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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We thank the NASA Emerging Worlds Program for funding via award #NNX16AI28G and #80NSSC21K0275, and DFG for funding via award RA1797-1. A visit of A.B. at Freie Universität Berlin was funded by DFG CRC-TRR 170 (Project-ID 263649064). We thank M. Feth and K. Hammerschmidt for assistance and discussions. We thank the Smithsonian Institution in Washington, DC, USA, and the Antarctic Meteorite Collection at the NASA Johnson Space Center in Houston, TX, USA, for samples. This is TRR 170 publication no. 168.
The authors declare no competing interests.
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Extended data figures and tables
The expected s-deficit Nd anomalies when using stellar model abundances and an internal 146Nd/144Nd normalization.
The top panel shows the weighted average μiNd compositions for enstatite chondrites (EC), ordinary chondrites (OC), carbonaceous chondrites (CC) and CAIs. The external reproducibility of the JNdi standard (2 s.d.) is shown for each isotope as a grey bar. 143Nd is not represented as any measured deviation is mostly radiogenic. The bottom panel shows the relative contributions of p-, s- and r-process nucleosynthesis for each Nd isotope are show below as percentages10.
A) μ142Nd versus μ145Nd, B) 142Nd versus 148Nd, (C) For μ142Nd versus μ150Nd, D) μ148Nd versus μ150Nd, E) 145Nd versus 148Nd, and F) 145Nd versus 150Nd. The modelled s-deficit lines (black) for an Earth with present-day μ142Nd = 0 ± 1.1 are plotted. Group averages are from Supplementary Tables 1 and 4: enstatite chondrites, ordinary chondrites, carbonaceous chondrites, CAIs, Allende and CAI-free Allende are plotted in each figure. Also plotted are group averages using only data from Burkhardt et al.1. for enstatite chondrites, ordinary chondrites, Allende and CAI-free Allende. In each figure, the stellar s-deficit line is shown as solid black, the SiC s-deficit line is shown as dotted black and the chondrite leachate s-deficit line is shown as dashed black. For A, B and C that plot μ142Nd on the y axis, the modelled s-deficit lines (green) for an Earth with present-day μ142Nd = −7.3 ± 1.6 (green diamond) are plotted. The mixing lines between CAI’s and CAI-free Allende that go through the Allende values are shown in solid grey. All μ142Nd values for CAIs and chondrites have been corrected for radiogenic ingrowth. All uncertainties show the 95% CI for the weighted group average. Where no error bars are shown, the symbols for the respective compositions are larger than the errors. Note that for diagrams D–F that do not plot μ142Nd on the y axis, all Earth μNd values are 0 and only one set of s-deficit lines are needed and used. In these diagrams, all of the group averages show that the differences in chondrites and Earth at 0 are consistent with s-process abundance differences and confirms earlier studies1. The deviations in the carbonaceous chondrite group average from the s-deficit lines relative to Earth in E and F, may reflect and additional and poorly constrained Nd isotope component in the CC nebular region not found in the inner Solar System. Alternatively, it may reflect the lack of removal of a CAI component in these rocks, which cannot be done without additional study (i.e. not enough data for CAIs on these meteorites. In all 6 diagrams, the group averages using all data from the literature and this study (Supplementary Table 2) are consistent within uncertainty to group averages using only data from Burkhardt et al,1. Slopes for the s-deficit lines for each diagram is from Burkhardt et al.1. See main text for additional discussion.
Compilation of measured and calculated Nd isotope compositions for bulk chondrites, CAIs and the present-day accessible mantle. Reference numbers listed as [XX]. Values not used in group averages in grey shading. μ148Nd values for Berlin measurements (this study) are highlighted in green shade and not used in group averages. See Methods for discussion on data filtering.
Nd isotope ratios and values for samples and standards analysed in this study. Measured 143Nd/144Nd Values are reported in Extended Data Table 3.
Measured and corrected 142Nd values.
Average Nd isotope compositions for chondritic and terrestrial sample groups.
Compilation of Nd isotope data used to calculate group averages for Allende CAIs and Allende.
Values used for collisional erosion models in Fig. 2. Equations used for Sm–Nd isotope evolution are adapted from ref. 24 (Supplementary equations (1) and (2)).
Values used for mixing models in Fig. 3.
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Johnston, S., Brandon, A., McLeod, C. et al. Nd isotope variation between the Earth–Moon system and enstatite chondrites. Nature 611, 501–506 (2022). https://doi.org/10.1038/s41586-022-05265-0