One of the interesting things about
Superman: The Movie is that time appears kind of malleable. At least on an aesthetic level.
First off, of course, we have the child narrator who seems to be framing the opening shot as happening circa the Great Depression -- a reference, of course, to the original publication date of
Action Comics #1 in 1938.
After the credits, we see Krypton.. and it's unclear how far in the past the scenes set in Krypton take place, or how long Baby Clark is in transit from Krypton to Earth. Ghost Jor-El says, "By [Earth] reckoning, I will have been dead for many thousands of your years" when Clark discovers him. So apparently Baby Clark was in something approaching suspended animation for thousands of years in transit? (He appears to have aged at least a year between his infancy on Krypton and his emergence on Earth though.) But then later in the film, Lex Luthor says that Superman reported Krypton to have exploded in 1948 in his interview with Lois.
The "present-day" scenes all appear to be set in 1978 and make use of then-contemporary aesthetic techniques such as flat lighting, overlapping dialogue, etc. It has a very "70s movie" vibe to it. They come after the Jor-El Ghost says that Clark has seemingly spent 12 years learning from him (it?) after his discovery/construction of the Fortress of Solitude at age 18.
So if you do the math, the scenes of 18-year-old Clark in Smallville would presumably be set in 1966, and Clark himself would have landed in either 1948 or 1949... But of course, those scenes in Smallville don't aesthetically match up at all. From the clothing to the cars to the music heard playing on the radio, everything about 18-year-old Clark's scenes scream 1950s. And the scenes with Baby Clark just after his spaceship has landed all seem to scream 1940s or 1930s. The filmmaking techniques are different, too -- dynamic lighting, stylized dialogue. These scenes have a strong John Ford vibe.
So, the nominal timeline would be:
1978: Clark arrives in Metropolis and assumes the identity of Superman, defeats Lex Luthor
1966-1978: Clark in training under Ghost Jor-El
1966: Jonathan dies; Clark graduates from Smallville High School, learns of his true origins, discovers/constructs the Fortress of Solitude
1948 or 1949 (depending on age of baby): Baby Clark lands in Smallville, is discovered by Jonathan and Martha
Thousands of years in the past OR 1948, whichever: Baby Kal-El escapes the destruction of Krypton
But... yeah, nothing about that meshes with how we see the denizens of Smallville actually
living.
But, as Bob Chipman points out in his
Superman: The Movie entry for
Really That Good -- that's okay, because the cumulative impact of these slightly-anachronistic elements is to reinforce an important thematic element of Superman's personality: he embodies an idealized vision of American culture. He didn't just grow up in a small Kansas town -- "he grew up in a Norman Rockwell painting."