Search for supernova produced 60Fe in Earth's microfossil record

The detection of supernova debris on Earth can be achieved by use of accelerator mass spectrometry (AMS) to search for radionuclides like 60Fe. This long-lived isotope (T1/2=2.6 Myr) is produced in massive stars and is expected to be present in the debris of type II supernovae. The discovery of 60Fe in a ferromanganese crust from the Pacific ocean (Knie et al., 2004) was interpreted as the input of a supernova explosion about 2.2 Myr ago. Currently, several projects are aiming for the confirmation of the signature of 60Fe in terrestrial and lunar samples. In this talk, the search for this 60Fe signature in Earth's microfossil record is presented. The sample material for this study is marine sediment from the eastern equatorial Pacific. A specific kind of secondary (formed in situ) magnetite mineral contained in the sample material are magnetofossils, which are the remains of magnetotactic bacteria, which are the target for extraction. The chemical extraction technique used to produce AMS samples has been characterized using newly developed magnetic analysis methods and has been shown to be extremely selective towards secondary magnetite. The AMS samples produced in this way are uniquely suited for the search for supernova 60Fe. Preliminary AMS results are presented.