36 million years ago, Late Eocene (Pakistan/Tethys Sea) Filming location: Florida

The second episode is set in late Eocene, when the polar caps froze over and drastically changed the Earth's ocean currents and climate. The first part of the episode explains how an early whale, Basilosaurus mates and how the world is changing into an ocean famine. On land there is an Andrewsarchus driven to the beach to feed on sea turtles. The narrator explains that Andrewsarchus, the largest land mammal predator ever to walk the earth, has hooves and is related to sheep, so it is, in a sense, a "sheep in wolf's clothing". Back in the ocean, a starving mother Basilosaurus is forced to hunt in the mangrove swamps of Africa, which will later become the Sahara Desert. Unable to catch a primate called Apidium due to a shark killing one of the primates and spooking the others, she is then hunting a lone Moeritherium. The Moeritherium crawls on to land, but in the mangroves, land does not last long. However the Moeritherium escapes and the Basilosaurus returns to the sea. The cast moves on to land where a herd of Embolotherium (identified as Brontothere) struggle to survive : one of their calves dies after birth and two Andrewsarchus feast on it but the mother Embolotherium drives them away because she has a strong bond with her offspring, even if it is dead. Back in the sea the mother Basilosaurus preys on a group of Dorudon and is successful. The episode ends with the mother Basilosaurus swimming with her newborn calf.

Animals: Basilosaurus · Andrewsarchus · Embolotherium (identified as Brontothere) · Dorudon · Moeritherium · Apidium · Physogaleus (identified as a shark) · Puppigerus (identified as a turtle)

3.2 million years ago, Late Pliocene (Ethiopia) Filming location: South Africa, Ethiopia

The fourth episode takes place in the Great Rift Valley in northeastern Africa of the late Pliocene. The climate has changed, and now great grasslands have replaced trees. The episode focuses around a tribe of small hominids known as Australopithecus, one of the first apes able to walk upright and a close ancestor to humans. The Australopithecus has evolved to walk upright so as to better maneuver the plains as well as the climb the trees. However, it notes that although the Australopithecus looks human, it still only has the mind the size of a chimpanzee's. Some of the topics explored in the episode are the close social bonds among the tribe, how they use grooming as a means of communication, and how they work together to forage for food and to defend one another from attacks from such animals as an angry male Deinotherium, an ancestor of the modern elephant which they have to run from to avoid being crushed, and the feline predator Dinofelis. It touches upon how competing tribes of Australopithecus war among one another, although most of fighting is for show. It also explains the hierarchy in the tribe among the males (who are much larger than the females) and tells a story of how the dominating male is eventually overcome by another male, who wins the right to feed first at a carrion and to mate with the females. The main story tells of a young Australopithecus nicknamed Blue whose mother has been killed by malaria. He and his tribe are later forced to flee their homeland during a fight over a waterhole with a rival tribe. After a long journey in search of a new home, Blue fits into his tribe by causing them to scare off a hungry Dinofelis.

Animals: Australopithecus · Dinofelis · Deinotherium · Ancylotherium · Warthog · Rhinoceros · Jackal · Vulture · Zebra (carcass) · Ostrich