Marvel’s Guardians of the Galaxy is currently dominating the box office, and the soundtrack for the hit alien superhero film is proving to be just as successful. Guardians of the Galaxy: Awesome Mix Vol. 1 is on top of both iTunes’ and Amazon’s digital-album lists, helping the 1970s pop classics featured on the soundtrack rapidly rise in popularity once more.

Adamant about filling Guardians with hits by pop stalwarts Blue Swede, the Raspberries, Redbone and the Runaways, director James Gunn found the perfect way to include the old classics into the film. In the first scene, central character Peter Quill’s mother gave him a Sony Walkman and a mix tape of her favorite songs before her death, so songs like David Bowie’s Moonage Daydream and Rupert Holmes’ Escape play behind Quill’s outer-space adventures. Sixteen old-school, late 70s model Walkmans were used during the film.

“It’s the kind of Walkman that hipsters in Silver Lake or Brooklyn would pay $4,000 for and pretend like they bought it at a thrift shop,” said Chris Pratt, who stars as Peter Quill. “It’s super vintage and really kick-ass.”

Guardians of the Galaxy producer Kevin Feige believes that the soundtrack helped keep the film anchored and relatable for mainstream audiences, saying that their goal while choosing the songs was to attract “the very people who would go, ‘What? A tree, a raccoon, outer space, what is this?’ You hear Hooked on a Feeling, and it starts to humanize even the most alien of the characters.”

“We may not know the name or the band that sings it, but we know the songs,” said Gunn. “Keeping the attachment to Earth helps to keep the movie grounded throughout the whole thing.”