Frommega- +‎year.

megayear (pluralmegayears)

2. Amillionyears: athousandthousandyears.

   Synonyms:Myr,My,Ma(symbols);mega-annum,millionennium

   Holonyms:petasecond <giga-annum,gigayear <exasecond <zettasecond <yottasecond <ronnasecond <quettasecond

   Meronyms:quectosecond <rontosecond <yoctosecond <zeptosecond <attosecond <femtosecond <picosecond <nanosecond <microsecond <millisecond <centisecond <decisecond <second <decasecond <minute <hectosecond <kilosecond <hour <day <week <megasecond <fortnight <month <year <gigasecond <century <kiloannum,kiloyear,millennium <terasecond

   • 1984, J. B. Cadwallader-Cohen, W. W. Zysiczk, R. B. Donnelly, “The chaostron: an important advance in learning machines”, inCommunications of the ACM,27(4), p.357:

     After three hours the machine had not printed its response to the first input pattern; evidently the rate of learning under these conditions is very low (we judge it to be on the order of 10^-6 concepts formegayear).

   • 1997, Ian Lerche,Geological Risk and Uncertainty in Oil Exploration, page231:

     We know from isotopic measurements, stereochemistry, and gas chromatography/mass spectrometry, that the production of hydrocarbons in the Earth occurs on timescales ranging from fractions of amegayear to hundreds of megayears, in a temperature regime in the rough range of 0-200°C, and in an evolving environmental "smog" of sedimentary pores containing water laced with varying amounts of ions, molecules, and minerals.

   • 2001, Fred Howard,Taming the Vipers in the Slough, page400:

     As to that time span, all clearly definite forms of life or species seem to take amegayear more or less to come about and be present for a while.

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