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Encyclopedia of Astrobiology
Mega annum; Megayear; Myr Definition Ma is a common scientific abbreviation for Megayears = 1 million (10 6 ) years derived from the Latin Mega-annum. Note that the Latin accusative, annum, expresses an absolute age (e.g., the Earth is 4,560 Ma old), while the English accusative, years, expresses a period of time (e.g., the Archean eon lasted for 2,000 Myr). Ma is the most common unit of time used to describe events through most of the history of the Earth, the other planets, and meteorites.doi:10.1007/978-3-662-44185-5_912 fatcat:v2en4jninbbbjeubtc255fdw4m