A nearby supernova (SN) explosion in the past can be confirmed by the detection of radioisotopes on Earth that were produced and ejected by the SN. We have now measured a well resolved time profile of the ${}^{60}\mathrm{F}\mathrm{e}$ concentration in a deep-sea ferromanganese crust and found a highly significant increase 2.8 Myr ago. The amount of ${}^{60}\mathrm{F}\mathrm{e}$ is compatible with the deposition of ejecta from a SN at a distance of a few 10 pc. The well defined time of the SN explosion makes it possible to search for plausible correlations with other events in Earth’s history.

We have made a new determination of the half-life of the radioactive isotope ${}^{60}\mathrm{Fe}$ using high precision measurements of the number of ${}^{60}\mathrm{Fe}$ atoms and their activity in a sample containing over ${10}^{15}$ ${}^{60}\mathrm{Fe}$ atoms. Our new value for the half-life of ${}^{60}\mathrm{Fe}$ is $(2.62\pm 0.04)\times {10}^6\mathrm{yr}$, significantly above the previously reported value of $(1.49\pm 0.27)\times {10}^6\mathrm{yr}$. Our new measurement for the lifetime of ${}^{60}\mathrm{Fe}$ has significant implications for interpretations of galactic nucleosynthesis, for determinations of formation time scales of solids in the early Solar System, and for the interpretation of live ${}^{60}\mathrm{Fe}$ measurements from supernova-ejecta deposits on Earth.

In a deep ocean ferromanganese crust an excess of ${}^{60}\mathrm{Fe}$ radioactivity was measured by means of high sensitivity accelerator mass spectrometry. The enhanced concentrations measured in the first two of three layers (corresponding to a time span of 0–2.8 Myr and 3.7–5.9 Myr, respectively) suggest the deposition of supernova produced ${}^{60}\mathrm{Fe}$ on earth. There is even a weak indication that the flux into the crust was higher about 5 Myr ago.

Half of the heavy elements including all actinides are produced in r-process nucleosynthesis, whose sites and history remain a mystery. If continuously produced, the Interstellar Medium is expected to build-up a quasi-steady state of abundances of short-lived nuclides (with half-lives ≤100 My), including actinides produced in r-process nucleosynthesis. Their existence in today’s interstellar medium would serve as a radioactive clock and would establish that their production was recent. In particular ²⁴⁴Pu, a radioactive actinide nuclide (half-life=81 My), can place strong constraints on recent r-process frequency and production yield. Here we report the detection of live interstellar ²⁴⁴Pu, archived in Earth’s deep-sea floor during the last 25 My, at abundances lower than expected from continuous production in the Galaxy by about 2 orders of magnitude. This large discrepancy may signal a rarity of actinide r-process nucleosynthesis sites, compatible with neutron-star mergers or with a small subset of actinide-producing supernovae.