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Using isotope analysis of ancient (4555 Ma) radiogenic Pb by ID-TIMS as an example, I evaluate the sample size required to achieve the target precision of the 207Pb/206Pb ratio 0.007% (2σ), corresponding to the uncertainty of the 207Pb*/206Pb* age of 0.1 million years, considering various analytical uncertainties. In a hypothetical perfect analytical setup that would enable measuring isotopic ratios without noise, losses and biases, this precision can be achieved by analysis of a sample containing 2.9 picograms of Pb. Assessment of the sources of noise, loss and bias introduced by sample preparation and mass spectrometry shows that incomplete ionization of Pb during evaporation from the filament and baseline noise of a mass spectrometer make the greatest contributions to the additional uncertainty. Subtraction of analytical blank and minor spike isotopes can also substantially increase the uncertainty under some analytical conditions. The contributions from the other sources are smaller, but can become significant if a higher precision level is sought.

Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. The ¹⁷⁶Lu− ¹⁷⁶Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of silicate differentiation on Earth, but the data interpretation requires accurate estimation of Hf isotope evolution of the bulk Earth. Because both Lu and Hf are refractory lithophile elements, the isotope evolution can be potentially extrapolated from the present-day ¹⁷⁶Hf/ ¹⁷⁷Hf and ¹⁷⁶Lu/ ¹⁷⁷Hf in undifferentiated chondrite meteorites. However, these ratios in chondrites are highly variable due to the metamorphic redistribution of Lu and Hf, making it difficult to ascertain the correct reference values for the bulk Earth. In addition, it has been proposed that chondrites contain excess ¹⁷⁶Hf due to the accelerated decay of ¹⁷⁶Lu resulting from photoexcitation to a short-lived isomer. If so, the paradigm of a chondritic Earth would be invalid for the Lu−Hf system. Herein we report the first, to our knowledge, high-precision Lu−Hf isotope analysis of meteorite crystalline zircon, a mineral that is resistant to metamorphism and has low Lu/Hf. We use the meteorite zircon data to define the Solar System initial ¹⁷⁶Hf/ ¹⁷⁷Hf (0.279781 ± 0.000018) and further to identify pristine chondrites that contain no excess ¹⁷⁶Hf and accurately represent the Lu−Hf system of the bulk Earth ( ¹⁷⁶Hf/ ¹⁷⁷Hf = 0.282793 ± 0.000011; ¹⁷⁶Lu/ ¹⁷⁷Hf = 0.0338 ± 0.0001). Our results provide firm evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir on Earth as far back as 4.5 billion years ago. Significance The radioactive decay of lutetium-176 to hafnium-176 has been used to study Earth’s crust−mantle differentiation that is the primary agent of the chemical and thermal evolution of the silicate Earth. Yet the data interpretation requires a well-defined hafnium isotope growth curve of the bulk Earth, which is notoriously difficult to reconstruct from the variable bulk compositions of undifferentiated chondrite meteorites. Here we use lutetium–hafnium systematics of meteorite zircon crystals to define the initial hafnium isotope composition of the Solar System and further to identify pristine chondrites that are the best representative of the lutetium–hafnium system of the bulk Earth. The established bulk Earth growth curve provides evidence for Earth’s crust−mantle differentiation as early as 4.5 billion years ago.

We report developing a procedure for measuring concentrations of U, Th and Pb (including all natural Pb isotopes) to establish the distribution of these elements in meteorite minerals and correctly interpret Pb-isotopic ages of meteorites. The concentrations were measured on KBSI SHRIMP IIe by peak jumping using a discrete-dynode secondary electron multiplier. The concentrations were calculated relative to BCR-2G glass and monitored by analysis of the NIST glasses SRM-615 and SRM-617 as secondary reference materials. The detection limits using the spot sizes of ca. 180 μm2, primary O2− beam current of 10.6 nA, and with amplifier dark noise of 0.015 counts per second are ~ 0.2 parts per billion (ppb) for U (500 s integration), ~ 0.6 ppb for Pb (100 s integration for each of the major isotopes), and ~ 1.2 ppb for Th (100 s integration). Analyses of the NIST glasses confirm that the measured concentrations of U and Th are consistent with their certified values, while the Pb concentrations are about four times too low, most likely due to the compositional mismatch between the primary and secondary reference materials. The achieved level of sensitivity and concentration precision (~ 20–30%) is adequate for measuring U, Th and Pb distributions in both rock-forming and accessory minerals in chondrites, achondrites, and their components.

The short-lived radionuclide aluminium-26 ( 26 Al) isotope is a major heat source for early planetary melting. The aluminium-26 – magnesium-26 ( 26 Al- 26 Mg) decay system also serves as a high-resolution relative chronometer. In both cases, however, it is critical to establish whether 26 Al was homogeneously or heterogeneously distributed throughout the solar nebula. Here we report a precise lead-207 – lead-206 ( 207 Pb- 206 Pb) isotopic age of 4565.56 ± 0.12 million years (Ma) for the andesitic achondrite Erg Chech 002. Our analysis, in conjunction with published 26 Al- 26 Mg data, reveals that the initial 26 Al/ 27 Al in the source material of this achondrite was notably higher than in various other well-preserved and precisely dated achondrites. Here we demonstrate that the current data clearly indicate spatial heterogeneity of 26 Al by a factor of 3-4 in the precursor molecular cloud or the protoplanetary disk of the Solar System, likely associated with the late infall of stellar materials with freshly synthesized radionuclides. The homogeneity of Aluminium-26 (Al-26) isotope distribution in the accreting solar nebula is debated. Here, the authors show that the age determination of meteorite Erg Chech 002, compared with other igneous meteorites, indicates that Al-26 was heterogeneously distributed in the early Solar System.

We present analyses of mass-dependent isotope fractionation of strontium (Sr) and neodymium (Nd) from a number of petrologically and chemically diverse calcium–aluminium-rich inclusions (CAIs) from the CV chondrite Allende. Combined with literature data, our results reveal systematic variations of elemental and isotopic fractionation signatures that depend on element volatility and CAI type. In most CAIs with little volatility-driven elemental fractionation (which we collectively refer to as “nongroup-II” CAIs), moderately refractory elements such as Nd and Ti are not isotopically fractionated relative to chondrites, while less refractory elements such as Sr and Ca show light isotope enrichments correlated with their lowered abundances. In contrast, in CAIs with the “group-II” type elemental fractionation pattern, refractory elements show more variable isotopic compositions uncorrelated to element abundances. The coupled elemental and isotopic fractionation in nongroup-II CAIs are consistent with a simple evaporation–condensation–reevaporation origin in the solar nebula, while group-II CAIs require more extensive and complex thermal processing histories. The disparate thermal evolutions of group-II and nongroup-II CAIs indicate distinct physical conditions in their formation pathways, corresponding to different localities in the protoplanetary disk. Nongroup-II CAIs may represent materials that were more effectively transported between high-temperature and low-temperature disk zones and thus experienced more intensive heating and cooling, while group-II CAIs represent particles that more frequently traversed between those zones but were neither heated nor cooled as thoroughly as the former.

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ 26Mg* and μ 25Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ 25Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ 25Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ 25Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ 26Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ 26Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26Al given their respective 27Al/24Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26Al/27Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.

Rock fragments of the Cb-type asteroid Ryugu returned to Earth by the JAXA Hayabusa2 mission share mineralogical, chemical, and isotopic properties with the Ivuna-type (CI) carbonaceous chondrites. Similar to CI chondrites, these fragments underwent extensive aqueous alteration and consist predominantly of hydrous minerals likely formed in the presence of liquid water on the Ryugu parent asteroid. Here we present an in situ analytical survey performed by secondary ion mass spectrometry from which we have estimated the D/H ratio of Ryugu’s hydrous minerals, D/HRyugu, to be [165 ± 19] × 10−6, which corresponds to δDRyugu = +59 ± 121‰ (2σ). The hydrous mineral D/HRyugu’s values for the two sampling sites on Ryugu are similar; they are also similar to the estimated D/H ratio of hydrous minerals in the CI chondrites Orgueil and Alais. This result reinforces a link between Ryugu and CI chondrites and an inference that Ryugu’s samples, which avoided terrestrial contamination, are our best proxy to estimate the composition of water at the origin of hydrous minerals in CI-like material. Based on this data and recent literature studies, the contribution of CI chondrites to the hydrogen of Earth’s surficial reservoirs is evaluated to be ∼3%. We conclude that the water responsible for the alteration of Ryugu’s rocks was derived from water ice precursors inherited from the interstellar medium; the ice partially re-equilibrated its hydrogen with the nebular H2 before being accreted on the Ryugu’s parent asteroid.

High precision Chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) U-Pb zircon results from tuff marker beds that are interstratified within the Upper Permian deposits of the northern Sydney Basin add constraints on the timing of sediment deposition, and afford a better understanding of the regional stratigraphy. The results indicate a magmatic influence during the deposition of the sediments, with episodic events spanning at least from 255.65 ± 0.08 to 255.08 ± 0.09 Ma. The zircon data suggest that the studied sedimentary rocks and tuffs have accumulated simultaneously over a short time interval, which contrasts with current stratigraphic models that suggest a much greater period of deposition and stratigraphic thickness. Therefore, an updated stratigraphic correlation of the basin is suggested, which combines the presently defined Lambton, Adamstown, and Boolaroo sub-groups into a single Lambton sub-group. This updated correlation framework is stratigraphically and geochronologically constrained and provides a more precise exploration model for the northern Sydney Basin. This case study highlights the valuable contribution of the CA-IDTIMS method in intrabasinal correlations of sedimentary successions, when integrated with a robust sedimentological framework, to minimize the stratigraphic uncertainties.

Continental crust forms from, and thus chemically depletes, the Earth's mantle. Evidence that the Earth's mantle was already chemically depleted by melting before the formation of today's oldest surviving crust has been presented in the form of Sm–Nd isotope studies of 3.8–4.0 billion years old rocks from Greenland 1 , 2 , 3 , 4 , 5 and Canada 5 , 6 , 7 . But this interpretation has been questioned because of the possibility that subsequent perturbations may have re-equilibrated the neodymium-isotope compositions of these rocks 8 . Independent and more robust evidence for the origin of the earliest crust and depletion of the Archaean mantle can potentially be provided by hafnium-isotope compositions of zircon, a mineral whose age can be precisely determined by U–Pb dating, and which can survive metamorphisms 4 . But the amounts of hafnium in single zircon grains are too small for the isotopic composition to be precisely analysed by conventional methods. Here we report hafnium-isotope data, obtained using the new technique of multiple-collector plasma-source mass spectrometry 9 , for 37 individual grains of the oldest known terrestrial zircons (from the Narryer Gneiss Complex, Australia, with U–Pb ages of up to 4.14 Gyr ( 10 – 13 ). We find that none of the grains has a depleted mantle signature, but that many were derived from a source with a hafnium-isotope composition similar to that of chondritic meteorites. Furthermore, more than half of the analysed grains seem to have formed by remelting of significantly older crust, indicating that crustal preservation and subsequent reworking might have been important processes from earliest times.