"global chronostratigraphic units"
   (Eon) Phanerozoic Eon (541.0 Ma - present)
     (Era) †Paleozoic Era (541.0 - 251.902 Ma)
       (Period) †Ordovician Period (485.4 - 443.8 Ma)
         (Subperiod) †Bala Sub-period
           (Epoch) †Ashgill Epoch
             (Stage) †Hirnantian Stage (445.2 - 443.8 Ma)