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https://en.m.wiktionary.org/wiki/gigayear WotD? I didn't know SI prefixes were used for years : I've always seen bya (billion years ago). Not sure I've ever seen byo (billion years old) though.
https://en.m.wiktionary.org/wiki/gigayear WotD? I didn't know SI prefixes were used for years : I've always seen bya (billion years ago). Not sure I've ever seen byo (billion years old) though.