- 94 total number
- Not Applicable ()
In 1971, US scientist Darleane Hoffman published her discovery of small amounts of plutonium-244 in Precambrian phosphate from southern California, USA, which were several billion years old. Present in the Earth’s crust since its formation, natural plutonium has mostly decayed radioactively and most plutonium found in the natural environment today results from human activity. Plutonium has an atomic number of 94.