Supernova may have left biological \'signature\' in ancient Earth

Samples from the Pacific Ocean floor may hold the signature of a distant supernova that bathed the Earth with high energy millions of years ago, scientists say. Shawn Bishop, a physicist at the Technical University of Munich in Germany, said sediment in a deep-sea core may hold traces of radioactive iron spewed by a supernova 2.2 million years ago, preserved in the fossilized remains of iron-loving bacteria. Addressing a meeting of the American Physical Society in Denver, Bishop said if his findings are confirmed it would be the first biological signature of a specific exploding star. The sediment core contained the isotope iron-60, which does not form on Earth, and scientists said the source was likely a supernova in our cosmic neighborhood, the journal Nature reported Monday. While the levels of iron-60 are low, the only place they seem to appear is in sea floor layers dated to around 2.2 million years ago, the researchers said. The iron-60 could have been gathered by certain species of bacteria that accumulates and concentrates iron from its environment, as radioactive supernova debris showered on them from the atmosphere after crossing inter-stellar space at nearly the speed of light, they said.