⁶⁰Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity

Abstract

Nuclides synthesized in massive stars are ejected into space viastellar winds and supernova explosions. The solar system (SS)moves through the interstellar medium and collects these nucle-osynthesis products. One such product is 60Fe, a radio nuclide witha half-life of 2.6 My that is predominantly produced in mas-sive stars and ejected in supernova explosions. Extraterres-trial60Fe has been found on Earth, suggesting close-by supernovaexplosions∼2to3and∼6Ma.Here,wereportonthedetectionof a continuous interstellar 60Fe influx on Earth over the past∼33,000 y. This time period coincides with passage of our SSthrough such interstellar clouds, which have a significantly largerparticle density compared to the local average interstellar me-dium embedding our SS for the past few million years. The inter-stellar 60Fe was extracted from five deep-sea sediment samplesand accelerator mass spectrometry was used for single-atomcounting. The low number of 19 detected atoms indicates a con-tinued but low influx of interstellar60Fe. The measured 60Fe time profile over the 33 ky, obtained with a time resolution of about±9 ky, does not seem to reflect any large changes in the inter-stellar particle density during Earth’s passage through local in-terstellar clouds, which could be expected if the local cloudrepresented an isolated remnant of the most recent supernovaejecta that traversed the Earth∼2 to 3 Ma. The identified 60 Fe influx may signal a late echo of some million-year-old supernovaewith the 60Fe-bearing dust particles still permeating the interstellar medium