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Introduction

The leading hypothesis for the formation of the Earth–Moon system is the Giant Impact hypothesis where a Mars-sized object collided with the growing proto-Earth (Cameron and Ward, 1976

Cameron, A.G.W., Ward, W.R. (1976) The origin of the Moon. Lunar and Planetary Science Conference 7, 120.

; Canup, 2004

Canup, R.M. (2004) Dynamics of lunar formation. Annual Review of Astronomy and Astrophysics 42, 441–475. https://doi.org/10.1146/annurev.astro.41.082201.113457

), which may have resulted in a globally molten Moon known as the lunar magma ocean (LMO; Wood et al., 1970

Wood, J.A., Dickey, J.S., Jr., Marvin, U.B., Powell, B.N. (1970) Lunar anorthosites and a geophysical model of the moon. Proceedings of the Apollo 11 Lunar Science Conference 1, 965–988.

; Warren, 1985

Warren, P.H. (1985) The magma ocean concept and lunar evolution. Annual Review of Earth and Planetary Sciences 13, 201–240. https://doi.org/10.1146/annurev.ea.13.050185.001221

). The LMO model explains the proposed structure of the lunar interior, with dense mafic materials forming the mantle (the source of mare basalts), ferroan anorthosite forming the crust, and a residual liquid with high concentrations of incompatible elements potassium, rare-earth elements, and phosphorus (KREEP) crystallising between the two (Warren, 1985

Warren, P.H. (1985) The magma ocean concept and lunar evolution. Annual Review of Earth and Planetary Sciences 13, 201–240. https://doi.org/10.1146/annurev.ea.13.050185.001221

). The density difference between some crustal materials (ilmenite-bearing cumulates) and mantle materials caused a so-called mantle overturn, which allowed magmas to intrude the anorthositic crust forming the plutonic Mg-suite rocks (Shearer et al., 2015

Shearer, C.K., Elardo, S.M., Petro, N.E., Borg, L.E., McCubbin, F.M. (2015) Origin of the lunar highlands Mg-suite: An integrated petrology, geochemistry, chronology, and remote sensing perspective. American Mineralogist 100, 294–325. https://doi.org/10.2138/am-2015-4817

).

The timing of the Giant Impact and LMO crystallisation is debated (Borg et al., 2015

Borg, L.E., Gaffney, A.M., Shearer. C.K. (2015) A review of lunar chronology revealing a preponderance of 4.34–4.37 Ga ages. Meteoritics and Planetary Science 50, 715–732. https://doi.org/10.1111/maps.12373

). The ¹⁸²Hf-¹⁸²W radiogenic systematics (Thiemens et al., 2019

Thiemens, M.M., Sprung, P., Fonseca, R.O.C., Leitzke, F.P., Münker, C. (2019) Early Moon formation inferred from hafnium–tungsten systematics. Nature Geoscience 12, 696–700. https://doi.org/10.1038/s41561-019-0398-3

), Hf model ages of lunar zircons (Barboni et al., 2017

Barboni, M., Boehnke, P., Keller, B., Kohl, I.E., Schoene, B., Young, E.D., McKeegan, K.D. (2017) Early formation of the Moon 4.51 billion years ago. Science Advances 3. https://doi.org/10.1126/sciadv.1602365

), and dynamical modelling (Bottke et al., 2015

Bottke, W.F., Vokrouhlicky, D., Marchi, S., Swindle, T., Scott, E.R.D., Weirich, J.R., Levison, H. (2015) Dating the Moon-forming impact event with asteroidal meteorites. Science 348, 321–323. https://doi.org/10.1126/science.aaa0602

) place the Moon-forming event early in the solar system’s history, between 4.52 to 4.47 Ga. In contrast, lunar Pb model ages (Connelly and Bizzarro, 2016

Connelly, J.N., Bizzarro, M. (2016) Lead isotope evidence for a young formation age of the Earth–Moon system. Earth and Planetary Science Letters 452, 36–43. https://doi.org/10.1016/j.epsl.2016.07.010

) and thermal modelling (Maurice et al., 2020

Maurice, M., Tosi, N., Schwinger, S., Breuer, D., Kleine, T. (2020) A long-lived magma ocean on a young Moon. Science advances 6. https://doi.org/10.1126/sciadv.aba8949

) place it in the range of 4.43 to 4.42 Ga. A precise lower age limit for LMO crystallisation is given in Nemchin et al. (2009)

Nemchin, A., Timms, N., Pidgeon, R., Geisler, T., Reddy, S., Meyer, C. (2009) Timing of crystallization of the lunar magma ocean constrained by the oldest zircon. Nature Geoscience 2, 133–136. https://doi.org/10.1038/ngeo417

, which reported a ²⁰⁷Pb/²⁰⁶Pb date of 4417 ± 6 Ma measured by sensitive high-resolution ion microprobe (SHRIMP) for a zircon grain from the Apollo impact melt breccia 72215. Later Giant Impact and LMO crystallisation are favoured by the concordant formation of the source of mare basalts, selected ferroan anorthosites, Mg-suite rocks, and zircons (primarily derived from the Mg-suite) at ∼4.3 Ga (Borg et al., 2015

Borg, L.E., Gaffney, A.M., Shearer. C.K. (2015) A review of lunar chronology revealing a preponderance of 4.34–4.37 Ga ages. Meteoritics and Planetary Science 50, 715–732. https://doi.org/10.1111/maps.12373

).

The vast majority of lunar zircon crystallisation was likely part of, or post-dated, the urKREEP – the primordial KREEP component – because of the enrichment in incompatible elements (those remaining in the melt until the last rock suite is solidified) needed to form this mineral (e.g., Warren and Wasson, 1979

Warren, P.H., Wasson, J.T. (1979) The origin of KREEP. Reviews of Geophysics 17, 73–88. https://doi.org/10.1029/RG017i001p00073

), and therefore occurred at, and after, the late stage of the LMO crystallisation. The U-Pb system in zircon is a particularly robust chronometer, as zircon readily incorporates U and excludes Pb from crystal lattices, and zircon is a refractory mineral both structurally and geochemically resistant to post-crystallisation thermal alteration (Finch and Hanchar, 2003

Finch, R.J., Hanchar. J.M. (2003) Structure and chemistry of zircon and zircon-group minerals. Reviews in mineralogy and geochemistry 53, 1–25. https://doi.org/10.1515/9781501509322-004

). The U-Pb chronology of the oldest lunar zircon would thus provide constraints on the LMO crystallisation and the minimum timing of the Giant Impact.

Zhang et al. (2021)

Zhang, B., Lin, Y., Moser, D.E., Hao, J., Liu, Y., Zhang, J., Barker, I.R., Li, Q., Shieh, S.R., Bouvier, A. (2021) Radiogenic Pb mobilization induced by shock metamorphism of zircons in the Apollo 72255 Civet Cat norite clast. Geochimica et Cosmochimica Acta 302, 175–192. https://doi.org/10.1016/j.gca.2021.03.012

reported the U-Pb isotopic composition of 21 zircon grains measured with nanoscale secondary ionisation mass spectrometry (NanoSIMS) on a total of 42 spots in the Apollo 17 72255 Civet Cat norite clast (Meyer, 2009

Meyer, C. (2009) Lunar Sample Compendium. Astromaterials Research & Exploration Science, National Aeronautics and Space Administration, https://curator.jsc.nasa.gov/lunar/lsc/.

). The euhedral and subhedral zircon grains in this sample are small (10 to 25 μm in length; Fig. 1). The oldest six spots on these zircon grains have a concordant U-Pb average date of 4460 ± 31 Ma and define a weighted mean ²⁰⁷Pb/²⁰⁶Pb date of 4453 ± 34 Ma (all 2σ uncertainties). These dates have the potential to constrain the lower limit of the timing of the Giant Impact and LMO crystallisation at 4460 Ma. These ancient zircon dates reported by Zhang et al. (2021)

Zhang, B., Lin, Y., Moser, D.E., Hao, J., Liu, Y., Zhang, J., Barker, I.R., Li, Q., Shieh, S.R., Bouvier, A. (2021) Radiogenic Pb mobilization induced by shock metamorphism of zircons in the Apollo 72255 Civet Cat norite clast. Geochimica et Cosmochimica Acta 302, 175–192. https://doi.org/10.1016/j.gca.2021.03.012

could result either from unsupported Pb clusters caused by radiogenic Pb mobilisation or from Pb-retention domains that survived normal Pb loss. In the former scenario, radiogenic Pb mobilisation could compromise the authenticity of zircon U-Pb dates (Kusiak et al., 2013a

Kusiak, M.A., Whitehouse, M.J., Wilde, S.A., Dunkley, D.J., Menneken, M., Nemchin, A.A., Clark, C. (2013a) Changes in zircon chemistry during Archean UHT metamorphism in the Napier Complex, Antarctica. American Journal of Science 313, 933–967. https://doi.org/10.2475/09.2013.05

,b

Kusiak, M.A., Whitehouse, M.J., Wilde, S.A., Nemchin, A.A., Clark C. (2013b) Mobilization of radiogenic Pb in zircon revealed by ion imaging: Implications for early Earth geochronology. Geology 41, 291–294. https://doi.org/10.1130/G33920.1

; Ge et al., 2019

Ge, R., Wilde, S.A., Nemchin, A.A., Whitehouse, M.J., Bellucci, J.J., Erickson, T.M. (2019) Mechanisms and consequences of intra-crystalline enrichment of ancient radiogenic Pb in detrital Hadean zircons from the Jack Hills, Western Australia. Earth and Planetary Science Letters 517, 38–49. https://doi.org/10.1016/j.epsl.2019.04.005

), while in the latter, the widespread U-Pb dates of the Civet Cat norite zircons are due to normal Pb loss in some of the crystal domains (Arcuri et al., 2020

Arcuri, G.A., Moser, D.E., Reinhard, D.A., Langelier, B., Larson, D.J. (2020) Impact-triggered nanoscale Pb clustering and Pb loss domains in Archean zircon. Contributions to Mineralogy and Petrology 175, 1–13. https://doi.org/10.1007/s00410-020-01698-w

).

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Methods

We used atom-probe tomography (APT), a time-of-flight mass spectrometry method with nanoscale spatial resolution, to investigate the Pb spatial distribution within an old lunar zircon domain to test if the ancient zircon dates in the Civet Cat norite obtained by Zhang et al. (2021)

Zhang, B., Lin, Y., Moser, D.E., Hao, J., Liu, Y., Zhang, J., Barker, I.R., Li, Q., Shieh, S.R., Bouvier, A. (2021) Radiogenic Pb mobilization induced by shock metamorphism of zircons in the Apollo 72255 Civet Cat norite clast. Geochimica et Cosmochimica Acta 302, 175–192. https://doi.org/10.1016/j.gca.2021.03.012

are authentic or potentially affected by nanoscale redistribution and clustering processes. Because zircon Z14 (²⁰⁷Pb/²⁰⁶Pb date = 4453 ± 34 Ma, Th/U ≈ 7.2) has one of the six oldest domains in the Civet Cat norite, we selected it for APT analysis to investigate its Pb distribution at the nanoscale. During APT analyses, surface atoms of a sample nanotip are field-evaporated in a high electric field thermally activated by picosecond laser pulses and analysed with a position-sensitive time-of-flight mass spectrometer, yielding 3-D atom-by-atom distributions of elements and their isotopes with nanoscale spatial resolution (Fig. 2).

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APT has been used in conjunction with secondary ion mass spectrometry (SIMS) to investigate Pb mobility at the nanoscale and reliably date 4.4 Ga Hadean zircon from Jack Hills (Valley et al., 2014

Valley, J.W., Cavosie, A.J., Ushikubo, T., Reinhard, D.A., Lawrence, D.F., Larson, D.J., Clifton, P.H., Kelly, T.F., Wilde, S.A., Moser, D.E., Spicuzza, M.J. (2014) Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience 7, 219–223. https://doi.org/10.1038/ngeo2075

; Valley et al., 2015

Valley, J.W., Reinhard, D.A., Cavosie, A.J., Ushikubo, T., Lawrence, D.F., Larson, D.J., Kelly, T.F., Snoeyenbos, D.R., Strickland, A. (2015) Nano-and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals. American Mineralogist 100, 1355–1377. https://doi.org/10.2138/am-2015-5134

) and 3.8 Ga Archean zircons from Beartooth Mountains (Blum et al., 2018

Blum, T.B., Reinhard, D.A., Chen, Y. Prosa, T.J., Larson, D.J., Valley, J.W. (2018) Uncertainty and sensitivity analysis for spatial and spectral processing of Pb isotopes in zircon by atom probe tomography. In: Moser, D.E., Corfu, F., Darling, J.R., Reddy, S.M., Tait, K. (Eds.) Microstructural Geochronology: Planetary Records Down to Atom Scale, American Geophysical Union, 327–350. https://doi.org/10.1002/9781119227250.ch16

); other studies have used APT to look at lunar Pb-bearing minerals (i.e. Blum et al., 2019

Blum, T.B., Reinhard, D.A., Coble, M.A., Spicuzza, M.J., Chen, Y., Cavosie, A.J., Nasdala, L., Chanmuang, C., Prosa, T.J., Larson, D.J., Valley, J.W. (2019) A Nanoscale Record of Impact-Induced Pb Mobility in Lunar Zircon. Microscopy and Microanalysis 25, 2448–2449. https://doi.org/10.1017/S1431927619012972

; White et al., 2019

White, L.F., Moser, D.E., Tait, K.T., Langelier, B., Barker, I., Darling, J.R. (2019) Crystallization and impact history of a meteoritic sample of early lunar crust (NWA 3163) refined by atom probe geochronology. Geoscience Frontiers 10, 1841–1848. https://doi.org/10.1016/j.gsf.2018.11.005

). Valley et al. (2014)

Valley, J.W., Cavosie, A.J., Ushikubo, T., Reinhard, D.A., Lawrence, D.F., Larson, D.J., Clifton, P.H., Kelly, T.F., Wilde, S.A., Moser, D.E., Spicuzza, M.J. (2014) Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nature Geoscience 7, 219–223. https://doi.org/10.1038/ngeo2075

demonstrated that nanoscale Pb clustering is associated with Y clustering, which is the result of the enrichment of less compatible elements after the formation of the zircon given sufficient atomic mobility. The Pb clusters detected in these samples, while demonstrating heterogeneity in Pb distribution, are much smaller than the size of the SIMS pit used to date the zircon (clusters are ∼10 nm in diameter whereas pits produced by the SIMS primary beam have diameters of 5 to 10s of μm) and are therefore homogenous when averaged over the scale of the SIMS analysis. APT has several orders of magnitude greater spatial resolution (near-atomic) than the previous analyses of this zircon using NanoSIMS, which for this analysis produced a pit size of a few μm across to analyse a statistically significant number of atoms to produce a date.

Details on the sample preparation methods and analytical conditions can be found in the supplementary information.

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Results

A total of five nanotips were successfully produced from a lamella of zircon Z14 lifted out of two pits (Fig. 1, Fig. S-1) produced by NanoSIMS analyses. The nanotips were shaped to sample a volume immediately adjacent to the material analysed by NanoSIMS, and as to not include material that had been amorphised due to the primary ion beam damage created by the NanoSIMS, the nanotips were instead extracted from a depth of several hundreds of nanometres beneath the analysed surface. Species that were detected in APT include the major elements in zircon (Zr, Si, O), Y, Hf, Pb, Th, H, and oxide/hydride molecular ions (Fig. 2, Fig. S-2). The only isotope of Pb detected above background is ²⁰⁸Pb²⁺, which can be used as a proxy for all Pb radiogenic isotopes as they are expected to exhibit the same chemical behaviour during secondary alteration processes such as shock metamorphism (e.g., Deutsch and Schärer, 1990

Deutsch, A., Schärer, U. (1990) Isotope systematics and shock-wave metamorphism: I. U-Pb in zircon, titanite and monazite, shocked experimentally up to 59 GPa. Geochimica et Cosmochimica Acta 54, 3427–3434. https://doi.org/10.1016/0016-7037(90)90295-V

). In the 3D tomographic reconstructions of the datasets, we found no evidence of clustering of Pb, Y, or any other elements. We used the nearest neighbour distribution analysis (Stephenson et al., 2007

Stephenson, L.T., Moody, M.P., Liddicoat, P.V., Ringer, S.P. (2007) New techniques for the analysis of fine-scaled clustering phenomena within atom probe tomography (APT) data. Microscopy and Microanalysis 13, 448–463. https://doi.org/10.1017/S1431927607070900

), one of the most robust ways to assess heterogeneity in concentration, including clustering. In the nearest neighbour analysis, each Pb atom was examined for the closest distance to the next Pb atom, and the frequency distribution of the distances was plotted (red, Fig. 3). This was then compared to a randomised distribution of points (black, Fig. 3) with the same volume concentration as in the dataset. This method is very sensitive to any type of inhomogeneity as concentration gradients would cause broadening of the distributions (Stephenson et al., 2007

Stephenson, L.T., Moody, M.P., Liddicoat, P.V., Ringer, S.P. (2007) New techniques for the analysis of fine-scaled clustering phenomena within atom probe tomography (APT) data. Microscopy and Microanalysis 13, 448–463. https://doi.org/10.1017/S1431927607070900

).

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Validating the Oldest Lunar Zircon Age

All datasets had prominent 104 Da peaks (²⁰⁸Pb²⁺) above background. There is an isobaric overlap at 104 Da with ²⁸Si₂¹⁶O₃⁺. However, other peaks associated with this molecular ion (e.g., ²⁸Si²⁹Si¹⁶O₃⁺ at 105 Da) in the terrestrial/lunar abundance pattern are not present. Instead, the isotopic pattern of 105–110 Da matches that of the distribution of Zr¹⁶O²⁺ molecular species, which does not overlap with the 104 Da peak. Therefore, we conclude that the 104 Da peak is ²⁰⁸Pb²⁺. Even in hypothetical samples where the peak at 104 Da would represent the combined concentration of ²⁰⁸Pb²⁺ and ²⁸Si₂¹⁶O₃⁺, any Pb clustering, if present, would be observable in the dataset from the combined peak if the Pb signal which contributes to the 104 Da peak is above background. Additionally, we determined our method is robust and not sensitive to the peak brackets or windows (referred to as the peak ranges in APT), for which Pb abundances are determined; ranging does not affect the result of the nearest neighbour distribution and clustering (Fig. S-3).

Valley et al. (2015)

Valley, J.W., Reinhard, D.A., Cavosie, A.J., Ushikubo, T., Lawrence, D.F., Larson, D.J., Kelly, T.F., Snoeyenbos, D.R., Strickland, A. (2015) Nano-and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals. American Mineralogist 100, 1355–1377. https://doi.org/10.2138/am-2015-5134

reported correlated clustering for both the Pb and Y distributions. The most prominent Y peak occurs at 29.67 Da, corresponding to ⁸⁹Y³⁺. While only Tip A has this Y peak above background (Fig. S-4), there are no major overlaps at this position, so this determination is unambiguous. In Valley et al. (2015)

Valley, J.W., Reinhard, D.A., Cavosie, A.J., Ushikubo, T., Lawrence, D.F., Larson, D.J., Kelly, T.F., Snoeyenbos, D.R., Strickland, A. (2015) Nano-and micro-geochronology in Hadean and Archean zircons by atom-probe tomography and SIMS: New tools for old minerals. American Mineralogist 100, 1355–1377. https://doi.org/10.2138/am-2015-5134

, the Y clusters were more prominent than the Pb clusters and thus can be used as a proxy when Pb concentration is low. In addition, even if ²⁸Si₂¹⁶O₃⁺ significantly contributes to the signal at 104 Da, the absence of Y clusters (Fig. 4) at the overlap-free 29.67 Da peak implies that there is no Pb clustering, thus demonstrating that the zircon is homogenous on the nanoscale for all detected species. While the absence of clustering in one dataset may suggest a larger inter-cluster distance compared to the sampled volume, it is noteworthy that none of the sampled volumes display any clusters (Fig. 3). This observation remains consistent even when the volumes are separated by distances of 1–2 μm, indicating the absence of nanoscale clustering within the analysed domain of this zircon (a volume that spans ∼7 μm across the zircon and comprises a total analysed volume of ∼1 μm in length, larger than the NanoSIMS spot size of ∼5 μm).

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There are heterogeneities in the Pb distribution at the microscale, as shown by Zhang et al. (2021)

Zhang, B., Lin, Y., Moser, D.E., Hao, J., Liu, Y., Zhang, J., Barker, I.R., Li, Q., Shieh, S.R., Bouvier, A. (2021) Radiogenic Pb mobilization induced by shock metamorphism of zircons in the Apollo 72255 Civet Cat norite clast. Geochimica et Cosmochimica Acta 302, 175–192. https://doi.org/10.1016/j.gca.2021.03.012

; however, this cannot be due to the mixing of Pb nanoclusters. NanoSIMS analyses that report younger dates sampled domains with Pb-loss which occurred post-crystallisation, while the oldest dates sampled domains where radiogenic Pb was retained. The other explanation for these ancient dates, the presence of clusters of radiogenic Pb due to mobilisation, is ruled out by our APT analyses. We conclude that the weighted average date of 4460 ± 31 Ma (2σ) obtained for these zircons corresponds to its crystallisation age. Therefore, the minimum formation age of this old zircon population is the oldest evidence found to date for lunar zircon crystallisation.

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Anchoring the Age of the Moon

Lunar silicate samples show ¹⁸²W excesses due to the decay of ¹⁸²Hf (with a half-life of ∼8.9 Myr), and because of this, the Moon should have formed at ∼4.51 Ga (Thiemens et al., 2019

Thiemens, M.M., Sprung, P., Fonseca, R.O.C., Leitzke, F.P., Münker, C. (2019) Early Moon formation inferred from hafnium–tungsten systematics. Nature Geoscience 12, 696–700. https://doi.org/10.1038/s41561-019-0398-3

). Thermal modelling by Elkins-Tanton et al. (2011)

Elkins-Tanton, L.T., Burgess, S., Yin, Q.-Z. (2011) The lunar magma ocean: Reconciling the solidification process with lunar petrology and geochronology. Earth and Planetary Science Letters 304, 326–336. https://doi.org/10.1016/j.epsl.2011.02.004

suggests that lunar differentiation took place rapidly, with 80 vol. % of the LMO solidified within thousands of years. With this timeframe, the Civet Cat norite zircon age (4.46 Ga) given by Zhang et al. (2021)

Zhang, B., Lin, Y., Moser, D.E., Hao, J., Liu, Y., Zhang, J., Barker, I.R., Li, Q., Shieh, S.R., Bouvier, A. (2021) Radiogenic Pb mobilization induced by shock metamorphism of zircons in the Apollo 72255 Civet Cat norite clast. Geochimica et Cosmochimica Acta 302, 175–192. https://doi.org/10.1016/j.gca.2021.03.012

is a strong indication that the LMO had largely solidified by then. The ²⁰⁷Pb/²⁰⁶Pb date of the zircon (4.42 Ga) from Apollo 72215 likely points to the formation of the evolved, late-forming alkali suite in the lunar crust (Nemchin et al., 2009

Nemchin, A., Timms, N., Pidgeon, R., Geisler, T., Reddy, S., Meyer, C. (2009) Timing of crystallization of the lunar magma ocean constrained by the oldest zircon. Nature Geoscience 2, 133–136. https://doi.org/10.1038/ngeo417

). The concordant formation ages for the source of mare basalts, some ferroan anorthosites and Mg-suite rocks, and numerous zircons at ∼4.3 Ga may mark a secondary large-scale event on the near side of the Moon. Subsequent bombardment events reworked or melted the earliest crust, modifying parts of the Civet Cat norite zircons, while pristine domains were preserved. The significance of the 4.46 Ga age holds on the preservation of domains within a grain despite post-crystallisation processes; such preservation is demonstrated by nanoscale analyses.

These findings require pushing the timing of the solidification of the lunar crust to within at least the first 100 Myr of the formation of the solar system and provide a minimum age for the Giant Impact event that formed the Earth-Moon system. Together with ¹⁸²Hf-¹⁸²W isotopic evidence that the core-mantle differentiation of the Moon occurred ∼50 Myr after the formation of the solar system (Thiemens et al., 2019

Thiemens, M.M., Sprung, P., Fonseca, R.O.C., Leitzke, F.P., Münker, C. (2019) Early Moon formation inferred from hafnium–tungsten systematics. Nature Geoscience 12, 696–700. https://doi.org/10.1038/s41561-019-0398-3

), we can now place an age bracket on the timing of the Giant Impact, subsequent LMO crystallisation and the onset of Mg-suite magmatism to between 4.51 and 4.46 Ga. This serves as an anchoring age interval for the onset of the intense gravitational effects that the early, much closer Moon had on the young Earth, as well as when the Moon began recording a history of bombardments.

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Acknowledgements

We are indebted to the NASA Apollo program and astronauts for collecting the samples, and to Ryan Zeigler and the curation team of NASA Johnson Space Center for allocating the lunar samples used in this research. JG acknowledges funding from the Field Museum’s Women’s Board Women in Science Graduate Fellowship. PRH acknowledges funding from the TAWANI Foundation. BZ’s work is supported by NASA grants 80NSSC19K1238 and 80NSSC23K0035. Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with grants from the NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, N00014-0910781, N00014-1712870) programs. NUCAPT received support from the MRSEC program (NSF DMR-2308691) at the Materials Research Center, the SHyNE Resource (NSF ECCS-2025633), and the Initiative for Sustainability and Energy (ISEN) at Northwestern University. We also thank the constructive reviews from an anonymous reviewer and editor Romain Tartèse.

Editor: Romain Tartèse

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References

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Supplementary Information

The Supplementary Information includes:

• Methods
• Table S-1
• Figures S-1 to S-4
• Supplementary Information References

Download the Supplementary Information (PDF)