22 lines
1.2 KiB
Markdown
22 lines
1.2 KiB
Markdown
---
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title: "Bya"
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chunk: 1/1
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source: "https://en.wikipedia.org/wiki/Bya"
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category: "reference"
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tags: "science, encyclopedia"
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date_saved: "2026-05-05T14:27:45.666284+00:00"
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instance: "kb-cron"
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---
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bya or b.y.a. is an abbreviation for "billion years ago". It is commonly used as a unit of time to denote length of time before the present in 109 years. This initialism is often used in the sciences of astronomy, geology, and paleontology.
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The "billion" in bya is the 109 "billion" of the short scale of the US, not the long-scale 1012 "billion" of some European usage. Billion by this convention (109) is often called a "thousand million" in the UK and a "milliard" in some other countries. 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.
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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.
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== See also ==
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Geologic time scale
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Ga (unit)
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Before Present
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== References == |