High Quality Content by WIKIPEDIA articles! Since the mid-20th century, plutonium in the environment has primarily been produced by human activity. The majority of plutonium isotopes are short-lived on a geological timescale, though it has been argued that some natural plutonium, like the long-lived 244Pu isotope, can be found in nature. This isotope has been found in lunar soil,meteorites, and in the Oklo natural reactor. However, one paper on marine sediments for plutonium in marine sediments, atomic bomb fallout is responsible for 66% of the 239Pu and 59% 240Pu found in the English Channel, while nuclear reprocessing is responsible for the majority of the 238Pu and 241Pu present in the Earth`s oceans (nuclear weapons testing is only responsible for 6.5 and 16.5% of these isotopes respectively).