Forty years ago it would have been unthinkable to see the top 10 of the Billboard Hot 100 singles chart made up entirely of black artists.

This week, for the first time ever, the top 10 chart is comprised exclusively of black hip-hop and R&B performers, including superstars Beyoncé (search), 50 Cent (search) and Nelly (search), alongside up-and-comers like Chingy and YoungBloodZ.

"This is obviously a landmark week for R&B and hip-hop artists, and black artists on the charts," says Billboard rap editor Rashaun Hall.

"It's been an ebb and flow for the last couple of years, and this is clearly the most dominant time. It's two genres whose time has come. Hip-hop dominates every other segment of pop culture, whether it's film or television or just music in general. It was just a matter of time before it took over the charts."

Unlike the Soundscan sales-based Billboard Top 200 album chart - whose top 10 this week features five hip-hop and R&B albums - the Hot 100 singles chart is based on a number of elements, including Nielsen radio ratings, Soundscan numbers and radio station playlists.

This week's chart is led by Beyoncé's "Baby Boy," which features reggae singer Sean Paul. While the other entries in the top 10 are all rap songs, two of them feature choruses by R&B singers, a trend that has grown over time in songs by rappers such as Ja Rule and may contribute to some of the crossover potential of hip-hop tracks.

"It's definitely a best of both worlds scenario," Hall says.

Other entries in this week's top 10 include Lil Jon at No. 3, with the club fave "Get Low"; 50 Cent with "P.I.M.P," at No. 7; and Black Eyed Peas at No. 10, with "Where Is the Love?" - the only song to feature a white singer, thanks to an uncredited Justin Timberlake appearance in the chorus.

"It's a huge day in that the singles-sweep makes tangible what kids all over the world have known for decades: that black music is the engine that drives American pop," says author Donnell Alexander, whose book "Ghetto Celebrity" explores his journey from son to father in a hip-hop-saturated world.

"Look at the range of talent on this list: Beyoncé, 50 Cent, everyone really. These aren't just artists who sell a ton of CDs. They also help lift the bar, in terms of artistic achievement.

"It's like once you go black, you never go back. There will be Asian artists on these lists, Latin artists. But we certainly won't ever go back to white pop."

But Z100 DJ Paul "Cubby" Bryant is more pragmatic in his analysis.

"I don't see this being all that surprising considering hip-hop and R&B are really crossing over in all areas. It's appealing to all different colors and races," he says.

"It comes in waves. You're always going to have different music. Who knows? The boy bands may be ruling the top 100 in about a year. It all comes in cycles, but I don't think skin color is a big issue.

"A hit's a hit."

Billboard top 10

1) Baby Boy - Beyoncé featuring Sean Paul

2) Shake Ya Tailfeather - Nelly, P. Diddy & Murphy Lee

3) Get Low - Lil Jon & The East Side Boyz featuring Ying Yang Twins

4) Right Thurr - Chingy

5) Frontin' - Pharrell Featuring Jay-Z

6) Damn! - YoungBloodZ featuring Lil' Jon

7) P.I.M.P. - 50 Cent

8) Into You - Fabolous featuring Tamia or Ashanti

9) Stand Up - Ludacris featuring Shawnna

10) Where is The Love? - Black Eyed Peas