I saw only the last part of this movie years ago. A spaceship lands on a planet that has a hostile environment (volcanoes, dinosaurs) and the ship must leave. Two of the crew get left behind, one man and one woman. The view from inside the ship as it leaves orbit shows that the planet is Earth, implying the stranded crew members are Adam and Eve. What is the name of this movie?
"Women of the Prehistoric Planet" (1966)?
Not to be confused with "Voyage to the Planet of Prehistoric Women" (1968). Below is the plot synopsis from Wikipedia which seems to match the details you remember from the plot:
A spacefaring crew from an advanced civilization is preparing to return home after an extended voyage. The crew includes "humans" (represented in the film by Caucasian actors and actresses) and "Centaurians" (represented in the film by Asian actors and actresses). The Centaurians have been rescued from their home planet after a catastrophic event, not explained in the movie, has devastated their planet. They are being brought back with the spacefaring explorers with an expectation that they will be assimilated into their new parent culture. One of the ships in the fleet is hijacked by a few of its Centaurian passengers and crash-lands on a prehistoric planet in the "Solaris" system. Countermanding orders, the rest of the fleet returns to search for survivors after the crash. In the film's "twist," by the time that the rescuers (traveling at fast sublight speeds) are able to return to the planet, they are encountering the descendants of the original crash survivors - explained in a simplified version of time dilation. Linda, a Centaurian from the rescue ship, falls in love with Tang after he saves her from drowning. After fighting with the planet's indigenous species (including giant iguanas meant to represent dinosaurs), Tang and Linda are marooned on the prehistoric planet - and the latter is revealed to be the captain's own daughter. In the film's coda, this savage and primitive planet is revealed to be Earth.
Here is the complete film from YouTube. You can see the couple being left on the planet at 1:23:00 and at 1:25:20 you can see the captain of the ship referring to the planet they are leaving as Earth, at which point the view from the spaceship shows us the image of Earth we're all familiar with.