Happy birthday, rock! Er, how old are you now?

Forget religion and politics. When it comes to controversial subjects, the 50th anniversary of rock 'n' roll is the topic du jour. For many people, that milestone will occur this year on July 5, the day five decades ago when a young Southerner named Elvis Presley recorded "That's All Right (Mama)" in a Memphis studio. That city is planning a year-long celebration in honor of the event, calling Elvis's single "the first rock and roll song ever recorded, making Memphis the birthplace of a musical revolution."

But even after 50 years of gyrating hips, not everyone agrees the King's song was the one to launch a thousand careers. Rock 'n' roll evolved - growing out disciplines such as rhythm and blues, country, and gospel. It didn't arrive, Jerry Lee Lewis style, in a great ball of fire, argue some who track music history.

"There is no one song or one moment for the beginning of rock 'n' roll," says Richard Aquila, a historian and former host of National Public Radio's "Rock & Roll America." "Maybe that's good, because it contributes to the mythology of the music, in the sense that its origins are shrouded in mystery, and people can argue about it."

The genre that influenced hair length and TV shows, politics and movies, is getting some attention this year in particular, even if historians and rock critics can't agree whether it's really 50 or not.

By some accounts, the 50th anniversary has already passed - or is still to come. Some of the confusion arises because rock was influenced by music from the black community, much of which was getting people out of their seats long before the King's 1954 session. Besides the Elvis song, other contenders for the birth of rock include the Ike Turner/Jackie Brenston recording of "Rocket 88" in 1951, the first rock and roll concert in 1952, and "Rock Around the Clock," by Bill Haley and His Comets, which hit No. 1 in 1955.

The history of the term "rock 'n' roll" doesn't help much with the search for rock's roots. The phrase was used in the early part of the 20th century to refer to everything from dancing to having sex, but was popularized in its current form in the early 1950s by Alan Freed, a DJ who hosted the first "rock" concert.

That 1952 show, featuring black R&B artists, drew far more people that the 10,000-seat, Cleveland venue could hold, resulting in a riot.

The Rock and Roll Hall of Fame and Museum in Cleveland used that event to celebrate the 50th anniversary of rock in 2002. So did Life magazine, which published a book in 2002 called, "LIFE Rock & Roll at 50," with an introduction by Dick Clark.

Apparently even the dean of rock sees the dawn of rock as a moving target, since Mr. Clark announced that 2004 was the 50th anniversary year on his recent New Year's Eve program.

"Regardless of where you place the origin, it's a thing worth celebrating," says Warren Zanes, former guitarist for the Del Fuegos and head of education at the Rock and Roll Hall of Fame. "But I'd also say that anyone's choice of where rock 'n' roll started from is ultimately an arbitrary choice."

Although Professor Aquila, who teaches at Ball State University in Muncie, Ind., warns that oversimplifying rock's origins could "distort the true history and cultural significance of rock 'n' roll," musician Isaac Hayes - one of the ambassadors for the Memphis celebration - disagrees. "You have to find a point along the chain, where everybody can focus on it," says the soul and funk singer.

This year, commemorative events will originate in Memphis, including a "Global Moment in Time" on July 5, where radio stations around the world are being asked to play "That's All Right (Mama)" simultaneously. At Graceland, the King's birthday was celebrated on Jan. 8, part of a full-year celebration of the start of his career. Folks working there won't talk about Elvis as the father of rock, but they don't mind if others do.

"Elvis never claimed to have invented rock 'n' roll, and we don't claim that he did, but the majority of the world at large does look at July 5, 1954 - the day Elvis Presley's career began with that first recording - as the big bang," says Todd Morgan, director of media and creative development at Graceland.

Zanes and Aquila have different views on the influence of "That's All Right (Mama)," Elvis's remake (which was not a hit on the pop charts) of a rhythm and blues song by Arthur Crudup. Zanes says it's perhaps the most salient example "of a white artist going in and saying, 'I'm going to capture the sprit of that black music.' "

Aquila has a slightly different take. He says there's no question that Elvis popularized rock, but he suggests another song showed more clearly the point where R&B changed into something else: Bill Haley and His Comet's "Crazy, Man, Crazy" from 1953. "That's the first time you have what used to be R&B transformed into white performers singing it, and white audiences buying it," he says.

That's not going to stop the people in Memphis from celebrating this year. A mix of musical styles in that city gave birth to rock, says Hayes: "Had Memphis not happened, music would be different today. And that's why rock 'n' roll was born in Memphis, Tennessee."

Roy Brown, an African-American, releases "Good Rockin' Tonight," an R&B song that influences Elvis and Buddy Holly (right).

Alan Freed, a disc jockey in Ohio, launches a radio show of mostly black music called "Moondog Rock 'n' Roll Party."

Ike Turner's "Rocket 88," hailed by some as the first rock record ever, is released.

Sam Phillips founds Sun studios. He went on to launch the careers of Elvis, Carl Perkins, Jerry Lee Lewis, and Roy Orbison.

The TV show "Bob Horn's Bandstand" debuts. It would later change its title to "American Bandstand" in 1956.

Bill Haley and His Comets enter the Billboard charts with "Crazy, Man, Crazy."

Big Joe Turner records "Shake, Rattle and Roll," later a hit for Bill Haley.

Chuck Berry makes his mark with "Maybelline" in May. On July 9, Bill Haley's "Rock Around the Clock" is the first rock 'n' roll song to reach No. 1.

Little Richard (below) releases "Tutti Frutti" in January. In April, Elvis Presley becomes a superstar with "Heartbreak Hotel," a No. 1 hit for eight weeks.

The Everly Brothers sell millions with "Bye Bye Love" and "Wake Up, Little Susie."

Elvis joins the Army. Teen acts such as Bobby Darin and Paul Anka fill the void.

Buddy Holly, The Big Bopper, and Richie Valens die in a Feb. 3 plane crash.