After 15 big red-letter seasons, NBC’s ER came to an end on Thursday night, earning its largest audience in nearly three years—some 16.2 million viewers, according to Nielsen estimates. This audience represents the largest showing for a dramatic series finale since CBS’s Murder, She Wrote ended back in 1996.

The two-hour finale of the long-running, ensemble medical drama was informed by the real-life tragedy of Shelby Lyn Allen, a 17-year-old Redding, California, native who died of alcohol poisoning in December.

I won’t spoil the details (mainly because NBC continues to repeat the finale for those who missed it), but suffice it to say it capped the end of an era in more ways than one. Dr. Carter (Noah Wyle) opening his brand-new medical facility in Chicago for the less fortunate was the new beginning at the end of ER; the question is, where might a Wyle-anchored spin-off end up in this day and age, if at all?

ER’s finale wasn’t just the end of an era for the Peacock’s 10 PM drama slot, which surrenders to Jay Leno’s new weeknight prime-time show in the fall. It also appears to be the front end of a trend to come: where more high-impact network dramas adapt to new delivery methods, migrate to cable, or die on the vine for affordability reasons.

That “adapt, migrate, or die” thought was an interesting one to ponder in the context of television. That’s how ecologists describe options for a species when a “forcing function” like climate change is looming . It’s a perfect parallel for TV in the 21st century: programming decisions are increasingly met by forcing function(s) like the down economy, rising production costs, varying delivery technologies, wider battles for smaller audiences and so on.

How else can one explain the end of Guiding Light—the longest running show in broadcasting history— which will cancel on CBS after a monumental run? The archetypical “soap opera” was a staple for Procter & Gamble to “peddle” household cleaning products and sundries to women. P&G’s people are changing with the times; they’re thinking about web portal content with original digital material to connect with increasingly wired homes (and moms). They’re certainly not the only ones.

And lastly, speaking of digital, the brain robots in the second-to-last Life on Mars (ABC) really had me thrown—especially when yours truly had it figured as the last episode. Serves me right for paying more attention to my NCAA brackets than the TV guide lately. Or perhaps I was having my own weird, asteroid-interrupted dream involving Mackenzie Phillips and Valerie Bertinelli. I know, TMI.

Ahem. Anyway, I never had Mars pegged for a sci-fi, 2001:A Space Odyssey-meets-Mission to Mars that it revealed itself to be. It all made me wish this freshman show had carried on. I didn’t figure Gene was Sam’s dad or that they had all been asleep during a two-year Mars mission. I couldn’t have imagined that what we were following were “neurological simulations” that were warped by faulty tech after an asteroid shower.

The only thing missing? The HAL-9000.

One thing is certain after this week: none of us are going to wake up to television like in 1973 (or 1975, to honor my One Day at a Time daydream) anytime soon.