#aeon__eon  the longest division of geological time; two or more eras
  supertype:  geological_time__geologic_time__geologictime  the time of the physical formation and development of the earth (especially prior to human history)
  part:  geological_era__era  a major division of geological time; an era is usually divided into two or more periods
     part:  geological_period__period  a unit of geological time during which a system of rocks formed; "ganoid fishes swarmed during the earlier geological periods"
        part:  epoch  a unit of geological time

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