Celebrations to mark the 100th birthday of renowned British naturalist David Attenborough start next week with a show delving deeper into his milestone 1979 TV series "Life on Earth".

That programme - with its famous face-to-face encounters with mountain gorillas in Rwanda - set the pattern for natural history documentaries in the decades that followed and helped establish him as one of the world's most authoritative voices on conservation.

The new show, "Making Life on Earth: Attenborough's Greatest Adventure", goes into the stories behind the series and includes more footage of a baby gorilla climbing on the presenter and of a lioness hunting.

Reading from the diary he kept during filming, Attenborough recalls how he and the crew were detained by the Rwandan army and threatened in Saddam Hussein's Iraq.

His team talk about the challenge of setting up shoots abroad when letters took weeks to arrive, and worrying about getting precious film rolls back to Britain in metal cans.

There are also more details on their hunt for an Indian Ocean fish often called a "living fossil".

They finally got footage of the coelacanth after a fisherman caught it by accident and then tipped off the crew after releasing it. "It was the first time it was filmed alive, but only just," Attenborough jokes in the new programme.

The series was game-changing, said Mike Gunton, creative director of the Natural History Unit at the BBC, who worked with Attenborough on later shows.

"All we really have done is remake 'Life on Earth'," Gunton told Reuters.

Attenborough was born on May 8, 1926, in London. His BBC career started in 1952 and two years later he got his big break with "Zoo Quest", which he ended up presenting after the original candidate fell ill on their first shoot.

He moved into BBC management. Then, in his late 40s, he decided he wanted to return to making nature programmes and pitched the idea for "Life on Earth", a series which would track the story of evolution.

Before three years of filming started he wrote all the scripts for the 13 hours of the show.

"He has, without doubt, defined natural history and how we see the world," the new show's producer/director, Victoria Bobin, said.

"Making Life on Earth: Attenborough's Greatest Adventure" premieres on the BBC on Sunday.

There will also be a new series "Secret Garden", a concert in London and events at museums across Britain to celebrate the naturalist's birthday.

-Sarah Young and Francesca Halliwell/Reuters