65,000,000 years ago, a mountain-sized meteor, bristling with unknown energies, crashed into the Earth in what is now the Yucatán Peninsula in Mexico, with a major chunk of the object landing in Central Africa. The impact and resulting ecological catastrophe causes the extinction of the dinosaurs.
In present day, wealthy industrialist John Greystoke has been funding an expedition into the jungles of Africa to locate the meteor, now a legend, and harness its unique energy as a solution to the looming energy crisis. Despite the best efforts by scientist and adventurer James Porter, the expedition is a failure, and John is preparing to leave Africa with his wife, Alice, and their son, John Jr. As their pilot takes them over the jungle, the family sees a lone male mountain gorilla journeying to find a new family. The huge ape makes a threat display at the passing helicopter and continues on his way.
Not far away, the rogue, Tublat, comes across a troop of his fellow gorillas, led by a silverback male named Kerchak. In a fight for dominance, Kerchak defeats the rogue and begins to return to his mate, Kala, and their newborn child, only for Tublat to deal him a fatal blow by smashing a huge stone over Kerchak’s head. Kala and the others can only look on in horror as Tublat asserts his control over the family.
On a course that takes them over a semi-active volcano, the Greystokes’ helicopter’s instruments begin to go haywire. As the pilot struggles to regain control, they find themselves over the resting site of the meteor, now a mountain in the heart of the jungle and guarded by baboons. Landing to investigate, John explores a cave that leads him into the heart of the mountain, where he discovers rock formations that glow with a pulsing red light. Using his pickax, John attempts to collect a sample for study, only to cause a chain reaction that awakens the nearby volcano. Despite their best efforts to escape, the helicopter crashes, and only John Jr. is spared. Johnny is discovered by Kala, who has recently lost her child to Tublat’s regime after he falls to his death into the valley, and taken back to her nest, where the kindly she-ape nurses him back to health. Befriending three young gorillas, Johnny is adopted into the troop and discards his former identity, choosing to be called “Tarzan”, a name he made up meaning “Ape with no fur”.