Plutonium is generally thought of as an artificial element created by humans, primarily to make the pits of nuclear weapons, but naturally occurring plutonium can be found in ancient rocks. Plutonium 244 is the longest lived isotope of Plutonium, but it's not easy to make, and finding this specific isotope in interstellar dust grains laid down on the ocean floors tells us important things about the formation of the elements that make up the Earth.Based on this paper:60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae A. Wallner et al