- Byr
Byr was formerly used in
English-language geology andastronomy as a unit of one billionyear s. The "B" is an abbreviation for "billion" (meaning thousand million), with "yr" simply an abbreviation for "year". Today, the termgigaannum (Ga) is also used, but Gy or Gyr are still sometimes used in English-language works (at the risk of confusion with the gray). Some scientists use Gyr as an abbreviation for Gigayear.cite journal | url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?2007A%26A...476.1373S&db_key=AST&nosetcookie=1 | author=Selsis et al. | title=Habitable planets around the star Gl 581? | journal=Astronomy and Astrophysics | volume=476 | issue=3 | year=2007 | pages =1373 – 1387 | doi=10.1051/0004-6361:20078091] Specifically, one Gyr is equal to 109year s.Because a billion means 1000 million in some countries but can mean a million million in others its use is deprecated in favour of
giga- which unambiguously means 109 andannum which for precision may be qualified by (sidereal ), (Julian), etc.ee also
*
Myr
*annum
*Before Present
* Gigaannum or Ga
*Gya
*mya (unit)
*Orders of magnitude (time)#Years Notes
Wikimedia Foundation. 2010.