When Did the Seventies Begin and End?

I think most of us would agree that the 70's did not begin on 1/1/70 and end on 12/31/79. The whole feel of the Sixties was alive at the begining of the decade. And the feel (or lack of feeling) of the Aweful Eighties didn't kick in exactly at midnight on 12/31/79. Here are a few ideas. Your comments and suggestions are welcome.

When the Seventies Began

1. With the breakup of the Beatles in 1970
2. When Nixon won re-election and demolished George McGovern in 1972
3. When Nixon resigned in 1974
   
4. When the last US service member left Vietnam in 1975

When the Seventies Ended (or when the Eighties began)

1. With the election of Reagan in 1980
2. When John Lennon was murdered in 1980
   
3. With the freeing of the Iran hostages in 1981
4. With the release of Michael Jackson's "Thriller" in 1982