On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova

Brian D. Fields; John Ellis

doi:10.1016/s1384-1076(99)00034-2

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arXiv · astro-ph/9811457

On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova

Brian D. Fields·John Ellis

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Abstract

Live $^{60}$Fe has recently been reported in a deep-ocean ferromanganese crust. Analysis of the isotopic ratios in the sample suggests that the measured $^{60}$Fe abundance exceeds the levels generated by terrestrial and cosmogenic sources, and it has been proposed that the excess of $^{60}$Fe is a signature of a supernova that exploded near the earth several Myr ago. In this paper, we consider the possible background sources, and confirm that the measured $^{60}$Fe is significantly higher than all known backgrounds, in contrast with the reported abundance of live $^{53}$Mn. We discuss scenarios in which the data are consistent with a supernova event at a distance $D \sim 30$ pc and an epoch $t_{\rm SN} \sim 5$ Myr ago. We propose tests that could confirm or refute the interpretation of the $^{60}$Fe discovery, including searches for $^{10}$Be, $^{129}$I and $^{146}$Sm. Such a nearby supernova event might have had some impact on the earth's biosphere, principally by enhancing the cosmic-ray flux. This might have damaged the earth's ozone layer, enhancing the penetration of solar ultraviolet radiation. In this connection, we comment on the Middle Miocene and Pliocene mini-extinction events. We also speculate on the possibility of a supernova-induced "cosmic-ray winter," if cosmic rays play a significant role in seeding cloud formation.

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Brian D. Fields, John Ellis. 1998-11-29. On Deep-Ocean Fe-60 as a Fossil of a Near-Earth Supernova. https://doi.org/10.1016/s1384-1076(99)00034-2

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