bya

bya or b.y.a. is an abbreviation for "billion years ago". It is 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.

The "billion" in bya is the 10⁹ "billion" of the short scale of the United States,^[1] 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.^[2] 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.^[1] In 1974, the UK switched from the long scale to the short scale.^[1]

Related units are mya ("million years ago"), and byr ("billion years"), which are traditionally written uncapitalized, while Ga or Gya starts with a capital letter.

References

1 2 3 Gale, Joseph (2009). Astrobiology of Earth: The Emergence. Oxford: Oxford University Press, p. 21.
↑ Chartrand, Mark (2004). Satellite Communications for the Nonspecialist. New York: SPIE Press, p. 73.

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[Gale20092-1] 1 2 3 Gale, Joseph (2009). Astrobiology of Earth: The Emergence. Oxford: Oxford University Press, p. 21.

[2] Chartrand, Mark (2004). Satellite Communications for the Nonspecialist. New York: SPIE Press, p. 73.

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bya

See also

References