As one of the top nominees for the 55th Annual GRAMMY Awards, Mumford & Sons share nominations for Best Rock Performance and Best Rock Song with Alabama Shakes, Jack White, the Black Keys, and Bruce Springsteen, while their sophomore album, Babel, is nominated for Album Of The Year as well as Best Americana Album alongside releases by the Avett Brothers, the Lumineers, John Fullbright, and Bonnie Raitt.

One might wonder how an acoustic, banjo-driven "hoedown folk" band, to quote British publication The Guardian, could land next to White and the Black Keys, two blues-oriented electric acts, and the Southern soul/R&B-inspired Alabama Shakes.

But the presence of the Shakes and the folk-rocking Lumineers in the Best New Artist category — along with Babel's distinction as the fourth best-selling album of 2012 — suggests that the lines between roots and rock are continuing to blur, and those crossing them are gaining more acceptance than ever, and at a faster pace. Alabama Shakes, the Lumineers and Fullbright are all nominated for debut albums or songs from debut albums.

Some music experts and artists alike say it's all about shared roots — in fact, roots-rock is a label commonly used to define these artists' work. And even though Americana was labeled alternative country before it found a place in Merriam-Webster's dictionary, it contains elements of blues, R&B and rock, as well as folk and bluegrass. Jed Hilly, executive director of the Americana Music Association, says artists today gain inspiration from tracing the music back to its roots, similar to how legendary artists such as the Rolling Stones, the Beatles and Led Zeppelin channeled their respective inspirations.

"I see a direct link from Emmylou [Harris] to Gillian Welch and Dave Rawlings to Old Crow Medicine Show, the Avett [Brothers], Mumford [& Sons] and now the Lumineers, with these artists passing the torch from one to another, and back," Hilly says.

The Avett Brothers' Scott Avett didn't set out to become part of that chain, it just happened."

"When I was a teenager, I really admired a very fast and loud and abrasive aesthetic," says Avett. "I was listening to hardcore, hard rock; I was looking for what's after this great movement of grunge and punk rock and what happens now?"

Some cite Americana's authenticity — whether rooted in Appalachia, the Delta or the industrial Midwest — as key to its growth. But according to GRAMMY Awards telecast Co-Producer and "Austin City Limits" Executive Producer Terry Lickona, other factors include the Internet, the increasing influence of independent record labels and the popularity of music festivals, along with the cyclic nature of a business in which something old becomes new nearly every decade.

"Somebody hears a Mumford & Sons song, it spreads by word of mouth, [and] kids go searching for the music online," Lickona notes. "Hundreds of thousands of kids see them at music festivals all over the country, and then maybe radio finally gets onboard and the artists start showing up on the Billboard charts."

"A lot of it has to do with younger people having the ability to learn every detail of an artist they like in about 10 seconds," Fullbright adds. "People used to have to scour through record stores in the dusty sections to find guys like Muddy Waters and Townes Van Zandt. Now you've got a Wiki page that's got a little section that says 'influences' under almost every artist."

Alabama Shakes' Brittany Howard says one distinction these artists share is a willingness to take chances and not follow trends — not to mention an aversion to categorization.

"I think people my age and younger are yearning for something different," she offers. "The thing I love about the Alabama Shakes is that we are just as influenced by AC/DC, Led Zeppelin or Black Sabbath as we are by Otis Redding, Aretha Franklin or James Brown."   

The Lumineers' drummer Jeremiah Fraites says a notable characteristic of his band, Mumford & Sons and the Avett Brothers is "a big pulse."

"There's a beat, there's a pop sensibility to it all," says Fraites. "It's not as folky as a lot of people are trying to categorize it."

Avett, who shared the stage with Mumford & Sons and Bob Dylan in a tacit tribute to Americana music at the 53rd Annual GRAMMY Awards in 2011, suggests an even larger commonality.

"Ultimately, a Beyoncé song and a Ryan Adams song and an Avett Brothers song and a Queen song and a Mumford & Sons song, when you break it down, it all ends up being about a melody and lyric," he says. "There's really nothing dividing any of them." 

In another testament to the influence of roots music, the 55th GRAMMY telecast will feature a special tribute to the late Levon Helm. Artists set to perform in tribute to the American icon include Elton John, Howard, Mumford & Sons, and Zac Brown.

As Fullbright  notes, "American roots is the continuing innovation of somebody else's roots. All music is roots music."

(Austin-based journalist Lynne Margolis currently contributes to American Songwriter, NPR's Song of the Day and newspapers nationwide, as well as several regional magazines and NPR-affiliate KUT-FM's "Texas Music Matters." A contributing editor to The Ties That Bind: Bruce Springsteen from A To E To Z, she has also previously written for Rollingstone.com and Paste magazine.)