Given the following context:  A cave family called the Croods survives a natural disaster, due to the overprotective nature of their stubborn and stern patriarch named Grug. The only one who questions the family's sheltered life is his teenaged daughter Eep, who frequently disobeys her father's orders out of curiosity, which he finds dangerous. Grug and Eep, along with her mother and his wife Ugga, her grandmother Gran, and her younger brother and sister, Thunk and Sandy, face time sheltered in their cave home. Eep sneaks out when she sees what she discovers to be a torch of fire, and she encounters an inventive modern human boy named Guy and his pet sloth Belt. He warns her of an impending apocalypse and offers to take her with him, but concerned for her family, Eep stays, getting a shell horn from him to blow in case she needs his help. Reuniting with her frantic family, she tries to tell them what Guy told her, but fearing things that are "different" and "new", they destroy her horn. A massive earthquake then destroys their home, and to avoid carnivores and omnivores, they descend down into a tropical forest that lay hidden behind their cave all the time. Encountering a "Macawnivore", a brightly colored feline that Gran dubs "Chunky", the family flees him until he is scared off by swarms of piranhakeets that devour a ground whale. Using another horn, Eep calls to Guy who rescues them from the birds with his fire. After a great deal of confusion regarding their first contact with fire, Grug imprisons Guy in a log until he can guide them somewhere safe. Guy suggests the Croods go to a mountain where there are caves because the Crood family desires a cave. Grug refuses at first, but he decides to go with the promise of a cave. The other Croods were worried that they would get tired and bicker, but Grug doesn't listen.  answer the following question:  What does the apocalypse Guy warns Eep about turn out to be?
Answer:
A massive earthquake