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25-477: Eras or ERAS may refer to: A plural for era , a specific period of time The Eras Tour , a concert tour by Taylor Swift, or may refer to the timeline of her albums discography Eras (typeface) , a typeface Electronic Residency Application Service , in the United States Committee for a Radical Left Rally , a political organisation in

50-557: A group of calendar eras based on a calculation of the age of the world , assuming it was created as described in the Book of Genesis . In Jewish religious contexts one of the versions is still used, and many Eastern Orthodox religious calendars used another version until 1728. Hebrew year 5772 AM began at sunset on 28 September 2011 and ended on 16 September 2012. In the Western church, Anno Domini ( AD also written CE ), counting

75-506: Is 1741. In chronology , an "era" is the highest level for the organization of the measurement of time. A " calendar era " indicates a span of many years which are numbered beginning at a specific reference date (epoch) , which often marks the origin of a political state or cosmology , dynasty, ruler, the birth of a leader, or another significant historical or mythological event; it is generally called after its focus accordingly as in " Victorian era ". In large-scale natural science, there

100-403: Is a rather impractical system, and a challenge for historians if a single piece of the historical chronology is missing, and often reflects the preponderance in public life of an absolute ruler in many ancient cultures. Such traditions sometimes outlive the political power of the throne, and may even be based on mythological events or rulers who may not have existed (for example Rome numbering from

125-413: Is an abbreviation for " before present "). The older Proterozoic and Archean eons are also divided into eras. For periods in the history of the universe , the term " epoch " is typically preferred, but "era" is used e.g. of the " Stelliferous Era ". Calendar eras count the years since a particular date (epoch), often one with religious significance. Anno mundi (year of the world) refers to

150-621: Is different from Wikidata All article disambiguation pages All disambiguation pages Era Comparable terms are epoch , age , period , saeculum , aeon (Greek aion ) and Sanskrit yuga . The word has been in use in English since 1615, and is derived from Late Latin aera "an era or epoch from which time is reckoned," probably identical to Latin æra "counters used for calculation," plural of æs "brass, money". The Latin word use in chronology seems to have begun in 5th century Visigothic Spain, where it appears in

175-488: Is need for another time perspective, independent from human activity, and indeed spanning a far longer period (mainly prehistoric), where " geologic era " refers to well-defined time spans. The next-larger division of geologic time is the eon . The Phanerozoic Eon, for example, is subdivided into eras. There are currently three eras defined in the Phanerozoic; the following table lists them from youngest to oldest (BP

200-538: The History of Isidore of Seville , and in later texts. The Spanish era is calculated from 38 BC, Before Christ, perhaps because of a tax (cfr. indiction ) levied in that year, or due to a miscalculation of the Battle of Actium , which occurred in 31 BC. Like epoch, "era" in English originally meant "the starting point of an age"; the meaning "system of chronological notation" is c. 1646; that of "historical period"

225-533: The Roman era , Elizabethan era , Victorian era , etc. Use of the term for more recent periods or topical history might include Soviet era , and "musical eras" in the history of modern popular music , such as the " big band era ", " disco era ", etc. Before present Before Present ( BP ) or " years before present ( YBP )" is a time scale used mainly in archaeology , geology, and other scientific disciplines to specify when events occurred relative to

250-664: The University of Copenhagen instead uses the unambiguous "b2k", for "years before 2000 AD", often in combination with the Greenland Ice Core Chronology 2005 (GICC05) time scale. Some authors who use the YBP dating format also use "YAP" ("years after present") to denote years after 1950. SI prefix multipliers may be used to express larger periods of time, e.g. ka BP (thousand years BP), Ma BP (million years BP) and many others . Radiocarbon dating

275-448: The carbon isotopes in the atmosphere, which scientists must account for. In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present". The BP scale is sometimes used for dates established by means other than radiocarbon dating, such as stratigraphy . This usage differs from

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300-584: The Japanese used the imperial year system ( kōki ), counting from the year when the legendary Emperor Jimmu founded Japan, which occurred in 660 BC. Many Buddhist calendars count from the death of the Buddha , which according to the most commonly used calculations was in 545–543 BCE or 483 BCE. Dates are given as "BE" for "Buddhist Era"; 2000 AD was 2543 BE in the Thai solar calendar . Other calendar eras of

325-567: The Republic of Cyprus See also [ edit ] Era (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Eras . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Eras&oldid=1180055237 " Category : Disambiguation pages Hidden categories: Short description

350-636: The United Kingdom until quite recently, but only for formal official writings: in daily life the ordinary year A.D. has been used for a long time, but Acts of Parliament were dated according to the years of the reign of the current monarch , so that "61 & 62 Vict c. 37" refers to the Local Government (Ireland) Act 1898 passed in the session of Parliament in the 61st/62nd year of the reign of Queen Victoria . "Era" can be used to refer to well-defined periods in historiography, such as

375-476: The exponential decay relation and the "Libby half-life" 5568 a. The ages are expressed in years before present (BP) where "present" is defined as AD 1950. The year 1950 was chosen because it was the standard astronomical epoch at that time. It also marked the publication of the first radiocarbon dates in December 1949, and 1950 also antedates large-scale atmospheric testing of nuclear weapons , which altered

400-480: The global ratio of carbon-14 to carbon-12 . Dates determined using radiocarbon dating come as two kinds: uncalibrated (also called Libby or raw ) and calibrated (also called Cambridge ) dates. Uncalibrated radiocarbon dates should be clearly noted as such by "uncalibrated years BP", because they are not identical to calendar dates. This has to do with the fact that the level of atmospheric radiocarbon ( carbon-14 or C) has not been strictly constant during

425-516: The name (standard codes are used) of the laboratory concerned, and other information such as confidence levels, because of differences between the methods used by different laboratories and changes in calibrating methods. Conversion from Gregorian calendar years to Before Present years is by starting with the 1950-01-01 epoch of the Gregorian calendar and increasing the BP year count with each year into

450-416: The origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale, with 1950 being labelled as the "standard year". The abbreviation "BP" has been interpreted retrospectively as "Before Physics", which refers to the time before nuclear weapons testing artificially altered the proportion of

475-543: The past counted from political events, such as the Seleucid era and the Ancient Roman ab urbe condita ("AUC"), counting from the foundation of the city. The word era also denotes the units used under a different, more arbitrary system where time is not represented as an endless continuum with a single reference year, but each unit starts counting from one again as if time starts again. The use of regnal years

500-496: The recommendation by van der Plicht & Hogg, followed by the Quaternary Science Reviews , both of which requested that publications should use the unit "a" (for "annum", Latin for "year") and reserve the term "BP" for radiocarbon estimations. Some archaeologists use the lowercase letters bp , bc and ad as terminology for uncalibrated dates for these eras. The Centre for Ice and Climate at

525-439: The rule of Romulus and Remus ). In a manner of speaking the use of the supposed date of the birth of Christ as a base year is a form of an era. In East Asia , each emperor's reign may be subdivided into several reign periods, each being treated as a new era. The name of each was a motto or slogan chosen by the emperor. Different East Asian countries utilized slightly different systems, notably: A similar practice survived in

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550-596: The span of time that can be radiocarbon-dated. Uncalibrated radiocarbon ages can be converted to calendar dates by calibration curves based on comparison of raw radiocarbon dates of samples independently dated by other methods, such as dendrochronology (dating based on tree growth-rings) and stratigraphy (dating based on sediment layers in mud or sedimentary rock). Such calibrated dates are expressed as cal BP, where "cal" indicates "calibrated years", or "calendar years", before 1950. Many scholarly and scientific journals require that published calibrated results be accompanied by

575-593: The years since the birth of Jesus on traditional calculations, was always dominant. The Islamic calendar , which also has variants, counts years from the Hijra or emigration of the Islamic prophet Muhammad from Mecca to Medina , which occurred in 622 AD. The Islamic year is some days shorter than 365; January 2012 fell in 1433 AH ("After Hijra"). For a time ranging from 1872 to the Second World War ,

600-446: Was first used in 1949. Beginning in 1954, metrologists established 1950 as the origin year for the BP scale for use with radiocarbon dating, using a 1950-based reference sample of oxalic acid . According to scientist A. Currie Lloyd: The problem was tackled by the international radiocarbon community in the late 1950s, in cooperation with the U.S. National Bureau of Standards . A large quantity of contemporary oxalic acid dihydrate

625-525: Was prepared as NBS Standard Reference Material (SRM) 4990B. Its C concentration was about 5% above what was believed to be the natural level, so the standard for radiocarbon dating was defined as 0.95 times the C concentration of this material, adjusted to a C reference value of −19 per mil (PDB). This value is defined as "modern carbon" referenced to AD 1950. Radiocarbon measurements are compared to this modern carbon value, and expressed as "fraction of modern" (fM). "Radiocarbon ages" are calculated from fM using

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