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See also: ERA (disambiguation page).

An era is a (usually lengthy) period of time with common characteristics. For example: -- the Biblical era, the Roman era, the Elizabethan era, the Victorian era . Era is also popularly used to denote the passing of shorter periods, such as the Big Band era, Disco era. Something like the death of Frank Sinatra is called the end of an era. (see also: period)

In Geology, era refers to four well defined time spans covering the history of the Earth. From oldest to youngest, these are the Proterozoic, Paleozoic, Mesozoic, and Cenozoic eras.

Calendar era

In a calendar, the era is the date from which years in the calendar are counted. For example, in the Gregorian and Julian calendars, dates are measured from the beginning of the Christian era. There are many different calendar era systems. Some are listed below along with the abbreviations. (see also: History of Dating in the Christian World)