<page_title> Primordial nuclide </page_title> <section_title> List of 34 radioactive primordial nuclides and measured half-lives </section_title> <table> <cell> 232Th <col_header> Nuclide </col_header> </cell> <cell> 1.406×1010 <col_header> Half- life (years) </col_header> </cell> <cell> 238U <col_header> Nuclide </col_header> </cell> <cell> 4.471×109 <col_header> Half- life (years) </col_header> </cell> <cell> 40K <col_header> Nuclide </col_header> </cell> <cell> 1.25×109 <col_header> Half- life (years) </col_header> </cell> <cell> 235U <col_header> Nuclide </col_header> </cell> <cell> 7.04×108 <col_header> Half- life (years) </col_header> </cell> </table>
The four shortest-lived primordial nuclides (i.e. nuclides with shortest half-lives) are ²³² Th, ²³⁸ U, ⁴⁰ K, and ²³⁵ U.