The title is from the 1974 song "Life Is a Rock (But the Radio Rolled Me)" written by Paul Di Franco and Norman Dolph.
Another "it always comes back to David Bowie" reference - Det. Carling is quite unkind to Ruth Tyler when she's reporting her son missing, and as Carling and another detective are leaving to find them, she mutters "Look at those cavemen go." It's a line from the chorus of the song for which the series is named.
Last show of the series.