Life on Our Planet

Covers the origin of life and the rules of evolution, including natural selection, adaptation, interaction and speciation, in addition to an overview of the series. A pair of Smilodon brothers successfully take down a terror bird,^[a] a mother Maiasaura navigates the nesting grounds to reach her own nest, and a female Tyrannosaurus & her offspring unsuccessfully attempt to hunt a female Triceratops.

In the Precambrian seas, plankton develops and sets the stage for future organisms. Marine invertebrates slowly evolve and the prehistoric seas are ruled by jellyfish until the Cambrian explosion. In the shallow seas of the Cambrian, an Anomalocaris attempts to hunt a trilobite,^[b] but is foiled by the arthropod's hard exoskeleton. By the Ordovician, trilobite armor has become even more advanced to deal with new predators, but is no match for the beaks of cephalopods such as Cameroceras, while Arandaspis, an early vertebrate, lives in the shadow of the invertebrates. The Late Ordovician mass extinction sees a massive global cooling that wipes out a majority of life on Earth, causing many invertebrates to retreat to the deep sea and leaving the vertebrates with a path to dominance. In the Devonian, a family of Dunkleosteus, one of the largest new vertebrates, hunts ammonoids^[c] using a vital new adaptation: jaws. Massive blooms of plankton cause global deoxygenation, leading to the second mass extinction event: the Late Devonian extinction. However, on land, plants come to dominate and transform the ecosystem, and animals soon follow.

The destabilization of rock by lichen creates the first soil, allowing plants to grow and eventually dominate. In the coal forests of the Carboniferous, a male Arthropleura follows the scent trail left by a female, and performs his courtship with her. In the water, several young lobe-finned fish^[d] narrowly escape a hungry adult by moving onto land, but one is eaten by an early tetrapod, Anthracosaurus. As the Carboniferous gives way to the drier Permian, some of these amphibious tetrapods develop hard-shelled eggs that are more resistant to desiccation, becoming the first amniotes. The Permian is dominated by reptiles such as Scutosaurus and proto-mammals, or mammal-like reptiles, such as Lystrosaurus. A female gorgonopsid^[e] successfully hunts down a Scutosaurus with her saber-like teeth. Massive volcanic eruptions in the Siberian Traps lead to great floods of lava, an atmosphere of noxious chemicals, and rapid global warming, prompting the Permian–Triassic extinction event, the largest mass extinction event in Earth's history, which wipes out almost all life. However, some species such as Lystrosaurus manage to survive.

During the Triassic, in the aftermath of the recent extinction, surviving species recoup and Lystrosaurus quickly becomes the dominant animal on Earth, reaching an abundance unmatched by any other past or future animal. However, reptiles continue to evolve on the arid margins of Pangaea, and future Lystrosaurus populations find themselves at the mercy of predators such as erythrosuchids, "possibly" being the reason of spelling their extinction. Reptiles diversify and come to dominate both the land and the sea; in a flash-forward to the Jurassic, early sea turtles face predation from plesiosaurs,^[f] and their hatchlings must avoid pterosaurs as they race to the water. Back in the Triassic, a massive precipitation event brings an end to the Pangaean desert, turning the world lush and green. Plateosaurus roams these forests, signaling the eventual future dominance of the Dinosaurs.

Near the beginning of the Early Jurassic, heavy volcanic activity during the breakup of Pangaea leads to another mass extinction. However, the new environments facilitate the evolution of the survivors, including the dinosaurs. By the Late Jurassic, large dinosaurs of all kinds have evolved. An Allosaurus unsuccessfully hunts for Diplodocus hatchlings in a rainstorm at night. Flowering plants evolve and revolutionize life on Earth, as numerous lineages of insects adapt to pollinate them while other lineages evolve to feed on these pollinators, and by the Cretaceous, there are more species on the land than in the ocean for the first time. During the Early Cretaceous, the evolution of feathers benefits theropod dinosaurs such as Deinonychus, which hunt in packs to take down an Arkansaurus. Tectonic changes in the Late Cretaceous create shallow seas that increasingly isolate landmasses from one another. Ornithischian dinosaurs such as Maiasaura develop the ability to chew the newly-evolving plants and travel in massive herds. Meanwhile, early mammals also take advantage of the diversifying plants and evolve complex behavior. A male Tyrannosaurus successfully courts a female.

On the last day of the Cretaceous, Edmontosaurus, Triceratops, Tyrannosaurus, Alamosaurus, azhdarchid pterosaurs and a plesiosaur go about their daily lives just before an asteroid the size of Mount Everest hits the Earth, causing the Cretaceous-Paleogene extinction event. Megatsunamis, burning ejecta from the impact, an overheated atmosphere, and acid rain wipe out a majority of life on Earth, bringing to an end the reign of non-avian dinosaurs and destabilizing the marine food web. Abyssal scavengers and insects survive by feeding on the dead organisms. Some reptiles, amphibians, and small mammals manage to survive the impact from below the ground, while a single lineage of dinosaurs, the birds, also survive via eggs laid in the ground. These survivors are said to follow in the dinosaurs' footsteps to take their places in taking over the world. A flashback to the Jurassic shows the origins of flight as a female Anchiornis uses her gliding abilities to evade a juvenile Sinraptor. Despite the impact winter, the adaptations of conifers to the cold allow them to dominate the northern latitudes shortly after impact. Meanwhile, flowering plants come to dominate the tropics, forming tropical rainforests, the most biodiverse ecosystem on Earth. By the Neogene, the plains of South America are dominated by the giant terror birds,^[g] which hunt mammals such as Theosodon. As Australia moves north, coral reefs dominate the Arafura Sea, serving as centers of diversification for marine life. Seabirds spread across the planet to take advantage of the wealth of prey. Despite the success of birds, it was the mammals that would dominate the Cenozoic, as mammals like Smilodon were able to kill even a terror bird.

In a flashback to the Jurassic, early mammals^[h] live in the shadow of the dinosaurs. Following the K-Pg mass extinction, they quickly rebounded and diversified, and were to follow in the dinosaurs' footsteps in taking their places to dominate the planet. However, in the middle of the Paleogene, the separation of Antarctica and South America drives a global cooling and drying event, leading to new adaptations in mammals such as large sizes. A male Megacerops, one of these new giant mammals, unsuccessfully spars with a rival male over a female. The drying trend from Antarctica's separation continues and leads to the replacement of forests with grasslands over a fifth of Earth's area, leading to the extinction of many mammals. Surviving grazing mammals evolve specialized adaptations to process grass. In early Quaternary South America, a curious young Smilodon investigates a herd of Doedicurus and attempts to prey on a juvenile, but is warded off by their tails. The Himalayas are shown as an example of major geologic changes during the Cenozoic. Mammals conquer both the sky and the sea; in a flashback to the Paleogene, Maiacetus, a semiaquatic early whale, evades the giant shark Otodus. As the planet cooled, the descendants of Maiacetus would evolve into the largest animals ever known: the baleen whales. The cooling intensifies, plunging the planet into an ice age and leading to the dominance of a new type of mammal.

Near the beginning of the Quaternary, changes in Earth's orbit, currents, and atmosphere lead to the ice age. By the middle of the Quartenary, the tundra-steppe circles the northern latitudes south of the ice sheets. On their migration through the steppe, a herd of woolly mammoths is ambushed by a pride of cave lions, who successfully take down a subadult male. A drying trend leads to the expansion of deserts south of the tundra-steppe, and the rainforests of Africa are almost entirely replaced with savanna. At the end of the glaciation, the ice sheets melt as the Earth's orbit shifts again and the climate warms. In North America, massive proglacial lakes form from the melting, and one such melting event leads to immense floods that carve a path across North America, but rapidly recede. The climate stabilizes and the world greens over in the current epoch, allowing for a recovery of forests and wetlands. Many megafauna worldwide are mysteriously driven to extinction, which allows bison to dominate the Great Plains, where they are killed en masse in buffalo jumps by early human hunters, who had previously contributed to the megafaunal extinctions. Humans develop agriculture and give up the hunter-gatherer lifestyle, leading to the formation of complex society and civilization, and eventually technology. Humanity's dominance threatens the balance of Earth through habitat destruction and climate change, leading to the potential for a sixth mass extinction, which can only be halted through a concerted effort from humanity. However, Freeman notes that no matter what future awaits the Earth, "life has always found a way",^[i] as a dragonfly metamorphosizes and flies through a lush, post-apocalyptic London.