The new trailer for the upcoming “unrestored” rerelease of 2001: A Space Odyssey opens with a surprising “green-card” featuring the MPAA’s rating for the film: Somehow, 2001 is rated G.

According to the ratings system’s official website, G means a movie that “contains nothing in theme, language, nudity, sex, violence, or other matters that, in the view of the Rating board, would offend parents whose younger children view the motion picture ... some snippets of language may go beyond polite conversation but they are common everyday expressions. No stronger words are present in G-rated motion pictures. Depictions of violence are minimal. No nudity, sex scenes or drug use are present in the motion picture.” So bring your kids to the theater this summer for 2001, and let them see how an artificial intelligence goes mad, tries to murder its crew, and then leads to the birth of a gigantic alien Star Child.

2018 is the 50th anniversary of the original release of 2001. It is also the 50th anniversary of the creation of the MPAA’s ratings system. Initiated in 1968 by then-MPAA president Jack Valenti, the Classification and Ratings System (CARA) was designed to replace the dated and restrictive Motion Pictures Code that had governed Hollywood content for decades. By now, the ratings and their contours are well-established, but the first few years were a little rocky; the initial CARA ratings looked very different than the ones we‘re used to. There were initially just four ratings, only two of which have survived: G, M (essentially the precursor to PG), R, and X, which barred anyone under 16 from the theater. Eventually M became GP and then PG; in 1984, PG-13 was added as an intermediary between PG and R. NC-17 officially became the adults-only rating in 1990.

Because there were fewer ratings in the late 1960s and early 1970s, and because cultural standards were different (and because once ratings are set they’re set for life, unless the movie’s content is changed, as in a director’s cut) some of the movies of that era (and older movies which were rated for the first time for re-releases then) have very surprising ratings — like the decidedly not-for-children 2001: A Space Odyssey. Here’s a brief list of some of the most shocking G ratings in history.

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