#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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