Mya is an abbreviation for million years ago, a unit of time equal to 1,000,000 years (i.e. 1×106 years), or 31.556926 teraseconds. It is equivalent to one megaannum (symbol Ma), based on the metric prefixmega-.
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya or Ma (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 astronomyMyr 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).
Debateedit
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".
^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.
million, years, redirects, here, adele, song, million, years, song, million, disambiguation, this, article, about, million, years, taake, song, noregs, vaapen, other, uses, disambiguation, abbreviation, million, years, unit, time, equal, years, years, 556926, . Million years ago redirects here For the Adele song see Million Years Ago song For 1 000 000 BC see one million disambiguation This article is about million years ago Mya For the Taake song see Noregs vaapen For other uses see Myr disambiguation Mya is an abbreviation for million years ago a unit of time equal to 1 000 000 years i e 1 106 years or 31 556926 teraseconds It is equivalent to one megaannum symbol Ma based on the metric prefix mega Contents 1 Usage 2 Debate 3 See also 4 ReferencesUsage editMyr million years is in common use in fields such as Earth science and cosmology Myr is also used with Mya or Ma 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 editIn 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 writtenThe 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 inThe 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 editBillion years ago Kyr Megaannum Ma Symbols y and yrReferences edit Mozley Peter Discussion of GSA Time Unit Conventions web page Geological Society of America Archived from the original on 2016 03 03 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 Portals nbsp Earth science nbsp Mathematics nbsp Astronomy nbsp Stars Retrieved from https en wikipedia org w index php title Myr amp oldid 1201844757, wikipedia, wiki, book, books, library,
