Geologic division (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">geologic division</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for era that I've seen before include "Eon" , "Distinct period in history" , "Important date" , "Long period of time" , "Important historical period" .)