Conversation so far:
What did Casey Kasem have to do with the American Top 40?
Kasem, along with Don Bustany, Tom Rounds, and Ron Jacobs, launched the weekly radio program American Top 40 (AT40).
When did they launch the program?
On July 4, 1970.
What else happened during this time period?
Loosely based on the TV program Your Hit Parade, the show counted down from #40 on the pop charts to #1-.

Question: How long did the show run?
Self-contained rewrite: How long did the weekly radio program American Top 40 (AT40) run?