Nitrogen is an essential nutrient for all organisms that must have been available since the origi... more Nitrogen is an essential nutrient for all organisms that must have been available since the origin of life. Abiotic processes including hydrothermal reduction, photochemical reactions, or lightning discharge could have converted atmospheric N2 into assimilable NH4(+), HCN, or NOx species, collectively termed fixed nitrogen. But these sources may have been small on the early Earth, severely limiting the size of the primordial biosphere. The evolution of the nitrogen-fixing enzyme nitrogenase, which reduces atmospheric N2 to organic NH4(+), thus represented a major breakthrough in the radiation of life, but its timing is uncertain. Here we present nitrogen isotope ratios with a mean of 0.0 ± 1.2‰ from marine and fluvial sedimentary rocks of prehnite-pumpellyite to greenschist metamorphic grade between 3.2 and 2.75 billion years ago. These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitro...
ABSTRACT Minor sulfur isotope anomalies indicate the absence of O2 from the Archean atmosphere. A... more ABSTRACT Minor sulfur isotope anomalies indicate the absence of O2 from the Archean atmosphere. A rich dataset showing large variations in magnitude and sign of Δ33S and Δ36S, preserved in both sulfates and sulfides, suggests that further constraints on Archean atmospheric chemistry are possible. We review previous quantitative constraints on atmospheric Δ33S production, and suggest that a new approach is needed. We added sulfur species containing 33S and 34S to a 1-D photochemical model and describe the numerical methodology needed to ensure accurate prediction of the magnitude and sign of Δ33S produced by and deposited from the Archean atmosphere. This methodology can test multiple MIF-S formation mechanisms subject to a variety of proposed atmospheric compositions, yielding Δ33S predictions that can be compared to the rock record. We systematically test SO2 isotopologue absorption effects in SO2 photolysis (Danielache et al., 2008), one of the primary proposed mechanisms for Δ33S formation. We find that differential absorption through the Danielache et al. (2008) cross sections is capable of altering predicted Δ33S as a function of multiple atmospheric variables, including trace O2 concentration, total sulfur flux, CO2 content, and the presence of hydrocarbons, but find a limited role for OCS and H2S. Under all realistic conditions, the Danielache et al. (2008) cross sections yield Δ33S predictions at odds with the geologic record, implying that additional pathways for sulfur MIF formation exist and/or the cross sections have significant errors. The methodology presented here will allow for quantitative constraints on the Archean atmosphere beyond the absence of O2, as soon as additional experimental measurements of MIF-S producing processes become available.
The 2009 AbGradCon was held at the University of Washington in July 2009. It brought together 67 ... more The 2009 AbGradCon was held at the University of Washington in July 2009. It brought together 67 participants from 8 different countries and 34 different universities. AbGradCon also took place in the virtual world of Second Life.
ABSTRACT Selenium has a complex biogeochemical cycle with many similarities to that of sulfur. Fr... more ABSTRACT Selenium has a complex biogeochemical cycle with many similarities to that of sulfur. Fractionations of selenium isotopes induced in bacterial respiration reactions have been recognized as potential recorders of environmental oxidation states, opening up the possibility of further constraining bioproductivity and the redox evolution of the Earth's atmosphere and ocean over time. However, analyses of selenium isotopes are complicated by interferences with organic compounds as well as a number of isobaric interferences. Application of existing sample preparation protocols to geological samples replete with organic carbon can result in incomplete extraction yields and incomplete removal of isobarically interfering germanium and arsenic. We present measurements of three different organic-rich shales of varying ages prepared with eight different sample preparation protocols and identify a method with which high selenium yields are obtained for all three samples while the concentration of germanium is greatly reduced. We further investigate the quantitative importance of isobaric interferences and present new post-analytical data correction protocols. If selenium concentrations in standards and samples are matched to within 5%, the ratios of five isotopes of selenium (74Se, 76Se, 77Se, 78Se and 82Se) can be measured with precisions better than 0.2‰ for δ76/78Se, δ77/78Se and δ82/78Se and 0.5‰ for δ74/78Se, allowing analytical accuracy to be monitored with three-isotope diagrams and thus enabling the detection of any mass-independent isotopic fractionation.
Many decades of experimental and theoretical research on the origin of life have yielded importan... more 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. Did life originate from a global chemical reactor? 103 Serpentinization (Fischer-Tropsch-type reactions), heat Deamer (2007) Carbohydrates Extraterrestrial synthesis (meteors), peridotite-hosted hydrothermal vents, atmosphere/ocean, alkaline streams Serpentinization (Fischer-Tropsch-type reactions), lightning, heat Deamer (2007); Benner et al. (2010)
Using a Pulse Amplitude Modulation Flourometer (PAM), the photosynthetic yields of Nannochloropsi... more Using a Pulse Amplitude Modulation Flourometer (PAM), the photosynthetic yields of Nannochloropsis salina and Spirulina platensis were monitored during phases of micro-, normal and hyper-gravity on a parabolic flight, in order to determine the effects of changing gravity conditions on the photosynthetic activity of the microalgae. Fluctuations in the otherwise stable value for the photosynthetic yield were observed in and immediately after the phases of abnormal gravity. Since a series of parameters such as light intensity, temperature, pH, oxygen concentration, or obstruction of the measurements via air bubbles could be excluded as cause of this effect it is likely that it is connected with the changes in gravity. For N. salina the negative peaks mainly occurred during the transitions between different acceleration levels, whereas for S. platensis continuous depressions during abnormal gravity phases were observed. Due to the quick change from hyper-into microgravity and vice versa, and the short duration of microgravity phases during a parabolic flight it is, however, difficult to conclude whether the observed changes were an effect of the reduced, the increased gravity or a combination of the two.
Nitrogen is an essential nutrient for all organisms that must have been available since the origi... more Nitrogen is an essential nutrient for all organisms that must have been available since the origin of life. Abiotic processes including hydrothermal reduction, photochemical reactions, or lightning discharge could have converted atmospheric N2 into assimilable NH4(+), HCN, or NOx species, collectively termed fixed nitrogen. But these sources may have been small on the early Earth, severely limiting the size of the primordial biosphere. The evolution of the nitrogen-fixing enzyme nitrogenase, which reduces atmospheric N2 to organic NH4(+), thus represented a major breakthrough in the radiation of life, but its timing is uncertain. Here we present nitrogen isotope ratios with a mean of 0.0 ± 1.2‰ from marine and fluvial sedimentary rocks of prehnite-pumpellyite to greenschist metamorphic grade between 3.2 and 2.75 billion years ago. These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitro...
ABSTRACT Minor sulfur isotope anomalies indicate the absence of O2 from the Archean atmosphere. A... more ABSTRACT Minor sulfur isotope anomalies indicate the absence of O2 from the Archean atmosphere. A rich dataset showing large variations in magnitude and sign of Δ33S and Δ36S, preserved in both sulfates and sulfides, suggests that further constraints on Archean atmospheric chemistry are possible. We review previous quantitative constraints on atmospheric Δ33S production, and suggest that a new approach is needed. We added sulfur species containing 33S and 34S to a 1-D photochemical model and describe the numerical methodology needed to ensure accurate prediction of the magnitude and sign of Δ33S produced by and deposited from the Archean atmosphere. This methodology can test multiple MIF-S formation mechanisms subject to a variety of proposed atmospheric compositions, yielding Δ33S predictions that can be compared to the rock record. We systematically test SO2 isotopologue absorption effects in SO2 photolysis (Danielache et al., 2008), one of the primary proposed mechanisms for Δ33S formation. We find that differential absorption through the Danielache et al. (2008) cross sections is capable of altering predicted Δ33S as a function of multiple atmospheric variables, including trace O2 concentration, total sulfur flux, CO2 content, and the presence of hydrocarbons, but find a limited role for OCS and H2S. Under all realistic conditions, the Danielache et al. (2008) cross sections yield Δ33S predictions at odds with the geologic record, implying that additional pathways for sulfur MIF formation exist and/or the cross sections have significant errors. The methodology presented here will allow for quantitative constraints on the Archean atmosphere beyond the absence of O2, as soon as additional experimental measurements of MIF-S producing processes become available.
The 2009 AbGradCon was held at the University of Washington in July 2009. It brought together 67 ... more The 2009 AbGradCon was held at the University of Washington in July 2009. It brought together 67 participants from 8 different countries and 34 different universities. AbGradCon also took place in the virtual world of Second Life.
ABSTRACT Selenium has a complex biogeochemical cycle with many similarities to that of sulfur. Fr... more ABSTRACT Selenium has a complex biogeochemical cycle with many similarities to that of sulfur. Fractionations of selenium isotopes induced in bacterial respiration reactions have been recognized as potential recorders of environmental oxidation states, opening up the possibility of further constraining bioproductivity and the redox evolution of the Earth's atmosphere and ocean over time. However, analyses of selenium isotopes are complicated by interferences with organic compounds as well as a number of isobaric interferences. Application of existing sample preparation protocols to geological samples replete with organic carbon can result in incomplete extraction yields and incomplete removal of isobarically interfering germanium and arsenic. We present measurements of three different organic-rich shales of varying ages prepared with eight different sample preparation protocols and identify a method with which high selenium yields are obtained for all three samples while the concentration of germanium is greatly reduced. We further investigate the quantitative importance of isobaric interferences and present new post-analytical data correction protocols. If selenium concentrations in standards and samples are matched to within 5%, the ratios of five isotopes of selenium (74Se, 76Se, 77Se, 78Se and 82Se) can be measured with precisions better than 0.2‰ for δ76/78Se, δ77/78Se and δ82/78Se and 0.5‰ for δ74/78Se, allowing analytical accuracy to be monitored with three-isotope diagrams and thus enabling the detection of any mass-independent isotopic fractionation.
Many decades of experimental and theoretical research on the origin of life have yielded importan... more 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. Did life originate from a global chemical reactor? 103 Serpentinization (Fischer-Tropsch-type reactions), heat Deamer (2007) Carbohydrates Extraterrestrial synthesis (meteors), peridotite-hosted hydrothermal vents, atmosphere/ocean, alkaline streams Serpentinization (Fischer-Tropsch-type reactions), lightning, heat Deamer (2007); Benner et al. (2010)
Using a Pulse Amplitude Modulation Flourometer (PAM), the photosynthetic yields of Nannochloropsi... more Using a Pulse Amplitude Modulation Flourometer (PAM), the photosynthetic yields of Nannochloropsis salina and Spirulina platensis were monitored during phases of micro-, normal and hyper-gravity on a parabolic flight, in order to determine the effects of changing gravity conditions on the photosynthetic activity of the microalgae. Fluctuations in the otherwise stable value for the photosynthetic yield were observed in and immediately after the phases of abnormal gravity. Since a series of parameters such as light intensity, temperature, pH, oxygen concentration, or obstruction of the measurements via air bubbles could be excluded as cause of this effect it is likely that it is connected with the changes in gravity. For N. salina the negative peaks mainly occurred during the transitions between different acceleration levels, whereas for S. platensis continuous depressions during abnormal gravity phases were observed. Due to the quick change from hyper-into microgravity and vice versa, and the short duration of microgravity phases during a parabolic flight it is, however, difficult to conclude whether the observed changes were an effect of the reduced, the increased gravity or a combination of the two.
Uploads
Papers by E. Stüeken