LAUSR

Meteorites record processes that occurred before and during the formation of the Solar System in the form of nucleosynthetic anomalies: isotopic compositions that differ from the Solar System patterns. Nucleosynthetic anomalies are rarely seen in volatile elements such as potassium at bulk meteorite scale. We measured potassium isotope ratios in 32 meteorites and identified nucleosynthetic anomalies in the isotope potassium-40. The anomalies are larger and more variable in carbonaceous chondrite (CC) meteorites than in noncarbonaceous (NC) meteorites, indicating that CCs inherited more material produced in supernova nucleosynthesis. The potassium-40 anomaly of Earth is close to that of the NCs, implying that Earth’s potassium was mostly delivered by NCs. Description Nucleosynthetic anomalies in meteorites The origins of the material that accreted to form Earth can be constrained using meteorites that contain leftover material from planet formation. Nucleosynthetic anomalies are small differences in isotope ratios left by incomplete mixing of presolar material. They are already known for refractory elements, which condense into dust grains first, but it has been unclear whether more volatile elements were fully mixed before planet formation. In two complementary papers, Martins et al. and Nie et al. identified nucleosynthetic anomalies in the moderately volatile elements zinc and potassium, respectively. They used cosmochemical models to determine that about 90% of Earth’s mass was contributed by noncarbonaceous inner Solar System material, whereas about 10% came from carbonaceous outer Solar System material. The latter source contributed about 20% of Earth’s potassium and half of its zinc. —KTS Potassium isotope ratios in meteorites show nucleosynthetic anomalies that constrain the assembly of Earth.