David Mrazek kept returning to ‘‘a teachable moment’’ in the minutes before ‘‘From Billions to None’’ made its world premiere as a finished film Tuesday at the Peggy Notebaert Nature Museum.

Before and after the film about extinction, as viewed through passenger pigeons, I walked the second floor of the museum and looked at various passenger-pigeon specimens on display, the last of the physical form from more than a century ago. Call it a ‘‘teachable space.’’

Passenger pigeons are a unique medium to use to contemplate extinction. There is a definite end to a species that once existed by the billions. The last passenger pigeon, Martha, died Sept. 1, 1914, at the Cincinnati Zoo.

With the film, Mrazek, the producer/director/writer, was making ‘‘teachable art.’’

That’s no small feat because, at its heart, ‘‘From Billions to None’’ is a polemic or a prophetic sermon. Polemics or prophetic sermons deal in assertions and the certainty of hellfire and brimstone, not in the ambiguity that often strolls arm in arm with art.

Joel Greenberg nailed the central thrust of the film late when he said: ‘‘As a cautionary tale, to the proposition that no matter how common something is — water, oil, something alive — if we’re not careful with it, we can lose it.’’

If you don’t think that applies today, pay better attention.

Greenberg is both a main character in the film and a co-writer/co-producer. He authored A Feathered River Across the Sky: The Passenger Pigeon’s Flight to Extinction, which is earning worldwide acclaim. It does for a universal topic what he did for the Chicago natural world with A Natural History of the Chicago Region. (Full disclosure: Greenberg and I co-hosted the ‘‘Outside’’ radio show in 2011.)

In A Feathered River, Greenberg meticulously marks the demise of what was once the most abundant bird in North America. To capture the whole of Greenberg’s book would require a Ken Burns-length epic.

Mrazek has an hour. To make the story work, art plays a big role. Two things were notable:

The movie has a visual problem — and a big one: The central character has been dead for nearly a century. But in the 21st century, that is merely a challenge for CGI. Wyatt Mitchell was the main CGI animator. He started the project as a student at Tribeca Flashpoint and continued after graduation. That is a strong point of the movie on the art side.

Another big plus is the aerial visuals shot by Greg D’Aquila and two other quadcopter ‘‘pilots’’ in Wisconsin.

Mrazek takes the film beyond the specific of passenger pigeons to the global by tying it to what we are doing with pillaging the natural resources in the ocean.

I appreciated the ambiguity with which Greenberg, both in the film and in the question-and-answer session afterward, approached the possibility — a real one — of a hybrid passenger pigeon being developed from the DNA in specimens.

The passenger pigeons are gone, long gone. Their story, though, is far from over.

The film was financed through crowd funding, but more financial help is needed for publicity and distribution. It will be broadcast on public television this fall. To help or for more information, go to billionstonone.com.