George Pal wanted to film the novel's sequel, "After Worlds Collide," which depicted the struggle of human survivors on the alien planet. However, the failure of his film Conquest of Space (1955) badly damaged his career and the sequel was never made.
There is a shot toward the end of a group of people sitting around a country store listening to the radio. Among them the little boy and dog later rescued by helicopter. The same shot shows up in The War of the Worlds (1953)
The rights to the story by Philip Wylie and Edwin Balmer were originally bought in 1933 by Paramount, when director Cecil B. DeMille was planning a related project called "The End of the World." DeMille had hoped to rush the project into production after filming wrapped on This Day and Age (1933), but the script was never even written and the studio scrapped the project.
George Pal originally envisioned this as a big budget sci-fi movie. However, he found he was unable to secure the proper financing so he had to scale his ambition back considerably for the finished film.
The trivia items below may give away important plot points.
In the final shot we see the Ark passengers disembarking with an obvious painted background depicting Zyra. This bad painting was tacked on for the film's sneak previews. Originally, producer George Pal wanted to depict Zyra as a miniature set, but Paramount shipped the film out before this could be done.