The heaviest three confirmed primordial nuclides, 232 Th, 235 U, and 238 U, are the only isotopes beyond bismuth that have half-lives measured in billions of years, and thus have survived since their production around ten billion years ago.
The heaviest three confirmed primordial nuclides, 232 Th, 235 U, and 238 U, are the only isotopes beyond bismuth that have half-lives measured in billions of years. Thus, they are the only such heavy isotopes to have survived since their production around ten billion years ago.