Complex sentence: 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.
Split into simpler sentences: 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.