The Experts below are selected from a list of 786 Experts worldwide ranked by ideXlab platform
Audrey Bouvier - One of the best experts on this subject based on the ideXlab platform.
-
formation of the ce nd mantle array crustal extraction vs recycling by subduction
Earth and Planetary Science Letters, 2020Co-Authors: Claudine Israel, M Boyet, Regis Doucelance, P Bonnand, P Frossard, D Auclair, Audrey BouvierAbstract:Abstract We present new measurements of 138Ce/142Ce and 143Nd/144Nd isotopic ratios in terrestrial and extra-terrestrial samples. The mean value obtained from nine chondrites defines the 138Ce/142Ce ratio of the chondritic uniform reservoir (CHUR) as 0.02256577 ± 66 (2sd). MORBs and OIBs define the mantle array in the eNd vs. eCe diagram to be e Nd = − 7.3 ( ± 0.5 ) × e Ce + 0.4 ( ± 0.3 ) . From MORB measurements, we derive the isotopic composition of the depleted MORB mantle (DMM) to be e Ce = − 1.1 ± 0.6 (2sd). Both CHUR and a modelled early-depleted mantle reservoir plot on the mantle array. Thus, the precise determination of the mantle array does not further constrain the La/Ce and Sm/Nd ratios of the bulk silicate Earth (BSE; i.e., primitive mantle). The composition of 1.8 Ga upper continental crust obtained from aeolian sediments is e Ce = 1.8 ± 0.3 (2sd; e Nd = − 11.2 ), and that of its 2.2 Ga equivalent is e Ce = 2.3 ± 0.3 (2sd; e Nd = − 17 ). Binary mixing models between depleted (DMM) and enriched (upper crust or mafic crust composition) components do not reproduce the linear Ce-Nd mantle array but plots close to the island arc basalt data. When the bulk Ce isotopic composition of the continental crust is calculated from the range of accepted Nd isotope values and a mass-balance budget of the BSE, the mixing curves are closer to the mantle array. However the calculated Ce isotopic composition for the bulk crust is always less radiogenic than measurements. Adjusting the Ce-Nd isotopic composition or the Ce/Nd ratio of the end-members to fully linearise the mixing curve leads to unrealistic values never measured in terrestrial samples. We propose a recycling model to reconstruct the mantle array with the participation of both oceanic crust and sediments in the mantle through time. Cerium is a redox sensitive element, making the La-Ce and Sm-Nd systematics an ideal combination to investigate sediment recycling through time. In this recycling model, the most extreme EM-like signatures require the involvement of oceanic sediments that formed under reduced conditions before the Great Oxygenation Event at 2.4 Ga, and which are devoid of Ce elemental anomalies.
Patrick M. Shih - One of the best experts on this subject based on the ideXlab platform.
-
phanerozoic radiation of ammonia oxidizing bacteria
Scientific Reports, 2021Co-Authors: Lewis M. Ward, Patrick M. Shih, D JohnstonAbstract:The modern nitrogen cycle consists of a web of microbially mediated redox transformations. Among the most crucial reactions in this cycle is the oxidation of ammonia to nitrite, an obligately aerobic process performed by a limited number of lineages of bacteria (AOB) and archaea (AOA). As this process has an absolute requirement for O2, the timing of its evolution-especially as it relates to the Great Oxygenation Event ~ 2.3 billion years ago-remains contested and is pivotal to our understanding of nutrient cycles. To estimate the antiquity of bacterial ammonia oxidation, we performed phylogenetic and molecular clock analyses of AOB. Surprisingly, bacterial ammonia oxidation appears quite young, with crown group clades having originated during Neoproterozoic time (or later) with major radiations occurring during Paleozoic time. These results place the evolution of AOB broadly coincident with the pervasive Oxygenation of the deep ocean. The late evolution AOB challenges earlier interpretations of the ancient nitrogen isotope record, predicts a more substantial role for AOA during Precambrian time, and may have implications for understanding of the size and structure of the biogeochemical nitrogen cycle through geologic time.
-
phanerozoic radiation of ammonia oxidizing bacteria
bioRxiv, 2020Co-Authors: Lewis M. Ward, D Johnston, Patrick M. ShihAbstract:The modern nitrogen cycle consists of a web of microbially mediated redox transformations. Among the most crucial steps in this cycle is the oxidation of ammonia to nitrite, an obligately aerobic process performed by a limited number of lineages of bacteria (AOB) and archaea (AOA). As this process has an absolute requirement for O2, the timing of its evolution--specially as it relates to the Great Oxygenation Event ~2.3 billion years ago--remains contested. To estimate the antiquity of bacterial ammonia oxidation, we performed phylogenetic and molecular clock analyses of AOB. Surprisingly, bacterial ammonia oxidation appears quite young, with crown group clades having originated during Neoproterozoic time (or later) with major radiations occurring during Paleozoic time. These results place the evolution of AOB broadly coincident with the pervasive Oxygenation of the deep ocean. The late evolution AOB challenges earlier interpretations of the ancient nitrogen isotope record, predicts a more substantial role for AOA during Precambrian time, and may have implications for understanding of the size and structure of the biogeochemical nitrogen cycle through geologic time.
-
The evolution and productivity of carbon fixation pathways in response to changes in oxygen concentration over geological time.
Free Radical Biology and Medicine, 2019Co-Authors: Lewis M. Ward, Patrick M. ShihAbstract:Abstract The fixation of inorganic carbon species like CO2 to more reduced organic forms is one of the most fundamental processes of life as we know it. Although several carbon fixation pathways are known to exist, on Earth today nearly all global carbon fixation is driven by the Calvin cycle in oxygenic photosynthetic plants, algae, and Cyanobacteria. At other times in Earth history, other organisms utilizing different carbon fixation pathways may have played relatively larger roles, with this balance shifting over geological time as the environmental context of life has changed and evolutionary innovations accumulated. Among the most dramatic changes that our planet and the biosphere have undergone are those surrounding the rise of O2 in our atmosphere—first during the Great Oxygenation Event at ∼2.3 Ga, and perhaps again during Neoproterozoic or Paleozoic time. These Oxygenation Events likely represent major step changes in the tempo and mode of biological productivity as a result of the increased productivity of oxygenic photosynthesis and the introduction of O2 into geochemical and biological systems, and likely involved shifts in the relative contribution of different carbon fixation pathways. Here, we review what is known from both the rock record and comparative biology about the evolution of carbon fixation pathways, their contributions to primary productivity through time, and their relationship to the evolving Oxygenation state of the fluid Earth following the evolution and expansion of oxygenic photosynthesis.
Joseph L Kirschvink - One of the best experts on this subject based on the ideXlab platform.
-
origin of microbial biomineralization and magnetotaxis during the archean
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Wei Lin, Dennis A. Bazylinski, Greig A Paterson, Qiyun Zhu, Yinzhao Wang, Evguenia Kopylova, Rob Knight, Rixiang Zhu, Joseph L KirschvinkAbstract:Microbes that synthesize minerals, a process known as microbial biomineralization, contributed substantially to the evolution of current planetary environments through numerous important geochemical processes. Despite its geological significance, the origin and evolution of microbial biomineralization remain poorly understood. Through combined metagenomic and phylogenetic analyses of deep-branching magnetotactic bacteria from the Nitrospirae phylum, and using a Bayesian molecular clock-dating method, we show here that the gene cluster responsible for biomineralization of magnetosomes, and the arrangement of magnetosome chain(s) within cells, both originated before or near the Archean divergence between the Nitrospirae and Proteobacteria. This phylogenetic divergence occurred well before the Great Oxygenation Event. Magnetotaxis likely evolved due to environmental pressures conferring an evolutionary advantage to navigation via the geomagnetic field. Earth’s dynamo must therefore have been sufficiently strong to sustain microbial magnetotaxis in the Archean, suggesting that magnetotaxis coevolved with the geodynamo over geological time.
-
a negative fold test on the lorrain formation of the huronian supergroup uncertainty on the paleolatitude of the paleoproterozoic gowganda glaciation and implications for the Great Oxygenation Event
Earth and Planetary Science Letters, 2005Co-Authors: I A Hilburn, Joseph L Kirschvink, Eiichi Tajika, Ryuji Tada, Yozo Hamano, Shinji YamamotoAbstract:Previous paleomagnetic studies of the glaciogenic Gowganda and Lorrain formations have identified several low-inclination magnetic components of high thermal stability, which suggest low-latitude glaciation during deposition of the Huronian Supergroup, Canada. While extraordinary claims demand extraordinary proof, prior authors have been unable to support their interpretations of these components conclusively with any of the classic field stability tests (e.g., conglomerate, fold, and baked contact) capable of demonstrating that the magnetization was acquired at or soon enough after the time of deposition to be used to constrain the paleolatitude of the Gowganda or Lorrain formations. We report here the results of a fold test from the “purple siltstone” member of the Lorrain Formation near the town of Desbarats, Ontario, which indicate that none of the reported components dates to the time of deposition. Hence, the paleolatitude of the Gowganda glaciation is uncertain. Comparison of the lithostratigraphic, paleomagnetic, and radiometric constraints on the Huronian sequence and the Transvaal Supergroup of Southern Africa implies that the one verified low-latitude Paleoproterozoic glacial Event (the Makganyene glaciation, Transvaal Supergroup, South Africa) is younger than the three glacial units of Canada. With this correlation, the physical rock record indicates that the ‘Great Oxygenation Event’ began in the time interval between the Gowganda and Makganyene glaciations. These data are consistent with the sudden evolution of oxygenic photosynthesis destroying a methane greenhouse and thereby triggering the first Snowball Earth Event in Earth history.
Lewis M. Ward - One of the best experts on this subject based on the ideXlab platform.
-
phanerozoic radiation of ammonia oxidizing bacteria
Scientific Reports, 2021Co-Authors: Lewis M. Ward, Patrick M. Shih, D JohnstonAbstract:The modern nitrogen cycle consists of a web of microbially mediated redox transformations. Among the most crucial reactions in this cycle is the oxidation of ammonia to nitrite, an obligately aerobic process performed by a limited number of lineages of bacteria (AOB) and archaea (AOA). As this process has an absolute requirement for O2, the timing of its evolution-especially as it relates to the Great Oxygenation Event ~ 2.3 billion years ago-remains contested and is pivotal to our understanding of nutrient cycles. To estimate the antiquity of bacterial ammonia oxidation, we performed phylogenetic and molecular clock analyses of AOB. Surprisingly, bacterial ammonia oxidation appears quite young, with crown group clades having originated during Neoproterozoic time (or later) with major radiations occurring during Paleozoic time. These results place the evolution of AOB broadly coincident with the pervasive Oxygenation of the deep ocean. The late evolution AOB challenges earlier interpretations of the ancient nitrogen isotope record, predicts a more substantial role for AOA during Precambrian time, and may have implications for understanding of the size and structure of the biogeochemical nitrogen cycle through geologic time.
-
phanerozoic radiation of ammonia oxidizing bacteria
bioRxiv, 2020Co-Authors: Lewis M. Ward, D Johnston, Patrick M. ShihAbstract:The modern nitrogen cycle consists of a web of microbially mediated redox transformations. Among the most crucial steps in this cycle is the oxidation of ammonia to nitrite, an obligately aerobic process performed by a limited number of lineages of bacteria (AOB) and archaea (AOA). As this process has an absolute requirement for O2, the timing of its evolution--specially as it relates to the Great Oxygenation Event ~2.3 billion years ago--remains contested. To estimate the antiquity of bacterial ammonia oxidation, we performed phylogenetic and molecular clock analyses of AOB. Surprisingly, bacterial ammonia oxidation appears quite young, with crown group clades having originated during Neoproterozoic time (or later) with major radiations occurring during Paleozoic time. These results place the evolution of AOB broadly coincident with the pervasive Oxygenation of the deep ocean. The late evolution AOB challenges earlier interpretations of the ancient nitrogen isotope record, predicts a more substantial role for AOA during Precambrian time, and may have implications for understanding of the size and structure of the biogeochemical nitrogen cycle through geologic time.
-
The evolution and productivity of carbon fixation pathways in response to changes in oxygen concentration over geological time.
Free Radical Biology and Medicine, 2019Co-Authors: Lewis M. Ward, Patrick M. ShihAbstract:Abstract The fixation of inorganic carbon species like CO2 to more reduced organic forms is one of the most fundamental processes of life as we know it. Although several carbon fixation pathways are known to exist, on Earth today nearly all global carbon fixation is driven by the Calvin cycle in oxygenic photosynthetic plants, algae, and Cyanobacteria. At other times in Earth history, other organisms utilizing different carbon fixation pathways may have played relatively larger roles, with this balance shifting over geological time as the environmental context of life has changed and evolutionary innovations accumulated. Among the most dramatic changes that our planet and the biosphere have undergone are those surrounding the rise of O2 in our atmosphere—first during the Great Oxygenation Event at ∼2.3 Ga, and perhaps again during Neoproterozoic or Paleozoic time. These Oxygenation Events likely represent major step changes in the tempo and mode of biological productivity as a result of the increased productivity of oxygenic photosynthesis and the introduction of O2 into geochemical and biological systems, and likely involved shifts in the relative contribution of different carbon fixation pathways. Here, we review what is known from both the rock record and comparative biology about the evolution of carbon fixation pathways, their contributions to primary productivity through time, and their relationship to the evolving Oxygenation state of the fluid Earth following the evolution and expansion of oxygenic photosynthesis.
Bohlin Madeleine - One of the best experts on this subject based on the ideXlab platform.
-
Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions
'Elsevier BV', 2021Co-Authors: Neubeck Anna, Hemmingsson Christoffer, Boosman Arjen, Rouxel Olivier, Bohlin MadeleineAbstract:The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO3 salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to Greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 +/- 0.17 parts per thousand). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5 parts per thousand. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the delta Ni-60 values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry
-
Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions
'Elsevier BV', 2020Co-Authors: Neubeck Anna, Hemmingsson Christoffer, Boosman Arjen, Rouxel Olivier, Bohlin MadeleineAbstract:The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO3 salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to Greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 ± 0.17‰). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5‰. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the δ60Ni values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry
