Two new shows debut this week with time travel as their themes: NBC’s “Timeless” and The CW’s “Frequency.” Time travel, of course, is a well-worn TV trope that has been used many times over the years. Here are five of the quirkiest examples:

PEABODY’S IMPROBABLE HISTORY (1959-64) This regular segment on “Rocky and His Friends” featured talking dog Mr. Peabody and his nerdy adopted son, Sherman, traversing time in his Way-Bac Machine.

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THE TIME TUNNEL (1966-67) James Darren and Robert Colbert played scientists who prematurely activated the secret government project that gave the series its name and thus found themselves adrift in time, unable to return to the present.

IT’S ABOUT TIME (1966-67) Two astronauts (Jack Mullaney, Frank Aletter) crashed through the time barrier, ending up among friendly cave people (Joe E. Ross and Imogene Coca).

THE FLINTSTONES MEET THE JETSONS (1987) In this animated TV movie (perhaps inspired by “It’s About Time”), young Elroy builds a time machine that his dog, Astro, accidentally sets to “past,” hurtling the Jetsons all the way back to prehistoric Bedrock.

BACK TO THE FUTURE (1991-92) Saturday-morning cartoon based on the movie franchise focused mostly on eccentric scientist Doc Brown, who was voiced by Dan Castellaneta (“The Simpsons”).