#geological_period__period  a unit of geological time during which a system of rocks formed; "ganoid fishes swarmed during the earlier geological periods"
  supertype:  #geological_time__geologic_time__geologictime  the time of the physical formation and development of the earth (especially prior to human history)
  subtype:  #ice_age  any period of time during which glaciers covered a large part of the earth's surface
  instance:  #Quaternary_period  #Tertiary_period  #Cretaceous_period  #Jurassic_period  #Triassic_period  #Permian_period  #Carboniferous_period  #Pennsylvanian_period  #Missippian_period  #Devonian_period  #Silurian_period  #Ordovician_period  #Cambrian_period
  part:  #epoch
  part of:  #geological_era__era  a major division of geological time; an era is usually divided into two or more periods
     part of:  #aeon__eon  the longest division of geological time; two or more eras

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