Specifically, Bishop was searching for the isotope iron–60, which is produced during a supernova and blasted out into space. Bishop's hypothesis was that iron–60 particles from a supernova would oxidize as they passed through the Earth's atmosphere, becoming rust that settled on the ocean floor where it was consumed by "magneto tactic" bacteria to create the magnetite chains they use to detect magnetic fields. By examining sediment core samples using accelerator mass spectrometry, Bishop found atoms of iron–60 preserved in the microfossil remains of these ancient bacteria. Once he compared the iron-60 concentrations in several different core samples, Bishop believes he found a terrestrial record of a supernova that occurred 2.2 million years ago in the Scorpio Centauri cluster --- which actually corresponds nicely to iron-60 deposits found on the moon.

A second study led by Anton Wallner of The Australian National University published similar findings in the journal Nature earlier this year, identifying evidence of a particularly rough period when the Earth was being blasted by a series of nearby explosions. What's more: the evidence also suggests that one of the supernova events found in the fossil record may have set off the ice ages of the Pleistocene era, some 2.5 million years ago.