Search for supernova-⁶⁰Fe in Earth’s microfossil record

Supernova (SN) explosions eject copious amounts of material into the interstellar medium. It is possible that supernova ejecta are incorporated into solar system reservoirs. ⁶⁰Fe is an ideal isotope to search for such a signature, since it is produced in massive stars and can be ejected in their subsequent SN explosions, and has almost no terrestrial background. For this study, the ratio of ⁶⁰Fe/Fe was determined with AMS using the GAMS setup in Garching, Germany, in a set of samples extracted from two Pacific Ocean sediment cores of 0 to 7 Ma of age. The Fe samples were obtained using a novel chemical extraction technique targeting specifically magnetofossils, chains of magnetite crystals produced by magnetotactic bacteria, and other small-grained Fe-bearing minerals, to prevent signal dilution. Our findings reveal a ⁶⁰Fe signature in the age range of 1.8-2.5 Ma, which is attributed to input of SN ejecta.