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In astronomy, geology, and paleontology, mya or "m.y.a." is an abbreviation for "million years ago". Like the related unit bya, mya is traditionally written in lower case. The deprecated [1] abbreviation m.yr. is still used informally to refer to remote time intervals.[2]

Modern SI usage prefixes the suggested[3] year (or annum) symbol "a" with a multiplier symbol such as "M" (for mega) or "G" (for giga):[1][2]

mega + annum = megannum or Ma
giga + annum = gigannum or Ga

Contents

Events around 1 mya

Geologic periods (Neogene)

See also

Notes

  1. ^ a b "AGU Editorial Style Guide for Authors". American Geophysical Union. 21 September 2007. Archived from the original on 14 July 2008. http://web.archive.org/web/20080714134306/http://www.agu.org/pubs/style_guide_intro.html. "Annum (a) is used to denote year as a unit of measure; use a, ka, Ma, or Ga rather than year (or yr) kyr, Myr (or m.y.), or Gyr."   (a later version is available at http://www.agu.org/pubs/authors/manuscript_tools/journals/pdf/AGU_grammar_style.pdf)
  2. ^ a b North American Commission on Stratigraphic Nomenclature. "North American Stratigraphic Code". http://ngmdb.usgs.gov/Info/NACSN/Code2/code2.html#Article13. "(c) Convention and abbreviations. -The age of a stratigraphic unit or the time of a geologic event, as commonly determined by numerical dating or by reference to a calibrated time-scale, may be expressed in years before the present. The unit of time is the modern year as presently recognized worldwide. Recommended (but not mandatory) abbreviations for such ages are SI (International System of Units) multipliers coupled with "a" for annum: ka, Ma, and Ga for kilo-annum (103 years), Mega-annum (106 years), and Giga-annum (109 years), respectively. Use of these terms after the age value follows the convention established in the field of C-14 dating. The "present" refers to 1950 AD, and such qualifiers as "ago" or "before the present" are omitted after the value because measurement of the duration from the present to the past is implicit in the designation. In contrast, the duration of a remote interval of geologic time, as a number of years, should not be expressed by the same symbols. Abbreviations for numbers of years, without reference to the present, are informal (e.g., y or yr for years; my, m.y., or m.yr. for millions of years; and so forth, as preference dictates). For example, boundaries of the Late Cretaceous Epoch currently are calibrated at 63 Ma and 96 Ma, but the interval of time represented by this epoch is 33 m.y."  
  3. ^ "Special Publication 811 : Guide for the Use of the International System of Units (SI)". National Institute of Standards and Technology (NIST). 2008. pp. 23. http://physics.nist.gov/Document/sp811.pdf. Retrieved 2009-04-07. "Although there is no universally accepted symbol for the year, Ref. [4: ISO 80000-3] suggests the symbol a."  
  4. ^ Clement, Bradford M. (8 April 2004). "Dependence of the duration of geomagnetic polarity reversals on site latitude". Nature 428. doi:10.1038/nature02459. PMID 15071591.  







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