Original: Plutonium is the heaviest primordial element ( see also primordial nuclide ) , by virtue of its most stable isotope , plutonium-244 , whose half-life of about 80 million years is just long enough for the element to be found in trace quantities in nature .
Simplified: Plutonium-244 has a half-life of about 80 million years . The half life of 244Pu is long enough that some of this isotope of plutonium is found in very small amounts in nature .