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The symbol myr was formerly used in English-language geology and astronomy as a unit of one million years. English is a West Germanic language originating in England and is the First language for most people in the United Kingdom, the United States Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study The word million In standard English, the -lli- in million is pronounced with an l-sound followed by a A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun 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. ISO 31-1 is the part of International standard ISO 31 that defines names and symbols for quantities and units related to Space "M" denotes mega- (106), and "a" denotes years (from the Latin annum. Mega- (symbol M) is an SI prefix in the SI system of units denoting a factor of 106, 1000000 (one Million Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular 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 106 years. Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular 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.
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This standards- or measurement-related article is a stub. Annum is one form of the Latin noun meaning Year, not a form normally used for derivatives in modern languages the accusative singular Byr was formerly used in English-language Geology and Astronomy as a unit of one billion The symbol kyr was formerly common in some English-language works especially in Geology and Astronomy, for the unit of one Thousand Standardization (or standardisation) is the process of developing and agreeing upon technical standards. Measurement is the process of estimating the magnitude of some attribute of an object such as its length or weight relative to some standard ( unit of measurement) such as You can help Wikipedia by expanding it. |
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