The distribution of volatile elements during rocky planet formation

Core segregation and atmosphere formation are two of the major processes that redistribute the volatile elements—hydrogen (H), carbon (C), nitrogen (N), and sulfur (S)—in and around rocky planets during their formation. The volatile elements by definition accumulate in gaseous reservoirs and form atmospheres. However, under conditions of early planet formation, these elements can also behave as siderophiles (i.e., iron-loving) and become concentrated in core-forming metals. Current models of core formation suggest that metal-silicate reactions occurred over a wide pressure, temperature, and compositional space to ultimately impose the chemistries of the cores and silicate portions of rocky planets. Additionally, the solubilities of volatile elements in magmas determine their transfer between the planetary interiors and atmospheres, which has recently come into sharper focus in the context of highly irradiated, potentially molten exoplanets. Recently, there has been a significant push to experimentally investigate the metal-silicate and magma-gas exchange coefficients for volatile elements over a wide range of conditions relevant to rocky planet formation. Qualitatively, results from the metal-silicate partitioning studies suggest that cores of rocky planets could be major reservoirs of the volatile elements though significant amounts will remain in mantles. Results from solubility studies imply that under oxidizing conditions, most H and S are sequestered in the magma ocean, while most N is outgassed to the atmosphere, and C is nearly equally distributed between the atmosphere and the interior. Under reducing conditions, nearly all N dissolves in the magma ocean, the atmosphere becomes the dominant C reservoir, while H becomes more equally distributed between the interior and the atmosphere, and S remains dominantly in the interior. These chemical trends bear numerous implications for the chemical differentiation of rocky planets and the formation and longevity of secondary atmospheres in the early Solar System and exoplanetary systems. Further experimental and modeling efforts are required to understand the potential of chemical and physical disequilibria during core formation and magma ocean crystallization and to constrain the distributions of volatile elements in the interiors and atmospheres of rocky planets through their formation and long-term geologic evolution.</p

Partage du soufre et du platine entre un réservoir métallique et un réservoir silicaté lors de la formation du noyau terrestre

Measurements of the metal-silicate partitioning behavior of siderophile and volatile elements at the conditions of the deep primitive Earth can provide constraints on the mechanisms of terrestrial core formation. Experiments were conducted in a laser-heated diamond anvil cell to investigate the metal-silicate partitioning of sulfur and platinum at high pressures and temperatures. The partitioning behaviors were quantified post-experiment by high resolution NanoSIMS imaging. Sulfur was found to be moderately siderophile at core formation conditions and this, together with cosmochemical estimates, argue that it cannot be a major light element in the core. Accretion modeling with this new partitioning data implies that a heterogeneous accretion scenario can best explain the mantle and bulk Earth sulfur contents. The measured partitioning values for platinum are such that the mantle's platinum abundance can be sufficiently explained by core-mantle equilibration. Overall these results support the hypothesis that the cores of large impactors did not equilibrate fully with the magma ocean and metal could have sequestered to the Earth's core without leaving a record in the mantle. A late sulfide segregation event also likely played a role in establishing the observed mantle compositions. These findings help to further elucidate the accretion history of the Earth and core-mantle differentiation processes.La détermination du partage des éléments sidérophiles et volatils entre métal et silicates aux conditions du manteau profond de la Terre primitive peut fournir des contraintes relatives au mécanisme de formation du noyau terrestre. Des expériences ont été réalisées dans des cellules à enclumes de diamant (DAC) chauffées par laser afin d'étudier l'évolution du partage métal-silicate du soufre et du platine à haute température et haute pression. Le partage est déterminé grâce à la mesure sur échantillons trempés des concentrations par NanoSIMS et sonde électronique. L’affinité du soufre avec le métal, mesurée aux conditions de formation du noyau terrestre, est moins grande qu’attendue. En accord avec les observables cosmochimiques (météorites), il semble que la quantité de soufre dans le noyau ne peut excéder 2 poids%. Les modèles d’accrétion de la Terre, combinés à nos mesures du coefficient de partage du soufre en fonction de la pression et la température, indiquent que la concentration globale de soufre du manteau terrestre doit être le résultat d'une accrétion hétérogène. Ces données indiquent également un apport tardif des éléments volatils au cours de l’accrétion et de la formation du noyau. Les valeurs de partage du platine suggèrent que son abondance dans le manteau terrestre peut être expliquée simplement par la formation du noyau. De manière générale, ces résultats supportent les hypothèses selon lesquelles les noyaux des gros impacteurs n’ont pas pu s’équilibrer entièrement avec le manteau terrestre. Certaines fractions métalliques ont donc pu atteindre le noyau terrestre sans affecter le manteau. L’hypothèse d’un évènement tardif de ségrégation de sulfure durant la formation de la terre pourrait aussi expliquer les compositions du manteau terrestre observées. Ces résultats permettent de caractériser les processus de différenciation du manteau et du noyau et de mieux comprendre la formation de la Terre

Partage du soufre et du platine entre un réservoir métallique et un réservoir silicaté lors de la formation du noyau terrestre

Measurements of the metal-silicate partitioning behavior of siderophile and volatile elements at the conditions of the deep primitive Earth can provide constraints on the mechanisms of terrestrial core formation. Experiments were conducted in a laser-heated diamond anvil cell to investigate the metal-silicate partitioning of sulfur and platinum at high pressures and temperatures. The partitioning behaviors were quantified post-experiment by high resolution NanoSIMS imaging. Sulfur was found to be moderately siderophile at core formation conditions and this, together with cosmochemical estimates, argue that it cannot be a major light element in the core. Accretion modeling with this new partitioning data implies that a heterogeneous accretion scenario can best explain the mantle and bulk Earth sulfur contents. The measured partitioning values for platinum are such that the mantle's platinum abundance can be sufficiently explained by core-mantle equilibration. Overall these results support the hypothesis that the cores of large impactors did not equilibrate fully with the magma ocean and metal could have sequestered to the Earth's core without leaving a record in the mantle. A late sulfide segregation event also likely played a role in establishing the observed mantle compositions. These findings help to further elucidate the accretion history of the Earth and core-mantle differentiation processes.La détermination du partage des éléments sidérophiles et volatils entre métal et silicates aux conditions du manteau profond de la Terre primitive peut fournir des contraintes relatives au mécanisme de formation du noyau terrestre. Des expériences ont été réalisées dans des cellules à enclumes de diamant (DAC) chauffées par laser afin d'étudier l'évolution du partage métal-silicate du soufre et du platine à haute température et haute pression. Le partage est déterminé grâce à la mesure sur échantillons trempés des concentrations par NanoSIMS et sonde électronique. L’affinité du soufre avec le métal, mesurée aux conditions de formation du noyau terrestre, est moins grande qu’attendue. En accord avec les observables cosmochimiques (météorites), il semble que la quantité de soufre dans le noyau ne peut excéder 2 poids%. Les modèles d’accrétion de la Terre, combinés à nos mesures du coefficient de partage du soufre en fonction de la pression et la température, indiquent que la concentration globale de soufre du manteau terrestre doit être le résultat d'une accrétion hétérogène. Ces données indiquent également un apport tardif des éléments volatils au cours de l’accrétion et de la formation du noyau. Les valeurs de partage du platine suggèrent que son abondance dans le manteau terrestre peut être expliquée simplement par la formation du noyau. De manière générale, ces résultats supportent les hypothèses selon lesquelles les noyaux des gros impacteurs n’ont pas pu s’équilibrer entièrement avec le manteau terrestre. Certaines fractions métalliques ont donc pu atteindre le noyau terrestre sans affecter le manteau. L’hypothèse d’un évènement tardif de ségrégation de sulfure durant la formation de la terre pourrait aussi expliquer les compositions du manteau terrestre observées. Ces résultats permettent de caractériser les processus de différenciation du manteau et du noyau et de mieux comprendre la formation de la Terre

Metal-silicate partitioning of sulfur and platinum during terrestrial core formation

La détermination du partage des éléments sidérophiles et volatils entre métal et silicates aux conditions du manteau profond de la Terre primitive peut fournir des contraintes relatives au mécanisme de formation du noyau terrestre. Des expériences ont été réalisées dans des cellules à enclumes de diamant (DAC) chauffées par laser afin d'étudier l'évolution du partage métal-silicate du soufre et du platine à haute température et haute pression. Le partage est déterminé grâce à la mesure sur échantillons trempés des concentrations par NanoSIMS et sonde électronique. L’affinité du soufre avec le métal, mesurée aux conditions de formation du noyau terrestre, est moins grande qu’attendue. En accord avec les observables cosmochimiques (météorites), il semble que la quantité de soufre dans le noyau ne peut excéder 2 poids%. Les modèles d’accrétion de la Terre, combinés à nos mesures du coefficient de partage du soufre en fonction de la pression et la température, indiquent que la concentration globale de soufre du manteau terrestre doit être le résultat d'une accrétion hétérogène. Ces données indiquent également un apport tardif des éléments volatils au cours de l’accrétion et de la formation du noyau. Les valeurs de partage du platine suggèrent que son abondance dans le manteau terrestre peut être expliquée simplement par la formation du noyau. De manière générale, ces résultats supportent les hypothèses selon lesquelles les noyaux des gros impacteurs n’ont pas pu s’équilibrer entièrement avec le manteau terrestre. Certaines fractions métalliques ont donc pu atteindre le noyau terrestre sans affecter le manteau. L’hypothèse d’un évènement tardif de ségrégation de sulfure durant la formation de la terre pourrait aussi expliquer les compositions du manteau terrestre observées. Ces résultats permettent de caractériser les processus de différenciation du manteau et du noyau et de mieux comprendre la formation de la Terre.Measurements of the metal-silicate partitioning behavior of siderophile and volatile elements at the conditions of the deep primitive Earth can provide constraints on the mechanisms of terrestrial core formation. Experiments were conducted in a laser-heated diamond anvil cell to investigate the metal-silicate partitioning of sulfur and platinum at high pressures and temperatures. The partitioning behaviors were quantified post-experiment by high resolution NanoSIMS imaging. Sulfur was found to be moderately siderophile at core formation conditions and this, together with cosmochemical estimates, argue that it cannot be a major light element in the core. Accretion modeling with this new partitioning data implies that a heterogeneous accretion scenario can best explain the mantle and bulk Earth sulfur contents. The measured partitioning values for platinum are such that the mantle's platinum abundance can be sufficiently explained by core-mantle equilibration. Overall these results support the hypothesis that the cores of large impactors did not equilibrate fully with the magma ocean and metal could have sequestered to the Earth's core without leaving a record in the mantle. A late sulfide segregation event also likely played a role in establishing the observed mantle compositions. These findings help to further elucidate the accretion history of the Earth and core-mantle differentiation processes

The distribution of volatile elements during rocky planet formation

Core segregation and atmosphere formation are two of the major processes that redistribute the volatile elements—hydrogen (H), carbon (C), nitrogen (N), and sulfur (S)—in and around rocky planets during their formation. The volatile elements by definition accumulate in gaseous reservoirs and form atmospheres. However, under conditions of early planet formation, these elements can also behave as siderophiles (i.e., iron-loving) and become concentrated in core-forming metals. Current models of core formation suggest that metal-silicate reactions occurred over a wide pressure, temperature, and compositional space to ultimately impose the chemistries of the cores and silicate portions of rocky planets. Additionally, the solubilities of volatile elements in magmas determine their transfer between the planetary interiors and atmospheres, which has recently come into sharper focus in the context of highly irradiated, potentially molten exoplanets. Recently, there has been a significant push to experimentally investigate the metal-silicate and magma-gas exchange coefficients for volatile elements over a wide range of conditions relevant to rocky planet formation. Qualitatively, results from the metal-silicate partitioning studies suggest that cores of rocky planets could be major reservoirs of the volatile elements though significant amounts will remain in mantles. Results from solubility studies imply that under oxidizing conditions, most H and S are sequestered in the magma ocean, while most N is outgassed to the atmosphere, and C is nearly equally distributed between the atmosphere and the interior. Under reducing conditions, nearly all N dissolves in the magma ocean, the atmosphere becomes the dominant C reservoir, while H becomes more equally distributed between the interior and the atmosphere, and S remains dominantly in the interior. These chemical trends bear numerous implications for the chemical differentiation of rocky planets and the formation and longevity of secondary atmospheres in the early Solar System and exoplanetary systems. Further experimental and modeling efforts are required to understand the potential of chemical and physical disequilibria during core formation and magma ocean crystallization and to constrain the distributions of volatile elements in the interiors and atmospheres of rocky planets through their formation and long-term geologic evolution.</p

A sulfur-poor terrestrial core inferred from metal–silicate partitioning experiments

International audienceAs a siderophile and a volatile element, sulfur's partitioning behavior allows constraints to be placed on processes in the primitive Earth. Sulfur's core–mantle distribution during Earth's accretion has consequences for core content and implications for volatile accretion. In this study, metal–silicate partitioning experiments of sulfur were conducted in a diamond anvil cell at pressures from 46 to 91 GPa and temperatures between 3100 and 4100 K, conditions that are directly relevant to core segregation in a deep magma ocean. The sulfur partition coefficients measured from these experiments are an order of magnitude less than those obtained from extrapolation of previous results to core formation conditions (e.g., Rose-Weston et al., 2009; Boujibar et al., 2014). These measurements challenge the idea that sulfur becomes a highly siderophile element at high pressures and temperatures. A relationship was derived that describes sulfur's partitioning behavior at the pressure–temperature range of core formation. This relationship combined with an accretion model was used to explore the effects of varying impactor sizes and volatile compositions on the sulfur contents of the Earth's core and mantle. The results show that homogeneous delivery of sulfur throughout accretion would overenrich the mantle in sulfur relative to the present day observations of 200 ± 80 ppm (Lorand et al., 2013) unless the bulk Earth sulfur content is lower than its cosmochemical estimate of ∼6400 ppm (e.g., McDonough, 2003). On the other hand, the mantle's sulfur content is matched if sulfur is delivered with large bodies (3 to 10% Earth mass) during the last 20% of Earth's accretion, combined with a chondritic late veneer of 0.5% Earth mass. These results are conditional on the lowered equilibration efficiency of large impactor cores in a terrestrial magma ocean. In each accretion scenario, the core sulfur content remains below ∼2 wt.% in close agreement with cosmochemical estimates and is a further indication that sulfur is not a dominant light element in the core

Cosmic deuterium and social networking software

We discuss social networking software and give examples of its applicability for bringing together references for the study of cosmic deuterium. Our websi te at www.cosmicdeuterium.info provides links to all papers in the field, which is relevant to cosmology since all the Universe's deuterium was formed in the first 1000 seconds after the Big Bang . Understanding cosmic deuterium is one of the pillars of modem cosmology. Studies of deuterium are also imponant for understanding galactic chemical evolution, ast:rochemistry, interstellar processes, and planetary formation. By 2006, social networking software had advanced with popular sites like faeebook.com and MySpace .com; the Astrophysical Data System had even set up My ADS. Social tagging software sites like del.icio.us have made it easy to share sets of links to papers already available online. We have set up del.icio.us/deuterium to provide links to many of the papers on www.cosmicdeuterium.info. Links to a del.icio.us site are easily added, the prime advantage of such software. Use of keywords allows subsets to be displayed, though only papers already online can be linked without being separately scanned. The opportunity to expose knowledge and build an ecosystem of web pages that through its use by many people captures knowledge collaboratively is considerable. Setting up such a system marries one of the earliest stages of the Universe with the latest software technologies. The method of setting up a del. icio.us social-tagging site, which is so easy, is applicable to a wide range of educational purposes

Reconciling metal–silicate partitioning and late accretion in the Earth

International audienceHighly siderophile elements (HSE), including platinum, provide powerful geochemical tools for studying planet formation. Late accretion of chondritic components to Earth after core formation has been invoked as the main source of mantle HSE. However, core formation could also have contributed to the mantle's HSE content. Here we present measurements of platinum metal-silicate partitioning coefficients, obtained from laser-heated diamond anvil cell experiments, which demonstrate that platinum partitioning into metal is lower at high pressures and temperatures. Consequently, the mantle was likely enriched in platinum immediately following core-mantle differentiation. Core formation models that incorporate these results and simultaneously account for collateral geochemical constraints, lead to excess platinum in the mantle. A subsequent process such as iron exsolution or sulfide segregation is therefore required to remove excess platinum and to explain the mantle's modern HSE signature. A vestige of this platinum-enriched mantle can potentially account for 186 Os-enriched ocean island basalt lavas