The longest-lived non- ground state nuclear isomer is the nuclide tantalum-180m (73 Ta), which has a half-life in excess of 1,000 trillion years. This nuclide occurs primordially, and has never been observed to decay to the ground state. (In contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8 hours to Hf (86%) or W (14%).)