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Chiera NM, Sprung P, Amelin Y, Dressler R, Schumann D, Talip Z. The 146 Sm half-life re-measured: consolidating the chronometer for events in the early Solar System. Sci Rep 2024; 14:17436. [PMID: 39090187 PMCID: PMC11294585 DOI: 10.1038/s41598-024-64104-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2024] [Accepted: 06/05/2024] [Indexed: 08/04/2024] Open
Abstract
The half-life of the extinct radiolanthanide146 Sm , important for both geochronological and astrophysical applications, was re-determined by a combination of mass spectrometry and α -decay counting. Earlier studies provided only limited information on all potential factors that could influence the quantification of the half-life of146 Sm . Thus, special attention was given here to a complete documentation of all experimental steps to provide information about any possible artifacts in the data analysis. The half-life of146 Sm was derived to be 92.0 Ma ± 2.6 Ma, with an uncertainty coverage factor of k = 1 .
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Affiliation(s)
- Nadine M Chiera
- Center of Nuclear Engineering and Science, Paul Scherrer Institut, Forschungsstrasse 111, Villigen-PSI, 5232, Switzerland
| | - Peter Sprung
- Center of Nuclear Engineering and Science, Paul Scherrer Institut, Forschungsstrasse 111, Villigen-PSI, 5232, Switzerland
| | - Yuri Amelin
- Research School of Earth Sciences, The Australian National University, 142 Mills Road, Acton, ACT, 0200, Australia
| | - Rugard Dressler
- Center of Nuclear Engineering and Science, Paul Scherrer Institut, Forschungsstrasse 111, Villigen-PSI, 5232, Switzerland.
| | - Dorothea Schumann
- Center of Nuclear Engineering and Science, Paul Scherrer Institut, Forschungsstrasse 111, Villigen-PSI, 5232, Switzerland
| | - Zeynep Talip
- Center of Nuclear Engineering and Science, Paul Scherrer Institut, Forschungsstrasse 111, Villigen-PSI, 5232, Switzerland
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2
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Johnston S, Brandon A, McLeod C, Rankenburg K, Becker H, Copeland P. Nd isotope variation between the Earth-Moon system and enstatite chondrites. Nature 2022; 611:501-506. [PMID: 36203033 DOI: 10.1038/s41586-022-05265-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 08/23/2022] [Indexed: 11/09/2022]
Abstract
Reconstructing the building blocks that made Earth and the Moon is critical to constrain their formation and compositional evolution to the present. Neodymium (Nd) isotopes identify these building blocks by fingerprinting nucleosynthetic components. In addition, the 146Sm-142Nd and 147Sm-143Nd decay systems, with half-lives of 103 million years and 108 billion years, respectively, track potential differences in their samarium (Sm)/Nd ratios. The difference in Earth's present-day 142Nd/144Nd ratio compared with chondrites1,2, and in particular enstatite chondrites, is interpreted as nucleosynthetic isotope variation in the protoplanetary disk. This necessitates that chondrite parent bodies have the same Sm/Nd ratio as Earth's precursor materials2. Here we show that Earth and the Moon instead had a Sm/Nd ratio approximately 2.4 ± 0.5 per cent higher than the average for chondrites and that the initial 142Nd/144Nd ratio of Earth's precursor materials is more similar to that of enstatite chondrites than previously proposed1,2. The difference in the Sm/Nd ratio between Earth and chondrites probably reflects the mineralogical distribution owing to mixing processes within the inner protoplanetary disk. This observation simplifies lunar differentiation to a single stage from formation to solidification of a lunar magma ocean3. This also indicates that no Sm/Nd fractionation occurred between the materials that made Earth and the Moon in the Moon-forming giant impact.
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Affiliation(s)
- Shelby Johnston
- Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
| | - Alan Brandon
- Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA.
| | - Claire McLeod
- Department of Geology and Environmental Earth Science, Miami University, Oxford, OH, USA
| | - Kai Rankenburg
- John De Laeter Centre, Curtin University, Bentley, Western Australia, Australia
| | | | - Peter Copeland
- Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA
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3
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Precise initial abundance of Niobium-92 in the Solar System and implications for p-process nucleosynthesis. Proc Natl Acad Sci U S A 2021; 118:2017750118. [PMID: 33608458 DOI: 10.1073/pnas.2017750118] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The niobium-92-zirconium-92 (92Nb-92Zr) decay system with a half-life of 37 Ma has great potential to date the evolution of planetary materials in the early Solar System. Moreover, the initial abundance of the p-process isotope 92Nb in the Solar System is important for quantifying the contribution of p-process nucleosynthesis in astrophysical models. Current estimates of the initial 92Nb/93Nb ratios have large uncertainties compromising the use of the 92Nb-92Zr cosmochronometer and leaving nucleosynthetic models poorly constrained. Here, the initial 92Nb abundance is determined to high precision by combining the 92Nb-92Zr systematics of cogenetic rutiles and zircons from mesosiderites with U-Pb dating of the same zircons. The mineral pair indicates that the 92Nb/93Nb ratio of the Solar System started with (1.66 ± 0.10) × 10-5, and their 92Zr/90Zr ratios can be explained by a three-stage Nb-Zr evolution on the mesosiderite parent body. Because of the improvement by a factor of 6 of the precision of the initial Solar System 92Nb/93Nb, we can show that the presence of 92Nb in the early Solar System provides further evidence that both type Ia supernovae and core-collapse supernovae contributed to the light p-process nuclei.
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Ku Y, Jacobsen SB. Potassium isotope anomalies in meteorites inherited from the protosolar molecular cloud. SCIENCE ADVANCES 2020; 6:eabd0511. [PMID: 33036981 PMCID: PMC7546711 DOI: 10.1126/sciadv.abd0511] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Accepted: 08/19/2020] [Indexed: 05/31/2023]
Abstract
Potassium (K) and other moderately volatile elements are depleted in many solar system bodies relative to CI chondrites, which closely match the composition of the Sun. These depletions and associated isotopic fractionations were initially believed to result from thermal processing in the protoplanetary disk, but so far, no correlation between the K depletion and its isotopic composition has been found. Our new high-precision K isotope data correlate with other neutron-rich nuclides (e.g., 64Ni and 54Cr) and suggest that the observed 41K variations have a nucleosynthetic origin. We propose that K isotope anomalies are inherited from an isotopically heterogeneous protosolar molecular cloud, and were preserved in bulk primitive meteorites. Thus, the heterogeneous distribution of both refractory and moderately volatile elements in chondritic meteorites points to a limited radial mixing in the protoplanetary disk.
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Affiliation(s)
- Y Ku
- Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA.
| | - S B Jacobsen
- Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
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Schiller M, Bizzarro M, Siebert J. Iron isotope evidence for very rapid accretion and differentiation of the proto-Earth. SCIENCE ADVANCES 2020; 6:eaay7604. [PMID: 32095530 PMCID: PMC7015677 DOI: 10.1126/sciadv.aay7604] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Accepted: 11/26/2019] [Indexed: 06/02/2023]
Abstract
Nucleosynthetic isotope variability among solar system objects provides insights into the accretion history of terrestrial planets. We report on the nucleosynthetic Fe isotope composition (μ54Fe) of various meteorites and show that the only material matching the terrestrial composition is CI (Ivuna-type) carbonaceous chondrites, which represent the bulk solar system composition. All other meteorites, including carbonaceous, ordinary, and enstatite chondrites, record excesses in μ54Fe. This observation is inconsistent with protracted growth of Earth by stochastic collisional accretion, which predicts a μ54Fe value reflecting a mixture of the various meteorite parent bodies. Instead, our results suggest a rapid accretion and differentiation of Earth during the ~5-million year disk lifetime, when the volatile-rich CI-like material is accreted to the proto-Sun via the inner disk.
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Affiliation(s)
- Martin Schiller
- Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen, Denmark
| | - Martin Bizzarro
- Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen, Denmark
- Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, 75005 Paris, France
| | - Julien Siebert
- Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, 75005 Paris, France
- Institut Universitaire de France, Paris, France
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6
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Lin YB, Wei HZ, Jiang SY, Hohl S, Lei HL, Liu X, Dong G. Accurate Determination of Barium Isotopic Compositions in Sequentially Leached Phases from Carbonates by Double Spike-Thermal Ionization Mass Spectrometry (DS-TIMS). Anal Chem 2020; 92:2417-2424. [PMID: 31880432 DOI: 10.1021/acs.analchem.9b03137] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recent studies have proposed barium isotopes as a novel proxy for studying primary productivity in paleo-oceangraphical studies and elements cycling through the critical zone. Pristine marine carbonates are generally assumed to preserve Ba isotope compositions of ancient seawater. However, Ba incorporated in or adsorbed on detrital minerals such as clays in impure carbonates may limit the accurate application of the Ba isotope proxy for paleo-ocean environmental reconstruction purposes. We present here a sequential extraction procedure and show that a considerable range of Ba concentrations can be associated with the four operationally defined sequential leaching fractions (water-soluble, exchangeable, carbonate, and oxidizable fractions). Chemical separation of Ba from these leachates is achieved with a recovery of >98.6% by our modified ion exchange procedure. Potential instrumental mass bias effects and barium isotope fractionation during the chemical separation are corrected using a carefully optimized 130Ba-135Ba double-spike method. A long-term reproducibility better than ±0.03‰ (2SD) for δ137/134Ba has been achieved by using the double spike-thermal ionization mass spectrometry (DS-TIMS) in this study. We demonstrate that significant variations of δ137/134Ba in the analyzed leachates suggest a considerable Ba isotope fractionation between carbonate mineral phase and noncarbonate phases of marine carbonate rocks. The barium isotope distribution in a set of standard reference materials and natural geological samples under various geological settings has been presented. When utilizing Ba isotopes as a proxy for primary productivity and the biogeochemical cycling of Ba, our new findings from sequential Ba extraction as well as our modified precise DS-TIMS analytical setup should be taken into account.
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Affiliation(s)
- Yi-Bo Lin
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering , Nanjing University , Nanjing 210023 , PR China
| | - Hai-Zhen Wei
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering , Nanjing University , Nanjing 210023 , PR China.,CAS Center for Excellence in Comparative Planetology , Hefei , Anhui 230026 , PR China
| | - Shao-Yong Jiang
- State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Resources , China University of Geosciences , Wuhan 430074 , PR China
| | - Simon Hohl
- State Key Laboratory of Marine Geology, School of Ocean and Earth Science , Tongji University , Shanghai 200092 , PR China
| | - Huan-Ling Lei
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering , Nanjing University , Nanjing 210023 , PR China
| | - Xi Liu
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering , Nanjing University , Nanjing 210023 , PR China
| | - Ge Dong
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering , Nanjing University , Nanjing 210023 , PR China
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7
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Shollenberger QR, Wittke A, Render J, Mane P, Schuth S, Weyer S, Gussone N, Wadhwa M, Brennecka GA. Combined mass-dependent and nucleosynthetic isotope variations in refractory inclusions and their mineral separates to determine their original Fe isotope compositions. GEOCHIMICA ET COSMOCHIMICA ACTA 2019; 263:215-234. [PMID: 33353988 PMCID: PMC7751496 DOI: 10.1016/j.gca.2019.07.021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials that provide crucial information about the isotopic reservoirs present in the early Solar System. For a variety of elements, CAIs have isotope compositions that are uniform yet distinct from later formed solid material. However, despite being the most abundant metal in the Solar System, the isotopic composition of Fe in CAIs is not well constrained. In an attempt to determine the Fe isotopic compositions of CAIs, we combine extensive work from a previously studied CAI sample set with new isotopic work characterizing mass-dependent and mass-independent (nucleosynthetic) signatures in Mg, Ca, and Fe. This investigation includes work on three mineral separates of the Allende CAI Egg 2. For all isotope systems investigated, we find that in general, fine-grained CAIs exhibit light mass-dependent isotopic signatures relative to terrestrial standards, whereas igneous CAIs have heavier isotopic compositions relative to the fine-grained CAIs. Importantly, the mass-dependent Fe isotope signatures of bulk CAIs show a range of both light (fine-grained CAIs) and heavy (igneous CAIs) isotopic signatures relative to bulk chondrites, suggesting that Fe isotope signatures in CAIs largely derive from mass fractionation events such as condensation and evaporation occurring in the nebula. Such signatures show that a significant portion of the secondary alteration experienced by CAIs, particularly prevalent in fine-grained inclusions, occurred in the nebula prior to accretion into their respective parent bodies. Regarding nucleosynthetic Fe isotope signatures, we do not observe any variation outside of analytical uncertainty in bulk CAIs compared to terrestrial standards. In contrast, all three Egg 2 mineral separates display resolved mass-independent excesses in 56Fe compared to terrestrial standards. Furthermore, we find that the combined mass-dependent and nucleosynthetic Fe isotopic compositions of the Egg 2 mineral separates are well correlated, likely indicating that Fe indigenous to the CAI is mixed with less anomalous Fe, presumably from the solar nebula. Thus, these reported nucleosynthetic anomalies may point in the direction of the original Fe isotope composition of the CAI-forming region, but they likely only provide a minimum isotopic difference between the original mass-independent Fe isotopic composition of CAIs and that of later formed solids.
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Affiliation(s)
- Quinn R. Shollenberger
- Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
| | - Andreas Wittke
- Institut für Mineralogie, University of Münster, Corrensstraße 24, 48149 Münster, Germany
| | - Jan Render
- Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
| | - Prajkta Mane
- School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, AZ 85287-1404 USA
| | - Stephan Schuth
- Institut für Mineralogie, Leibniz University Hannover, Callinstraße 3, 30167 Hannover, Germany
| | - Stefan Weyer
- Institut für Mineralogie, Leibniz University Hannover, Callinstraße 3, 30167 Hannover, Germany
| | - Nikolaus Gussone
- Institut für Mineralogie, University of Münster, Corrensstraße 24, 48149 Münster, Germany
| | - Meenakshi Wadhwa
- School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, AZ 85287-1404 USA
| | - Gregory A. Brennecka
- Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
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8
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Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon. Nature 2018; 555:507-510. [PMID: 29565359 PMCID: PMC5884421 DOI: 10.1038/nature25990] [Citation(s) in RCA: 100] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 01/22/2018] [Indexed: 11/10/2022]
Abstract
Nucleosynthetic isotope variability amongst Solar System objects is commonly used to probe the genetic relationship between meteorite groups and rocky planets, which, in turn, may provide insights into the building blocks of the Earth-Moon system1–5. Using this approach, it is inferred that no primitive meteorite matches the terrestrial composition such that the nature of the disk material that accreted to form the Earth and Moon is unconstrained6. This conclusion, however, is based on the assumption that the observed nucleosynthetic variability amongst inner Solar System objects predominantly reflects spatial heterogeneity. Here, we use the isotopic composition of the refractory element calcium to show that the inner Solar System’s nucleosynthetic variability in the mass-independent 48Ca/44Ca ratio (μ48Ca) primarily represents a rapid change in the μ48Ca composition of disk solids associated with early mass accretion to the proto-Sun. In detail, the μ48Ca values of samples originating from the ureilite and angrite parent bodies as well as Vesta, Mars and Earth are positively correlated to the masses of the inferred parent asteroids and planets – a proxy of their accretion timescales – implying a secular evolution of the bulk μ48Ca disk composition in the terrestrial planet-forming region. Individual chondrules from ordinary chondrites formed within 1 Myr of proto-Sun collapse7 record the full range of inner Solar System μ48Ca compositions, indicating a rapid change in the composition of the disk material. We infer that this secular evolution reflects admixing of pristine outer Solar System material to the thermally-processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. The indistinguishable μ48Ca composition of the Earth (0.2±3.9 ppm) and Moon (3.7±1.9 ppm) reported here is a prediction of our model if the Moon-forming impact involved protoplanets or precursors that completed their accretion near the end of the disk lifetime.
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9
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Bermingham K, Worsham E, Walker R. New insights into Mo and Ru isotope variation in the nebula and terrestrial planet accretionary genetics. EARTH AND PLANETARY SCIENCE LETTERS 2018; 487:221-229. [PMID: 30880823 PMCID: PMC6417891 DOI: 10.1016/j.epsl.2018.01.017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
When corrected for the effects of cosmic ray exposure, Mo and Ru nucleosynthetic isotope anomalies in iron meteorites from at least nine different parent bodies are strongly correlated in a manner consistent with variable depletion in s-process nucleosynthetic components. In contrast to prior studies, the new results show no significant deviations from a single correlation trend. In the refined Mo-Ru cosmic correlation, a distinction between the non-carbonaceous (NC) group and carbonaceous chondrite (CC) group is evident. Members of the NC group are characterized by isotope compositions reflective of variable s-process depletion. Members of the CC group analyzed here plot in a tight cluster and have the most s-process depleted Mo and Ru isotopic compositions, with Mo isotopes also slightly enriched in r- and possibly p-process contributions. This indicates that the nebular feeding zone of the NC group parent bodies was characterized by Mo and Ru with variable s-process contributions, but with the two elements always mixed in the same proportions. The CC parent bodies sampled here, by contrast, were derived from a nebular feeding zone that had been mixed to a uniform s-process depleted Mo-Ru isotopic composition. Six molybdenite samples, four glacial diamictites, and two ocean island basalts were analyzed to provide a preliminary constraint on the average Mo isotope composition of the bulk silicate Earth (BSE). Combined results yield an average μ 97Mo value of +3 ± 6. This value, coupled with a previously reported μ 100Ru value of +1 ± 7 for the BSE, indicates that the isotopic composition of the BSE falls precisely on the refined Mo-Ru cosmic correlation. The overlap of the BSE with the correlation implies that there was homogeneous accretion of siderophile elements for the final accretion of 10 to 20 wt% of Earth's mass. The only known cosmochemical materials with an isotopic match to the BSE, with regard to Mo and Ru, are some members of the IAB iron meteorite complex and enstatite chondrites.
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Affiliation(s)
- K.R. Bermingham
- Department of Geology, University of Maryland, College Park, MD 20742, USA
| | | | - R.J. Walker
- Department of Geology, University of Maryland, College Park, MD 20742, USA
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10
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Charbonnier Q, Moynier F, Bouchez J. Barium isotope cosmochemistry and geochemistry. Sci Bull (Beijing) 2018; 63:385-394. [PMID: 36658876 DOI: 10.1016/j.scib.2018.01.018] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Revised: 01/09/2018] [Accepted: 01/10/2018] [Indexed: 01/21/2023]
Abstract
While the isotopic variations of barium were reported for the first time fourty years ago, the number of studies on barium isotopes significantly increased only after 2010. Barium isotope anomalies in meteorites have been successfully used to provide constraints about the origin of presolar SiC grains. In carbonaceous chondrites Ba isotope anomalies are indicative of the heterogeneity of the early solar system, possibly resulting from of a later injection of material after the cooling of solar system. Barium isotope fractionation in the same carbonaceous chondrites suggests that a strong magnetic field was present in the innermost part of the early solar system. Barium mass-dependent isotope fractionation has also been detected throughout Earth surface materials. While igneous rocks show limited Ba isotopic variations, relatively large isotopic variations are observed amongst and within soils, rivers, and biological materials. Indeed, plants seem to fractionate Ba isotopes during Ba uptake from soil solutions. Therefore, Ba isotope signatures have the potential to provide clues on the biological cycling of Ba at the Earth surface. In seawater, Ba isotopic variations have been mapped out, and are mainly related to barite precipitation, which is in turn related to organic matter remineralization in the water column. This makes Ba isotopes a potentially powerful tool to reconstruct past ocean productivity, although constraints are still lacking regarding the inputs of dissolved Ba to the oceans by rivers or hydrothermalism.
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Affiliation(s)
- Quentin Charbonnier
- Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS, UMR 7154, 1 rue Jussieu, 75238 Paris, France.
| | - Frédéric Moynier
- Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS, UMR 7154, 1 rue Jussieu, 75238 Paris, France; Institut Universitaire de France and Université Paris Diderot, 75231 Paris, France
| | - Julien Bouchez
- Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS, UMR 7154, 1 rue Jussieu, 75238 Paris, France
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11
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Fukuhara M. Possible generation of heat from nuclear fusion in Earth's inner core. Sci Rep 2016; 6:37740. [PMID: 27876860 PMCID: PMC5120317 DOI: 10.1038/srep37740] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 11/01/2016] [Indexed: 12/02/2022] Open
Abstract
The cause and source of the heat released from Earth's interior have not yet been determined. Some research groups have proposed that the heat is supplied by radioactive decay or by a nuclear georeactor. Here we postulate that the generation of heat is the result of three-body nuclear fusion of deuterons confined in hexagonal FeDx core-centre crystals; the reaction rate is enhanced by the combined attraction effects of high-pressure (~364 GPa) and high-temperature (~5700 K) and by the physical catalysis of neutral pions: 2D + 2D + 2D → 21H + 4He + 2 + 20.85 MeV. The possible heat generation rate can be calculated as 8.12 × 1012 J/m3, based on the assumption that Earth's primitive heat supply has already been exhausted. The H and He atoms produced and the anti-neutrino are incorporated as Fe-H based alloys in the H-rich portion of inner core, are released from Earth's interior to the universe, and pass through Earth, respectively.
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Affiliation(s)
- Mikio Fukuhara
- New Industry Creation Hatchery Centre, Tohoku University, Sendai, 980-8579, Japan
- Waseda University Research Organization for Nano & Life Innovation, Green Device Laboratory, Tokyo, Japan
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12
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Primitive Solar System materials and Earth share a common initial (142)Nd abundance. Nature 2016; 537:399-402. [PMID: 27629644 DOI: 10.1038/nature19351] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2015] [Accepted: 08/04/2016] [Indexed: 11/08/2022]
Abstract
The early evolution of planetesimals and planets can be constrained using variations in the abundance of neodymium-142 ((142)Nd), which arise from the initial distribution of (142)Nd within the protoplanetary disk and the radioactive decay of the short-lived samarium-146 isotope ((146)Sm). The apparent offset in (142)Nd abundance found previously between chondritic meteorites and Earth has been interpreted either as a possible consequence of nucleosynthetic variations within the protoplanetary disk or as a function of the differentiation of Earth very early in its history. Here we report high-precision Sm and Nd stable and radiogenic isotopic compositions of four calcium-aluminium-rich refractory inclusions (CAIs) from three CV-type carbonaceous chondrites, and of three whole-rock samples of unequilibrated enstatite chondrites. The CAIs, which are the first solids formed by condensation from the nebular gas, provide the best constraints for the isotopic evolution of the early Solar System. Using the mineral isochron method for individual CAIs, we find that CAIs without isotopic anomalies in Nd compared to the terrestrial composition share a (146)Sm/(144)Sm-(142)Nd/(144)Nd isotopic evolution with Earth. The average (142)Nd/(144)Nd composition for pristine enstatite chondrites that we calculate coincides with that of the accessible silicate layers of Earth. This relationship between CAIs, enstatite chondrites and Earth can only be a result of Earth having inherited the same initial abundance of (142)Nd and chondritic proportions of Sm and Nd. Consequently, (142)Nd isotopic heterogeneities found in other CAIs and among chondrite groups may arise from extrasolar grains that were present in the disk and incorporated in different proportions into these planetary objects. Our finding supports a chondritic Sm/Nd ratio for the bulk silicate Earth and, as a consequence, chondritic abundances for other refractory elements. It also removes the need for a hidden reservoir or for collisional erosion scenarios to explain the (142)Nd/(144)Nd composition of Earth.
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A nucleosynthetic origin for the Earth's anomalous (142)Nd composition. Nature 2016; 537:394-8. [PMID: 27629643 PMCID: PMC5026299 DOI: 10.1038/nature18956] [Citation(s) in RCA: 104] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 06/03/2016] [Indexed: 12/03/2022]
Abstract
A long-standing paradigm assumes that the chemical and isotopic composition of many elements in the bulk silicate Earth are the same as in chondrites1–4. However, the accessible Earth has a greater 142Nd/144Nd than chondrites. Because 142Nd is the decay product of now-extinct 146Sm (t1/2= 103 million years5), this 142Nd difference seems to require a higher-than-chondritic Sm/Nd of the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation6 and implies the formation of a complementary 142Nd-depleted reservoir that either is hidden in the deep Earth6, or was lost to space by impact erosion3,7. Whether this complementary reservoir existed, and whether or not it has been lost from Earth is a matter of debate3,8,9, but has tremendous implications for determining the bulk composition of Earth, its heat content and structure, and for constraining the modes and timescales of its geodynamical evolution3,7,9,10. Here, we show that compared to chondrites, Earth’s precursor bodies were enriched in Nd produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher 142Nd/144Nd, and, after correction for this effect, the 142Nd/144Nd of chondrites and the accessible Earth are indistinguishable within 5 parts per million. The 142Nd offset between the accessible silicate Earth and chondrites, therefore, reflects a higher proportion of s-process Nd in the Earth, and not early differentiation processes. As such, our results obviate the need for hidden reservoir or super-chondritic Earth models, and imply a chondritic Sm/Nd for bulk Earth. Thus, although chondrites formed at greater heliocentric distance and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth’s bulk chemical composition.
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Kagami S, Yokoyama T. Chemical separation of Nd from geological samples for chronological studies using 146Sm–142Nd and 147Sm–143Nd systematics. Anal Chim Acta 2016; 937:151-9. [DOI: 10.1016/j.aca.2016.07.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 07/01/2016] [Accepted: 07/03/2016] [Indexed: 10/21/2022]
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Saji NS, Wielandt D, Paton C, Bizzarro M. Ultra-high-precision Nd-isotope measurements of geological materials by MC-ICPMS. JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 2016; 31:1490-1504. [PMID: 27429505 PMCID: PMC4946631 DOI: 10.1039/c6ja00064a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We report novel techniques allowing the measurement of Nd-isotope ratios with unprecedented accuracy and precision by multi-collector inductively coupled plasma mass spectrometry. Using the new protocol, we have measured the Nd-isotopic composition of rock and synthetic Nd standards as well as that of the Allende carbonaceous chondrite. Analyses of BCR-2, BHVO-2 and GSP-2 rock standards yield mass-independent compositions identical to the JNdi-1 Nd-reference standard, with an external reproducibility of 2.4, 1.6, 1.6 and 3.5 ppm respectively, on μ142Nd, μ145Nd, μ146Nd and μ150Nd (μ representing the ppm-deviation of the ratios from JNdi-1) using 148Nd/144Nd for internal normalization. This represents an improvement in precision by a factor of 2, 7 and 9 respectively for μ142Nd, μ145Nd and μ150Nd. Near-quantitative recovery from purification chemistry and sample-standard bracketing allow for the determination of mass-dependent Nd-isotopic composition of samples. Synthetic standards, namely La Jolla and AMES, record mass-dependent variability of up to 1.2 ε per atomic mass unit and mass-independent compositions resolvable by up to 3 ppm for μ142Nd and 8 ppm for μ150Nd, relative to JNdi-1. The mass-independent compositions are consistent with equilibrium mass fractionation during purification. The terrestrial rock standards define a uniform stable ε145Nd of -0.24 ± 0.19 (2SD) relative to JNdi-1, indistinguishable from the mean Allende ε145Nd of -0.19 ± 0.09. We consider this value to represent the mass-dependent Nd-isotope composition of Bulk Silicate Earth (BSE). The modest mass-dependent fractionation of JNdi-1 relative to BSE results in potential effects on mass-independent composition that cannot be resolved within the reproducibility of our analyses when correcting for natural and instrumental mass fractionation by kinetic law, making it a suitable reference standard for analysis of unknowns. Analysis of Allende (CV3) carbonaceous chondrite returns an average μ142Nd deficit of -30.1 ± 3.7 ppm in agreement with previous studies. The apparent deficit is, however, lowered to -23.8 ± 4.0 ppm while normalizing to 148Nd/144Nd instead of 146Nd/144Nd. We interpret this as the effect of a possible nucleosynthetic anomaly of -6.3 ± 0.5 ppm in μ146Nd. As 142Nd and 146Nd are both s-process-dominated nuclides, this hints at the possibility that terrestrial μ142Nd excess may not reflect 146Sm decay as widely accepted.
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Affiliation(s)
- Nikitha Susan Saji
- Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, DK-1350, Copenhagen, Denmark
| | - Daniel Wielandt
- Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, DK-1350, Copenhagen, Denmark
| | - Chad Paton
- Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, DK-1350, Copenhagen, Denmark
| | - Martin Bizzarro
- Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, DK-1350, Copenhagen, Denmark
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Rizo H, Walker RJ, Carlson RW, Horan MF, Mukhopadhyay S, Manthos V, Francis D, Jackson MG. Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts. Science 2016; 352:809-12. [DOI: 10.1126/science.aad8563] [Citation(s) in RCA: 113] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 04/05/2016] [Indexed: 11/02/2022]
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Carlson RW, Borg LE, Gaffney AM, Boyet M. Rb-Sr, Sm-Nd and Lu-Hf isotope systematics of the lunar Mg-suite: the age of the lunar crust and its relation to the time of Moon formation. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130246. [PMID: 25114305 PMCID: PMC4128267 DOI: 10.1098/rsta.2013.0246] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
New Rb-Sr, (146,147)Sm-(142,143)Nd and Lu-Hf isotopic analyses of Mg-suite lunar crustal rocks 67667, 76335, 77215 and 78238, including an internal isochron for norite 77215, were undertaken to better define the time and duration of lunar crust formation and the history of the source materials of the Mg-suite. Isochron ages determined in this study for 77215 are: Rb-Sr=4450±270 Ma, (147)Sm-(143)Nd=4283±23 Ma and Lu-Hf=4421±68 Ma. The data define an initial (146)Sm/(144)Sm ratio of 0.00193±0.00092 corresponding to ages between 4348 and 4413 Ma depending on the half-life and initial abundance used for (146)Sm. The initial Nd and Hf isotopic compositions of all samples indicate a source region with slight enrichment in the incompatible elements in accord with previous suggestions that the Mg-suite crustal rocks contain a component of KREEP. The Sm/Nd-(142)Nd/(144)Nd correlation shown by both ferroan anorthosite and Mg-suite rocks is coincident with the trend defined by mare and KREEP basalts, the slope of which corresponds to ages between 4.35 and 4.45 Ga. These data, along with similar ages for various early Earth differentiation events, are in accord with the model of lunar formation via giant impact into Earth at ca 4.4 Ga.
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Affiliation(s)
- Richard W Carlson
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington DC 20015, USA
| | - Lars E Borg
- Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue L-231, Livermore, CA 94550, USA
| | - Amy M Gaffney
- Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue L-231, Livermore, CA 94550, USA
| | - Maud Boyet
- Laboratoire Magmas et Volcans, Universite Blaise Pascal, CNRS UMR 6524, 5 Rue Kessler, Clermont-Ferrand 63038, France
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18
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Dauphas N, Burkhardt C, Warren PH, Fang-Zhen T. Geochemical arguments for an Earth-like Moon-forming impactor. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130244. [PMID: 25114316 PMCID: PMC4128266 DOI: 10.1098/rsta.2013.0244] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Geochemical evidence suggests that the material accreted by the Earth did not change in nature during Earth's accretion, presumably because the inner protoplanetary disc had uniform isotopic composition similar to enstatite chondrites, aubrites and ungrouped achondrite NWA 5363/5400. Enstatite meteorites and the Earth were derived from the same nebular reservoir but diverged in their chemical evolutions, so no chondrite sample in meteorite collections is representative of the Earth's building blocks. The similarity in isotopic composition (Δ(17)O, ε(50)Ti and ε(54)Cr) between lunar and terrestrial rocks is explained by the fact that the Moon-forming impactor came from the same region of the disc as other Earth-forming embryos, and therefore was similar in isotopic composition to the Earth. The heavy δ(30)Si values of the silicate Earth and the Moon relative to known chondrites may be due to fractionation in the solar nebula/protoplanetary disc rather than partitioning of silicon in Earth's core. An inversion method is presented to calculate the Hf/W ratios and ε(182)W values of the proto-Earth and impactor mantles for a given Moon-forming impact scenario. The similarity in tungsten isotopic composition between lunar and terrestrial rocks is a coincidence that can be explained in a canonical giant impact scenario if an early formed embryo (two-stage model age of 10-20 Myr) collided with the proto-Earth formed over a more protracted accretion history (two-stage model age of 30-40 Myr).
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Affiliation(s)
- Nicolas Dauphas
- Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
| | - Christoph Burkhardt
- Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, USA
| | - Paul H Warren
- Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA
| | - Teng Fang-Zhen
- Isotope Laboratory, Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA
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Evidence for supernova injection into the solar nebula and the decoupling of r-process nucleosynthesis. Proc Natl Acad Sci U S A 2013; 110:17241-6. [PMID: 24101483 DOI: 10.1073/pnas.1307759110] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The isotopic composition of our Solar System reflects the blending of materials derived from numerous past nucleosynthetic events, each characterized by a distinct isotopic signature. We show that the isotopic compositions of elements spanning a large mass range in the earliest formed solids in our Solar System, calcium-aluminum-rich inclusions (CAIs), are uniform, and yet distinct from the average Solar System composition. Relative to younger objects in the Solar System, CAIs contain positive r-process anomalies in isotopes A < 140 and negative r-process anomalies in isotopes A > 140. This fundamental difference in the isotopic character of CAIs around mass 140 necessitates (i) the existence of multiple sources for r-process nucleosynthesis and (ii) the injection of supernova material into a reservoir untapped by CAIs. A scenario of late supernova injection into the protoplanetary disk is consistent with formation of our Solar System in an active star-forming region of the galaxy.
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Rauscher T, Dauphas N, Dillmann I, Fröhlich C, Fülöp Z, Gyürky G. Constraining the astrophysical origin of the p-nuclei through nuclear physics and meteoritic data. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:066201. [PMID: 23660558 DOI: 10.1088/0034-4885/76/6/066201] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A small number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-processes. Their origin is not well understood. Massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called γ-process requires high stellar plasma temperatures and occurs mainly in explosive O/Ne burning during a core-collapse supernova. Although the γ-process in massive stars has been successful in producing a large range of p-nuclei, significant deficiencies remain. An increasing number of processes and sites has been studied in recent years in search of viable alternatives replacing or supplementing the massive star models. A large number of unstable nuclei, however, with only theoretically predicted reaction rates are included in the reaction network and thus the nuclear input may also bear considerable uncertainties. The current status of astrophysical models, nuclear input and observational constraints is reviewed. After an overview of currently discussed models, the focus is on the possibility to better constrain those models through different means. Meteoritic data not only provide the actual isotopic abundances of the p-nuclei but can also put constraints on the possible contribution of proton-rich nucleosynthesis. The main part of the review focuses on the nuclear uncertainties involved in the determination of the astrophysical reaction rates required for the extended reaction networks used in nucleosynthesis studies. Experimental approaches are discussed together with their necessary connection to theory, which is especially pronounced for reactions with intermediate and heavy nuclei in explosive nuclear burning, even close to stability.
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Affiliation(s)
- T Rauscher
- Department of Physics, University of Basel, 4056 Basel, Switzerland.
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147Sm-143Nd systematics of Earth are inconsistent with a superchondritic Sm/Nd ratio. Proc Natl Acad Sci U S A 2013; 110:4929-34. [PMID: 23479630 DOI: 10.1073/pnas.1222252110] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The relationship between the compositions of the Earth and chondritic meteorites is at the center of many important debates. A basic assumption in most models for the Earth's composition is that the refractory elements are present in chondritic proportions relative to each other. This assumption is now challenged by recent (142)Nd/(144)Nd ratio studies suggesting that the bulk silicate Earth (BSE) might have an Sm/Nd ratio 6% higher than chondrites (i.e., the BSE is superchondritic). This has led to the proposal that the present-day (143)Nd/(144)Nd ratio of BSE is similar to that of some deep mantle plumes rather than chondrites. Our reexamination of the long-lived (147)Sm-(143)Nd isotope systematics of the depleted mantle and the continental crust shows that the BSE, reconstructed using the depleted mantle and continental crust, has (143)Nd/(144)Nd and Sm/Nd ratios close to chondritic values. The small difference in the ratio of (142)Nd/(144)Nd between ordinary chondrites and the Earth must be due to a process different from mantle-crust differentiation, such as incomplete mixing of distinct nucleosynthetic components in the solar nebula.
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22
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Abstract
Barium isotopic compositions of primitive materials in the solar system are generally affected by s- and r-process nucleosynthetic components that hide the contribution of the isotopic excess of (135)Ba formed by decay of radioactive (135)Cs. However, the Ba isotopic composition of the chemical separates from chondrules in the Sayama CM2 chondrite shows an excess of (135)Ba isotopic abundance up to (0.33 ± 0.06)%, which is independent of the isotopic components from s- and r-process nucleosyntheses. The isotopic excesses of (135)Ba correlate with the elemental abundance of Ba relative to Cs, providing chemical and isotopic evidence for the existence of the presently extinct radionuclide (135)Cs (t(1/2) = 2.3 million years) in the early solar system. The estimated abundance of (135)Cs/(133)Cs = (6.8 ± 1.9) × 10(-4) is more than double that expected from the uniform production model of the short-lived radioisotopes, suggesting remobilization of Cs including (135)Cs in the chondrules of the meteorite parent body.
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23
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Abstract
The (142)Nd/(144)Nd ratio of the Earth is greater than the solar ratio as inferred from chondritic meteorites, which challenges a fundamental assumption of modern geochemistry--that the composition of the silicate Earth is 'chondritic', meaning that it has refractory element ratios identical to those found in chondrites. The popular explanation for this and other paradoxes of mantle geochemistry, a hidden layer deep in the mantle enriched in incompatible elements, is inconsistent with the heat flux carried by mantle plumes. Either the matter from which the Earth formed was not chondritic, or the Earth has lost matter by collisional erosion in the later stages of planet formation.
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Affiliation(s)
- Ian H Campbell
- Research School of Earth Science, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
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24
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146Sm-142Nd systematics measured in enstatite chondrites reveals a heterogeneous distribution of 142Nd in the solar nebula. Proc Natl Acad Sci U S A 2011; 108:7693-7. [PMID: 21515828 DOI: 10.1073/pnas.1017332108] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The short-lived (146)Sm-(142)Nd chronometer (T(1/2) = 103 Ma) is used to constrain the early silicate evolution of planetary bodies. The composition of bulk terrestrial planets is then considered to be similar to that of primitive chondrites that represent the building blocks of rocky planets. However for many elements chondrites preserve small isotope differences. In this case it is not always clear to what extent these variations reflect the isotope heterogeneity of the protosolar nebula rather than being produced by the decay of parent isotopes. Here we present Sm-Nd isotopes data measured in a comprehensive suite of enstatite chondrites (EC). The EC preserve (142)Nd/(144)Nd ratios that range from those of ordinary chondrites to values similar to terrestrial samples. The EC having terrestrial (142)Nd/(144)Nd ratios are also characterized by small (144)Sm excesses, which is a pure p-process nuclide. The correlation between (144)Sm and (142)Nd for chondrites may indicate a heterogeneous distribution in the solar nebula of p-process matter synthesized in supernovae. However to explain the difference in (142)Nd/(144)Nd ratios, 20% of the p-process contribution to (142)Nd is required, at odds with the value of 4% currently proposed in stellar models. This study highlights the necessity of obtaining high-precision (144)Sm measurements to interpret properly measured (142)Nd signatures. Another explanation could be that the chondrites sample material formed in different pulses of the lifetime of asymptotic giant branch stars. Then the isotope signature measured in SiC presolar would not represent the unique s-process signature of the material present in the solar nebula during accretion.
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O’Neil J, Carlson RW, Francis D, Stevenson RK. Response to Comment on “Neodymium-142 Evidence for Hadean Mafic Crust”. Science 2009. [DOI: 10.1126/science.1169695] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Jonathan O’Neil
- Earth and Planetary Sciences Department, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada
| | - Richard W. Carlson
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
| | - Don Francis
- Earth and Planetary Sciences Department, McGill University, 3450 University Street, Montreal, Quebec H3A 2A7, Canada
| | - Ross K. Stevenson
- GEOTOP (Centre de recherche en géochemie et géodynamique), Université du Québec à Montréal, Post Office Box 8888, Succursale Centre-ville, 210, Président-Kennedy Avenue, Montreal, Quebec H3C 3P8, Canada
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Andreasen R, Sharma M. Comment on “Neodymium-142 Evidence for Hadean Mafic Crust”. Science 2009; 325:267; author reply 267. [DOI: 10.1126/science.1169604] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Rasmus Andreasen
- Imperial College London, Department of Earth Science and Engineering, South Kensington SW7 2AZ, UK
| | - Mukul Sharma
- Dartmouth College, Department of Earth Sciences, Hanover, NH 03755, USA
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27
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(142)Nd evidence for an enriched Hadean reservoir in cratonic roots. Nature 2009; 459:1118-21. [PMID: 19553997 DOI: 10.1038/nature08089] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 04/23/2009] [Indexed: 11/08/2022]
Abstract
The isotope (146)Sm undergoes alpha-decay to (142)Nd, with a half-life of 103 million years. Measurable variations in the (142)Nd/(144)Nd values of rocks resulting from Sm-Nd fractionation could therefore only have been produced within about 400 million years of the Solar System's formation (that is, when (146)Sm was extant). The (142)Nd/(144)Nd compositions of terrestrial rocks are accordingly a sensitive monitor of the main silicate differentiation events that took place in the early Earth. High (142)Nd/(144)Nd values measured in some Archaean rocks from Greenland hint at the existence of an early incompatible-element-depleted mantle. Here we present measurements of low (142)Nd/(144)Nd values in 1.48-gigayear-(Gyr)-old lithospheric mantle-derived alkaline rocks from the Khariar nepheline syenite complex in southeastern India. These data suggest that a reservoir that was relatively enriched in incompatible elements formed at least 4.2 Gyr ago and traces of its isotopic signature persisted within the lithospheric root of the Bastar craton until at least 1.48 Gyr ago. These low (142)Nd/(144)Nd compositions may represent a diluted signature of a Hadean (4 to 4.57 Gyr ago) enriched reservoir that is characterized by even lower values. That no evidence of the early depleted mantle has been observed in rocks younger than 3.6 Gyr (refs 3, 4, 7) implies that such domains had effectively mixed back into the convecting mantle by then. In contrast, some early enriched components apparently escaped this fate. Thus, the mantle sampled by magmatism since 3.6 Gyr ago may be biased towards a depleted composition that would be balanced by relatively more enriched reservoirs that are 'hidden' in Hadean crust, the D'' layer of the lowermost mantle or, as we propose here, also within the roots of old cratons.
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Bourdon B, Touboul M, Caro G, Kleine T. Early differentiation of the Earth and the Moon. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:4105-4128. [PMID: 18826925 DOI: 10.1098/rsta.2008.0125] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We examine the implications of new 182W and 142Nd data for Mars and the Moon for the early evolution of the Earth. The similarity of 182W in the terrestrial and lunar mantles and their apparently differing Hf/W ratios indicate that the Moon-forming giant impact most probably took place more than 60Ma after the formation of calcium-aluminium-rich inclusions (4.568Gyr). This is not inconsistent with the apparent U-Pb age of the Earth. The new 142Nd data for Martian meteorites show that Mars probably has a super-chondritic Sm/Nd that could coincide with that of the Earth and the Moon. If this is interpreted by an early mantle differentiation event, this requires a buried enriched reservoir for the three objects. This is highly unlikely. For the Earth, we show, based on new mass-balance calculations for Nd isotopes, that the presence of a hidden reservoir is difficult to reconcile with the combined 142Nd-143Nd systematics of the Earth's mantle. We argue that a likely possibility is that the missing component was lost during or prior to accretion. Furthermore, the 142Nd data for the Moon that were used to argue for the solidification of the magma ocean at ca 200Myr are reinterpreted. Cumulate overturn, magma mixing and melting following lunar magma ocean crystallization at 50-100Myr could have yielded the 200Myr model age.
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Affiliation(s)
- Bernard Bourdon
- Institute of Isotope Geochemistry and Mineral Resources, ETH Zurich, Clausiusstrasse 25, Zurich 8092, Switzerland.
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29
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Carlson RW, Boyet M. Composition of the Earth's interior: the importance of early events. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:4077-4103. [PMID: 18826922 DOI: 10.1098/rsta.2008.0166] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The detection of excess 142Nd caused by the decay of 103Ma half-life 146Sm in all terrestrial rocks compared with chondrites shows that the chondrite analogue compositional model cannot be strictly correct, at least for the accessible portion of the Earth. Both the continental crust (CC) and the mantle source of mid-ocean ridge basalts (MORB) originate from the material characterized by superchondritic 142Nd/144Nd. Thus, the mass balance of CC plus mantle depleted by crust extraction (the MORB-source mantle) does not sum back to chondritic compositions, but instead to a composition with Sm/Nd ratio sufficiently high to explain the superchondritic 142Nd/144Nd. This requires that the mass of mantle depleted by CC extraction expand to 75-100 per cent of the mantle depending on the composition assumed for average CC. If the bulk silicate Earth has chondritic relative abundances of the refractory lithophile elements, then there must exist within the Earth's interior an incompatible-element-enriched reservoir that contains roughly 40 per cent of the Earth's 40Ar and heat-producing radioactive elements. The existence of this enriched reservoir is demonstrated by time-varying 142Nd/144Nd in Archaean crustal rocks. Calculations of the mass of the enriched reservoir along with seismically determined properties of the D'' layer at the base of the mantle allow the speculation that this enriched reservoir formed by the sinking of dense melts deep in a terrestrial magma ocean. The enriched reservoir may now be confined to the base of the mantle owing to a combination of compositionally induced high density and low viscosity, both of which allow only minimal entrainment into the overlying convecting mantle.
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Affiliation(s)
- Richard W Carlson
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.
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30
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Jacobsen SB, Ranen MC, Petaev MI, Remo JL, O'Connell RJ, Sasselov DD. Isotopes as clues to the origin and earliest differentiation history of the Earth. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:4129-4162. [PMID: 18826920 DOI: 10.1098/rsta.2008.0174] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Measurable variations in (182)W/(183)W, (142)Nd/(144)Nd, (129)Xe/(130)Xe and (136)XePu/(130)Xe in the Earth and meteorites provide a record of accretion and formation of the core, early crust and atmosphere. These variations are due to the decay of the now extinct nuclides (182)Hf, (146)Sm, (129)I and (244)Pu. The (l82)Hf-(182)W system is the best accretion and core-formation chronometer, which yields a mean time of Earth's formation of 10Myr, and a total time scale of 30Myr. New laser shock data at conditions comparable with those in the Earth's deep mantle subsequent to the giant Moon-forming impact suggest that metal-silicate equilibration was rapid enough for the Hf-W chronometer to reliably record this time scale. The coupled (146)Sm-(147)Sm chronometer is the best system for determining the initial silicate differentiation (magma ocean crystallization and proto-crust formation), which took place at ca 4.47Ga or perhaps even earlier. The presence of a large (129)Xe excess in the deep Earth is consistent with a very early atmosphere formation (as early as 30Myr); however, the interpretation is complicated by the fact that most of the atmospheric Xe may be from a volatile-rich late veneer.
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Affiliation(s)
- Stein B Jacobsen
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
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31
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Are there nuclear reactors at Earth's core? Nature 2008. [DOI: 10.1038/news.2008.822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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32
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Caro G, Bourdon B, Halliday AN, Quitté G. Super-chondritic Sm/Nd ratios in Mars, the Earth and the Moon. Nature 2008; 452:336-9. [DOI: 10.1038/nature06760] [Citation(s) in RCA: 136] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Accepted: 01/18/2008] [Indexed: 11/09/2022]
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Bennett VC, Brandon AD, Nutman AP. Coupled 142Nd-143Nd isotopic evidence for Hadean mantle dynamics. Science 2008; 318:1907-10. [PMID: 18096803 DOI: 10.1126/science.1145928] [Citation(s) in RCA: 192] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The oldest rocks-3.85 billion years old-from southwest Greenland have coupled neodymium-142 excesses (from decay of now-extinct samarium-146; half-life, 103 million years) and neodymium-143 excesses (from decay of samarium-147; half-life, 106 billion years), relative to chondritic meteorites, that directly date the formation of chemically distinct silicate reservoirs in the first 30 million to 75 million years of Earth history. The differences in 142Nd signatures of coeval rocks from the two most extensive crustal relicts more than 3.6 billion years old, in Western Australia and southwest Greenland, reveal early-formed large-scale chemical heterogeneities in Earth's mantle that persisted for at least the first billion years of Earth history. Temporal variations in 142Nd signatures track the subsequent incomplete remixing of very-early-formed mantle chemical domains.
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Affiliation(s)
- Vickie C Bennett
- Research School of Earth Sciences, Australian National University, Canberra ACT, 0200 Australia.
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Richter JM, Whitefield BW, Maimone TJ, Lin DW, Castroviejo MP, Baran PS. Scope and mechanism of direct indole and pyrrole couplings adjacent to carbonyl compounds: total synthesis of acremoauxin A and oxazinin 3. J Am Chem Soc 2007; 129:12857-69. [PMID: 17900115 PMCID: PMC2631414 DOI: 10.1021/ja074392m] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Full details are provided for a recently invented method to couple indoles and pyrroles to carbonyl compounds. The reaction is ideally suited for structurally complex substrates and exhibits high levels of chemoselectivity (functional group tolerability), regioselectivity (coupling occurs exclusively at C-3 of indole or C-2 of pyrrole), stereoselectivity (substrate control), and practicality (amenable to scaleup). In addition, quaternary stereocenters are easily and predictably generated. The reaction has been applied to a number of synthetic problems including total syntheses of members of the hapalindole family of natural products, ketorolac, acremoauxin A, and oxazinin 3. Mechanistically, this coupling protocol appears to operate by a single electron-transfer process requiring generation of an electron-deficient radical adjacent to a carbonyl which is then intercepted by an indole or pyrrole anion.
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Affiliation(s)
- Jeremy M. Richter
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - Brandon W. Whitefield
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - Thomas J. Maimone
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - David W. Lin
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - M. Pilar Castroviejo
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
| | - Phil S. Baran
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
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