Billion years
Lua error in package.lua at line 80: module 'strict' not found.
A billion years (109 years) is a unit of time on the petasecond scale, more precisely equal to 3.16×1016 seconds.
It is sometimes abbreviated Gy, Ga ("giga-annum"), Byr and variants. The abbreviations Gya or bya are for "billion years ago", i.e. billion years before present.[1] The terms are used in geology, paleontology, geophysics, astronomy and physical cosmology.
The prefix giga- is preferred to billion- to avoid confusion in the long and short scales over the meaning of billion; the postfix annum may be further qualified for precision as a sidereal year or Julian year:
- 1 Gaj=3.15576×1016 s,
- 1 Gas=3.15581×1016 s (epoch J2000.0).
Byr was formerly used in English-language geology and astronomy as a unit of one billion years. Subsequently the term gigaannum (Ga) has increased in usage, with Gy or Gyr still sometimes used in English-language works, at the risk of confusion with the gray). Astronomers use Gyr or Gy as an abbreviation for gigayear.[2]
See also
- Myr
- mya (unit)
- Annum
- Year#SI prefix multipliers
- Gya
- Orders of magnitude (time)
- Year#Symbols y and yr
