Radioactive elements synthesized in massive stars are ejected into space via stellar winds and supernova explosions. Our Solar System moves through the interstellar medium and collects these extrasolar products. One such product is iron-60. Because it is not naturally produced on Earth, the presence of this radioactive isotope is a sensitive indicator of supernova explosions within the last few million years. Australian National University’s Dr. Anton Wallner and colleagues previously found traces of iron-60 at about 2.6 million years ago, and possibly another at around 6 million years ago, suggesting our planet had traveled through fallout clouds from nearby supernovae....