history as the subject and approached Attenborough in 1970 with the idea. Attenborough was receptive, even to the idea that he should present the series, but both men realised at that time that it was beyond the scope of the Unit's capabilities. When Attenborough resigned from his administrative duties to return to programme making at the start of 1973, planning for the proposed series resumed. It was another three years before the resourcing and financing were agreed, the outline episode scripts written (by Attenborough) and a production team in place. Parsons would serve as series producer and share production duties for the individual episodes with Richard Brock and John Sparks. Filming took place in 39 countries, featured over 650 different species and involved over 1 million miles of travel. Attenborough himself has said that if it had not been for computerised airline schedules, the series would have probably been impossible to undertake. When it was finally broadcast in 1979 on BBC 1, Life on Earth drew an audience of 15 million people in the UK and was eventually seen by an estimated 500 million people worldwide. Building on success The Natural History Unit made its name with Life on Earth, and was rewarded by being awarded departmental status by BBC management in December 1979. Christopher Parsons, by then its most experienced producer, became the first official Head of the Unit. It celebrated its silver jubilee in 1982 with the miniseries Flight of the Condor, and sealed its reputation as one of the foremost production companies for popular natural history films in the following decades. A succession of series have followed the format established by Life on Earth, often presented or narrated by Attenborough, and transmitted on the BBC's main channel. The Blue Planet (2001) and Planet Earth (2006) typify these signature programmes, characterised by high production values, specially-commissioned musical scores and often ground-breaking footage of wildlife from around the globe. The NHU has also diversified into other programme formats. Its Diary series have featured African big cats, elephants, orang-utans and bears in a nightly wildlife soap opera. Among of the longest-running programmes has been Wildlife on One (1977–2005) which was broadcast in a regular evening slot. The Continents strand on BBC Two has featured series on all the world's major land areas over the past eighteen years, including Spirits of the Jaguar (1996), Land of the Tiger (1997), Andes to