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In [[astronomy]], [[geology]], and [[paleontology]], '''bya''' or "'''b.y.a.'''" is an [[initialism]] for '''[[1000000000 (number)|billion]] years ago'''. This abbreviation is commonly used as a [[Units of measurement|unit]] of [[time]] to denote length of time before the present |
In [[astronomy]], [[geology]], and [[paleontology]], "'''bya'''" or "'''b.y.a.'''" is an [[initialism]] for "'''[[1000000000 (number)|billion]] years ago'''". This abbreviation is commonly used as a [[Units of measurement|unit]] of [[time]] to denote length of time before the present in billions of years. |
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The "billion" in bya is, by convention, the 10<SUP>9</SUP> "billion" of the [[Long and short scales|short scale]] of the [[United States|U.S.]], not the long-scale 10<SUP>12</SUP> "billion" of some [[Europe|European]] usage. For this reason, there is potential for some confusion; and some scientists prefer the unit [[Gya]], while others prefer [[Giga-annum|Ga]] (Giga-annum) |
The "billion" in bya is, by convention, the 10<SUP>9</SUP> "billion" of the [[Long and short scales|short scale]] of the [[United States|U.S.]]{{cn}}, not the long-scale 10<SUP>12</SUP> "billion" of some [[Europe|European]] usage. For this reason, there is potential for some confusion; and some scientists prefer the unit [[Gya]], while others prefer [[Giga-annum|Ga]] (Giga-annum), however bya remains in more widespread use{{cn}}. In 1974, the UK switched from the long scale to the short scale{{cn}}. |
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Related units are [[Mya (unit)|mya]] ("million years ago"), and '''byr''' ("billion years"). These are traditionally written in [[lowercase]]. [[Giga-annum|Ga]] or Gya has a [[capitalization|capitalized]] first letter instead. |
Related units are [[Mya (unit)|mya]] ("million years ago"), and '''byr''' ("billion years"). These are traditionally written in [[lowercase]]. [[Giga-annum|Ga]] or Gya has a [[capitalization|capitalized]] first letter instead. |
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Revision as of 18:36, 24 April 2016
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In astronomy, geology, and paleontology, "bya" or "b.y.a." is an initialism for "billion years ago". This abbreviation is commonly used as a unit of time to denote length of time before the present in billions of years.
The "billion" in bya is, by convention, the 109 "billion" of the short scale of the U.S.[citation needed], not the long-scale 1012 "billion" of some European usage. For this reason, there is potential for some confusion; and some scientists prefer the unit Gya, while others prefer Ga (Giga-annum), however bya remains in more widespread use[citation needed]. In 1974, the UK switched from the long scale to the short scale[citation needed].
Related units are mya ("million years ago"), and byr ("billion years"). These are traditionally written in lowercase. Ga or Gya has a capitalized first letter instead.