixed nitrogen to early Earth's atmosphere and biosphere. With regard to the modeled average NH3 flux (2.1 kg N m-2 year-1) and outlier removed average flux (1.2 kg N m-2 year-1), the Archean Earth's surface would need to be 0.0092, and 0.017% terrestrial hydrothermal features, respectively, for the flux to match the annual amount of N produced by biogenic fixation on modern Earth. Water-air NH3 flux from terrestrial hydrothermal features may have played a significant role in supplying bioavailable nitrogen to early life.
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Affiliation(s)
- J David Felix
- Physical and Environmental Sciences Department, Center for Water Supply Studies, Texas A&M University - Corpus Christi, Corpus Christi, USA.
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4
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González-Ramírez LA, Moreno A, Ng JD, García-Ruiz JM. Investigations on the Role of Iron (III) and Silica-Iron (III) for DNA Protection Against Highly Intense UV Radiation: Tracking the Connection of Prebiotic Chemistry to Biology. ASTROBIOLOGY 2023; 23:33-42. [PMID: 36257639 DOI: 10.1089/ast.2022.0004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
The mineral reaction pathways that yield organic compounds of increasing complexity would have required a means of protective screening against strong ultraviolet radiation for macromolecular assembly on early Earth. In this study, a bacterial chromosomal plasmid DNA was used as a model biomolecule that represents a complex polymeric nucleic acid containing genetic information. The plasmid DNA was exposed to UV radiation through a medium containing air, water, iron (Fe3+), or silica-iron rich aqueous solutions. Our results demonstrate that the plasmid DNA underwent covalent breakage in an aqueous solution when exposed to UV radiation but was shielded against damage due to the presence of iron and silica. It is demonstrated that a suspension of ca. 40 nm colloidal particles of silica gel embedded with Fe3+ ions adsorbed on silanol groups that formed nanoclusters of noncrystalline iron hydroxide is an extremely efficient shelter against intense UV radiation. The implications for our understanding of primitive Earth and Earth-like planets, moons, and asteroids are discussed. The stability of a chromosomal DNA molecule against UV radiation in the presence of iron and silica may provide support on how macromolecules endured early Earth environments and brought forth important implications on early molecular survival against UV radiation.
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Affiliation(s)
- Luis A González-Ramírez
- Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, Armilla, Spain
| | - Abel Moreno
- Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, Armilla, Spain
- Instituto de Química, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Joseph D Ng
- Department of Biological Sciences, University of Alabama in Huntsville, Huntsville, Alabama, USA
| | - Juan M García-Ruiz
- Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, CSIC-UGR, Armilla, Spain
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5
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Limaye SS, Mogul R, Baines KH, Bullock MA, Cockell C, Cutts JA, Gentry DM, Grinspoon DH, Head JW, Jessup KL, Kompanichenko V, Lee YJ, Mathies R, Milojevic T, Pertzborn RA, Rothschild L, Sasaki S, Schulze-Makuch D, Smith DJ, Way MJ. Venus, an Astrobiology Target. ASTROBIOLOGY 2021; 21:1163-1185. [PMID: 33970019 DOI: 10.1089/ast.2020.2268] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We present a case for the exploration of Venus as an astrobiology target-(1) investigations focused on the likelihood that liquid water existed on the surface in the past, leading to the potential for the origin and evolution of life, (2) investigations into the potential for habitable zones within Venus' present-day clouds and Venus-like exo atmospheres, (3) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus' clouds and Venus-like atmospheres, and (4) application of these investigative approaches toward better understanding the atmospheric dynamics and habitability of exoplanets. The proximity of Venus to Earth, guidance for exoplanet habitability investigations, and access to the potential cloud habitable layer and surface for prolonged in situ extended measurements together make the planet a very attractive target for near term astrobiological exploration.
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Affiliation(s)
- Sanjay S Limaye
- Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Rakesh Mogul
- Chemistry and Biochemistry Department, Cal Poly Pomona, Pomona, California, USA
| | - Kevin H Baines
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | | | - Charles Cockell
- School of Physics and Astronomy, University of Edinburgh, Edinburgh, Scotland
| | - James A Cutts
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Diana M Gentry
- NASA Ames Research Center, Moffett Field, California, USA
| | | | - James W Head
- Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island, USA
| | | | - Vladimir Kompanichenko
- Institute for Complex Analysis of Regional Problems, Russian Academy of Sciences, Birobidzhan, Russia
| | - Yeon Joo Lee
- Zentrum für Astronomie und Astrophysik, Technical University of Berlin, Berlin, Germany
| | - Richard Mathies
- Chemistry Department and Space Sciences Lab, University of California, Berkeley, Berkeley, California, USA
| | - Tetyana Milojevic
- Department of Biophysical Chemistry, University of Vienna, Vienna, Austria
| | - Rosalyn A Pertzborn
- Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | | | - Satoshi Sasaki
- School of Health Sciences, Tokyo University of Technology, Hachioji, Japan
| | - Dirk Schulze-Makuch
- Center for Astronomy and Astrophysics (ZAA), Technische Universität Berlin, Berlin, Germany
- German Research Centre for Geosciences (GFZ), Potsdam, Germany
- Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Stechlin, Germany
| | - David J Smith
- NASA Ames Research Center, Moffett Field, California, USA
| | - Michael J Way
- NASA Goddard Institute for Space Studies, New York, New York, USA
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6
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Gaylor MO, Miro P, Vlaisavljevich B, Kondage AAS, Barge LM, Omran A, Videau P, Swenson VA, Leinen LJ, Fitch NW, Cole KL, Stone C, Drummond SM, Rageth K, Dewitt LR, González Henao S, Karanauskus V. Plausible Emergence and Self Assembly of a Primitive Phospholipid from Reduced Phosphorus on the Primordial Earth. ORIGINS LIFE EVOL B 2021; 51:185-213. [PMID: 34279769 DOI: 10.1007/s11084-021-09613-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 06/19/2021] [Indexed: 11/28/2022]
Abstract
How life arose on the primitive Earth is one of the biggest questions in science. Biomolecular emergence scenarios have proliferated in the literature but accounting for the ubiquity of oxidized (+ 5) phosphate (PO43-) in extant biochemistries has been challenging due to the dearth of phosphate and molecular oxygen on the primordial Earth. A compelling body of work suggests that exogenous schreibersite ((Fe,Ni)3P) was delivered to Earth via meteorite impacts during the Heavy Bombardment (ca. 4.1-3.8 Gya) and there converted to reduced P oxyanions (e.g., phosphite (HPO32-) and hypophosphite (H2PO2-)) and phosphonates. Inspired by this idea, we review the relevant literature to deduce a plausible reduced phospholipid analog of modern phosphatidylcholines that could have emerged in a primordial hydrothermal setting. A shallow alkaline lacustrine basin underlain by active hydrothermal fissures and meteoritic schreibersite-, clay-, and metal-enriched sediments is envisioned. The water column is laden with known and putative primordial hydrothermal reagents. Small system dimensions and thermal- and UV-driven evaporation further concentrate chemical precursors. We hypothesize that a reduced phospholipid arises from Fischer-Tropsch-type (FTT) production of a C8 alkanoic acid, which condenses with an organophosphinate (derived from schreibersite corrosion to hypophosphite with subsequent methylation/oxidation), to yield a reduced protophospholipid. This then condenses with an α-amino nitrile (derived from Strecker-type reactions) to form the polar head. Preliminary modeling results indicate that reduced phospholipids do not aggregate rapidly; however, single layer micelles are stable up to aggregates with approximately 100 molecules.
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Affiliation(s)
- Michael O Gaylor
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA.
| | - Pere Miro
- Department of Chemistry, University of South Dakota, Vermillion, SD, 57069, USA
| | - Bess Vlaisavljevich
- Department of Chemistry, University of South Dakota, Vermillion, SD, 57069, USA
| | | | - Laura M Barge
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA
| | - Arthur Omran
- School of Geosciences, University of South Florida, Tampa, FL, 33620, USA
- Department of Chemistry, University of North Florida, Jacksonville, FL, 32224, USA
| | - Patrick Videau
- Department of Biology, Southern Oregon University, Ashland, OR, 97520, USA
- Bayer Crop Science, Chesterfield, MO, 63017, USA
| | - Vaille A Swenson
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
- Department of Molecular Medicine, Mayo Clinic, Rochester, MN, 55905, USA
| | - Lucas J Leinen
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
| | - Nathaniel W Fitch
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
| | - Krista L Cole
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
| | - Chris Stone
- Department of Biology, Southern Oregon University, Ashland, OR, 97520, USA
| | - Samuel M Drummond
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
| | - Kayli Rageth
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
| | - Lillian R Dewitt
- Department of Chemistry, Dakota State University, Madison, SD, 57042, USA
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7
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Rouillard J, van Zuilen M, Pisapia C, Garcia-Ruiz JM. An Alternative Approach for Assessing Biogenicity. ASTROBIOLOGY 2021; 21:151-164. [PMID: 33544651 PMCID: PMC7876362 DOI: 10.1089/ast.2020.2282] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2020] [Accepted: 09/07/2020] [Indexed: 05/27/2023]
Abstract
The search for signs of life in the ancient rock record, extreme terrestrial environments, and other planetary bodies requires a well-established, universal, and unambiguous test of biogenicity. This is notably true for cellular remnants of microbial life, since their relatively simple morphologies resemble various abiogenic microstructures that occur in nature. Although lists of qualitative biogenicity criteria have been devised, debates regarding the biogenicity of many ancient microfossils persist to this day. We propose here an alternative quantitative approach for assessing the biogenicity of putative microfossils. In this theoretical approach, different hypotheses-involving biology or not and depending on the geologic setting-are put forward to explain the observed objects. These hypotheses correspond to specific types of microstructures/systems. Using test samples, the morphology and/or chemistry of these systems are then characterized at the scale of populations. Morphologic parameters include, for example, circularity, aspect ratio, and solidity, while chemical parameters could include elementary ratios (e.g., N/C ratio), isotopic enrichments (e.g., δ13C), or chirality (e.g., molar proportion of stereoisomers), among others. Statistic trends distinguishing the different systems are then searched for empirically. The trends found are translated into "decision spaces" where the different systems are quantitatively discriminated and where the potential microfossil population can be located as a single point. This approach, which is formulated here on a theoretical level, will solve several problems associated with the classical qualitative criteria of biogenicity. Most importantly, it could be applied to reveal the existence of cellular life on other planets, for which characteristics of morphology and chemical composition are difficult to predict.
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Affiliation(s)
- Joti Rouillard
- Laboratario de Estudios Cristalograficos, Instituto Andaluz de Ciencias de la Tierra, CSIC—Universidad de Granada, Armilla, Spain
| | - Mark van Zuilen
- Institut de Physique du Globe de Paris, Université de Paris, CNRS UMR 7154, Paris, France
| | - Céline Pisapia
- Institut de Physique du Globe de Paris, Université de Paris, CNRS UMR 7154, Paris, France
| | - Juan-Manuel Garcia-Ruiz
- Laboratario de Estudios Cristalograficos, Instituto Andaluz de Ciencias de la Tierra, CSIC—Universidad de Granada, Armilla, Spain
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8
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Turbet M, Bolmont E, Bourrier V, Demory BO, Leconte J, Owen J, Wolf ET. A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System. SPACE SCIENCE REVIEWS 2020; 216:100. [PMID: 32764836 PMCID: PMC7378127 DOI: 10.1007/s11214-020-00719-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 07/04/2020] [Indexed: 06/11/2023]
Abstract
TRAPPIST-1 is a fantastic nearby (∼39.14 light years) planetary system made of at least seven transiting terrestrial-size, terrestrial-mass planets all receiving a moderate amount of irradiation. To date, this is the most observationally favourable system of potentially habitable planets known to exist. Since the announcement of the discovery of the TRAPPIST-1 planetary system in 2016, a growing number of techniques and approaches have been used and proposed to characterize its true nature. Here we have compiled a state-of-the-art overview of all the observational and theoretical constraints that have been obtained so far using these techniques and approaches. The goal is to get a better understanding of whether or not TRAPPIST-1 planets can have atmospheres, and if so, what they are made of. For this, we surveyed the literature on TRAPPIST-1 about topics as broad as irradiation environment, planet formation and migration, orbital stability, effects of tides and Transit Timing Variations, transit observations, stellar contamination, density measurements, and numerical climate and escape models. Each of these topics adds a brick to our understanding of the likely-or on the contrary unlikely-atmospheres of the seven known planets of the system. We show that (i) Hubble Space Telescope transit observations, (ii) bulk density measurements comparison with H2-rich planets mass-radius relationships, (iii) atmospheric escape modelling, and (iv) gas accretion modelling altogether offer solid evidence against the presence of hydrogen-dominated-cloud-free and cloudy-atmospheres around TRAPPIST-1 planets. This means that the planets are likely to have either (i) a high molecular weight atmosphere or (ii) no atmosphere at all. There are several key challenges ahead to characterize the bulk composition(s) of the atmospheres (if present) of TRAPPIST-1 planets. The main one so far is characterizing and correcting for the effects of stellar contamination. Fortunately, a new wave of observations with the James Webb Space Telescope and near-infrared high-resolution ground-based spectrographs on existing very large and forthcoming extremely large telescopes will bring significant advances in the coming decade.
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Affiliation(s)
- Martin Turbet
- Observatoire Astronomique de l'Université de Genève, 51 chemin de Pégase, 1290 Sauverny, Switzerland
| | - Emeline Bolmont
- Observatoire Astronomique de l'Université de Genève, 51 chemin de Pégase, 1290 Sauverny, Switzerland
| | - Vincent Bourrier
- Observatoire Astronomique de l'Université de Genève, 51 chemin de Pégase, 1290 Sauverny, Switzerland
| | - Brice-Olivier Demory
- Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
| | - Jérémy Leconte
- Laboratoire d'astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
| | - James Owen
- Astrophysics Group, Department of Physics, Imperial College London, Prince Consort Rd, London, SW7 2AZ UK
| | - Eric T Wolf
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 USA
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9
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Kim JJ, Parker S, Henderson T, Kirby JN. Physiological fractals: visual and statistical evidence across timescales and experimental states. J R Soc Interface 2020; 17:20200334. [PMID: 32574539 DOI: 10.1098/rsif.2020.0334] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
A marker of engaging in compassion meditation and related processes is an increase in heart-rate variability (HRV), typically interpreted as a marker of parasympathetic nervous system response. While insightful, open questions remain. For example, which timescale is best to examine the effects of meditation and related practices on HRV? Furthermore, how might advanced time-series analyses--such as stationarity--be able to examine dynamic changes in the mean and variance of the HRV signal across time? Here we apply such methods to previously published data, which measured HRV pre- and post- a two-week compassionate mind training (CMT) intervention. Inspection of these data reveals that a visualization of HRV correlations across resting and compassion meditation states, pre- and post-two-week training, is retained across numerous recording timescales. Here, the fractal-like nature of our data indicates that the accuracy of representing HRV data can exist across timescales, albeit with greater or lesser granularity. Interestingly, inspection of the HRV signal at Time 2 compassion meditation versus Time 1 revealed a more highly correlated (i.e. potentially more stable) signal. We followed up these results with tests of stationarity, which revealed Time 2 had a less stochastic (variable) signal than Time 1, and a measure of distance in the time series, which showed that Time 2 had less of an average difference between rest and meditation than at Time 1. Our results provide novel assessment of visual and statistical markers of HRV change across distinct experimental states.
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Affiliation(s)
- Jeffrey J Kim
- Compassionate Mind Research Group, School of Psychology, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Stacey Parker
- Compassionate Mind Research Group, School of Psychology, The University of Queensland, Brisbane, QLD 4072, Australia
| | | | - James N Kirby
- Compassionate Mind Research Group, School of Psychology, The University of Queensland, Brisbane, QLD 4072, Australia
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10
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Ugelow MS, Berry JL, Browne EC, Tolbert MA. The Impact of Molecular Oxygen on Anion Composition in a Hazy Archean Earth Atmosphere. ASTROBIOLOGY 2020; 20:658-669. [PMID: 32159384 DOI: 10.1089/ast.2019.2145] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Atmospheric organic hazes are common in planetary bodies in our solar system and likely exoplanet atmospheres as well. In addition, geochemical data support the existence of an organic haze in the early Earth's atmosphere. Much of what is known about organic haze formation derives from studies of Saturn's moon Titan. It is believed that on Titan ions play an important role in haze formation. It is possible, by using Titan as an analog for the Archean Earth, to consider that an Archean haze could have formed by similar processes. Here, we examine the anion chemistry that occurs during laboratory simulations of early Earth haze formation and measure the composition of gaseous anions as a function of O2 mixing ratio. Gaseous anion composition and relative abundances are measured by an atmospheric pressure interface time-of-flight mass spectrometer and are compared to previous photochemical haze mass loading measurements. Numerous anions are observed spanning from mass-to-charge ratio 26 to 246, with a majority of the identified anions containing carbon, hydrogen, nitrogen, and/or oxygen. A shift in the anion composition occurs with increasing the precursor O2 mixing ratio. With 0-20 ppmv O2 in CH4/CO2/N2 mixtures, ions contain mostly organic nitrogen, with CNO- being the most intense ion peak. As the precursor O2 is increased to 200 and 2000 ppmv, inorganic nitrogen ions become the dominant chemical group, with NO3- having the most intense ion signal. The clear shift in the ionic composition could be indicative of a modification to the gas-phase chemistry that occurs in the transition from an anoxic atmosphere to an oxygen-containing atmosphere, with potential astrobiological significance.
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Affiliation(s)
- Melissa S Ugelow
- Department of Chemistry, University of Colorado, Boulder, Colorado
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado
- Now at Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
- University Space Research Association, Columbia, Maryland
| | - Jennifer L Berry
- Department of Chemistry, University of Colorado, Boulder, Colorado
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado
| | - Eleanor C Browne
- Department of Chemistry, University of Colorado, Boulder, Colorado
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado
| | - Margaret A Tolbert
- Department of Chemistry, University of Colorado, Boulder, Colorado
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado
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11
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When is Chemical Disequilibrium in Earth-like Planetary Atmospheres a Biosignature versus an Anti-biosignature? Disequilibria from Dead to Living Worlds. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/1538-4357/ab7b81] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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12
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Yu P, Toon OB, Bardeen CG, Zhu Y, Rosenlof KH, Portmann RW, Thornberry TD, Gao RS, Davis SM, Wolf ET, de Gouw J, Peterson DA, Fromm MD, Robock A. Black carbon lofts wildfire smoke high into the stratosphere to form a persistent plume. Science 2020; 365:587-590. [PMID: 31395782 DOI: 10.1126/science.aax1748] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 07/12/2019] [Indexed: 11/02/2022]
Abstract
In 2017, western Canadian wildfires injected smoke into the stratosphere that was detectable by satellites for more than 8 months. The smoke plume rose from 12 to 23 kilometers within 2 months owing to solar heating of black carbon, extending the lifetime and latitudinal spread. Comparisons of model simulations to the rate of observed lofting indicate that 2% of the smoke mass was black carbon. The observed smoke lifetime in the stratosphere was 40% shorter than calculated with a standard model that does not consider photochemical loss of organic carbon. Photochemistry is represented by using an empirical ozone-organics reaction probability that matches the observed smoke decay. The observed rapid plume rise, latitudinal spread, and photochemical reactions provide new insights into potential global climate impacts from nuclear war.
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Affiliation(s)
- Pengfei Yu
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA. .,Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA.,Institute for Environment and Climate Research, Jinan University, Guangzhou, China
| | - Owen B Toon
- Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, USA.,Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
| | - Charles G Bardeen
- National Center for Atmospheric Research, Atmospheric Chemistry Division, Boulder, CO, USA
| | - Yunqian Zhu
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
| | - Karen H Rosenlof
- Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
| | - Robert W Portmann
- Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
| | - Troy D Thornberry
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA.,Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
| | - Ru-Shan Gao
- Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
| | - Sean M Davis
- Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
| | - Eric T Wolf
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA.,Virtual Planetary Laboratory, Seattle, WA 98195, USA
| | - Joost de Gouw
- Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA.,Department of Chemistry, University of Colorado, Boulder, CO, USA
| | | | | | - Alan Robock
- Department of Environmental Sciences, Rutgers University, New Brunswick, NJ, USA
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13
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Wang J, Lee BHJ, Arya G. Kinetically assembled binary nanoparticle networks. NANOSCALE 2020; 12:5091-5102. [PMID: 32068755 DOI: 10.1039/c9nr09900j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Embedding percolating networks of nanoparticles (NPs) within polymers is a promising approach for mechanically reinforcing polymers and for introducing novel electronic, transport, and catalytic properties into otherwise inert polymers. While such networks may be obtained through kinetic assembly of unary system of NPs, the ensuing structures exhibit limited morphologies. Here, we investigate the possibility of increasing the diversity of NP networks through kinetic assembly of multiple species of NPs. Using lattice Monte Carlo simulations we show that networks obtained from co-assembly of two NP species of different sizes exhibit significantly more diverse morphology than those assembled from a single species. In particular, we achieved considerable variations in the particle spatial distribution, proportions of intra- and interspecies contacts, fractal dimension, and pore sizes of the networks by simply modulating the stoichiometry of the two species and their intra and inter-species affinities. We classified these distinct morphologies into "integrated", "coated", "leaved", and "blocked" phases, and provide relevant phase diagrams for achieving them. Our findings are relevant to controlled and predictable assembly of particle networks for creating multifunctional composites with improved properties.
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Affiliation(s)
- Jiuling Wang
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA.
| | - Brian Hyun-Jong Lee
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA.
| | - Gaurav Arya
- Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA.
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14
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Catling DC, Zahnle KJ. The Archean atmosphere. SCIENCE ADVANCES 2020; 6:eaax1420. [PMID: 32133393 PMCID: PMC7043912 DOI: 10.1126/sciadv.aax1420] [Citation(s) in RCA: 110] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 12/10/2019] [Indexed: 05/05/2023]
Abstract
The atmosphere of the Archean eon-one-third of Earth's history-is important for understanding the evolution of our planet and Earth-like exoplanets. New geological proxies combined with models constrain atmospheric composition. They imply surface O2 levels <10-6 times present, N2 levels that were similar to today or possibly a few times lower, and CO2 and CH4 levels ranging ~10 to 2500 and 102 to 104 times modern amounts, respectively. The greenhouse gas concentrations were sufficient to offset a fainter Sun. Climate moderation by the carbon cycle suggests average surface temperatures between 0° and 40°C, consistent with occasional glaciations. Isotopic mass fractionation of atmospheric xenon through the Archean until atmospheric oxygenation is best explained by drag of xenon ions by hydrogen escaping rapidly into space. These data imply that substantial loss of hydrogen oxidized the Earth. Despite these advances, detailed understanding of the coevolving solid Earth, biosphere, and atmosphere remains elusive, however.
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Affiliation(s)
- David C. Catling
- Department of Earth and Space Sciences and cross-campus Astrobiology Program, Box 351310, University of Washington, Seattle, WA 98195, USA
| | - Kevin J. Zahnle
- Space Sciences Division, NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035, USA
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15
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Sousa-Silva C, Seager S, Ranjan S, Petkowski JJ, Zhan Z, Hu R, Bains W. Phosphine as a Biosignature Gas in Exoplanet Atmospheres. ASTROBIOLOGY 2020; 20:235-268. [PMID: 31755740 DOI: 10.1089/ast.2018.1954] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A long-term goal of exoplanet studies is the identification and detection of biosignature gases. Beyond the most discussed biosignature gas O2, only a handful of gases have been considered in detail. In this study, we evaluate phosphine (PH3). On Earth, PH3 is associated with anaerobic ecosystems, and as such, it is a potential biosignature gas in anoxic exoplanets. We simulate the atmospheres of habitable terrestrial planets with CO2- and H2-dominated atmospheres and find that PH3 can accumulate to detectable concentrations on planets with surface production fluxes of 1010 to 1014 cm-2 s-1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition and ultraviolet (UV) irradiation. While high, the surface flux values are comparable to the global terrestrial production rate of methane or CH4 (1011 cm-2 s-1) and below the maximum local terrestrial PH3 production rate (1014 cm-2 s-1). As with other gases, PH3 can more readily accumulate on low-UV planets, for example, planets orbiting quiet M dwarfs or with a photochemically generated UV shield. PH3 has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared with other dominant spectroscopic molecules. Phosphine's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. We calculate that tens of hours of JWST (James Webb Space Telescope) time are required for a potential detection of PH3. Yet, because PH3 is spectrally active in the same wavelength regions as other atmospherically important molecules (such as H2O and CH4), searches for PH3 can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability. Phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection.
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Affiliation(s)
- Clara Sousa-Silva
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
- Department of Physics, and Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
| | - Sara Seager
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
- Department of Physics, and Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
- Department of Aeronautics and Astronautics, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
| | - Sukrit Ranjan
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
- SCOL Postdoctoral Fellow
| | - Janusz Jurand Petkowski
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
| | - Zhuchang Zhan
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
| | - Renyu Hu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California
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16
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Del Genio AD, Kiang NY, Way MJ, Amundsen DS, Sohl LE, Fujii Y, Chandler M, Aleinov I, Colose CM, Guzewich SD, Kelley M. Albedos, Equilibrium Temperatures, and Surface Temperatures of Habitable Planets. THE ASTROPHYSICAL JOURNAL 2019; 884:75. [PMID: 33100349 PMCID: PMC7580787 DOI: 10.3847/1538-4357/ab3be8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The potential habitability of known exoplanets is often categorized by a nominal equilibrium temperature assuming a Bond albedo of either ∼0.3, similar to Earth, or 0. As an indicator of habitability, this leaves much to be desired, because albedos of other planets can be very different, and because surface temperature exceeds equilibrium temperature due to the atmospheric greenhouse effect. We use an ensemble of general circulation model simulations to show that for a range of habitable planets, much of the variability of Bond albedo, equilibrium temperature and even surface temperature can be predicted with useful accuracy from incident stellar flux and stellar temperature, two known parameters for every confirmed exoplanet. Earth's Bond albedo is near the minimum possible for habitable planets orbiting G stars, because of increasing contributions from clouds and sea ice/snow at higher and lower instellations, respectively. For habitable M star planets, Bond albedo is usually lower than Earth's because of near-IR H2O absorption, except at high instellation where clouds are important. We apply relationships derived from this behavior to several known exoplanets to derive zeroth-order estimates of their potential habitability. More expansive multivariate statistical models that include currently non-observable parameters show that greenhouse gas variations produce significant variance in albedo and surface temperature, while increasing length of day and land fraction decrease surface temperature; insights for other parameters are limited by our sampling. We discuss how emerging information from global climate models might resolve some degeneracies and help focus scarce observing resources on the most promising planets.
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Affiliation(s)
- Anthony D Del Genio
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - Nancy Y Kiang
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - Michael J Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - David S Amundsen
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
| | - Linda E Sohl
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Yuka Fujii
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8550, Japan
| | - Mark Chandler
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Igor Aleinov
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Christopher M Colose
- NASA Postdoctoral Program, Goddard Institute for Space Studies, New York, NY 10025, USA
| | | | - Maxwell Kelley
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- SciSpace LLC, 2880 Broadway, New York, NY 10025, USA
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17
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Toon OB, Bardeen CG, Robock A, Xia L, Kristensen H, McKinzie M, Peterson RJ, Harrison CS, Lovenduski NS, Turco RP. Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe. SCIENCE ADVANCES 2019; 5:eaay5478. [PMID: 31616796 PMCID: PMC6774726 DOI: 10.1126/sciadv.aay5478] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Accepted: 09/09/2019] [Indexed: 06/02/2023]
Abstract
Pakistan and India may have 400 to 500 nuclear weapons by 2025 with yields from tested 12- to 45-kt values to a few hundred kilotons. If India uses 100 strategic weapons to attack urban centers and Pakistan uses 150, fatalities could reach 50 to 125 million people, and nuclear-ignited fires could release 16 to 36 Tg of black carbon in smoke, depending on yield. The smoke will rise into the upper troposphere, be self-lofted into the stratosphere, and spread globally within weeks. Surface sunlight will decline by 20 to 35%, cooling the global surface by 2° to 5°C and reducing precipitation by 15 to 30%, with larger regional impacts. Recovery takes more than 10 years. Net primary productivity declines 15 to 30% on land and 5 to 15% in oceans threatening mass starvation and additional worldwide collateral fatalities.
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Affiliation(s)
- Owen B. Toon
- Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO 80303, USA
| | - Charles G. Bardeen
- Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO 80307, USA
| | - Alan Robock
- Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA
| | - Lili Xia
- Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, USA
| | - Hans Kristensen
- Federation of American Scientists, 1112 16th St., N.W. Suite 400, Washington, DC 20036, USA
| | - Matthew McKinzie
- Natural Resources Defense Council, 40 West 20th St., 11th Floor, New York, NY 10011, USA
| | - R. J. Peterson
- Department of Physics, University of Colorado, Boulder, CO 80309-0390, USA
| | - Cheryl S. Harrison
- School of Earth, Environmental, and Marine Sciences, University of Texas Rio Grande Valley, Port Isabel, TX 78597, USA
- Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309-0450, USA
| | - Nicole S. Lovenduski
- Department of Atmospheric and Oceanic Sciences, Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO 80309-0450, USA
| | - Richard P. Turco
- Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
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18
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Alleon J, Summons RE. Organic geochemical approaches to understanding early life. Free Radic Biol Med 2019; 140:103-112. [PMID: 30858060 DOI: 10.1016/j.freeradbiomed.2019.03.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 03/02/2019] [Accepted: 03/05/2019] [Indexed: 11/25/2022]
Abstract
Here we discuss the early geological record of preserved organic carbon and the criteria that must be applied to distinguish biological from non-biological origins. Sedimentary graphite, irrespective of its isotopic composition, does not constitute a reliable biosignature because the rocks in which it is found are generally metamorphosed to the point where convincing signs of life have been erased. Rather, multiple lines of evidence, including sedimentary textures, microfossils, large accumulations of organic matter and isotopic data for co-existing carbon, nitrogen and sulfur are required before biological origin can be convincingly demonstrated.
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Affiliation(s)
- Julien Alleon
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Roger E Summons
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
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19
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Abstract
The habitable zone (HZ) is the circular region around a star(s) where standing bodies of water could exist on the surface of a rocky planet. Space missions employ the HZ to select promising targets for follow-up habitability assessment. The classical HZ definition assumes that the most important greenhouse gases for habitable planets orbiting main-sequence stars are CO2 and H2O. Although the classical HZ is an effective navigational tool, recent HZ formulations demonstrate that it cannot thoroughly capture the diversity of habitable exoplanets. Here, I review the planetary and stellar processes considered in both classical and newer HZ formulations. Supplementing the classical HZ with additional considerations from these newer formulations improves our capability to filter out worlds that are unlikely to host life. Such improved HZ tools will be necessary for current and upcoming missions aiming to detect and characterize potentially habitable exoplanets.
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20
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21
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Arney G, Domagal-Goldman SD, Meadows VS. Organic Haze as a Biosignature in Anoxic Earth-like Atmospheres. ASTROBIOLOGY 2018; 18:311-329. [PMID: 29189040 PMCID: PMC5867516 DOI: 10.1089/ast.2017.1666] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Accepted: 09/20/2017] [Indexed: 05/21/2023]
Abstract
Early Earth may have hosted a biologically mediated global organic haze during the Archean eon (3.8-2.5 billion years ago). This haze would have significantly impacted multiple aspects of our planet, including its potential for habitability and its spectral appearance. Here, we model worlds with Archean-like levels of carbon dioxide orbiting the ancient Sun and an M4V dwarf (GJ 876) and show that organic haze formation requires methane fluxes consistent with estimated Earth-like biological production rates. On planets with high fluxes of biogenic organic sulfur gases (CS2, OCS, CH3SH, and CH3SCH3), photochemistry involving these gases can drive haze formation at lower CH4/CO2 ratios than methane photochemistry alone. For a planet orbiting the Sun, at 30× the modern organic sulfur gas flux, haze forms at a CH4/CO2 ratio 20% lower than at 1× the modern organic sulfur flux. For a planet orbiting the M4V star, the impact of organic sulfur gases is more pronounced: at 1× the modern Earth organic sulfur flux, a substantial haze forms at CH4/CO2 ∼ 0.2, but at 30× the organic sulfur flux, the CH4/CO2 ratio needed to form haze decreases by a full order of magnitude. Detection of haze at an anomalously low CH4/CO2 ratio could suggest the influence of these biogenic sulfur gases and therefore imply biological activity on an exoplanet. When these organic sulfur gases are not readily detectable in the spectrum of an Earth-like exoplanet, the thick organic haze they can help produce creates a very strong absorption feature at UV-blue wavelengths detectable in reflected light at a spectral resolution as low as 10. In direct imaging, constraining CH4 and CO2 concentrations will require higher spectral resolution, and R > 170 is needed to accurately resolve the structure of the CO2 feature at 1.57 μm, likely the most accessible CO2 feature on an Archean-like exoplanet. Key Words: Organic haze-Organic sulfur gases-Biosignatures-Archean Earth. Astrobiology 18, 311-329.
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Affiliation(s)
- Giada Arney
- NASA Goddard Space Flight Center, Greenbelt, Maryland
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington
| | - Shawn D. Domagal-Goldman
- NASA Goddard Space Flight Center, Greenbelt, Maryland
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington
| | - Victoria S. Meadows
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington
- Astronomy Department, University of Washington, Seattle, Washington
- University of Washington Astrobiology Program, Seattle, Washington
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22
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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: 21] [Impact Index Per Article: 3.0] [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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23
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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: 42] [Impact Index Per Article: 6.0] [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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24
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On transient climate change at the Cretaceous-Paleogene boundary due to atmospheric soot injections. Proc Natl Acad Sci U S A 2017; 114:E7415-E7424. [PMID: 28827324 DOI: 10.1073/pnas.1708980114] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous-Paleogene boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wildfires ignited after the impact of a 10-km-diameter asteroid on the Yucatán Peninsula 66 million y ago. Following injection into the atmosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injection of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth's surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photosynthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.
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25
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Cantine MD, Fournier GP. Environmental Adaptation from the Origin of Life to the Last Universal Common Ancestor. ORIGINS LIFE EVOL B 2017; 48:35-54. [PMID: 28685374 DOI: 10.1007/s11084-017-9542-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 06/15/2017] [Indexed: 01/03/2023]
Abstract
Extensive fundamental molecular and biological evolution took place between the prebiotic origins of life and the state of the Last Universal Common Ancestor (LUCA). Considering the evolutionary innovations between these two endpoints from the perspective of environmental adaptation, we explore the hypothesis that LUCA was temporally, spatially, and environmentally distinct from life's earliest origins in an RNA world. Using this lens, we interpret several molecular biological features as indicating an environmental transition between a cold, radiation-shielded origin of life and a mesophilic, surface-dwelling LUCA. Cellularity provides motility and permits Darwinian evolution by connecting genetic material and its products, and thus establishing heredity and lineage. Considering the importance of compartmentalization and motility, we propose that the early emergence of cellularity is required for environmental dispersal and diversification during these transitions. Early diversification and the emergence of ecology before LUCA could be an important pre-adaptation for life's persistence on a changing planet.
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Affiliation(s)
- Marjorie D Cantine
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
| | - Gregory P Fournier
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
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Ranjan S, Sasselov DD. Constraints on the Early Terrestrial Surface UV Environment Relevant to Prebiotic Chemistry. ASTROBIOLOGY 2017; 17:169-204. [PMID: 28323482 DOI: 10.1089/ast.2016.1519] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The UV environment is a key boundary condition to abiogenesis. However, considerable uncertainty exists as to planetary conditions and hence surface UV at abiogenesis. Here, we present two-stream multilayer clear-sky calculations of the UV surface radiance on Earth at 3.9 Ga to constrain the UV surface fluence as a function of albedo, solar zenith angle (SZA), and atmospheric composition. Variation in albedo and latitude (through SZA) can affect maximum photoreaction rates by a factor of >10.4; for the same atmosphere, photoreactions can proceed an order of magnitude faster at the equator of a snowball Earth than at the poles of a warmer world. Hence, surface conditions are important considerations when computing prebiotic UV fluences. For climatically reasonable levels of CO2, fluence shortward of 189 nm is screened out, meaning that prebiotic chemistry is robustly shielded from variations in UV fluence due to solar flares or variability. Strong shielding from CO2 also means that the UV surface fluence is insensitive to plausible levels of CH4, O2, and O3. At scattering wavelengths, UV fluence drops off comparatively slowly with increasing CO2 levels. However, if SO2 and/or H2S can build up to the ≥1-100 ppm level as hypothesized by some workers, then they can dramatically suppress surface fluence and hence prebiotic photoprocesses. H2O is a robust UV shield for λ < 198 nm. This means that regardless of the levels of other atmospheric gases, fluence ≲198 nm is only available for cold, dry atmospheres, meaning sources with emission ≲198 (e.g., ArF excimer lasers) can only be used in simulations of cold environments with low abundance of volcanogenic gases. On the other hand, fluence at 254 nm is unshielded by H2O and is available across a broad range of [Formula: see text], meaning that mercury lamps are suitable for initial studies regardless of the uncertainty in primordial H2O and CO2 levels. Key Words: Radiative transfer-Origin of life-Planetary environments-UV radiation-Prebiotic chemistry. Astrobiology 17, 169-204.
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Affiliation(s)
- Sukrit Ranjan
- Harvard-Smithsonian Center for Astrophysics , Cambridge, Massachusetts
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27
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Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-4357/836/1/49] [Citation(s) in RCA: 100] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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28
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Arney G, Domagal-Goldman SD, Meadows VS, Wolf ET, Schwieterman E, Charnay B, Claire M, Hébrard E, Trainer MG. The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth. ASTROBIOLOGY 2016; 16:873-899. [PMID: 27792417 PMCID: PMC5148108 DOI: 10.1089/ast.2015.1422] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 07/13/2016] [Indexed: 05/21/2023]
Abstract
Recognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. This study presents simulations of a habitable yet dramatically different phase of Earth's history, when the atmosphere contained a Titan-like, organic-rich haze. Prior work has claimed a haze-rich Archean Earth (3.8-2.5 billion years ago) would be frozen due to the haze's cooling effects. However, no previous studies have self-consistently taken into account climate, photochemistry, and fractal hazes. Here, we demonstrate using coupled climate-photochemical-microphysical simulations that hazes can cool the planet's surface by about 20 K, but habitable conditions with liquid surface water could be maintained with a relatively thick haze layer (τ ∼ 5 at 200 nm) even with the fainter young Sun. We find that optically thicker hazes are self-limiting due to their self-shielding properties, preventing catastrophic cooling of the planet. Hazes may even enhance planetary habitability through UV shielding, reducing surface UV flux by about 97% compared to a haze-free planet and potentially allowing survival of land-based organisms 2.7-2.6 billion years ago. The broad UV absorption signature produced by this haze may be visible across interstellar distances, allowing characterization of similar hazy exoplanets. The haze in Archean Earth's atmosphere was strongly dependent on biologically produced methane, and we propose that hydrocarbon haze may be a novel type of spectral biosignature on planets with substantial levels of CO2. Hazy Archean Earth is the most alien world for which we have geochemical constraints on environmental conditions, providing a useful analogue for similar habitable, anoxic exoplanets. Key Words: Haze-Archean Earth-Exoplanets-Spectra-Biosignatures-Planetary habitability. Astrobiology 16, 873-899.
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Affiliation(s)
- Giada Arney
- Astronomy Department, University of Washington, Seattle, Washington, USA
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
- Now at: NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
- Now at: NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland, USA
| | - Shawn D. Domagal-Goldman
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Victoria S. Meadows
- Astronomy Department, University of Washington, Seattle, Washington, USA
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
| | - Eric T. Wolf
- Department of Atmospheric and Oceanic Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado at Boulder, Boulder, Colorado, USA
| | - Edward Schwieterman
- Astronomy Department, University of Washington, Seattle, Washington, USA
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
- Now at: NASA Postdoctoral Program, Universities Space Research Association, Columbia, Maryland, USA
- Now at: University of California at Riverside, Riverside, California, USA
- Blue Marble Institute of Science, Seattle, Washington, USA
| | - Benjamin Charnay
- Astronomy Department, University of Washington, Seattle, Washington, USA
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Astrobiology Program, University of Washington, Seattle, Washington, USA
- Now at: Paris-Meudon Observatory, Paris, France
| | - Mark Claire
- NASA Astrobiology Institute Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Blue Marble Institute of Science, Seattle, Washington, USA
- Department of Earth and Environmental Sciences, University of St Andrews, St Andrews, UK
| | - Eric Hébrard
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
- University of Exeter, Exeter, Devon, UK
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Hicks RK, Day DA, Jimenez JL, Tolbert MA. Follow the Carbon: Isotopic Labeling Studies of Early Earth Aerosol. ASTROBIOLOGY 2016; 16:822-830. [PMID: 27870584 DOI: 10.1089/ast.2015.1436] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Despite the faint young Sun, early Earth might have been kept warm by an atmosphere containing the greenhouse gases CH4 and CO2 in mixing ratios higher than those found on Earth today. Laboratory and modeling studies suggest that an atmosphere containing these trace gases could lead to the formation of organic aerosol haze due to UV photochemistry. Chemical mechanisms proposed to explain haze formation rely on CH4 as the source of carbon and treat CO2 as a source of oxygen only, but this has not previously been verified experimentally. In the present work, we use isotopically labeled precursor gases and unit-mass resolution (UMR) and high-resolution (HR) aerosol mass spectrometry to examine the sources of carbon and oxygen to photochemical aerosol formed in a CH4/CO2/N2 atmosphere. UMR results suggest that CH4 contributes 70-100% of carbon in the aerosol, while HR results constrain the value from 94% to 100%. We also confirm that CO2 contributes approximately 10% of the total mass to the aerosol as oxygen. These results have implications for the geochemical interpretations of inclusions found in Archean rocks on Earth and for the astrobiological potential of other planetary atmospheres. Key Words: Atmosphere-Early Earth-Planetary atmospheres-Carbon dioxide-Methane. Astrobiology 16, 822-830.
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Affiliation(s)
- Raea K Hicks
- Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado
| | - Douglas A Day
- Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado
| | - Jose L Jimenez
- Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado
| | - Margaret A Tolbert
- Department of Chemistry and Biochemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, Colorado
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de Wit MJ, Furnes H. 3.5-Ga hydrothermal fields and diamictites in the Barberton Greenstone Belt-Paleoarchean crust in cold environments. SCIENCE ADVANCES 2016; 2:e1500368. [PMID: 26933677 PMCID: PMC4771442 DOI: 10.1126/sciadv.1500368] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2015] [Accepted: 01/07/2016] [Indexed: 05/18/2023]
Abstract
Estimates of ocean temperatures on Earth 3.5 billion years ago (Ga) range between 26° and 85°C. We present new data from 3.47- to 3.43-Ga volcanic rocks and cherts in South Africa suggesting that these temperatures reflect mixing of hot hydrothermal fluids with cold marine and terrestrial waters. We describe fossil hydrothermal pipes that formed at ~200°C on the sea floor >2 km below sea level. This ocean floor was uplifted tectonically to sea level where a subaerial hydrothermal system was active at 30° to 270°C. We also describe shallow-water glacial diamictites and diagenetic sulfate mineral growth in abyssal muds. These new observations reveal that both hydrothermal systems operated in relatively cold environments and that Earth's surface temperatures in the early Archean were similar to those in more recent times.
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Affiliation(s)
- Maarten J. de Wit
- AEON and Earth Stewardship Science Research Institute, Nelson Mandela Metropolitan University 7701, Port Elizabeth 6031, South Africa
- Corresponding author. E-mail:
| | - Harald Furnes
- Department of Earth Science and Center for Geobiology, University of Bergen, Allegt. 41, Bergen 5007, Norway
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31
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Rapf RJ, Vaida V. Sunlight as an energetic driver in the synthesis of molecules necessary for life. Phys Chem Chem Phys 2016; 18:20067-84. [DOI: 10.1039/c6cp00980h] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
This review considers how photochemistry and sunlight-driven reactions can abiotically generate prebiotic molecules necessary for the evolution of life.
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Affiliation(s)
- Rebecca J. Rapf
- Department of Chemistry and Biochemistry
- CIRES
- University of Colorado at Boulder
- Boulder
- USA
| | - Veronica Vaida
- Department of Chemistry and Biochemistry
- CIRES
- University of Colorado at Boulder
- Boulder
- USA
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32
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Ranjan S, Sasselov DD. Influence of the UV Environment on the Synthesis of Prebiotic Molecules. ASTROBIOLOGY 2016; 16:68-88. [PMID: 26789356 DOI: 10.1089/ast.2015.1359] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Ultraviolet radiation is common to most planetary environments and could play a key role in the chemistry of molecules relevant to abiogenesis (prebiotic chemistry). In this work, we explore the impact of UV light on prebiotic chemistry that might occur in liquid water on the surface of a planet with an atmosphere. We consider effects including atmospheric absorption, attenuation by water, and stellar variability to constrain the UV input as a function of wavelength. We conclude that the UV environment would be characterized by broadband input, and wavelengths below 204 nm and 168 nm would be shielded out by atmospheric CO2 and water, respectively. We compare this broadband prebiotic UV input to the narrowband UV sources (e.g., mercury lamps) often used in laboratory studies of prebiotic chemistry and explore the implications for the conclusions drawn from these experiments. We consider as case studies the ribonucleotide synthesis pathway of Powner et al. (2009) and the sugar synthesis pathway of Ritson and Sutherland (2012). Irradiation by narrowband UV light from a mercury lamp formed an integral component of these studies; we quantitatively explore the impact of more realistic UV input on the conclusions that can be drawn from these experiments. Finally, we explore the constraints solar UV input places on the buildup of prebiotically important feedstock gasses like CH4 and HCN. Our results demonstrate the importance of characterizing the wavelength dependence (action spectra) of prebiotic synthesis pathways to determine how pathways derived under laboratory irradiation conditions will function under planetary prebiotic conditions.
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Affiliation(s)
- Sukrit Ranjan
- Harvard-Smithsonian Center for Astrophysics , Cambridge, Massachusetts
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33
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Zhang X, West RA, Irwin PGJ, Nixon CA, Yung YL. Aerosol influence on energy balance of the middle atmosphere of Jupiter. Nat Commun 2015; 6:10231. [PMID: 26694318 PMCID: PMC4703888 DOI: 10.1038/ncomms10231] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 11/18/2015] [Indexed: 11/09/2022] Open
Abstract
Aerosols are ubiquitous in planetary atmospheres in the Solar System. However, radiative forcing on Jupiter has traditionally been attributed to solar heating and infrared cooling of gaseous constituents only, while the significance of aerosol radiative effects has been a long-standing controversy. Here we show, based on observations from the NASA spacecraft Voyager and Cassini, that gases alone cannot maintain the global energy balance in the middle atmosphere of Jupiter. Instead, a thick aerosol layer consisting of fluffy, fractal aggregate particles produced by photochemistry and auroral chemistry dominates the stratospheric radiative heating at middle and high latitudes, exceeding the local gas heating rate by a factor of 5-10. On a global average, aerosol heating is comparable to the gas contribution and aerosol cooling is more important than previously thought. We argue that fractal aggregate particles may also have a significant role in controlling the atmospheric radiative energy balance on other planets, as on Jupiter.
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Affiliation(s)
- Xi Zhang
- Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, California 95064, USA
| | - Robert A West
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA
| | - Patrick G J Irwin
- Atmospheric, Oceanic and Planetary Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
| | - Conor A Nixon
- NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - Yuk L Yung
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
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34
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Karentz D. Beyond xeroderma pigmentosum: DNA damage and repair in an ecological context. A tribute to James E. Cleaver. Photochem Photobiol 2014; 91:460-74. [PMID: 25395165 DOI: 10.1111/php.12388] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 10/29/2014] [Indexed: 12/12/2022]
Abstract
The ability to repair DNA is a ubiquitous characteristic of life on Earth and all organisms possess similar mechanisms for dealing with DNA damage, an indication of a very early evolutionary origin for repair processes. James E. Cleaver's career (initiated in the early 1960s) has been devoted to the study of mammalian ultraviolet radiation (UVR) photobiology, specifically the molecular genetics of xeroderma pigmentosum and other human diseases caused by defects in DNA damage recognition and repair. This work by Jim and others has influenced the study of DNA damage and repair in a variety of taxa. Today, the field of DNA repair is enhancing our understanding of not only how to treat and prevent human disease, but is providing insights on the evolutionary history of life on Earth and how natural populations are coping with UVR-induced DNA damage from anthropogenic changes in the environment such as ozone depletion.
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Affiliation(s)
- Deneb Karentz
- Department of Biology, University of San Francisco, San Francisco, CA
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35
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Mills DB, Canfield DE. Oxygen and animal evolution: did a rise of atmospheric oxygen "trigger" the origin of animals? Bioessays 2014; 36:1145-55. [PMID: 25244426 DOI: 10.1002/bies.201400101] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Recent studies challenge the classical view that the origin of animal life was primarily controlled by atmospheric oxygen levels. For example, some modern sponges, representing early-branching animals, can live under 200 times less oxygen than currently present in the atmosphere - levels commonly thought to have been maintained prior to their origination. Furthermore, it is increasingly argued that the earliest animals, which likely lived in low oxygen environments, played an active role in constructing the well-oxygenated conditions typical of the modern oceans. Therefore, while oxygen is still relevant to understanding early animal evolution, the relationships between the two might be less straightforward than previously thought.
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Affiliation(s)
- Daniel B Mills
- Department of Biology and the Nordic Center for Earth Evolution, University of Southern Denmark, Odense M, Denmark
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36
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Wolf ET, Toon OB. Controls on the Archean climate system investigated with a global climate model. ASTROBIOLOGY 2014; 14:241-253. [PMID: 24621308 DOI: 10.1089/ast.2013.1112] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The most obvious means of resolving the faint young Sun paradox is to invoke large quantities of greenhouse gases, namely, CO2 and CH4. However, numerous changes to the Archean climate system have been suggested that may have yielded additional warming, thus easing the required greenhouse gas burden. Here, we use a three-dimensional climate model to examine some of the factors that controlled Archean climate. We examine changes to Earth's rotation rate, surface albedo, cloud properties, and total atmospheric pressure following proposals from the recent literature. While the effects of increased planetary rotation rate on surface temperature are insignificant, plausible changes to the surface albedo, cloud droplet number concentrations, and atmospheric nitrogen inventory may each impart global mean warming of 3-7 K. While none of these changes present a singular solution to the faint young Sun paradox, a combination can have a large impact on climate. Global mean surface temperatures at or above 288 K could easily have been maintained throughout the entirety of the Archean if plausible changes to clouds, surface albedo, and nitrogen content occurred.
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Affiliation(s)
- E T Wolf
- Department of Atmospheric and Oceanic Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado , Boulder, Colorado
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37
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Griffith EC, Shoemaker RK, Vaida V. Sunlight-initiated chemistry of aqueous pyruvic acid: building complexity in the origin of life. ORIGINS LIFE EVOL B 2013; 43:341-52. [PMID: 24362712 DOI: 10.1007/s11084-013-9349-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Accepted: 09/20/2013] [Indexed: 10/25/2022]
Abstract
Coupling chemical reactions to an energy source is a necessary step in the origin of life. Here, we utilize UV photons provided by a simulated sun to activate aqueous pyruvic acid and subsequently prompt chemical reactions mimicking some of the functions of modern metabolism. Pyruvic acid is interesting in a prebiotic context due to its prevalence in modern metabolism and its abiotic availability on early Earth. Here, pyruvic acid (CH3COCOOH, a C3 molecule) photochemically reacts to produce more complex molecules containing four or more carbon atoms. Acetoin (CH3CHOHCOCH3), a C4 molecule and a modern bacterial metabolite, is produced in this chemistry as well as lactic acid (CH3CHOHCOOH), a molecule which, when coupled with other abiotic chemical reaction pathways, can provide a regeneration pathway for pyruvic acid. This chemistry is discussed in the context of plausible environments on early Earth such as near the ocean surface and atmospheric aerosol particles. These environments allow for combination and exchange of reactants and products of other reaction environments (such as shallow hydrothermal vents). The result could be a contribution to the steady increase in chemical complexity requisite in the origin of life.
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Affiliation(s)
- Elizabeth C Griffith
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, Campus Box 215, Boulder, CO, 80309, USA
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38
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Trainer MG. Atmospheric Prebiotic Chemistry and Organic Hazes. CURR ORG CHEM 2013; 17:1710-1723. [PMID: 24143126 PMCID: PMC3796891 DOI: 10.2174/13852728113179990078] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Revised: 05/07/2013] [Accepted: 05/12/2013] [Indexed: 02/04/2023]
Abstract
Earth's atmospheric composition at the time of the origin of life is not known, but it has often been suggested that chemical transformation of reactive species in the atmosphere was a significant source of prebiotic organic molecules. Experimental and theoretical studies over the past half century have shown that atmospheric synthesis can yield molecules such as amino acids and nucleobases, but these processes are very sensitive to gas composition and energy source. Abiotic synthesis of organic molecules is more productive in reduced atmospheres, yet the primitive Earth may not have been as reducing as earlier workers assumed, and recent research has reflected this shift in thinking. This work provides a survey of the range of chemical products that can be produced given a set of atmospheric conditions, with a particular focus on recent reports. Intertwined with the discussion of atmospheric synthesis is the consideration of an organic haze layer, which has been suggested as a possible ultraviolet shield on the anoxic early Earth. Since such a haze layer - if formed - would serve as a reservoir for organic molecules, the chemical composition of the aerosol should be closely examined. The results highlighted here show that a variety of products can be formed in mildly reducing or even neutral atmospheres, demonstrating that contributions of atmospheric synthesis to the organic inventory on early Earth should not be discounted. This review intends to bridge current knowledge of the range of possible atmospheric conditions in the prebiotic environment and pathways for synthesis under such conditions by examining the possible products of organic chemistry in the early atmosphere.
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Affiliation(s)
- Melissa G. Trainer
- Planetary Environments Laboratory, NASA Goddard Space Flight Center, Code 699, Greenbelt, MD 20771, USA
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Harman CE, Kasting JF, Wolf ET. Atmospheric production of glycolaldehyde under hazy prebiotic conditions. ORIGINS LIFE EVOL B 2013; 43:77-98. [PMID: 23695543 DOI: 10.1007/s11084-013-9332-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Accepted: 04/11/2013] [Indexed: 10/26/2022]
Abstract
The early Earth's atmosphere, with extremely low levels of molecular oxygen and an appreciable abiotic flux of methane, could have been a source of organic compounds necessary for prebiotic chemistry. Here, we investigate the formation of a key RNA precursor, glycolaldehyde (2-hydroxyacetaldehyde, or GA) using a 1-dimensional photochemical model. Maximum atmospheric production of GA occurs when the CH4:CO2 ratio is close to 0.02. The total atmospheric production rate of GA remains small, only 1 × 10(7) mol yr(-1). Somewhat greater amounts of GA production, up to 2 × 10(8) mol yr(-1), could have been provided by the formose reaction or by direct delivery from space. Even with these additional production mechanisms, open ocean GA concentrations would have remained at or below ~1 μM, much smaller than the 1-2 M concentrations required for prebiotic synthesis routes like those proposed by Powner et al. (Nature 459:239-242, 2009). Additional production or concentration mechanisms for GA, or alternative formation mechanisms for RNA, are needed, if this was indeed how life originated on the early Earth.
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Affiliation(s)
- Chester E Harman
- Department of Geosciences, Penn State University, University Park, PA 16802, USA.
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Stüeken EE, Anderson RE, Bowman JS, Brazelton WJ, Colangelo-Lillis J, Goldman AD, Som SM, Baross JA. Did life originate from a global chemical reactor? GEOBIOLOGY 2013; 11:101-126. [PMID: 23331348 DOI: 10.1111/gbi.12025] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2012] [Accepted: 12/03/2012] [Indexed: 06/01/2023]
Abstract
Many decades of experimental and theoretical research on the origin of life have yielded important discoveries regarding the chemical and physical conditions under which organic compounds can be synthesized and polymerized. However, such conditions often seem mutually exclusive, because they are rarely encountered in a single environmental setting. As such, no convincing models explain how living cells formed from abiotic constituents. Here, we propose a new approach that considers the origin of life within the global context of the Hadean Earth. We review previous ideas and synthesize them in four central hypotheses: (i) Multiple microenvironments contributed to the building blocks of life, and these niches were not necessarily inhabitable by the first organisms; (ii) Mineral catalysts were the backbone of prebiotic reaction networks that led to modern metabolism; (iii) Multiple local and global transport processes were essential for linking reactions occurring in separate locations; (iv) Global diversity and local selection of reactants and products provided mechanisms for the generation of most of the diverse building blocks necessary for life. We conclude that no single environmental setting can offer enough chemical and physical diversity for life to originate. Instead, any plausible model for the origin of life must acknowledge the geological complexity and diversity of the Hadean Earth. Future research may therefore benefit from identifying further linkages between organic precursors, minerals, and fluids in various environmental contexts.
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Affiliation(s)
- E E Stüeken
- Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA.
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41
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Bada JL. New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments. Chem Soc Rev 2013; 42:2186-96. [PMID: 23340907 DOI: 10.1039/c3cs35433d] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
1953 was a banner year for biological chemistry: The double helix structure of DNA was published by Watson and Crick, Sanger's group announced the first amino acid sequence of a protein (insulin) and the synthesis of key biomolecules using simulated primordial Earth conditions has demonstrated by Miller. Miller's studies in particular transformed the study of the origin of life into a respectable field of inquiry and established the basis of prebiotic chemistry, a field of research that investigates how the components of life as we know it can be formed in a variety of cosmogeochemical environments. In this review, I cover the continued advances in prebiotic syntheses that Miller's pioneering work has inspired. The main focus is on recent state-of-the-art analyses carried out on archived samples of Miller's original experiments, some of which had never before been analyzed, discovered in his laboratory material just before his death in May 2007. One experiment utilized a reducing gas mixture and an apparatus configuration (referred to here as the "volcanic" apparatus) that could represent a water-rich volcanic eruption accompanied by lightning. Another included H(2)S as a component of the reducing gas mixture. Compared to the limited number of amino acids Miller identified, these new analyses have found that over 40 different amino acids and amines were synthesized, demonstrating the potential robust formation of important biologic compounds under possible cosmogeochemical conditions. These experiments are suggested to simulate long-lived volcanic island arc systems, an environment that could have provided a stable environment for some of the processes thought to be involved in chemical evolution and the origin of life. Some of the alternatives to the Miller-based prebiotic synthesis and the "primordial soup" paradigm are evaluated in the context of their relevance under plausible planetary conditions.
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Affiliation(s)
- Jeffrey L Bada
- Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093-0212, USA.
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Trainer MG, Jimenez JL, Yung YL, Toon OB, Tolbert MA. Nitrogen incorporation in CH(4)-N(2) photochemical aerosol produced by far ultraviolet irradiation. ASTROBIOLOGY 2012; 12:315-26. [PMID: 22519972 PMCID: PMC3330558 DOI: 10.1089/ast.2011.0754] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Nitrile incorporation into Titan aerosol accompanying hydrocarbon chemistry is thought to be driven by extreme UV wavelengths (λ<120 nm) or magnetospheric electrons in the outer reaches of the atmosphere. Far UV radiation (120-200 nm), which is transmitted down to the stratosphere of Titan, is expected to affect hydrocarbon chemistry only and not initiate the formation of nitrogenated species. We examined the chemical properties of photochemical aerosol produced at far UV wavelengths, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), which allows for elemental analysis of particle-phase products. Our results show that aerosol formed from CH(4)/N(2) photochemistry contains a surprising amount of nitrogen, up to 16% by mass, a result of photolysis in the far UV. The proportion of nitrogenated organics to hydrocarbon species is shown to be correlated with that of N(2) in the irradiated gas. The aerosol mass greatly decreases when N(2) is removed, which indicates that N(2) plays a major role in aerosol production. Because direct dissociation of N(2) is highly improbable given the immeasurably low cross section at the wavelengths studied, the chemical activation of N(2) must occur via another pathway. Any chemical activation of N(2) at wavelengths >120 nm is presently unaccounted for in atmospheric photochemical models. We suggest that reaction with CH radicals produced from CH(4) photolysis may provide a mechanism for incorporating N into the molecular structure of the aerosol. Further work is needed to understand the chemistry involved, as these processes may have significant implications for how we view prebiotic chemistry on early Earth and similar planets.
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Melott AL, Thomas BC. Astrophysical ionizing radiation and Earth: a brief review and census of intermittent intense sources. ASTROBIOLOGY 2011; 11:343-361. [PMID: 21545268 DOI: 10.1089/ast.2010.0603] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Cosmic radiation backgrounds are a constraint on life, and their distribution will affect the Galactic Habitable Zone. Life on Earth has developed in the context of these backgrounds, and characterizing event rates will elaborate the important influences. This in turn can be a base for comparison with other potential life-bearing planets. In this review, we estimate the intensities and rates of occurrence of many kinds of strong radiation bursts by astrophysical entities, ranging from gamma-ray bursts at cosmological distances to the Sun itself. Many of these present potential hazards to the biosphere; on timescales long compared with human history, the probability of an event intense enough to disrupt life on the land surface or in the oceans becomes large. Both photons (e.g., X-rays) and high-energy protons and other nuclei (often called "cosmic rays") constitute hazards. For either species, one of the mechanisms that comes into play even at moderate intensities is the ionization of Earth's atmosphere, which leads through chemical changes (specifically, depletion of stratospheric ozone) to increased ultraviolet B flux from the Sun reaching the surface. UVB is extremely hazardous to most life due to its strong absorption by the genetic material DNA and subsequent breaking of chemical bonds. This often leads to mutation or cell death. It is easily lethal to the microorganisms that lie at the base of the food chain in the ocean. We enumerate the known sources of radiation and characterize their intensities at Earth and rates or upper limits on these quantities. When possible, we estimate a "lethal interval," our best estimate of how often a major extinction-level event is probable given the current state of knowledge; we base these estimates on computed or expected depletion of stratospheric ozone. In general, moderate-level events are dominated by the Sun, but the far more severe infrequent events are probably dominated by gamma-ray bursts and supernovae. We note for the first time that so-called "short-hard" gamma-ray bursts are a substantial threat, comparable in magnitude to supernovae and greater than that of the higher-luminosity long bursts considered in most past work. Given their precursors, short bursts may come with little or no warning.
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Affiliation(s)
- Adrian L Melott
- Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, USA.
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Haqq-Misra J, Kasting JF, Lee S. Availability of O(2) and H(2)O(2) on pre-photosynthetic Earth. ASTROBIOLOGY 2011; 11:293-302. [PMID: 21545266 PMCID: PMC3097080 DOI: 10.1089/ast.2010.0572] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Old arguments that free O(2) must have been available at Earth's surface prior to the origin of photosynthesis have been revived by a new study that shows that aerobic respiration can occur at dissolved oxygen concentrations much lower than had previously been thought, perhaps as low as 0.05 nM, which corresponds to a partial pressure for O(2) of about 4 × 10(-8) bar. We used numerical models to study whether such O(2) concentrations might have been provided by atmospheric photochemistry. Results show that disproportionation of H(2)O(2) near the surface might have yielded enough O(2) to satisfy this constraint. Alternatively, poleward transport of O(2) from the equatorial stratosphere into the polar night region, followed by downward transport in the polar vortex, may have brought O(2) directly to the surface. Thus, our calculations indicate that this "early respiration" hypothesis might be physically reasonable.
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Affiliation(s)
- Jacob Haqq-Misra
- Department of Meteorology, The Pennsylvania State University, University Park, PA 16802, USA.
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Hasenkopf CA, Freedman MA, Beaver MR, Toon OB, Tolbert MA. Potential climatic impact of organic haze on early Earth. ASTROBIOLOGY 2011; 11:135-149. [PMID: 21417943 DOI: 10.1089/ast.2010.0541] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We have explored the direct and indirect radiative effects on climate of organic particles likely to have been present on early Earth by measuring their hygroscopicity and cloud nucleating ability. The early Earth analog aerosol particles were generated via ultraviolet photolysis of an early Earth analog gas mixture, which was designed to mimic possible atmospheric conditions before the rise of oxygen. An analog aerosol for the present-day atmosphere of Saturn's moon Titan was tested for comparison. We exposed the early Earth aerosol to a range of relative humidities (RHs). Water uptake onto the aerosol was observed to occur over the entire RH range tested (RH=80-87%). To translate our measurements of hygroscopicity over a specific range of RHs into their water uptake ability at any RH < 100% and into their ability to act as cloud condensation nuclei (CCN) at RH > 100%, we relied on the hygroscopicity parameter κ, developed by Petters and Kreidenweis. We retrieved κ=0.22 ±0.12 for the early Earth aerosol, which indicates that the humidified aerosol (RH < 100 %) could have contributed to a larger antigreenhouse effect on the early Earth atmosphere than previously modeled with dry aerosol. Such effects would have been of significance in regions where the humidity was larger than 50%, because such high humidities are needed for significant amounts of water to be on the aerosol. Additionally, Earth organic aerosol particles could have activated into CCN at reasonable-and even low-water-vapor supersaturations (RH > 100%). In regions where the haze was dominant, it is expected that low particle concentrations, once activated into cloud droplets, would have created short-lived, optically thin clouds. Such clouds, if predominant on early Earth, would have had a lower albedo than clouds today, thereby warming the planet relative to current-day clouds.
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Affiliation(s)
- Christa A Hasenkopf
- Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado 80309, USA.
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