Unix Time is seconds after 1 January 1970. 1 January 1970 is geologically close to 16 July 1945, Trinity Test. The Trinity Test was the first among many detonations of a nuclear device. The detonations spread radioactive elements. This created a stratigraphic presence and altered earth’s geology. The Space Race culminated with Apollo 11, 16 July 1969 - 24 July 1969. Therefore the Space Age, Nuclear Age, and Computer Age all started at roughly the same time. Therefore it makes sense to change calendar eras. BC to AD to ? (The Third Age?)