Myr 363092 198796048 2008-03-17T05:19:14Z WarthogDemon 2479636 rvnnband :''This article is about the unit of time. For the Magic: the Gathering creatures, see [[Creatures of Magic: The Gathering#Myr|Creatures of Magic: The Gathering]].'' The symbol '''myr''' was formerly used in [[English-language]] [[geology]] and [[astronomy]] as a [[physical unit|unit]] of one [[million]] [[year]]s. It is an abbreviation for 'million years' and lower case is usually used. In English-language technical literature in these fields, the term 'Ma' is preferred, as this conforms to [[ISO 31-1]] and NIST 811 recommended practices. "M" denotes [[mega-]] (10<sup>6</sup>), and "a" denotes years (from the Latin [[annum]]. Note that "ma" would technically imply a milliannum (also called a milliyear in English usage), a period of a thousandth of a year or about 8 hours. The correct ISO 31-1 usage is [[megaannum]] or Ma which unambiguously denotes a duration of 10<sup>6</sup> years. To denote a date one would add ''ago'' or ''bp'' to denote ''before present''. In non-SI usage, Ma was used to denote a specific number of millions of years ago, but it was not properly used to describe a ''duration'', so: the Cretaceous started 145 Ma and ended 65 Ma, but it lasted for 80 myr (or 80 My). More often, the term "mya" (million years ago) is used in these contexts. ==See also== * [[Megaannum]] * [[Byr]] * [[kyr]] [[Category:Units of time]] {{standard-stub}}