Doc, Jules and Verne take a trip to prehistoric times to test Doc's new invention, a device which effectively disintegrates objects. Doc uses it to disintegrate a meteorite heading straight for Earth, which has unforeseen consequences for the future.
This episode includes examples of the following tropes:
- Alternate-History Dinosaur Survival: Doc and his sons inadvertently cause this to happen when, during a trip to prehisoric times, they disintegrate the meteor that would have killed the dinosaurs. Returning to the future, they find themselves in an alternate 1991, where humans don't exist and dinosaurs have developed a human-like civilization. Before they can be erased from existence, the Browns return to the prehistoric era and Doc reintegrates the meteor, restoring the correct timeline.
- The Day the Dinosaurs Died: Doc Brown and Verne stop a meteor from hitting to save a dinosaur they befriended, only to find out it was the one that would have triggered the K-Pg extinction, and without it, dinosaurs still rule the earth.
- Ret-Gone: since they created a timeline where humans never evolved, Doc and his sons are slowly being erased from existence and have to restore history before they disappear completely.
