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No, Gya has not been superseded. Both terms are in use in the technical literature, and they are used differently. Ga just means a giga-annum (a billion years) and may also be used in contexts other than the past (such as half-lives of certain isotopes or future galactic evolution), whereas Gya means a billion years ago, denoting a specific point of time in the past. —
Lowellian (
reply)
17:23, 18 September 2011 (UTC)reply