NPR's "Invisibilia" has usurped "Serial" as the most-popular podcast on the iTunes charts.

The show, which investigates the invisible forces that affect human life, overtook the competition in January, a few weeks after it debuted. The launch was the biggest in public radio history, airing on 260 stations and quickly landing a third-place spot on the iTunes charts.

Since the launch and rise of "Serial" this fall, media commentators have alternatively proclaimed and declaimed the dawning of a so-called "golden age of podcasting."

Writing for New York magazine, Kevin Roose explained the "great podcast renaissance" might have been prompted by the integration of USB and smartphone connectors in cars:

Combined with the macro trends of on-demand audio and connected cars, these tools have made it possible for people like Roman Mars and Alex Blumberg (whose podcasting start-up has raised more than $1 million to date) to make a living doing podcasts. And the advertisers who aren't paying attention to long-form audio storytelling might soon be convinced to give the genre another look.

On Medium, podcaster Aaron Crocco warned that the success of podcasting was mostly among a few well-connected shows that could use existing popular shows like "This American Life" as a springboard to find instant audiences:

These methods are fantastic but when you’re Joe Blow from Chicago who wants to podcast, it’s important to remember these reports of “golden age” and “advertising breaking out in podcasts” are reserved for the few elite media properties that have a vital component: a built-in audience. Without that springboard, your show is a hobby with a tiny listenership.