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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{{Fact|date=September 2008}} used as a [[Units of measurement|unit]] of [[time]] to denote length of time before the present. Specifically, one bya is equal to 10<sup>9</sup> [[year]]s ago. |
In [[astronomy]], [[geology]], and [[paleontology]], '''bya''' or "'''b.y.a.'''" is an [[initialism]] for '''[[1000000000 (number)|billion]] years ago'''. This abbreviation is commonly{{Fact|date=September 2008}} used as a [[Units of measurement|unit]] of [[time]] to denote length of time before the present. Specifically, one bya is equal to 10<sup>9</sup> [[year]]s ago. |
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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 |
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). However, bya remains in more widespread use. In 1974 the UK switched from the long scale to the short scale. |
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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 17:00, 16 June 2014
In astronomy, geology, and paleontology, bya or "b.y.a." is an initialism for billion years ago. This abbreviation is commonly[citation needed] used as a unit of time to denote length of time before the present. Specifically, one bya is equal to 109 years ago.
The "billion" in bya is, by convention, the 109 "billion" of the short scale of the U.S., 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. In 1974 the UK switched from the long scale to the short scale.
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.