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Benjamin Fleury - One of the best experts on this subject based on the ideXlab platform.
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Organic chemistry in a CO2 rich Early Earth atmosphere
Earth and Planetary Science Letters, 2017Co-Authors: Benjamin Fleury, Nathalie Carrasco, Maeva Millan, Ludovic Vettier, Cyril SzopaAbstract:The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the Early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the Early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an Early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the Early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the Early Earth.
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Organic chemistry in a CO 2 rich Early Earth atmosphere
Earth and Planetary Science Letters, 2017Co-Authors: Benjamin Fleury, Nathalie Carrasco, Maeva Millan, Ludovic Vettier, Cyril SzopaAbstract:Abstract The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the Early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the Early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an Early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the Early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the Early Earth.
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The upper atmosphere of the Early Earth, a source of prebiotic organic compounds
2015Co-Authors: Benjamin FleuryAbstract:The origin of the organic matter on the Early Earth is an important subject of research in planetology. This thesis presents an experimental study of the formation of organic compounds in the atmosphere of the Early Earth investigating the reactivity of gaseous mixtures majority made of N2 and CO2. They present an important reactivity highlighted by the formation of gaseous products and solid products called tholins. The formation of these products points out CO2 as an efficiency source of carbon for the organic atmospheric growth. The identification of the gaseous products and the elemental analysis of the tholins showed a composition by C, N, H and O highlighting an efficiency coupling between the chemistry of these elements necessary for the formation of prebiotic compounds. This type of study have been applied then toTitan, which have a more reduced atmosphere, made of N2 and CH4, but, which contained also oxygenated trace species: principally CO. The addition of CO in the reactive medium involves also a coupling between the chemistry of O and the C, N, H chemistry currently considered for Titan. Finally I propose and investigate experimentally two phenomena, which may involve a chemical evolution of the aerosols of Titan during their sedimentation to the surface. First, an exposition of tholins to VUV photons, characteristic of the thermosphere of Titan, involves a selective depletion of amines function in favor of aliphatic functions. Second, an irradiation by UV photons of condensed species at the surface of tholins involves a reactivity of the solid species in interaction with the tholins, changing their chemical composition.
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Organic chemistry in the ionosphere of the Early Earth
2015Co-Authors: Benjamin Fleury, Ludovic Vettier, Nathalie CarrascoAbstract:The emergence of life on the Early Earth during the Archean has required a prior complex organic chemistry providing the prerequisite bricks of life. The origin of the organic matter and its evolution on the Early Earth is far from being understood. Several hypotheses are investigated, possibly complementary, which can be divided in two main categories: the endogenous and the exogenous sources. In this work we have been interested in the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the Early Earth. At these high altitudes, the VUV contribution of the young sun was important, involving an efficient production of reactive species. Here we address the issue whether this chemistry can lead to the production of larger molecules with a prebiotic interest in spite of the competitive lysing effect of the harsh irradiation at these altitudes.
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Water formation in the upper atmosphere of the Early Earth
The Astrophysical Journal, 2015Co-Authors: Benjamin Fleury, Nathalie Carrasco, Ludovic Vettier, Emmanuel Marcq, Anni MäättänenAbstract:The water concentration and distribution in the Early Earth's atmosphere are important parameters that contribute to the chemistry and the radiative budget of the atmosphere. If the atmosphere above the troposphere is generally considered as dry, photochemistry is known to be responsible for the production of numerous minor species. Here we used an experimental setup to study the production of water in conditions simulating the chemistry above the troposphere of the Early Earth with an atmospheric composition based on three major molecules: N2, CO2, and H2. The formation of gaseous products was monitored using infrared spectroscopy. Water was found as the major product, with approximately 10% of the gas products detected. This important water formation is discussed in the context of the Early Earth.
Margaret A. Tolbert - One of the best experts on this subject based on the ideXlab platform.
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Potential climatic impact of organic haze on Early Earth.
Astrobiology, 2011Co-Authors: Christa A. Hasenkopf, Miriam Arak Freedman, Melinda R. Beaver, Owen B. Toon, Margaret A. TolbertAbstract: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%, 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%). 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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Optical properties of Titan and Early Earth haze laboratory analogs in the mid-visible
Icarus, 2010Co-Authors: Christa A. Hasenkopf, Miriam Arak Freedman, Melinda R. Beaver, Owen B. Toon, Christopher P Mckay, Melissa G. Trainer, H. Langley Dewitt, Margaret A. TolbertAbstract:Scattering and absorption of sunlight by aerosols are integral to understanding the radiative balance of any planetary atmosphere covered in a haze, such as Titan and possibly the Early Earth. One key optical parameter of an aerosol is its refractive index. We have simulated both Titan and Early Earth organic haze aerosols in the laboratory and measured the real and imaginary portion of their refractive index at k = 532 nm using cavity ringdown aerosol extinction spectroscopy. This novel technique allows analysis on freely-floating particles minutes after formation. For our Titan analog particles, we find a real refractive index of n = 1.35 ± 0.01 and an imaginary refractive index k = 0.023 ± 0.007, and for the Early Earth analog particles we find n = 1.81 ± 0.02 and k = 0.055 ± 0.020. The Titan analog refractive index has a smaller real and similar imaginary refractive index compared to most previous laboratory measurements of Titan analog films, including values from Khare et al. (Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Callcott, T.A., Williams, M.W. [1984]. Icarus 60, 127–137). These newly measured Titan analog values have implications for spacecraft retrievals of aerosol properties on Titan. The Early Earth analog has a significantly higher real and imaginary refractive index than Titan analogs reported in the literature. These differences suggest that, for a given amount of aerosol, the Early Earth analog would act as a stronger anti-greenhouse agent than the Titan analog.
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organic haze on titan and the Early Earth
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: M G Trainer, Owen B. Toon, Alexander A Pavlov, Langley H Dewitt, Jose L Jimenez, Christopher P Mckay, Margaret A. TolbertAbstract:Abstract Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH4/N2 atmosphere. It has been suggested that a similar haze layer may have formed on the Early Earth. Here we report laboratory experiments that demonstrate the properties of haze likely to form through photochemistry on Titan and Early Earth. We have used a deuterium lamp to initiate particle production in these simulated atmospheres from UV photolysis. Using a unique analysis technique, the aerosol mass spectrometer, we have studied the chemical composition, size, and shape of the particles produced as a function of initial trace gas composition. Our results show that the aerosols produced in the laboratory can serve as analogs for the observed haze in Titan's atmosphere. Experiments performed under possible conditions for Early Earth suggest a significant optical depth of haze may have dominated the Early Earth's atmosphere. Aerosol size measurements are presented, and implications for the haze layer properties are discussed. We estimate that aerosol production on the Early Earth may have been on the order of 1014 g·year−1 and thus could have served as a primary source of organic material to the surface. planetary atmospheres tholins atmospheric aerosol Archaen astrobiology
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Inaugural Article: Organic haze on Titan and the Early Earth
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: M G Trainer, Owen B. Toon, Alexander A Pavlov, Jose L Jimenez, Christopher P Mckay, H. Langley Dewitt, Margaret A. TolbertAbstract:Titan has long been a subject of interest, because it provides an excellent example of abiotic processing of organic material. The irradiation of the CH4/N2 atmosphere with sunlight and energetic electrons leads to the formation of aerosol particles, which aggregate into fractal agglomerates and generate a thick haze layer. Until the recent Cassini/Huygens mission, this haze layer obscured the moon's surface (1). Specific mechanisms for particle formation are not known, but they have been a major focus of attempts to understand the chemistry in Titan's atmosphere. Observed gaseous constituents such as C2H2, C2H4, C2H6, C4H2, C6H6, and HCN provide evidence of the active pathways toward aerosol formation (2–4). Results from the Huygens Probe show the presence of HCN and NH3 within the particles but have not yet provided information on the overall chemical structure (5). Characterization of the chemical makeup of laboratory analogs, formed mostly as films produced in discharges, indicate that the haze aerosols are likely comprised of high-molecular-weight organic species including aromatic and aliphatic structures with some evidence of CN bonding such as amines, imines, and nitriles (6–11). Yung et al. (12) estimated that although the N-chemistry observed in the aerosols derives from energetic electrons in Saturn's magnetosphere, the majority of the organic constituents observed in Titan's atmosphere can be accounted for by photolysis. Other work studying production pathways concluded that polycyclic aromatic hydrocarbons formed through photochemistry were the primary contributors to the aerosol mass (13). Despite these positive modeling results, there have been no laboratory studies to directly measure the properties of aerosols expected from UV irradiation of CH4 in a simulated Titan atmosphere. Adamkovics and Boering (14) used the detection of gas-phase products of CH4 irradiation to infer the number of CC bonds present in particle form, but did not directly measure aerosol properties or formation rates. Tran et al. (15, 16) used a low-pressure Hg lamp with primary emissions at 185 and 254 nm to produce films from the photodissociation of trace species (C2H2, etc.) rather than the direct photolysis of CH4. Here, we describe a study in which the properties of aerosols formed from direct irradiation of CH4 with a continuum VUV source are measured and discussed with relevance to Titan. We will show that the properties of the photochemical aerosols appear similar to those measured for Titan's haze layer, and that the rate of aerosol production is proportional to the rate of CH4 photolysis. In addition to its attraction as a planetary subject, the organic chemistry on Titan has captured interest as a possible analog for the Early Earth (17, 18). The atmospheric composition of the Early Earth before the rise of O2 is a subject of debate. An atmosphere of only N2/CO2 raises concerns because it would not produce biologically interesting organic molecules, and geologic evidence restricts levels of CO2, indicating that it was not the sole greenhouse gas (19). Tian et al. (20) showed that the prebiotic atmosphere may have contained large concentrations of H2 in combination with CO2 and CH4. After the appearance of life, the atmospheric level of CH4 would have risen, owing to a large flux of CH4 from methanogen populations and a long chemical lifetime of CH4 in the anoxic environment (21, 22). An atmosphere with ≈1,000 ppmv each of CH4 and CO2 would counteract the faint young sun sufficiently to keep temperatures above freezing and is a plausible scenario for the Early Earth after the origin of life (23). It has been suggested that if the Early Earth atmosphere contained significant amounts of CH4, then photochemistry like that on Titan could be an important source of organics. However, with CO2 also present in the atmosphere, the haze photochemistry would likely be different from what is currently observed for Titan. Attempts at modeling the effects of an Early Earth haze layer suffer because of a lack of laboratory data for haze formation in CH4/CO2 atmospheres (22, 24). Some workers have studied organics formed in environments including CO, N2, and CH4, but these have either been focused on Titan conditions (25) or have looked only at amino acid production for Early Earth (26, 27). Previous work by our group examined CH4/CO2 hazes using an electric discharge source (28), but a UV energy source is needed to interpret the results for the Early Earth's atmosphere. Here, we use the results from CH4/CO2/N2 photolysis to determine how similar the atmospheric chemistry on the Early Earth may have been to Titan's current organic production and to explore the possibility of an Early Earth haze layer (Fig. 1). Fig. 1. A hazy Early Earth? It has been proposed that if the Early Earth's atmosphere contained CH4, photochemical formation of an organic haze layer may have made the Earth's appearance very similar to that of Saturn's moon Titan (44). The role of CO2 in the ...
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Haze aerosols in the atmosphere of Early Earth: manna from heaven.
Astrobiology, 2004Co-Authors: Melissa G. Trainer, Owen B. Toon, Alexander A Pavlov, Christopher P Mckay, Daniel B. Curtis, Douglas R. Worsnop, Alice E. Delia, Darin W. Toohey, Margaret A. TolbertAbstract:An organic haze layer in the upper atmosphere of Titan plays a crucial role in the atmospheric composition and climate of that moon. Such a haze layer may also have existed on the Early Earth, providing an ultraviolet shield for greenhouse gases needed to warm the planet enough for life to arise and evolve. Despite the implications of such a haze layer, little is known about the organic material produced under Early Earth conditions when both CO2 and CH4 may have been abundant in the atmosphere. For the first time, we experimentally demonstrate that organic haze can be generated in different CH4/CO2 ratios. Here, we show that haze aerosols are able to form at CH4 mixing ratios of 1,000 ppmv, a level likely to be present on Early Earth. In addition, we find that organic hazes will form at C/O ratios as low as 0.6, which is lower than the predicted value of unity. We also show that as the C/O ratio decreases, the organic particles produced are more oxidized and contain biologically labile compounds. After l...
Alexander A Pavlov - One of the best experts on this subject based on the ideXlab platform.
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organic haze on titan and the Early Earth
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: M G Trainer, Owen B. Toon, Alexander A Pavlov, Langley H Dewitt, Jose L Jimenez, Christopher P Mckay, Margaret A. TolbertAbstract:Abstract Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH4/N2 atmosphere. It has been suggested that a similar haze layer may have formed on the Early Earth. Here we report laboratory experiments that demonstrate the properties of haze likely to form through photochemistry on Titan and Early Earth. We have used a deuterium lamp to initiate particle production in these simulated atmospheres from UV photolysis. Using a unique analysis technique, the aerosol mass spectrometer, we have studied the chemical composition, size, and shape of the particles produced as a function of initial trace gas composition. Our results show that the aerosols produced in the laboratory can serve as analogs for the observed haze in Titan's atmosphere. Experiments performed under possible conditions for Early Earth suggest a significant optical depth of haze may have dominated the Early Earth's atmosphere. Aerosol size measurements are presented, and implications for the haze layer properties are discussed. We estimate that aerosol production on the Early Earth may have been on the order of 1014 g·year−1 and thus could have served as a primary source of organic material to the surface. planetary atmospheres tholins atmospheric aerosol Archaen astrobiology
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Inaugural Article: Organic haze on Titan and the Early Earth
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: M G Trainer, Owen B. Toon, Alexander A Pavlov, Jose L Jimenez, Christopher P Mckay, H. Langley Dewitt, Margaret A. TolbertAbstract:Titan has long been a subject of interest, because it provides an excellent example of abiotic processing of organic material. The irradiation of the CH4/N2 atmosphere with sunlight and energetic electrons leads to the formation of aerosol particles, which aggregate into fractal agglomerates and generate a thick haze layer. Until the recent Cassini/Huygens mission, this haze layer obscured the moon's surface (1). Specific mechanisms for particle formation are not known, but they have been a major focus of attempts to understand the chemistry in Titan's atmosphere. Observed gaseous constituents such as C2H2, C2H4, C2H6, C4H2, C6H6, and HCN provide evidence of the active pathways toward aerosol formation (2–4). Results from the Huygens Probe show the presence of HCN and NH3 within the particles but have not yet provided information on the overall chemical structure (5). Characterization of the chemical makeup of laboratory analogs, formed mostly as films produced in discharges, indicate that the haze aerosols are likely comprised of high-molecular-weight organic species including aromatic and aliphatic structures with some evidence of CN bonding such as amines, imines, and nitriles (6–11). Yung et al. (12) estimated that although the N-chemistry observed in the aerosols derives from energetic electrons in Saturn's magnetosphere, the majority of the organic constituents observed in Titan's atmosphere can be accounted for by photolysis. Other work studying production pathways concluded that polycyclic aromatic hydrocarbons formed through photochemistry were the primary contributors to the aerosol mass (13). Despite these positive modeling results, there have been no laboratory studies to directly measure the properties of aerosols expected from UV irradiation of CH4 in a simulated Titan atmosphere. Adamkovics and Boering (14) used the detection of gas-phase products of CH4 irradiation to infer the number of CC bonds present in particle form, but did not directly measure aerosol properties or formation rates. Tran et al. (15, 16) used a low-pressure Hg lamp with primary emissions at 185 and 254 nm to produce films from the photodissociation of trace species (C2H2, etc.) rather than the direct photolysis of CH4. Here, we describe a study in which the properties of aerosols formed from direct irradiation of CH4 with a continuum VUV source are measured and discussed with relevance to Titan. We will show that the properties of the photochemical aerosols appear similar to those measured for Titan's haze layer, and that the rate of aerosol production is proportional to the rate of CH4 photolysis. In addition to its attraction as a planetary subject, the organic chemistry on Titan has captured interest as a possible analog for the Early Earth (17, 18). The atmospheric composition of the Early Earth before the rise of O2 is a subject of debate. An atmosphere of only N2/CO2 raises concerns because it would not produce biologically interesting organic molecules, and geologic evidence restricts levels of CO2, indicating that it was not the sole greenhouse gas (19). Tian et al. (20) showed that the prebiotic atmosphere may have contained large concentrations of H2 in combination with CO2 and CH4. After the appearance of life, the atmospheric level of CH4 would have risen, owing to a large flux of CH4 from methanogen populations and a long chemical lifetime of CH4 in the anoxic environment (21, 22). An atmosphere with ≈1,000 ppmv each of CH4 and CO2 would counteract the faint young sun sufficiently to keep temperatures above freezing and is a plausible scenario for the Early Earth after the origin of life (23). It has been suggested that if the Early Earth atmosphere contained significant amounts of CH4, then photochemistry like that on Titan could be an important source of organics. However, with CO2 also present in the atmosphere, the haze photochemistry would likely be different from what is currently observed for Titan. Attempts at modeling the effects of an Early Earth haze layer suffer because of a lack of laboratory data for haze formation in CH4/CO2 atmospheres (22, 24). Some workers have studied organics formed in environments including CO, N2, and CH4, but these have either been focused on Titan conditions (25) or have looked only at amino acid production for Early Earth (26, 27). Previous work by our group examined CH4/CO2 hazes using an electric discharge source (28), but a UV energy source is needed to interpret the results for the Early Earth's atmosphere. Here, we use the results from CH4/CO2/N2 photolysis to determine how similar the atmospheric chemistry on the Early Earth may have been to Titan's current organic production and to explore the possibility of an Early Earth haze layer (Fig. 1). Fig. 1. A hazy Early Earth? It has been proposed that if the Early Earth's atmosphere contained CH4, photochemical formation of an organic haze layer may have made the Earth's appearance very similar to that of Saturn's moon Titan (44). The role of CO2 in the ...
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Response to Comment on "A Hydrogen-Rich Early Earth Atmosphere"
Science, 2006Co-Authors: Feng Tian, Owen B. Toon, Alexander A PavlovAbstract:Catling speculates that the exobase of Early Earth was hot and that the ancient nonthermal escape rate was more than 1000 times the present rate. However, low oxygen and high carbon dioxide on Early Earth yields a cold exobase, and nonthermal escape rates are limited and cannot balance the volcanic outgassing of hydrogen.
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A hydrogen-rich Early Earth atmosphere
Science (New York N.Y.), 2005Co-Authors: Feng Tian, Owen B. Toon, Alexander A Pavlov, H. De SterckAbstract:We show that the escape of hydrogen from Early Earth's atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have been more efficient than either exogenous delivery or synthesis in hydrothermal systems. The organic soup in the oceans and ponds on Early Earth would have been a more favorable place for the origin of life than previously thought.
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Haze aerosols in the atmosphere of Early Earth: manna from heaven.
Astrobiology, 2004Co-Authors: Melissa G. Trainer, Owen B. Toon, Alexander A Pavlov, Christopher P Mckay, Daniel B. Curtis, Douglas R. Worsnop, Alice E. Delia, Darin W. Toohey, Margaret A. TolbertAbstract:An organic haze layer in the upper atmosphere of Titan plays a crucial role in the atmospheric composition and climate of that moon. Such a haze layer may also have existed on the Early Earth, providing an ultraviolet shield for greenhouse gases needed to warm the planet enough for life to arise and evolve. Despite the implications of such a haze layer, little is known about the organic material produced under Early Earth conditions when both CO2 and CH4 may have been abundant in the atmosphere. For the first time, we experimentally demonstrate that organic haze can be generated in different CH4/CO2 ratios. Here, we show that haze aerosols are able to form at CH4 mixing ratios of 1,000 ppmv, a level likely to be present on Early Earth. In addition, we find that organic hazes will form at C/O ratios as low as 0.6, which is lower than the predicted value of unity. We also show that as the C/O ratio decreases, the organic particles produced are more oxidized and contain biologically labile compounds. After l...
Cyril Szopa - One of the best experts on this subject based on the ideXlab platform.
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Organic chemistry in a CO2 rich Early Earth atmosphere
Earth and Planetary Science Letters, 2017Co-Authors: Benjamin Fleury, Nathalie Carrasco, Maeva Millan, Ludovic Vettier, Cyril SzopaAbstract:The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the Early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the Early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an Early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the Early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the Early Earth.
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Organic chemistry in a CO 2 rich Early Earth atmosphere
Earth and Planetary Science Letters, 2017Co-Authors: Benjamin Fleury, Nathalie Carrasco, Maeva Millan, Ludovic Vettier, Cyril SzopaAbstract:Abstract The emergence of life on the Earth has required a prior organic chemistry leading to the formation of prebiotic molecules. The origin and the evolution of the organic matter on the Early Earth is not yet firmly understood. Several hypothesis, possibly complementary, are considered. They can be divided in two categories: endogenous and exogenous sources. In this work we investigate the contribution of a specific endogenous source: the organic chemistry occurring in the ionosphere of the Early Earth where the significant VUV contribution of the young Sun involved an efficient formation of reactive species. We address the issue whether this chemistry can lead to the formation of complex organic compounds with CO2 as only source of carbon in an Early atmosphere made of N2, CO2 and H2, by mimicking experimentally this type of chemistry using a low pressure plasma reactor. By analyzing the gaseous phase composition, we strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a solid organic phase is also observed, confirming the possibility to trigger organic chemistry in the upper atmosphere of the Early Earth. The identification of Nitrogen-bearing chemical functions in the solid highlights the possibility for an efficient ionospheric chemistry to provide prebiotic material on the Early Earth.
Owen B. Toon - One of the best experts on this subject based on the ideXlab platform.
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Potential climatic impact of organic haze on Early Earth.
Astrobiology, 2011Co-Authors: Christa A. Hasenkopf, Miriam Arak Freedman, Melinda R. Beaver, Owen B. Toon, Margaret A. TolbertAbstract: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%, 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%). 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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Optical properties of Titan and Early Earth haze laboratory analogs in the mid-visible
Icarus, 2010Co-Authors: Christa A. Hasenkopf, Miriam Arak Freedman, Melinda R. Beaver, Owen B. Toon, Christopher P Mckay, Melissa G. Trainer, H. Langley Dewitt, Margaret A. TolbertAbstract:Scattering and absorption of sunlight by aerosols are integral to understanding the radiative balance of any planetary atmosphere covered in a haze, such as Titan and possibly the Early Earth. One key optical parameter of an aerosol is its refractive index. We have simulated both Titan and Early Earth organic haze aerosols in the laboratory and measured the real and imaginary portion of their refractive index at k = 532 nm using cavity ringdown aerosol extinction spectroscopy. This novel technique allows analysis on freely-floating particles minutes after formation. For our Titan analog particles, we find a real refractive index of n = 1.35 ± 0.01 and an imaginary refractive index k = 0.023 ± 0.007, and for the Early Earth analog particles we find n = 1.81 ± 0.02 and k = 0.055 ± 0.020. The Titan analog refractive index has a smaller real and similar imaginary refractive index compared to most previous laboratory measurements of Titan analog films, including values from Khare et al. (Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Callcott, T.A., Williams, M.W. [1984]. Icarus 60, 127–137). These newly measured Titan analog values have implications for spacecraft retrievals of aerosol properties on Titan. The Early Earth analog has a significantly higher real and imaginary refractive index than Titan analogs reported in the literature. These differences suggest that, for a given amount of aerosol, the Early Earth analog would act as a stronger anti-greenhouse agent than the Titan analog.
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organic haze on titan and the Early Earth
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: M G Trainer, Owen B. Toon, Alexander A Pavlov, Langley H Dewitt, Jose L Jimenez, Christopher P Mckay, Margaret A. TolbertAbstract:Abstract Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn's moon, Titan. One of Titan's most captivating features is the thick organic haze layer surrounding the moon, believed to be formed from photochemistry high in the CH4/N2 atmosphere. It has been suggested that a similar haze layer may have formed on the Early Earth. Here we report laboratory experiments that demonstrate the properties of haze likely to form through photochemistry on Titan and Early Earth. We have used a deuterium lamp to initiate particle production in these simulated atmospheres from UV photolysis. Using a unique analysis technique, the aerosol mass spectrometer, we have studied the chemical composition, size, and shape of the particles produced as a function of initial trace gas composition. Our results show that the aerosols produced in the laboratory can serve as analogs for the observed haze in Titan's atmosphere. Experiments performed under possible conditions for Early Earth suggest a significant optical depth of haze may have dominated the Early Earth's atmosphere. Aerosol size measurements are presented, and implications for the haze layer properties are discussed. We estimate that aerosol production on the Early Earth may have been on the order of 1014 g·year−1 and thus could have served as a primary source of organic material to the surface. planetary atmospheres tholins atmospheric aerosol Archaen astrobiology
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Inaugural Article: Organic haze on Titan and the Early Earth
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: M G Trainer, Owen B. Toon, Alexander A Pavlov, Jose L Jimenez, Christopher P Mckay, H. Langley Dewitt, Margaret A. TolbertAbstract:Titan has long been a subject of interest, because it provides an excellent example of abiotic processing of organic material. The irradiation of the CH4/N2 atmosphere with sunlight and energetic electrons leads to the formation of aerosol particles, which aggregate into fractal agglomerates and generate a thick haze layer. Until the recent Cassini/Huygens mission, this haze layer obscured the moon's surface (1). Specific mechanisms for particle formation are not known, but they have been a major focus of attempts to understand the chemistry in Titan's atmosphere. Observed gaseous constituents such as C2H2, C2H4, C2H6, C4H2, C6H6, and HCN provide evidence of the active pathways toward aerosol formation (2–4). Results from the Huygens Probe show the presence of HCN and NH3 within the particles but have not yet provided information on the overall chemical structure (5). Characterization of the chemical makeup of laboratory analogs, formed mostly as films produced in discharges, indicate that the haze aerosols are likely comprised of high-molecular-weight organic species including aromatic and aliphatic structures with some evidence of CN bonding such as amines, imines, and nitriles (6–11). Yung et al. (12) estimated that although the N-chemistry observed in the aerosols derives from energetic electrons in Saturn's magnetosphere, the majority of the organic constituents observed in Titan's atmosphere can be accounted for by photolysis. Other work studying production pathways concluded that polycyclic aromatic hydrocarbons formed through photochemistry were the primary contributors to the aerosol mass (13). Despite these positive modeling results, there have been no laboratory studies to directly measure the properties of aerosols expected from UV irradiation of CH4 in a simulated Titan atmosphere. Adamkovics and Boering (14) used the detection of gas-phase products of CH4 irradiation to infer the number of CC bonds present in particle form, but did not directly measure aerosol properties or formation rates. Tran et al. (15, 16) used a low-pressure Hg lamp with primary emissions at 185 and 254 nm to produce films from the photodissociation of trace species (C2H2, etc.) rather than the direct photolysis of CH4. Here, we describe a study in which the properties of aerosols formed from direct irradiation of CH4 with a continuum VUV source are measured and discussed with relevance to Titan. We will show that the properties of the photochemical aerosols appear similar to those measured for Titan's haze layer, and that the rate of aerosol production is proportional to the rate of CH4 photolysis. In addition to its attraction as a planetary subject, the organic chemistry on Titan has captured interest as a possible analog for the Early Earth (17, 18). The atmospheric composition of the Early Earth before the rise of O2 is a subject of debate. An atmosphere of only N2/CO2 raises concerns because it would not produce biologically interesting organic molecules, and geologic evidence restricts levels of CO2, indicating that it was not the sole greenhouse gas (19). Tian et al. (20) showed that the prebiotic atmosphere may have contained large concentrations of H2 in combination with CO2 and CH4. After the appearance of life, the atmospheric level of CH4 would have risen, owing to a large flux of CH4 from methanogen populations and a long chemical lifetime of CH4 in the anoxic environment (21, 22). An atmosphere with ≈1,000 ppmv each of CH4 and CO2 would counteract the faint young sun sufficiently to keep temperatures above freezing and is a plausible scenario for the Early Earth after the origin of life (23). It has been suggested that if the Early Earth atmosphere contained significant amounts of CH4, then photochemistry like that on Titan could be an important source of organics. However, with CO2 also present in the atmosphere, the haze photochemistry would likely be different from what is currently observed for Titan. Attempts at modeling the effects of an Early Earth haze layer suffer because of a lack of laboratory data for haze formation in CH4/CO2 atmospheres (22, 24). Some workers have studied organics formed in environments including CO, N2, and CH4, but these have either been focused on Titan conditions (25) or have looked only at amino acid production for Early Earth (26, 27). Previous work by our group examined CH4/CO2 hazes using an electric discharge source (28), but a UV energy source is needed to interpret the results for the Early Earth's atmosphere. Here, we use the results from CH4/CO2/N2 photolysis to determine how similar the atmospheric chemistry on the Early Earth may have been to Titan's current organic production and to explore the possibility of an Early Earth haze layer (Fig. 1). Fig. 1. A hazy Early Earth? It has been proposed that if the Early Earth's atmosphere contained CH4, photochemical formation of an organic haze layer may have made the Earth's appearance very similar to that of Saturn's moon Titan (44). The role of CO2 in the ...
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Response to Comment on "A Hydrogen-Rich Early Earth Atmosphere"
Science, 2006Co-Authors: Feng Tian, Owen B. Toon, Alexander A PavlovAbstract:Catling speculates that the exobase of Early Earth was hot and that the ancient nonthermal escape rate was more than 1000 times the present rate. However, low oxygen and high carbon dioxide on Early Earth yields a cold exobase, and nonthermal escape rates are limited and cannot balance the volcanic outgassing of hydrogen.