Abstract
Approximately 2.8 Myr before the present our planet was subjected to the debris of a supernova explosion. The terrestrial proxy for this event was the discovery of live atoms of 60Fe in a deep-sea ferromanganese crust. The signature for this supernova event should also reside in magnetite (Fe 3O 4) microfossils produced by magnetotactic bacteria extant at the time of the Earth-supernova interaction, provided the bacteria preferentially uptake iron from fine-grained iron oxides and ferric hydroxides. Using estimates for the terrestrial supernova 60Fe flux, combined with our empirically derived microfossil concentrations in a deep-sea drill core, we deduce a conservative estimate of the 60Fe fraction as 60Fe/Fe ≈ 3.6 × 10 −15. This value sits comfortably within the sensitivity limit of present accelerator mass spectrometry capabilities. The implication is that a biogenic signature of this cosmic event is detectable in the Earth’s fossil record.
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