For this unaccredited historian, the 1990s began on Aug. 8, 1989. That was my 30th birthday, and I didn’t have much going on aside from an advance screening of James Cameron’s “The Abyss.

” And a resolution to quit smoking. I left the preview with a vision of future movies both exhilarating and a little threatening. Would all upcoming sci-fi action blockbusters be accomplished with such technical panache and personal idiosyncrasy? And would they all be so “You never backed away from anything in your life! Now FIGHT!” stressful? As it turns out, no, because they couldn’t be, of course.

But when I think about the decade that ended with unfounded worries about something we called “Y2K” and barely remember what the fuss was about (apparently all the world’s computers were going to forget to reset at midnight on Jan. 1, 2000, and then they would blow up and our brave new internet and email world would go with it), I put “The Abyss” on one side of what I see as the defining cultural divide of the 1990s. This was the decade in which irony and earnestness were at constant but constructive war with each other.

The irony would arrive in full bloom in 1994 with Quentin Tarantino’s “Pulp Fiction,” a diabolically constructed crime thriller/comedy whose every frame acknowledged that it was a construct. A construct made with love, for sure, but one whose self-knowing wink was a part of its charm. One cultural luminary who wasn’t charmed was the writer David Fo.