Supernova-produced ⁶⁰Fe in Earth’s microfossil record

It is possible for a nearby supernova (SN) explosion to deposit a fraction of its ejecta on Earth. Due to the lack of significant anthropogenic and cosmogenic background, ⁶⁰Fe (T_1/2 = 2.6 Ma) is perfectly suited to serve as a radioactive tracer of recent SN events. The ratio of ⁶⁰Fe/Fe was measured in over 100 samples extracted from two sediment cores from the Eastern Equatorial Pacific. The AMS samples were produced using a carefully tuned chemical leaching technique that specifically targets fine-grained iron-oxides, such as magnetofossils.
Magnetofossils are the remains of magnetosome chains, built up by magnetotactic bacteria, which are abundantly present in our sediment, as shown by magnetic analysis and electron microscopy.
The AMS samples were measured at the GAMS setup at the Maier-Leibnitz-Laboratory in Garching, where the use of a gas-filled magnet for isobaric suppression provides a sensitivity of ⁶⁰Fe/Fe ≈ 5 x 10^-17.
Our results reveal a ⁶⁰Fe signature over a time-range of about 1.7-2.7 Ma, which is attributed to the deposition of SN debris.