period
subdivision of geological time; shorter than an era and longer than an epoch
Cretaceous
third and final period of the Mesozoic Era
Devonian
fourth period of the Paleozoic Era
Tertiary
obsolete term for the geological period 66–2.58 million years ago
Marian year
any year chosen for specific adoration of Mary the mother of Jesus
Juan Crow era
de facto racial segregation and discrimination against Mexican Americans in the Southwestern United States
Quaternary
third and current period of the Cenozoic Era
Silurian
third period of the Paleozoic Era
Cambrian
first period of the Paleozoic Era
Neogene
second period of the Cenozoic Era
Tonian
first period of the Neoproterozoic Era
Imbrium
Lunar geological period
Paleogene
first period of the Cenozoic Era
Columbian
proposed period of the paleoproterozoic era
Jurassic
second period of the Mesozoic Era
Carboniferous
fifth period of the Paleozoic Era
Permian
sixth and final system and period of the Paleozoic erathem and era
Copernican period
Lunar geologic period
Triassic
first system and period of the Mesozoic erathem and era
Ordovician
second period of the Paleozoic Era