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era,period of historic time. In geology, it is the name applied to large divisions of geological process, e.g., Paleozoic era (see geologygeology,
science of the earth's history, composition, and structure, and the associated processes. It draws upon chemistry, biology, physics, astronomy, and mathematics (notably statistics) for support of its formulations.
..... Click the link for more information. ). In chronology an era is a period reckoned from a fixed point in time, as before or after the birth of Christ—before Christ, B.C.; Anno Domini [year of the Lord], A.D. The points best known for Western history are the creation of the world (Jewish, equivalent to 3761 B.C.; Byzantine, 5508 B.C.); the founding of the city of Rome [753 B.C.; year marked A.U.C. for ab urbe condita (from the founding of the city)]; the HegiraHegira
[Ar.,=Hijra=breaking off of relations], the departure of the prophet Muhammad from Mecca in Sept., 622. Muhammad was a monotheist and preached against the polytheism of the Meccan religion.
..... Click the link for more information. , the flight of Muhammad from Mecca (A.D. 622; abbreviation A.H.); and the founding of the Olympic games in ancient Greece (776 B.C.; time in Olympiads). Some people use C.E. (originally, Christian era, now common era) and B.C.E. (before common era) in place of A.D. and B.C., respectively. Since in different calendars years are of different lengths and do not begin on the same day (see calendarcalendar
[Lat., from Kalends], system of reckoning time for the practical purpose of recording past events and calculating dates for future plans. The calendar is based on noting ordinary and easily observable natural events, the cycle of the sun through the seasons with equinox
..... Click the link for more information. ), several factors have to be used in changing the year of one era to that of another, and even with conversion charts there are still difficulties. Because of poor time calculation in earlier times, there may be anomalies in dating. Thus, the beginning of the Christian era, originally fixed probably by Dionysius ExiguusDionysius Exiguus
, d. c.545, Roman monk, chronologist, and scholar, a transmitter of Greek thought to the Middle Ages. He made collections of 5th-century papal decretals and the canons of the early church councils.
..... Click the link for more information. , was set a little too late. Therefore the actual birth of Jesus must be dated a little earlier, probably in 4 B.C. The term epochepoch,
unit of geologic time that is a subdivision of a period. The Pleistocene and Holocene epochs, for example, are divisions of the Quaternary period. Epoch is also used to describe a short length of geologic time during a special occurrence, such as the glacial epoch.
..... Click the link for more information. is often confused with era in writing.
(1) In chronology, a fixed point in time that is connected with a real or legendary event and from which a series of years is reckoned. The term “era” is also applied to the system of chronological notation itself. The Christian era, or Common Era, for example, counts the years from a generally accepted date in the Christian religion: the birth of Christ. The peoples of ancient times used different eras that took as their starting point a real or mythical event or the founding of a ruling dynasty. The era of Nabonassar of Babylon, for example, began in 747 B.C.; in ancient Rome, time was reckoned from the founding of Rome (ab urbe condita), considered to have taken place in 753 B.C.; and the Muslim era (the Hegira) began in A.D. 622, the year in which, according to legend, Muhammad fled from Mecca to Medina.
Some eras are reckoned from a point in time chosen for astronomical reasons, which may be combined with religious considerations; examples include those systems that start from an assumed date of the creation of the world. In Judaism this date is 3761 B.C; in the Russian Orthodox Church it is 5508 B.C. In the same category is the Hindu Kali Yuga, which began in 3102 B.C. The Julian period, which was introduced at the end of the 16th century, provided a convenient system of reckoning for astronomical and chronological calculations; it began in 4713 B.C. (see and CALENDAR).
(2) A major historical period that differs fundamentally from the preceding period.