Geologic time (5)
'geologic time' is the definition.
(eon is a kind of geologic time)
This is all the clue.
(Other definitions for eon that I've seen before include "Geological period" , "Prolonged period" , "In time, long division" , "Major division of geological time" , "Era" .)
'geologic time' is the definition.
(epoch is a kind of geologic time)
This is all the clue.
(Other definitions for epoch that I've seen before include "Geological time period" , "extended period" , "Period of notable events" , "Point in time fixed by some great event" , "significant time" .)