Researchers report in the journal Science that they appear to have some clues about the origin of Earth's plutonium - which has been long debated. Correspondent Nell Greenfieldboyce explains that traces of rare forms of iron and plutonium have been found in extraterrestrial debris that had sunk to the bottom of the Pacific Ocean, hauled up by an oil company, then donated for research. By comparing the iron and the plutonium, scientists found the plutonium was likely forged in a cosmic cataclysm, perhaps a rare kind of supernova, and then rained down on Earth.Ever find yourself existentially musing? Wondering about the state of the cosmos? Drop us a line at shortwave@npr.org and we might jump into a wormhole with you.