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Molecular nitrogen (N2) comprises three-quarters of Earth's atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets.

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.

Rationale: The analysis of the three sulfur stable isotope ratios (33S/32S, 34S/32S, 36S/32S) is routinely performed by gas‐source isotope ratio mass spectrometry (IRMS) on the SF6 gaseous molecule, collecting SF5+ ions at m/z ~ 127, 128, 129 and 131. High precision and accuracy are commonly achieved owing to a lack of correction because fluorine has only one isotope and the inert nature of the SF6 molecule. The analysis of the 36S/32S ratio is, however, complicated by the low abundance of 36S (~0.015%) and the possible occurrence of trace amounts of fluorocarbon compounds leading to 12C3F5+ ions at m/z ~ 131, i.e. where 36SF5+ ions are collected. Methods: We used gas‐source high‐resolution IRMS to better characterize the nature of possible interferences, and we tested novel types of filaments in order to investigate their influence on possible interferences. Results: We confirm that the 12C3F5+ ion represents the main isobaric interference at m/z ~ 131. We also demonstrate that tungsten fluoride adducts are formed from the reaction of fluorine ions derived during fragmentation of the SF6 molecule with the hot tungsten filament. These reactions lead to the formation of e.g. WF5+, WF4+, WF3+ ions, including doubly charged ions. WF4++, in particular, leads to isobaric interference on m/z ~ 128, 129 and 131 from 180WF4++, 182WF4++ and 186 WF4++ ions, respectively. Because 180W (0.12%) is at low abundance, its influence on δ33S measurements would remain negligible, but 182W (26.5%) and 186W (28.4%) lead to scale contraction for both δ34S and δ36S. Conclusions: Rather than correcting for these interferences, or working at high mass resolution, we suggest avoiding W isobaric interferences by using other types of filaments, with initial reports on both pure Re filaments and Y2O3‐coated W filaments. [ABSTRACT FROM AUTHOR]

Abstract: We modeled the Δ17O of atmospheric O2 using 27 ordinary differential equations comprising a box model composed of the stratosphere, troposphere, geosphere, hydrosphere and biosphere. Results show that 57% of the deficit in 17O in O2 relative to a reference water fractionation line is the result of kinetic isotope fractionation attending the Dole effect, 33% balances the positive Δ17O of O(1D) in the stratosphere, and 10% is from evapotranspiration. The predicted Δ′17O O2 relative to waters is −0.410‰ as measured at the δ18O of air. The value for Δ′17O O2 varies at fixed δ18O with the concentration of atmospheric CO2, gross primary production, and net primary production as well as with reaction rates in the stratosphere. Our model prediction is consistent with our measurements of the oxygen isotopic composition of air O2 compared with rocks if rocks define a fractionation line with an intercept in δ′17O=103ln(δ17O/103 +1) vs. δ′18O=103ln(δ18O/103 +1) space less than SMOW but more positive than some recent measurements imply. The predicted Δ17O is less negative than that obtained from recent measurements of O2 directly against SMOW. Underestimation of Δ′17O O2 can only be ameliorated if the integrated (bulk) Δ′17O for stratospheric CO2 is significantly greater than measurements currently allow. Our results underscore the need for high-precision comparisons of the 17O/16O and 18O/16O ratios of atmospheric O2, VSMOW, and rocks. [Copyright &y& Elsevier]