The categorization of the past into discrete, quantified named blocks of time is called periodization. This is a list of such named time periods as defined in various fields of study. Major categorization systems include cosmological (time periods in the origin and evolution of the universe), geological (time periods in the origin and evolution of earth), anthropological (time periods in the origin and evolution of humans) and historical (written history).
Noun 1. an amount of time; "a time period of 30 years"; "hastened the period of time of his recovery"; "Picasso's blue period" (synonym) period of time, period (hypernym) fundamental quantity, fundamental measure (hyponym) trial period, test period