Women Of The Prehistoric Planet

This cheaply made science fiction film opens as a ship crash-lands on an unidentified planet. The only survivor is a young boy. Three months later, a reconnaissance craft comes to the ship's rescue, only to discover that 18 years have passed on the planet. The boy survivor, now 18 years older, takes one of the rescue mission's women for his companion. During a volcanic eruption, the ship is forced to leave the couple behind. As the ship leaves, the admiral decides to name the planet Earth, and presumably that is how all the begetting began.