This film is an animated short depicting a theory of how life could have began on Earth. The short is very colorful, with a very catchy song. While the subject is simplified for younger children, it does illustrate how the Carbon, Hydrogen, Oxygen and Nitrogen molecules 'combined' to form amino chains which were precursors to simple one-celled creatures. The new chains appear as small creatures comprised of the letters themselves (C-H-O-N) and dance around. While the animation isn't of the highest quality, the animated short has been showing continuously in the Smithsonian for as long as I have visited.
This film was (and may still be) running in the Smithsonian Museum of Natural History, in a dark alcove right by the Dinosaur wing on the first floor.