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. 2016 Apr 7;532(7597):69-72.
doi: 10.1038/nature17196.

Recent near-Earth Supernovae Probed by Global Deposition of Interstellar Radioactive (60)Fe

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Free PMC article

Recent near-Earth Supernovae Probed by Global Deposition of Interstellar Radioactive (60)Fe

A Wallner et al. Nature. .
Free PMC article

Abstract

The rate of supernovae in our local Galactic neighbourhood within a distance of about 100 parsecs from Earth is estimated to be one every 2-4 million years, based on the total rate in the Milky Way (2.0 ± 0.7 per century). Recent massive-star and supernova activity in Earth's vicinity may be traced by radionuclides with half-lives of up to 100 million years, if trapped in interstellar dust grains that penetrate the Solar System. One such radionuclide is (60)Fe (with a half-life of 2.6 million years), which is ejected in supernova explosions and winds from massive stars. Here we report that the (60)Fe signal observed previously in deep-sea crusts is global, extended in time and of interstellar origin from multiple events. We analysed deep-sea archives from all major oceans for (60)Fe deposition via the accretion of interstellar dust particles. Our results reveal (60)Fe interstellar influxes onto Earth at 1.5-3.2 million years ago and at 6.5-8.7 million years ago. The signal measured implies that a few per cent of fresh (60)Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ten million years at distances of up to 100 parsecs.

Figures

Figure 1
Figure 1. Deposition rates for sediment (150 kyr averaged data) and incorporation rates for two crust samples
60Fe concentrations (60Fe/g) for the sediment are given in the inset; they were on average 6.7×104 atoms/g between 1.7 and 3.2 Myr, but 260×104 atoms/g crust and 95×104 atoms/g nodule, reflecting the difference in growth rate and incorporation efficiency (see Supplement). The error bars (1σ) include all uncertainties and scale with decay correction, thus upper limits are becoming larger for older samples. The absolute ages for the sediment are uncertain by 0.1 Myr, but for the 5.5-Myr sediments ~1 Myr. Ages of Crust-1 are 0.3 and of Crust-2 0.5 Myr uncertain.

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