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Title: A nucleosynthetic origin for the Earth’s anomalous 142Nd composition

Journal Article · · Nature (London)
DOI:https://doi.org/10.1038/nature18956· OSTI ID:1395508
 [1];  [2];  [3];  [3];  [4];  [5]
  1. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences and Enrico Fermi Inst.; Munster Univ. (Germany). Inst. for Planetology
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Munster Univ. (Germany). Inst. for Planetology; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  4. Univ. of Chicago, IL (United States). Dept. of Geophysical Sciences and Enrico Fermi Inst.
  5. Munster Univ. (Germany). Inst. for Planetology

A long-standing paradigm assumes that the chemical and isotopic compositions of many elements in the bulk silicate Earth are the same as in chondrites(1-4). But, the accessible Earth has a greater Nd-142/Nd-144 ratio than do chondrites. Because Nd-142 is the decay product of the now-extinct Sm-146 (which has a half-life of 103 million years(5)), this Nd-142 difference seems to require a higher-than-chondritic Sm/Nd ratio for the accessible Earth. This must have been acquired during global silicate differentiation within the first 30 million years of Solar System formation(6) and implies the formation of a complementary Nd-142-depleted reservoir that either is hidden in the deep Earth(6), or lost to space by impact erosion(3,7). Whether this complementary reservoir existed, and whether or not it has been lost from Earth, is a matter of debate(3,8,9), and has implications for determining the bulk composition of Earth, its heat content and structure, as well as for constraining the modes and timescales of its geodynamical evolution(3,7,9,10). We show that, compared with chondrites, Earth's precursor bodies were enriched in neodymium that was produced by the slow neutron capture process (s-process) of nucleosynthesis. This s-process excess leads to higher Nd-142/Nd-144 ratios; after correction for this effect, the Nd-142/Nd-144 ratios of chondrites and the accessible Earth are indistinguishable within five parts per million. The Nd-142 offset between the accessible silicate Earth and chondrites therefore reflects a higher proportion of s-process neodymium in the Earth, and not early differentiation processes. Our results obviate the need for hidden-reservoir or super-chondritic Earth models and imply a chondritic Sm/Nd ratio for the bulk Earth. Although chondrites formed at greater heliocentric distances and contain a different mix of presolar components than Earth, they nevertheless are suitable proxies for Earth's bulk chemical composition.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1395508
Report Number(s):
LLNL-JRNL-689320; nature18956
Journal Information:
Nature (London), Vol. 537, Issue 7620; ISSN 0028-0836
Publisher:
Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 114 works
Citation information provided by
Web of Science

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Cited By (14)

Feedstocks of the Terrestrial Planets journal November 2018
Effect of Serpentinite Dehydration in Subducting Slabs on Isotopic Diversity in Recycled Oceanic Crust and Its Role in Isotopic Heterogeneity of the Mantle journal November 2019
Hot and Heterogenous High‐ 3 He/ 4 He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island journal December 2019
The isotopic nature of the Earth’s accreting material through time journal January 2017
Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth journal May 2019
In search of the Earth-forming reservoir: Mineralogical, chemical, and isotopic characterizations of the ungrouped achondrite NWA 5363/NWA 5400 and selected chondrites journal March 2017
The potential science and engineering value of samples delivered to Earth by Mars sample return: International MSR Objectives and Samples Team (iMOST) journal March 2019
Early formation of the Moon 4.51 billion years ago journal January 2017
Redox States of Initial Atmospheres Outgassed on Rocky Planets and Planetesimals journal July 2017
Nucleosynthetic Sr–Nd Isotope Correlations in Chondrites: Evidence for Nebular Thermal Processing and Dust Transportation in the Early Solar System journal July 2019
Xenon Isotopes Identify Large-scale Nucleosynthetic Heterogeneities across the Solar System journal January 2020
The potential science and engineering value of samples delivered to Earth by Mars sample return journal March 2019
The potential science and engineering value of samples delivered to Earth by Mars sample return text January 2019
Xenon Isotopes Identify Large-scale Nucleosynthetic Heterogeneities across the Solar System text January 2020