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{{about||the [[Adele]] song|Million Years Ago (song)}}
{{Short description|Abbreviation of 1,000,000 years}}{{redirect|million years ago|the [[Adele]] song|Million Years Ago (song)|1,000,000 BC|one million (disambiguation)}}
{{about|"million years" (Myr)|the [[Taake]] song|Noregs vaapen|other uses}}
{{Other uses}}
{{lowercase title}}
{{lowercase title}}
The abbreviation '''myr''', "million years", is a [[unit of measurement|unit]] of a quantity of {{val|fmt=commas|1000000}} (i.e. {{val|1|e=6}}) years, or 31.536 [[Terasecond and longer#Teraseconds|teraseconds]].
The abbreviation '''Myr''', "million years", is a [[unit of measurement|unit]] of a quantity of {{val|fmt=commas|1000000}} (i.e. {{val|1|e=6}}) years, or 31.556926 [[Terasecond and longer#Teraseconds|teraseconds]].


==Usage==
==Usage==
Myr is in common use where the term is often written, such as in [[Earth science]] and [[cosmology]]. Myr is seen with ''mya'', "million years ago". Together they make a reference system, one to a quantity, the other to a particular place in a [[calendar era|year numbering system]] that is ''time before the present''.
Myr (million years) is in common use in fields such as [[Earth science]] and [[cosmology]]. Myr is also used with '''Mya''' (million years ago). Together they make a reference system, one to a quantity, the other to a particular place in a [[calendar era|year numbering system]] that is ''time before the present''.


Myr is deprecated in [[geology]], but in [[astronomy]] ''myr'' is standard.
Myr is deprecated in [[geology]], but in [[astronomy]] ''Myr'' is standard. Where "myr" ''is'' seen in geology it is usually "Myr" (a unit of mega-years). In astronomy it is usually "Myr" (Million years).
Where "myr" ''is'' seen in geology it is usually "Myr" (a unit of mega-years). In astronomy it is usually "Myr" (million years).


== Debate ==
== Debate ==
In geology the debate of the millennia concerns the use of ''myr'' remains open concerning "the use of ''Myr'' plus ''Mya''" versus "using ''Mya'' only".<ref>{{cite web|last=Mozley|first=Peter|title=Discussion of GSA Time Unit Conventions|url=http://www.geosociety.org/TimeUnits/|work=web page|publisher=[[Geological Society of America]]|accessdate=2012-01-07}}</ref> In either case the term ''[[Year#SI prefix multipliers|Ma]]'' is used in geology literature conforming to [[ISO 31-1]] (now [[ISO 80000-3]]) and NIST 811 recommended practices. Traditional style geology literature is written {{Quote|The Cretaceous started 145 Ma and ended 66 Ma, lasting for 79 Myr.}}
In geology a debate remains open concerning the use of ''Myr'' (duration) plus ''Ma'' (million years ago) versus using only the term ''Ma''.<ref>{{cite web|last=Mozley|first=Peter|title=Discussion of GSA Time Unit Conventions|url=https://www.geosociety.org/TimeUnits/|work=web page|publisher=[[Geological Society of America]]|archive-url=https://web.archive.org/web/20160303232640/https://www.geosociety.org/TimeUnits/|archive-date=2016-03-03}}</ref><ref name="Biever-war">{{cite journal |first=Celeste |last=Biever |title=Push to define year sparks time war |journal=[[New Scientist]] |volume=210 |issue=2810 |pages=10 |url=https://www.newscientist.com/article/dn20423-push-to-define-year-sparks-time-war.html |date=April 27, 2011 |access-date=April 28, 2011|bibcode=2011NewSc.210R..10B |doi=10.1016/S0262-4079(11)60955-X }}</ref> In either case the term ''[[Year#SI prefix multipliers|Ma]]'' is used in geology literature conforming to [[ISO 31-1]] (now [[ISO 80000-3]]) and NIST 811 recommended practices. Traditional style geology literature is written {{Quote|The Cretaceous started 145 Ma and ended 66 Ma, lasting for 79 Myr.}}
The "ago" is implied, so that any such year number "X Ma" between 66 and 145 is "Cretaceous", for good reason. But the counter argument is that having ''myr'' for a duration and ''Mya'' for an age mixes unit systems, and tempts capitalization errors: "million" need not be capitalized, but "mega" must be; "ma" would technically imply a ''milliyear'' (a thousandth of a year, or 8 hours). On this side of the debate, one avoids ''myr'' and simply adds ''ago'' explicitly (or adds ''[[Before Present|BP]]''), as in {{Quote|The Cretaceous started 145 Ma ago and ended 66 Ma ago, lasting for 79 Ma.}}
The "ago" is implied, so that any such year number "X Ma" between 66 and 145 is "Cretaceous", for good reason. But the counter argument is that having ''myr'' for a duration and ''Mya'' for an age mixes unit systems, and tempts capitalization errors: "million" need not be capitalized, but "mega" must be; "ma" would technically imply a ''milliyear'' (a thousandth of a year, or 8 hours). On this side of the debate, one avoids ''myr'' and simply adds ''ago'' explicitly (or adds ''[[Before Present|BP]]''), as in {{Quote|The Cretaceous started 145 Ma ago and ended 66 Ma ago, lasting for 79 Ma.}}
In this case, "79 Ma" means only a quantity of 79 million years, without the meaning of "79 million years ago".
In this case, "79 Ma" means only a quantity of 79 million years, without the meaning of "79 million years ago".


== See also ==
== See also ==
* [[Billion years|Byr]]
* [[Kyr]]
* [[Year#SI prefix multipliers|Megaannum]] (Ma)
* [[Year#SI prefix multipliers|Megaannum]] (Ma)
* [[Year#Abbreviations yr and ya|Symbols y and yr]]
* [[Byr]]
* [[kyr]]
* [[Year#Symbols y and yr|Symbols y and yr]]


==References==
==References==
<references/>
<references/>

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[[Category:Units of time]]
[[Category:Units of time]]
[[Category:Astronomy]]
[[Category:Units of measurement in astronomy]]
[[Category:Geology]]
[[Category:Geology]]

Revision as of 18:34, 23 October 2022

The abbreviation Myr, "million years", is a unit of a quantity of 1,000,000 (i.e. 1×106) years, or 31.556926 teraseconds.

Usage

Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). Together they make a reference system, one to a quantity, the other to a particular place in a year numbering system that is time before the present.

Myr is deprecated in geology, but in astronomy Myr is standard. Where "myr" is seen in geology it is usually "Myr" (a unit of mega-years). In astronomy it is usually "Myr" (Million years).

Debate

In geology a debate remains open concerning the use of Myr (duration) plus Ma (million years ago) versus using only the term Ma.[1][2] In either case the term Ma is used in geology literature conforming to ISO 31-1 (now ISO 80000-3) and NIST 811 recommended practices. Traditional style geology literature is written

The Cretaceous started 145 Ma and ended 66 Ma, lasting for 79 Myr.

The "ago" is implied, so that any such year number "X Ma" between 66 and 145 is "Cretaceous", for good reason. But the counter argument is that having myr for a duration and Mya for an age mixes unit systems, and tempts capitalization errors: "million" need not be capitalized, but "mega" must be; "ma" would technically imply a milliyear (a thousandth of a year, or 8 hours). On this side of the debate, one avoids myr and simply adds ago explicitly (or adds BP), as in

The Cretaceous started 145 Ma ago and ended 66 Ma ago, lasting for 79 Ma.

In this case, "79 Ma" means only a quantity of 79 million years, without the meaning of "79 million years ago".

See also

References

  1. ^ Mozley, Peter. "Discussion of GSA Time Unit Conventions". web page. Geological Society of America. Archived from the original on 2016-03-03.
  2. ^ Biever, Celeste (April 27, 2011). "Push to define year sparks time war". New Scientist. 210 (2810): 10. Bibcode:2011NewSc.210R..10B. doi:10.1016/S0262-4079(11)60955-X. Retrieved April 28, 2011.