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Smit MA, Kooijman E. A common precursor for global hotspot lavas. NATURE GEOSCIENCE 2024; 17:1053-1058. [PMID: 39399208 PMCID: PMC11464371 DOI: 10.1038/s41561-024-01538-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/10/2024] [Accepted: 08/20/2024] [Indexed: 10/15/2024]
Abstract
Hotspot lavas exhibit chemical heterogeneity, much of which is ascribed to heterogeneous deep mantle sources that contain various components with distinct composition, origin and age. However, characterizing primary melt compositions and mantle heterogeneity directly is challenging. Here we investigate a global dataset of hotspot lavas to constrain the incompatible-element composition of their parental melts and sources. Trace-element ratios indicate that the compositional heterogeneity of global hotspot lavas is not primary, but reflects processes that hotspot melts undergo as they ascend to the surface. We find the parental melts of these lavas, as well as of kimberlites and basalts from large igneous provinces, to be uniform in their elemental, and radiogenic and noble-gas isotope, composition. We suggest that the parental melts to all of these lavas derive from a depleted and outgassed mantle reservoir that was replenished with incompatible element-enriched material during the Archaean. This interpretation explains the elemental, radiogenic and noble-gas isotope compositions of hotspot lavas without requiring a heterogeneous lower mantle or the long-term survival of undegassed relics from a primordial Earth.
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Affiliation(s)
- Matthijs A. Smit
- Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia Canada
- Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
| | - Ellen Kooijman
- Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
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2
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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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3
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Guo M, Korenaga J. The combined Hf and Nd isotope evolution of the depleted mantle requires Hadean continental formation. SCIENCE ADVANCES 2023; 9:eade2711. [PMID: 36961892 PMCID: PMC10038339 DOI: 10.1126/sciadv.ade2711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Accepted: 02/22/2023] [Indexed: 06/18/2023]
Abstract
The onset and rates of continental growth are first-order indicators of early Earth dynamics, and whether substantial crust existed in the Hadean or much later has long been debated. Here, we present a theoretical analysis of published Hf and Nd isotopic data representing the depleted mantle and demonstrate that continental growth must have started in the early Hadean. Whereas the traditional interpretation of depleted mantle signatures in crustal rocks assumes unrealistic instantaneous mantle mixing, our modeling incorporates the effect of a finite mixing time over which these signatures are recorded in rocks produced through mantle melting. This effect is shown to delay, by as much as 0.65 to 0.75 billion years, the appearance of the earliest depleted mantle signatures in continental crust. Our results suggest that published observations of εHf, ε143Nd, and μ142Nd require Hadean growth of continental crust, with a minimum of 50% of today's continental volume already existing by the end of Hadean.
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Westall F, Brack A, Fairén AG, Schulte MD. Setting the geological scene for the origin of life and continuing open questions about its emergence. FRONTIERS IN ASTRONOMY AND SPACE SCIENCES 2023; 9:1095701. [PMID: 38274407 PMCID: PMC7615569 DOI: 10.3389/fspas.2022.1095701] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/27/2024]
Abstract
The origin of life is one of the most fundamental questions of humanity. It has been and is still being addressed by a wide range of researchers from different fields, with different approaches and ideas as to how it came about. What is still incomplete is constrained information about the environment and the conditions reigning on the Hadean Earth, particularly on the inorganic ingredients available, and the stability and longevity of the various environments suggested as locations for the emergence of life, as well as on the kinetics and rates of the prebiotic steps leading to life. This contribution reviews our current understanding of the geological scene in which life originated on Earth, zooming in specifically on details regarding the environments and timescales available for prebiotic reactions, with the aim of providing experimenters with more specific constraints. Having set the scene, we evoke the still open questions about the origin of life: did life start organically or in mineralogical form? If organically, what was the origin of the organic constituents of life? What came first, metabolism or replication? What was the time-scale for the emergence of life? We conclude that the way forward for prebiotic chemistry is an approach merging geology and chemistry, i.e., far-from-equilibrium, wet-dry cycling (either subaerial exposure or dehydration through chelation to mineral surfaces) of organic reactions occurring repeatedly and iteratively at mineral surfaces under hydrothermal-like conditions.
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Affiliation(s)
| | - André Brack
- Centre de Biophysique Moléculaire, CNRS, Orléans, France
| | - Alberto G. Fairén
- Centro de Astrobiología (CAB, CSIC-INTA), Madrid, Spain
- Cornell University, Ithaca, NY, United States
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5
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Bajgain SK, Ashley AW, Mookherjee M, Ghosh DB, Karki BB. Insights into magma ocean dynamics from the transport properties of basaltic melt. Nat Commun 2022; 13:7590. [PMID: 36481757 PMCID: PMC9731987 DOI: 10.1038/s41467-022-35171-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Accepted: 11/17/2022] [Indexed: 12/13/2022] Open
Abstract
The viscosity of magma plays a crucial role in the dynamics of the Earth: from the crystallization of a magma ocean during its initial stages to modern-day volcanic processes. However, the pressure-dependence behavior of viscosity at high pressure remains controversial. In this study, we report the results of first-principles molecular dynamics simulations of basaltic melt to show that the melt viscosity increases upon compression along each isotherm for the entire lower mantle after showing minima at ~6 GPa. However, elevated temperatures of the magma ocean translate to a narrow range of viscosity, i.e., 0.01-0.03 Pa.s. This low viscosity implies that the crystallization of the magma ocean could be complete within a few million years. These results also suggest that the crystallization of the magma ocean is likely to be fractional, thus supporting the hypothesis that present-day mantle heterogeneities could have been generated during the early crystallization of the primitive mantle.
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Affiliation(s)
- Suraj K Bajgain
- Earth Materials Laboratory, Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, USA.
- Department of Geology, School of Natural Resources & Environment, Lake Superior State University, Sault Ste Marie, MI, USA.
| | - Aaron Wolfgang Ashley
- Earth Materials Laboratory, Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, USA
| | - Mainak Mookherjee
- Earth Materials Laboratory, Earth, Ocean and Atmospheric Sciences, Florida State University, Tallahassee, FL, USA.
| | - Dipta B Ghosh
- School of Electrical Engineering and Computer Science, Department of Geology and Geophysics, Center for Computation and Technology, Louisiana State University, Baton Rouge, LA, USA
| | - Bijaya B Karki
- School of Electrical Engineering and Computer Science, Department of Geology and Geophysics, Center for Computation and Technology, Louisiana State University, Baton Rouge, LA, USA.
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6
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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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7
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Frossard P, Israel C, Bouvier A, Boyet M. Earth's composition was modified by collisional erosion. Science 2022; 377:1529-1532. [PMID: 36173863 DOI: 10.1126/science.abq7351] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The samarium-146 (146Sm)-neodymium-142 (142Nd) short-lived decay system (half-life of 103 million years) is a powerful tracer of the early mantle-crust evolution of planetary bodies. However, an increased 142Nd/144Nd in modern terrestrial rocks relative to chondrite meteorites has been proposed to be caused by nucleosynthetic anomalies, obscuring early Earth's differentiation history. We use stepwise dissolution of primitive chondrites to quantify nucleosynthetic contributions on the composition of chondrites. After correction for nucleosynthetic anomalies, Earth and the silicate parts of differentiated planetesimals contain resolved excesses of 142Nd relative to chondrites. We conclude that only collisional erosion of primordial crusts can explain such compositions. This process associated with planetary accretion must have produced substantial loss of incompatible elements, including long-term heat-producing elements such as uranium, thorium, and potassium.
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Affiliation(s)
- Paul Frossard
- Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France.,Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
| | - Claudine Israel
- Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France
| | - Audrey Bouvier
- Bayerisches Geoinstitut, Universität Bayreuth, 95447 Bayreuth, Germany.,Department of Earth Sciences, University of Western Ontario, London, ON N6A 5B7, Canada
| | - Maud Boyet
- Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, F-63000 Clermont-Ferrand, France
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8
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Leinhardt ZM. Earth was seasoned by countless blows. Science 2022; 377:1490-1491. [PMID: 36173849 DOI: 10.1126/science.add3199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Earth's composition was shaped by collisions from external objects.
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Affiliation(s)
- Zoë Malka Leinhardt
- H.H. Wills Physics Laboratory, School of Physics, University of Bristol, Bristol BS8 1TL, UK
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9
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A simple method for Ce–Nd separation using nano-NaBiO3: Application in the isotopic analysis of U, Sr, Pb, Nd, and Hf in uranium ores. Talanta 2022; 245:123443. [DOI: 10.1016/j.talanta.2022.123443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 04/01/2022] [Accepted: 04/02/2022] [Indexed: 11/24/2022]
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10
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Heinitz S, Kajan I, Schumann D. How accurate are half-life data of long-lived radionuclides? RADIOCHIM ACTA 2022. [DOI: 10.1515/ract-2021-1135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Abstract
We have consulted existing half-life data available in Nuclear Data Sheets for radionuclides with Z < 89 in the range between 30 and 108 years with emphasis on their uncertainty. Based on this dataset, we have highlighted the lack of reliable data by giving examples for nuclides relevant for astrophysical, environmental and nuclear research. It is shown that half-lives for a substantial number of nuclides require a re-determination since existing data are either based on one single measurement, are contradictory or are associated with uncertainties above 5%.
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Affiliation(s)
| | - Ivan Kajan
- Paul Scherrer Institute (PSI) , Villigen , Switzerland
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11
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Nabiei F, Badro J, Boukaré C, Hébert C, Cantoni M, Borensztajn S, Wehr N, Gillet P. Investigating Magma Ocean Solidification on Earth Through Laser-Heated Diamond Anvil Cell Experiments. GEOPHYSICAL RESEARCH LETTERS 2021; 48:e2021GL092446. [PMID: 34219835 PMCID: PMC8244043 DOI: 10.1029/2021gl092446] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 05/18/2021] [Accepted: 05/22/2021] [Indexed: 05/09/2023]
Abstract
We carried out a series of silicate fractional crystallization experiments at lower mantle pressures using the laser-heated diamond anvil cell. Phase relations and the compositional evolution of the cotectic melt and equilibrium solids along the liquid line of descent were determined and used to assemble the melting phase diagram. In a pyrolitic magma ocean, the first mineral to crystallize in the deep mantle is iron-depleted calcium-bearing bridgmanite. From the phase diagram, we estimate that the initial 33%-36% of the magma ocean will crystallize to form such a buoyant bridgmanite. Substantial calcium solubility in bridgmanite is observed up to 129 GPa, and significantly delays the crystallization of the calcium silicate perovskite phase during magma ocean solidification. Residual melts are strongly iron-enriched as crystallization proceeds, making them denser than any of the coexisting solids at deep mantle conditions, thus supporting the terrestrial basal magma ocean hypothesis (Labrosse et al., 2007).
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Affiliation(s)
- Farhang Nabiei
- Earth and Planetary Science LaboratoryEPFLLausanneSwitzerland
- Electron Spectrometry and Microscopy LaboratoryEPFLLausanneSwitzerland
| | - James Badro
- Earth and Planetary Science LaboratoryEPFLLausanneSwitzerland
- Université de ParisInstitut de Physique du Globe de ParisCNRSParisFrance
| | - Charles‐Édouard Boukaré
- Earth and Planetary Science LaboratoryEPFLLausanneSwitzerland
- Université de ParisInstitut de Physique du Globe de ParisCNRSParisFrance
| | - Cécile Hébert
- Electron Spectrometry and Microscopy LaboratoryEPFLLausanneSwitzerland
| | - Marco Cantoni
- Interdisciplinary Centre for Electron MicroscopyEPFLLausanneSwitzerland
| | | | - Nicolas Wehr
- Université de ParisInstitut de Physique du Globe de ParisCNRSParisFrance
| | - Philippe Gillet
- Earth and Planetary Science LaboratoryEPFLLausanneSwitzerland
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12
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Remnants of early Earth differentiation in the deepest mantle-derived lavas. Proc Natl Acad Sci U S A 2020; 118:2015211118. [PMID: 33443165 DOI: 10.1073/pnas.2015211118] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The noble gas isotope systematics of ocean island basalts suggest the existence of primordial mantle signatures in the deep mantle. Yet, the isotopic compositions of lithophile elements (Sr, Nd, Hf) in these lavas require derivation from a mantle source that is geochemically depleted by melt extraction rather than primitive. Here, this apparent contradiction is resolved by employing a compilation of the Sr, Nd, and Hf isotope composition of kimberlites-volcanic rocks that originate at great depth beneath continents. This compilation includes kimberlites as old as 2.06 billion years and shows that kimberlites do not derive from a primitive mantle source but sample the same geochemically depleted component (where geochemical depletion refers to ancient melt extraction) common to most oceanic island basalts, previously called PREMA (prevalent mantle) or FOZO (focal zone). Extrapolation of the Nd and Hf isotopic compositions of the kimberlite source to the age of Earth formation yields a 143Nd/144Nd-176Hf/177Hf composition within error of chondrite meteorites, which include the likely parent bodies of Earth. This supports a hypothesis where the source of kimberlites and ocean island basalts contains a long-lived component that formed by melt extraction from a domain with chondritic 143Nd/144Nd and 176Hf/177Hf shortly after Earth accretion. The geographic distribution of kimberlites containing the PREMA component suggests that these remnants of early Earth differentiation are located in large seismically anomalous regions corresponding to thermochemical piles above the core-mantle boundary. PREMA could have been stored in these structures for most of Earth's history, partially shielded from convective homogenization.
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13
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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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14
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Hyung E, Jacobsen SB. The 142Nd/ 144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present. Proc Natl Acad Sci U S A 2020; 117:14738-14744. [PMID: 32541051 PMCID: PMC7334517 DOI: 10.1073/pnas.2006950117] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Early silicate differentiation events for the terrestrial planets can be traced with the short-lived 146Sm-142Nd system (∼100-My half-life). Resulting early Earth-produced 142Nd/144Nd variations are an excellent tracer of the rate of mantle mixing and thus a potential tracer of plate tectonics through time. Evidence for early silicate differentiation in the Hadean (4.6 to 4.0 Ga) has been provided by 142Nd/144Nd measurements of rocks that show both higher and lower (±20 ppm) values than the present-day mantle, demonstrating major silicate Earth differentiation within the first 100 My of solar system formation. We have obtained an external 2σ uncertainty at 1.7 ppm for 142Nd/144Nd measurements to constrain its homogeneity/heterogeneity in the mantle for the last 2 Ga. We report that most modern-day mid-ocean ridge basalt and ocean island basalt samples as well as continental crustal rocks going back to 2 Ga are within 1.7 ppm of the average Earth 142Nd/144Nd value. Considering mafic and ultramafic compositions, we use a mantle-mixing model to show that this trend is consistent with a mantle stirring time of about 400 My since the early Hadean. Such a fast mantle stirring rate supports the notion that Earth's thermal and chemical evolution is likely to have been largely regulated by plate tectonics for most of its history. Some young rocks have 142Nd/144Nd signatures marginally resolved (∼3 ppm), suggesting that the entire mantle is not equally well homogenized and that some silicate mantle signatures from an early differentiated mantle (>4.1 Ga ago) are preserved in the modern mantle.
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Affiliation(s)
- Eugenia Hyung
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
| | - Stein B Jacobsen
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
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15
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Davis DW. A simple method for rapid calibration of faraday and ion-counting detectors on movable multicollector mass spectrometers. JOURNAL OF MASS SPECTROMETRY : JMS 2020; 55:e4511. [PMID: 32219912 DOI: 10.1002/jms.4511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Revised: 03/02/2020] [Accepted: 03/03/2020] [Indexed: 06/10/2023]
Abstract
Methods are presented for rapid determination of relative efficiencies of Faraday cups in a multicollector array with movable cups and of Daly or electron multiplier detector dead time and gain values. The Faraday calibration approach is based on measuring the same isotopic ratio in two sequences with different collector configurations having one collector in common. Changes in thermal fractionation during the two measurement sequences are monitored using the same two collectors. Since the relative efficiencies are determined by measuring the same ratio in different cups corrected for time-dependent changes in fractionation, it is unnecessary to use a standard of known composition and calculations are simple, not requiring the solution of multiple equations. Determination of dead time and gain values for a Daly detector are shown based on multidynamic measurements of masses 207, 206, and 208 from Pb standard SRM982 in two sequences consisting of L1-Daly-H1 and Daly-H1-H2. This provides two equations that can be solved for Daly dead time and gain. This method uses static measurements and is therefore insensitive to signal instability. It also does not require use of a standard of known isotopic composition. The potential of using known cup efficiencies to help determine absolute isotopic abundances is discussed.
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Affiliation(s)
- Donald W Davis
- Department of Earth Sciences, University of Toronto, 22 Russell St., Toronto, Ontario, Canada, M5S 3B1
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16
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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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17
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Schaefer L, Elkins-Tanton LT. Magma oceans as a critical stage in the tectonic development of rocky planets. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2018; 376:rsta.2018.0109. [PMID: 30275166 PMCID: PMC6189560 DOI: 10.1098/rsta.2018.0109] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 07/19/2018] [Indexed: 05/23/2023]
Abstract
Magma oceans are a common result of the high degree of heating that occurs during planet formation. It is thought that almost all of the large rocky bodies in the Solar System went through at least one magma ocean phase. In this paper, we review some of the ways in which magma ocean models for the Earth, Moon and Mars match present-day observations of mantle reservoirs, internal structure and primordial crusts, and then we present new calculations for the oxidation state of the mantle produced during the magma ocean phase. The crystallization of magma oceans probably leads to a massive mantle overturn that may set up a stably stratified mantle. This may lead to significant delays or total prevention of plate tectonics on some planets. We review recent models that may help alleviate the mantle stability issue and lead to earlier onset of plate tectonics.This article is part of a discussion meeting issue 'Earth dynamics and the development of plate tectonics'.
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Affiliation(s)
- Laura Schaefer
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
| | - Linda T Elkins-Tanton
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
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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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Depletion of potassium and sodium in mantles of Mars, Moon and Vesta by core formation. Sci Rep 2018; 8:7053. [PMID: 29728585 PMCID: PMC5935680 DOI: 10.1038/s41598-018-25505-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Accepted: 04/24/2018] [Indexed: 11/10/2022] Open
Abstract
The depletions of potassium (K) and sodium (Na) in samples from planetary interiors have long been considered as primary evidence for their volatile behavior during planetary formation processes. Here, we use high-pressure experiments combined with laser ablation analyses to measure the sulfide-silicate and metal-silicate partitioning of K and Na at high pressure (P) – temperature (T) and find that their partitioning into metal strongly increases with temperature. Results indicate that the observed Vestan and Martian mantle K and Na depletions can reflect sequestration into their sulfur-rich cores in addition to their volatility during formation of Mars and Vesta. This suggests that alkali depletions are not affected solely by incomplete condensation or partial volatilization during planetary formation and differentiation, but additionally or even primarily reflect the thermal and chemical conditions during core formation. Core sequestration is also significant for the Moon, but lunar mantle depletions of K and Na cannot be reconciled by core formation only. This supports the hypothesis that measured isotopic fractionations of K in lunar samples represent incomplete condensation or extensive volatile loss during the Moon-forming giant impact.
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Chaudhuri T, Wan Y, Mazumder R, Ma M, Liu D. Evidence of Enriched, Hadean Mantle Reservoir from 4.2-4.0 Ga zircon xenocrysts from Paleoarchean TTGs of the Singhbhum Craton, Eastern India. Sci Rep 2018; 8:7069. [PMID: 29728630 PMCID: PMC5935743 DOI: 10.1038/s41598-018-25494-6] [Citation(s) in RCA: 82] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 04/19/2018] [Indexed: 11/25/2022] Open
Abstract
Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Pb analyses of zircons from Paleoarchean (~3.4 Ga) tonalite-gneiss called the Older Metamorphic Tonalitic Gneiss (OMTG) from the Champua area of the Singhbhum Craton, India, reveal 4.24-4.03 Ga xenocrystic zircons, suggesting that the OMTG records the hitherto unknown oldest precursor of Hadean age reported in India. Hf isotopic analyses of the Hadean xenocrysts yield unradiogenic 176Hf/177Hfinitial compositions (0.27995 ± 0.0009 to 0.28001 ± 0.0007; ɛHf[t] = −2.5 to −5.2) indicating that an enriched reservoir existed during Hadean eon in the Singhbhum cratonic mantle. Time integrated ɛHf[t] compositional array of the Hadean xenocrysts indicates a mafic protolith with 176Lu/177Hf ratio of ∼0.019 that was reworked during ∼4.2-4.0 Ga. This also suggests that separation of such an enriched reservoir from chondritic mantle took place at 4.5 ± 0.19 Ga. However, more radiogenic yet subchondritic compositions of ∼3.67 Ga (average 176Hf/177Hfinitial 0.28024 ± 0.00007) and ~3.4 Ga zircons (average 176Hf/177Hfinitial = 0.28053 ± 0.00003) from the same OMTG samples and two other Paleoarchean TTGs dated at ~3.4 Ga and ~3.3 Ga (average 176Hf/177Hfinitial is 0.28057 ± 0.00008 and 0.28060 ± 0.00003), respectively, corroborate that the enriched Hadean reservoir subsequently underwent mixing with mantle-derived juvenile magma during the Eo-Paleoarchean.
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Affiliation(s)
- Trisrota Chaudhuri
- Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Kolkata, 700019, India
| | - Yusheng Wan
- Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China
| | - Rajat Mazumder
- Department of Applied Geology, Faculty of Engineering and Science, Curtin University Malaysia, CDT 250, Miri, 98009, Sarawak, Malaysia.
| | - Mingzhu Ma
- Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China
| | - Dunyi Liu
- Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China
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Vago JL, Westall F. Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover. ASTROBIOLOGY 2017; 17:471-510. [PMID: 31067287 PMCID: PMC5685153 DOI: 10.1089/ast.2016.1533] [Citation(s) in RCA: 140] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 03/05/2017] [Indexed: 05/19/2023]
Abstract
The second ExoMars mission will be launched in 2020 to target an ancient location interpreted to have strong potential for past habitability and for preserving physical and chemical biosignatures (as well as abiotic/prebiotic organics). The mission will deliver a lander with instruments for atmospheric and geophysical investigations and a rover tasked with searching for signs of extinct life. The ExoMars rover will be equipped with a drill to collect material from outcrops and at depth down to 2 m. This subsurface sampling capability will provide the best chance yet to gain access to chemical biosignatures. Using the powerful Pasteur payload instruments, the ExoMars science team will conduct a holistic search for traces of life and seek corroborating geological context information. Key Words: Biosignatures-ExoMars-Landing sites-Mars rover-Search for life. Astrobiology 17, 471-510.
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Dauphas N. The isotopic nature of the Earth's accreting material through time. Nature 2017; 541:521-524. [PMID: 28128239 DOI: 10.1038/nature20830] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 11/25/2016] [Indexed: 11/09/2022]
Abstract
The Earth formed by accretion of Moon- to Mars-size embryos coming from various heliocentric distances. The isotopic nature of these bodies is unknown. However, taking meteorites as a guide, most models assume that the Earth must have formed from a heterogeneous assortment of embryos with distinct isotopic compositions. High-precision measurements, however, show that the Earth, the Moon and enstatite meteorites have almost indistinguishable isotopic compositions. Models have been proposed that reconcile the Earth-Moon similarity with the inferred heterogeneous nature of Earth-forming material, but these models either require specific geometries for the Moon-forming impact or can explain only one aspect of the Earth-Moon similarity (that is, 17O). Here I show that elements with distinct affinities for metal can be used to decipher the isotopic nature of the Earth's accreting material through time. I find that the mantle signatures of lithophile O, Ca, Ti and Nd, moderately siderophile Cr, Ni and Mo, and highly siderophile Ru record different stages of the Earth's accretion; yet all those elements point to material that was isotopically most similar to enstatite meteorites. This isotopic similarity indicates that the material accreted by the Earth always comprised a large fraction of enstatite-type impactors (about half were E-type in the first 60 per cent of the accretion and all of the impactors were E-type after that). Accordingly, the giant impactor that formed the Moon probably had an isotopic composition similar to that of the Earth, hence relaxing the constraints on models of lunar formation. Enstatite meteorites and the Earth were formed from the same isotopic reservoir but they diverged in their chemical evolution owing to subsequent fractionation by nebular and planetary processes.
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Affiliation(s)
- Nicolas Dauphas
- Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA
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Koelemeijer P, Deuss A, Ritsema J. Density structure of Earth's lowermost mantle from Stoneley mode splitting observations. Nat Commun 2017; 8:15241. [PMID: 28504262 PMCID: PMC5440685 DOI: 10.1038/ncomms15241] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Accepted: 03/13/2017] [Indexed: 11/09/2022] Open
Abstract
Advances in our understanding of Earth's thermal evolution and the style of mantle convection rely on robust seismological constraints on lateral variations of density. The large-low-shear-wave velocity provinces (LLSVPs) atop the core-mantle boundary beneath Africa and the Pacific are the largest structures in the lower mantle, and hence severely affect the convective flow. Here, we show that anomalous splitting of Stoneley modes, a unique class of free oscillations that are perturbed primarily by velocity and density variations at the core-mantle boundary, is explained best when the overall density of the LLSVPs is lower than the surrounding mantle. The resolved density variations can be explained by the presence of post-perovskite, chemical heterogeneity or a combination of the two. Although we cannot rule out the presence of a ∼100-km-thick denser-than-average basal structure, our results support the hypothesis that LLSVPs signify large-scale mantle upwelling in two antipodal regions of the mantle.
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Affiliation(s)
- Paula Koelemeijer
- Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland.,Department of Earth Sciences, University of Oxford, OX1 3AN Oxford, UK
| | - Arwen Deuss
- Department of Earth Sciences, Utrecht University, 3508 TC Utrecht, The Netherlands
| | - Jeroen Ritsema
- Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109-1005, USA
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O'Neil J, Carlson RW. Building Archean cratons from Hadean mafic crust. Science 2017; 355:1199-1202. [PMID: 28302856 DOI: 10.1126/science.aah3823] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 10/12/2016] [Accepted: 02/13/2017] [Indexed: 11/02/2022]
Abstract
Geologic processing of Earth's surface has removed most of the evidence concerning the nature of Earth's first crust. One region of ancient crust is the Hudson Bay terrane of northeastern Canada, which is mainly composed of Neoarchean felsic crust and forms the nucleus of the Northeastern Superior Province. New data show these ~2.7-billion-year-old rocks to be the youngest to yield variability in neodymium-142 (142Nd), the decay product of short-lived samarium-146 (146Sm). Combined 146-147Sm-142-143Nd data reveal that this large block of Archean crust formed by reworking of much older (>4.2 billion-year-old) mafic crust over a 1.5-billion-year interval of early Earth history. Thus, unlike on modern Earth, mafic crust apparently could survive for more than 1 billion years to form an important source rock for Archean crustal genesis.
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Affiliation(s)
- Jonathan O'Neil
- Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, Canada.
| | - Richard W Carlson
- Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC 20015, USA
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Lapen TJ, Righter M, Andreasen R, Irving AJ, Satkoski AM, Beard BL, Nishiizumi K, Jull AJT, Caffee MW. Two billion years of magmatism recorded from a single Mars meteorite ejection site. SCIENCE ADVANCES 2017; 3:e1600922. [PMID: 28164153 PMCID: PMC5287701 DOI: 10.1126/sciadv.1600922] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Accepted: 12/22/2016] [Indexed: 06/06/2023]
Abstract
The timing and nature of igneous activity recorded at a single Mars ejection site can be determined from the isotope analyses of Martian meteorites. Northwest Africa (NWA) 7635 has an Sm-Nd crystallization age of 2.403 ± 0.140 billion years, and isotope data indicate that it is derived from an incompatible trace element-depleted mantle source similar to that which produced a geochemically distinct group of 327- to 574-million-year-old "depleted" shergottites. Cosmogenic nuclide data demonstrate that NWA 7635 was ejected from Mars 1.1 million years ago (Ma), as were at least 10 other depleted shergottites. The shared ejection age is consistent with a common ejection site for these meteorites. The spatial association of 327- to 2403-Ma depleted shergottites indicates >2 billion years of magmatism from a long-lived and geochemically distinct volcanic center near the ejection site.
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Affiliation(s)
- Thomas J. Lapen
- Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204–5007, USA
| | - Minako Righter
- Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204–5007, USA
| | - Rasmus Andreasen
- Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204–5007, USA
- Department of Geoscience, Aarhus University, Aarhus, Denmark
| | - Anthony J. Irving
- Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195–1310, USA
| | - Aaron M. Satkoski
- Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706–1692, USA
- NASA Astrobiology Institute, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - Brian L. Beard
- Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706–1692, USA
- NASA Astrobiology Institute, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - Kunihiko Nishiizumi
- Space Sciences Laboratory, University of California, Berkeley, Berkeley, CA, USA
| | | | - Marc W. Caffee
- Department of Physics, Purdue University, West Lafayette, IN 47907–2036, USA
- Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907–2051, USA
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Barboni M, Boehnke P, Keller B, Kohl IE, Schoene B, Young ED, McKeegan KD. Early formation of the Moon 4.51 billion years ago. SCIENCE ADVANCES 2017; 3:e1602365. [PMID: 28097222 PMCID: PMC5226643 DOI: 10.1126/sciadv.1602365] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 11/29/2016] [Indexed: 05/19/2023]
Abstract
Establishing the age of the Moon is critical to understanding solar system evolution and the formation of rocky planets, including Earth. However, despite its importance, the age of the Moon has never been accurately determined. We present uranium-lead dating of Apollo 14 zircon fragments that yield highly precise, concordant ages, demonstrating that they are robust against postcrystallization isotopic disturbances. Hafnium isotopic analyses of the same fragments show extremely low initial 176Hf/177Hf ratios corrected for cosmic ray exposure that are near the solar system initial value. Our data indicate differentiation of the lunar crust by 4.51 billion years, indicating the formation of the Moon within the first ~60 million years after the birth of the solar system.
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Affiliation(s)
- Melanie Barboni
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Corresponding author.
| | - Patrick Boehnke
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
- Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
| | - Brenhin Keller
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
- Berkeley Geochronology Center, Berkeley, CA 94709, USA
| | - Issaku E. Kohl
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Blair Schoene
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
| | - Edward D. Young
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Kevin D. McKeegan
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90095, USA
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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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Revealing the Earth's mantle from the tallest mountains using the Jinping Neutrino Experiment. Sci Rep 2016; 6:33034. [PMID: 27611737 PMCID: PMC5017162 DOI: 10.1038/srep33034] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 08/18/2016] [Indexed: 12/03/2022] Open
Abstract
The Earth’s engine is driven by unknown proportions of primordial energy and heat produced in radioactive decay. Unfortunately, competing models of Earth’s composition reveal an order of magnitude uncertainty in the amount of radiogenic power driving mantle dynamics. Recent measurements of the Earth’s flux of geoneutrinos, electron antineutrinos from terrestrial natural radioactivity, reveal the amount of uranium and thorium in the Earth and set limits on the residual proportion of primordial energy. Comparison of the flux measured at large underground neutrino experiments with geologically informed predictions of geoneutrino emission from the crust provide the critical test needed to define the mantle’s radiogenic power. Measurement at an oceanic location, distant from nuclear reactors and continental crust, would best reveal the mantle flux, however, no such experiment is anticipated. We predict the geoneutrino flux at the site of the Jinping Neutrino Experiment (Sichuan, China). Within 8 years, the combination of existing data and measurements from soon to come experiments, including Jinping, will exclude end-member models at the 1σ level, define the mantle’s radiogenic contribution to the surface heat loss, set limits on the composition of the silicate Earth, and provide significant parameter bounds for models defining the mode of mantle convection.
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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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Caracausi A, Avice G, Burnard PG, Füri E, Marty B. Chondritic xenon in the Earth’s mantle. Nature 2016; 533:82-5. [DOI: 10.1038/nature17434] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 02/08/2016] [Indexed: 11/09/2022]
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Hallis LJ, Huss GR, Nagashima K, Taylor GJ, Halldórsson SA, Hilton DR, Mottl MJ, Meech KJ. Evidence for primordial water in Earth's deep mantle. Science 2015; 350:795-7. [PMID: 26564850 DOI: 10.1126/science.aac4834] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of Earth can be used to constrain the origin of its water. However, the most accessible reservoir, Earth's oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define Earth's original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep mantle has a low D/H ratio (δD more negative than -218 per mil). Such strongly negative values indicate the existence of a component within Earth's interior that inherited its D/H ratio directly from the protosolar nebula.
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Affiliation(s)
- Lydia J Hallis
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA.
| | - Gary R Huss
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA
| | - Kazuhide Nagashima
- Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA
| | - G Jeffrey Taylor
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA
| | - Sæmundur A Halldórsson
- Scripps Institution of Oceanography, University California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA
| | - David R Hilton
- Scripps Institution of Oceanography, University California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA
| | - Michael J Mottl
- Department of Oceanography, University of Hawai'i, Marine Sciences Building 304, 1000 Pope Road, Honolulu, HI 96822, USA
| | - Karen J Meech
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
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37
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Abstract
One key for understanding the stratification in the deep mantle lies in the determination of the density and structure of matter at high pressures, as well as the density contrast between solid and liquid silicate phases. Indeed, the density contrast is the main control on the entrainment or settlement of matter and is of fundamental importance for understanding the past and present dynamic behavior of the deepest part of the Earth's mantle. Here, we adapted the X-ray absorption method to the small dimensions of the diamond anvil cell, enabling density measurements of amorphous materials to unprecedented conditions of pressure. Our density data for MgSiO3 glass up to 127 GPa are considerably higher than those previously derived from Brillouin spectroscopy but validate recent ab initio molecular dynamics simulations. A fourth-order Birch-Murnaghan equation of state reproduces our experimental data over the entire pressure regime of the mantle. At the core-mantle boundary (CMB) pressure, the density of MgSiO3 glass is 5.48 ± 0.18 g/cm(3), which is only 1.6% lower than that of MgSiO3 bridgmanite at 5.57 g/cm(3), i.e., they are the same within the uncertainty. Taking into account the partitioning of iron into the melt, we conclude that melts are denser than the surrounding solid phases in the lowermost mantle and that melts will be trapped above the CMB.
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Wohlers A, Wood BJ. A Mercury-like component of early Earth yields uranium in the core and high mantle (142)Nd. Nature 2015; 520:337-40. [PMID: 25877203 PMCID: PMC4413371 DOI: 10.1038/nature14350] [Citation(s) in RCA: 79] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 02/20/2015] [Indexed: 11/13/2022]
Affiliation(s)
- Anke Wohlers
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
| | - Bernard J Wood
- Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK
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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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41
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Argon isotopic composition of Archaean atmosphere probes early Earth geodynamics. Nature 2013; 498:87-90. [PMID: 23739427 DOI: 10.1038/nature12152] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 04/02/2013] [Indexed: 11/08/2022]
Abstract
Understanding the growth rate of the continental crust through time is a fundamental issue in Earth sciences. The isotopic signatures of noble gases in the silicate Earth (mantle, crust) and in the atmosphere afford exceptional insight into the evolution through time of these geochemical reservoirs. However, no data for the compositions of these reservoirs exists for the distant past, and temporal exchange rates between Earth's interior and its surface are severely under-constrained owing to a lack of samples preserving the original signature of the atmosphere at the time of their formation. Here, we report the analysis of argon in Archaean (3.5-billion-year-old) hydrothermal quartz. Noble gases are hosted in primary fluid inclusions containing a mixture of Archaean freshwater and hydrothermal fluid. Our analysis reveals Archaean atmospheric argon with a (40)Ar/(36)Ar value of 143 ± 24, lower than the present-day value of 298.6 (for which (40)Ar has been produced by the radioactive decay of the potassium isotope (40)K, with a half-life of 1.25 billion years; (36)Ar is primordial in origin). This ratio is consistent with an early development of the felsic crust, which might have had an important role in climate variability during the first half of Earth's history.
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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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43
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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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Rizo H, Boyet M, Blichert-Toft J, O'Neil J, Rosing MT, Paquette JL. The elusive Hadean enriched reservoir revealed by 142Nd deficits in Isua Archaean rocks. Nature 2012; 491:96-100. [PMID: 23128231 DOI: 10.1038/nature11565] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2012] [Accepted: 08/30/2012] [Indexed: 11/09/2022]
Abstract
The first indisputable evidence for very early differentiation of the silicate Earth came from the extinct (146)Sm-(142)Nd chronometer. (142)Nd excesses measured in 3.7-billion-year (Gyr)-old rocks from Isua (southwest Greenland) relative to modern terrestrial samples imply their derivation from a depleted mantle formed in the Hadean eon (about 4,570-4,000 Gyr ago). As dictated by mass balance, the differentiation event responsible for the formation of the Isua early-depleted reservoir must also have formed a complementary enriched component. However, considerable efforts to find early-enriched mantle components in Isua have so far been unsuccessful. Here we show that the signature of the Hadean enriched reservoir, complementary to the depleted reservoir in Isua, is recorded in 3.4-Gyr-old mafic dykes intruding into the Early Archaean rocks. Five out of seven dykes carry (142)Nd deficits compared to the terrestrial Nd standard, with three samples yielding resolvable deficits down to -10.6 parts per million. The enriched component that we report here could have been a mantle reservoir that differentiated owing to the crystallization of a magma ocean, or could represent a mafic proto-crust that separated from the mantle more than 4.47 Gyr ago. Our results testify to the existence of an enriched component in the Hadean, and may suggest that the southwest Greenland mantle preserved early-formed heterogeneities until at least 3.4 Gyr ago.
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Affiliation(s)
- Hanika Rizo
- Clermont Université, Université Blaise Pascal, Laboratoire Magmas et Volcans, CNRS UMR 6524, IRD R 163, BP 10448, 63000 Clermont-Ferrand, France.
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45
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A dash of deep nebula on the rocks. Nature 2012; 486:40-1. [DOI: 10.1038/486040a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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46
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Kinoshita N, Paul M, Kashiv Y, Collon P, Deibel CM, DiGiovine B, Greene JP, Henderson DJ, Jiang CL, Marley ST, Nakanishi T, Pardo RC, Rehm KE, Robertson D, Scott R, Schmitt C, Tang XD, Vondrasek R, Yokoyama A. A Shorter
146
Sm Half-Life Measured and Implications for
146
Sm-
142
Nd Chronology in the Solar System. Science 2012; 335:1614-7. [PMID: 22461609 DOI: 10.1126/science.1215510] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The extinct p-process nuclide (146)Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its α-decay daughter (142)Nd. Based on analyses of (146)Sm/(147)Sm α-activity and atom ratios, we determined the half-life of (146)Sm to be 68 ± 7 (1σ) million years, which is shorter than the currently used value of 103 ± 5 million years. This half-life value implies a higher initial (146)Sm abundance in the early solar system, ((146)Sm/(144)Sm)(0) = 0.0094 ± 0.0005 (2σ), than previously estimated. Terrestrial, lunar, and martian planetary silicate mantle differentiation events dated with (146)Sm-(142)Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new (146)Sm half-life and ((146)Sm/(144)Sm)(0) values.
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Affiliation(s)
- N. Kinoshita
- Research Facility Center for Science and Technology, University of Tsukuba, Japan
| | - M. Paul
- Racah Institute of Physics, Hebrew University, Jerusalem, Israel 91904
| | - Y. Kashiv
- Department of Physics, University of Notre Dame, Notre Dame, IN 46556–5670, USA
| | - P. Collon
- Department of Physics, University of Notre Dame, Notre Dame, IN 46556–5670, USA
| | - C. M. Deibel
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
- Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 46624, USA
| | - B. DiGiovine
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - J. P. Greene
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - D. J. Henderson
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - C. L. Jiang
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - S. T. Marley
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - T. Nakanishi
- Faculty of Chemistry, Institute of Science and Engineering, Kanazawa University, Japan
| | - R. C. Pardo
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - K. E. Rehm
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - D. Robertson
- Department of Physics, University of Notre Dame, Notre Dame, IN 46556–5670, USA
| | - R. Scott
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - C. Schmitt
- Department of Physics, University of Notre Dame, Notre Dame, IN 46556–5670, USA
| | - X. D. Tang
- Department of Physics, University of Notre Dame, Notre Dame, IN 46556–5670, USA
| | - R. Vondrasek
- Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
| | - A. Yokoyama
- Faculty of Chemistry, Institute of Science and Engineering, Kanazawa University, Japan
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47
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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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48
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Touboul M, Puchtel IS, Walker RJ. 182W evidence for long-term preservation of early mantle differentiation products. Science 2012; 335:1065-9. [PMID: 22345398 DOI: 10.1126/science.1216351] [Citation(s) in RCA: 180] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Late accretion, early mantle differentiation, and core-mantle interaction are processes that could have created subtle (182)W isotopic heterogeneities within Earth's mantle. Tungsten isotopic data for Kostomuksha komatiites dated at 2.8 billion years ago show a well-resolved (182)W excess relative to modern terrestrial samples, whereas data for Komati komatiites dated at 3.5 billion years ago show no such excess. Combined (182)W, (186,187)Os, and (142,143)Nd isotopic data indicate that the mantle source of the Kostomuksha komatiites included material from a primordial reservoir that represents either a deep mantle region that underwent metal-silicate equilibration or a product of large-scale magmatic differentiation of the mantle. The preservation, until at least 2.8 billion years ago, of this reservoir-which likely formed within the first 30 million years of solar system history-indicates that the mantle may have never been well mixed.
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Affiliation(s)
- Mathieu Touboul
- Department of Geology, University of Maryland, College Park, MD 20742, USA.
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49
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Korenaga J. Thermal evolution with a hydrating mantle and the initiation of plate tectonics in the early Earth. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jb008410] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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50
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The tungsten isotopic composition of the Earth's mantle before the terminal bombardment. Nature 2011; 477:195-8. [PMID: 21901010 DOI: 10.1038/nature10399] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Accepted: 07/28/2011] [Indexed: 11/09/2022]
Abstract
Many precious, 'iron-loving' metals, such as gold, are surprisingly abundant in the accessible parts of the Earth, given the efficiency with which core formation should have removed them to the planet's deep interior. One explanation of their over-abundance is a 'late veneer'--a flux of meteorites added to the Earth after core formation as a 'terminal' bombardment that culminated in the cratering of the Moon. Some 3.8 billion-year-old rocks from Isua, Greenland, are derived from sources that retain an isotopic memory of events pre-dating this cataclysmic meteorite shower. These Isua samples thus provide a window on the composition of the Earth before such a late veneer and allow a direct test of its importance in modifying the composition of the planet. Using high-precision (less than 6 parts per million, 2 standard deviations) tungsten isotope analyses of these rocks, here we show that they have a isotopic tungsten ratio (182)W/(184)W that is significantly higher (about 13 parts per million) than modern terrestrial samples. This finding is in good agreement with the expected influence of a late veneer. We also show that alternative interpretations, such as partial remixing of a deep-mantle reservoir formed in the Hadean eon (more than four billion years ago) or core-mantle interaction, do not explain the W isotope data well. The decrease in mantle (182)W/(184)W occurs during the Archean eon (about four to three billion years ago), potentially on the same timescale as a notable decrease in (142)Nd/(144)Nd (refs 3 and 6). We speculate that both observations can be explained if late meteorite bombardment triggered the onset of the current style of mantle convection.
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