 As a writer and narrator, Attenborough continued to collaborate with the BBC Natural History Unit in the new millennium.Alastair Fothergill, a senior producer with whom Attenborough had worked on "The Trials of Life" and "Life in the Freezer", was making "The Blue Planet" (2001), the Unit's first comprehensive series on marine life.He decided not to use an on-screen presenter due to difficulties in speaking to a camera through diving apparatus, but asked Attenborough to narrate the films.