Over the past year, some of the biggest names in the music industry announced their retirement and end of touring, leaving younger musicians to rise to the occasion — and claim their spot on top.

Elton John, Neil Diamond, Rush, Paul Simon, Kenny Rogers, Joan Baez, Ozzy Osbourne and Aretha Franklin are among the baby-boomer stars that have reached the end of an era. Health is a major concern for most; Diamond was recently diagnosed with Parkinson’s Disease, Baez has lost her vocal range, Franklin cancelled upcoming shows with worried health concerns, and Rogers had to wrap up his farewell tour early due to a series of health challenges.

Next month, Simon begins a tour that he said would bring his career to a “natural end,” while Osbourne is headed out on his “No More Tours 2″ later this year. Additionally, Tom Petty died last year at 66-years-old, and Billy Joel, 68, has limited most of his performance schedule to gigs at Madison Square Garden as part of his ongoing residency.

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It’s difficult to comprehend the fact that these major stars will not be touring anymore, and it’s leaving industry veterans worried about the future.

“As these boomer rock & roll artists are passing and retiring and disappearing, I don’t see anything that’s going to take their place musically,” Jeff Jampol, who manages the estates for The Doors, Ramones, Otis Redding and Janis Joplin, told Rolling Stone. Additionally, Marsha Vlasic, agent for Neil Young and The Strokes, described her concern for the future, wondering who would be their replacements.

Right now, the concert industry is doing fairly well, with a good portion of sales rolling in from these music veterans. According to Pollstar‘s Top 100 last year, 23 of the artists were 65 or older.  Roger Waters brought in a whopping $92 million while on tour and Paul McCartney made $55 million from just 22 shows. Bruce Springsteen racked up $288 million from his 2016 world tour, and when old-timers McCartney, Rolling Stones, Young, Waters, Bob Dylan and The Who played at the Desert Trip festival that same year, the team brought in more than $160 million in sales.

Peter Shapiro, a well-known concert promoter who has booked rockers like Dead and Company and Steve Winwood at his venues, doesn’t have a clear view of the future.

“I don’t think people have thought it through a lot,” Shapiro told RS. “You’re about to lose that generation of classic arena bands.”

Some of these industry executives aren’t seeing the potential in these upcoming acts, though. There’s fifty-something acts like U2 and Metallica taking over the scene, along with Guns ‘N Roses and Garth Brooks. U2 brought in $176 million last year, and with a new album, the band doesn’t seem to be going anywhere. And that’s only for the older musicians.

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The new generation is making way. The baby boomers had their time to shine, but artists who grew up in the ’80s and ’90s are emerging. Bruno Mars, 32, was the youngest act to make it on Pollstar’s Top 5, Ed Sheeran is breaking concert records, and Dave Matthews Band, who emerged in the ’90s, are still going strong. Ladies like Taylor Swift, Beyonce, Lady Gaga, Adele, and Katy Perry are selling out stadiums with expensive seats. At Swift’s tour, she has a variety of price levels, including some at $475. Beyonce’s upcoming tour with Jay-Z had such high demand that the duo had to extend the show to more dates.

“Once somebody announces their retirement, it’s important,” Marc Geiger, the William Morris agent who represents Jack White, Neil Diamond, LCD Soundsystem and others told RS. “But people look at the next team.”

Bands are always compared to artists that came before them. Records are broken all the time, and new musicians are always on the horizon. Take the Beatles for example: people assumed no boy band could compare. Then, there was a slew of boybands in the early 2000s, inlcuding the Backstreet Boys and *NSYNC. Then, in 2012, One Direction emerged, surpassing the ’60s band’s record. These titles and records don’t necessarily make one artist better than the other, the revolution just naturally happens as each age group, well, ages.

Right now, Justin Timberlake, Halsey, Demi Lovato, Maroon 5 and Imagine Dragons made it into the top 20 spots on the Billboard Top 100 artists, with Jack White stealing the top spot of the week. The chart is an example of how fast music changes, and how much growth is yet to be made.

Longtime concert promoter Lucy Lawler-Freas told RS that she predicts acts like Foo Fighters and Pearl Jam will “step up” and take the spots that McCartney and Rolling Stones once filled, over time. Sure, there will probably be a gap once all of these legendary rock stars have announced the official end to their tours, but that gap will be replaced.

“The sky isn’t falling,” Freas said. “But it may be a little cloudy for a little bit.”

Just as fast as an artist retires, another one is ushered into the music industry, and who knows — the next “big hit” star that will replace these rock veterans could be on the horizon, about to emerge at any moment.