Ancient bacteria may show evidence of supernova

Nature : Iron-60 is produced in tiny amounts by cosmic rays and in large amounts by supernovae. Given that ⁶⁰Fe does not form naturally on Earth, any significant concentration of the isotope is most likely have come from a past supernova. In 2004 researchers found ⁶⁰Fe in a sample of deep-ocean crust 2.2 million years old and attributed it to a nearby supernova. Now, Shawn Bishop of the Technical University of Munich and his colleagues believe they have found further evidence of the supernova in fossilized bacteria. From core samples dating to between 1.7 million and 3.3 million years ago, they took samples from strata formed roughly 100â000 years apart. They washed the slices with a chemical that would remove ⁶⁰Fe that was present in any nonbiological sources. Then they examined the slices in a mass spectrometer and found what appeared to be ⁶⁰Fe, but only in the layer corresponding to 2.2 million years ago. Bishop says that the isotope was likely incorporated into magnetite (Fe ₃O ₄) chains by bacteria on the sea floor.