I
In geology, the basic unit of the geologic time scale.
During these spans of time, specific systems of rocks were formed. Originally, the method for defining the sequence of periods was relative; it was based on stratigraphy and paleontology .
II
[c mediumvioletred] (as used in expressions)
Baroque period
Cambrian Period
Carboniferous Period
Cretaceous Period
Devonian Period
Genroku period
Heian period
Heisei period
Jurassic Period
Kamakura period
Meiji period
Mesolithic Period
Mississippian Period
Muromachi period
Nara period
Neolithic Period
Ordovician Period
Paleolithic Period
Pennsylvanian Period
Permian Period
Quaternary Period
Showa period
sidereal period
Silurian Period
Spring and Autumn period
synodic period
Taisho period
{{link=Tertiary Period">Tertiary Period
Tokugawa period
Triassic Period
Warring States period