Original air dates: 6 January 1977 – 15 February 2005
The series actually started when Attenborough had just started freelancing after resigning his job at the BBC. Being freelance is a risky especially when you have a family as he did. Having the opportunity of small but regular income felt reassuring as BBC started short but regular programmes on wildlife that they wanted him to lend his voice to it to make it cohere as a series (p. 279 Life on Air).
The dates of the original broadcast were taken from (TV maze.com) which even has a seemingly complete episode list.
Reference:
Life on Air (2003) Original edition
Revised edition (2010). Even though the title of the series is in italics at the start of the chapter on “Life on Earth” the index system in both versions of the book missed it. The updated version does refer to that series near the end of the book.