This episode looks at our planet as a whole and considers the key factors that have shaped its natural history. The team use aerial technology to follow a million caribou as they trek across the Arctic wastes, record the annual transformation created by floods using time-lapse photography, and capture the most intimate and complete picture of polar bear life ever filmed.

Exploring the extreme landscape of rock, ice and snow, a vertical world as alien to humans as the surface of another planet is revealed and helps to explain the geological and volcanic forces that shaped the land and its mountain chains.

Humans like to think that once they’ve climbed a peak, they have somehow conquered it. But they can only ever be visitors to this hostile world. Planet Earth introduces the ‘real’ mountaineers and discovers the secrets of their survival on the mightiest peaks of our planet.

From a puma family in the Andes to the grizzlies in the Rockies, from the Snow Leopard in the Alps to the Giant Pandas of China, these shy and most secretive animals are filmed rising to the challenge of mountain life.

Just three per cent of the Planet’s water is fresh water and it is our most precious resource. Where it flows or falls, it controls the distribution of all terrestrial life.

This episode follows the descent of rivers from their mountain sources to the sea and showcases the unique and dramatic wildlife found within its unexplored waters.

Caves are one of the only habitats not directly driven by sunlight, but this doesn’t mean there is no wildlife. Cave angel fish are perhaps the most adapted creatures on earth since they live only on cave waterfalls - hanging on with microscopic hooks on their flattened fins.

Deer Cave in Borneo is a daytime retreat for five million bats and their droppings support an entire community of creatures. Shine a light on one massive pile of droppings and the whole place shimmers with millions of dung-eating insects.

This episode probes the mysterious, perpetual darkness and reveals the unknown underground world of caves, caverns and tunnels.

When astronauts peer down on Planet Earth, the one environment they all notice are the deserts, which make up a staggering 30% of the land’s surface. From space they look empty and lifeless. A closer look reveals a very different picture. Mongolia's Gobi Desert is home to wild Bactrian camels, one of the rarest mammals on the planet, which survive by eating snow instead of water. In Atacama, Chile, in the driest desert in the world guanacos survive by licking the dew off cactus spines.The final sequence illustrates one of nature's most fearsome spectacles: a billion-strong plague of desert locusts, destroying all vegetation in its path.

A journey to the polar extremes of our planet, where for most of the year the Arctic and Antarctic are locked in ice. As the sun abandons one pole and journeys to the other, these frozen worlds undergo the most extreme seasonal transformation on the planet – from the total darkness and numbing temperatures of the polar winter to the midnight sun of the summer, when the sun never sets.

The vast open wildernesses of African savannah, Asian steppe, Arctic tundra and North American prairie are the great plains of the planet. Together they cover more than a quarter of the land on Earth and one living thing is at their heart - grass. This humble plant feeds the greatest gatherings of wildlife found anywhere on Earth.

Over Africa's savannah, a swarm of 1.5 billion Red-billed Queleas are caught on camera, the largest flock of birds ever depicted.

Jungles cover roughly three per cent of our planet, yet contain a staggering 50 per cent of the world’s species. Located around the warm, sunny equatorial zone, complete with constant daylight, they are the most productive habitats on earth. Beautiful floating aerial shots introduce the world’s most spectacular forest vistas and high-definition cameras enable unprecedented views of the species that live on the dark jungle floor.

The newly discovered coral reefs in tropical Indonesia reveal that they are one of the richest in the world. They are home to fantasy-like creatures - such as the head-butting pygmy seahorse, the flashing ‘electric’ clam and bands of 30-strong sea snakes which have never been filmed before as they the hunt in packs, using cunning strategy.

As humpback whales traverse the crystal-clear waters of the shallow seas, returning to breeding grounds in the tropics, a mother and its calf are followed. While the latter takes in up to 500 litres of milk a day, its parent will starve until it travels back to the poles to feed — and it must do this while it still has sufficient energy left for the journey.

From the evergreen forests of the frozen North to the deciduous dry forests of the Equator, Seasonal Forests reveals the greatest woodlands on earth. Some of the strangest trees of all can be found in the baobab forests of Madagascar - these bizarre upside-down trees store water in their swollen trunks and harbour equally curious wildlife, such as the tiny mouse lemur.

Oceans cover two thirds of the planet, yet largely remain unexplored. For animals that dwell on the surface or within the deepest abyss, it is finding food and conserving energy that is paramount. Planet Earth travels the world to reveal the extraordinary lengths life takes in its bid to survive this immense and barren realm.

Off the Mexican coast, a large group of sailfish encircle another shoal of bait fish. The hunters change colour as a message of their intentions, since an attack could also be fatal to others of their number. The last sequence depicts the largest animal on Earth: the blue whale, of which 300,000 once roamed the world's oceans. Now fewer than 3% remain.