Division of geological time (3)

<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">division of geological time</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for era that I've seen before include "Significant time" , "Long historic period" , "Series of years" , "Important date" , "Aeon" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">division of geological time</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for eon that I've seen before include "An immense time" , "In time, long division" , "Major division of geological time" , "billion years" , "Long period of time" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">division of geological time</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for aeon that I've seen before include "Immeasurably long period of time" , "Eternity" , "An age; period" , "Epoch" , "With lots of time" .)
(Other definitions for epoch that I've seen before include "Period of time in history" , "Distinctive period of time" , "Period of time marked by a great event" , "Point in time fixed by some great event" , "Unit of geological time" .)