Planet Earth

Tour the mightiest mountain ranges, starting with the birth of a mountain at one of the lowest places on Earth and ending at the summit of Everest. One of Earth's rarest phenomena is a lava lake that has been erupting for over 100 years. The same forces built the Simian Mountains where troops of gelada baboons live, nearly a thousand strong. In the Rockies, grizzlies build winter dens inside avalanche-prone slopes. The programme also brings us astounding images of a snow leopard hunting on the Pakistan peaks, a world first.

Follow the descent of rivers from their mountain sources to the sea. Watch spectacular waterfalls, fly inside the Grand Canyon and explore the wildlife in the world's deepest lake. Planet Earth captures unique and dramatic moments of animal behaviour: a showdown between smooth-coated otters and mugger crocodiles; deep-diving long tailed macaques; massive flocks of snow geese on the wing and a piranha frenzy in the perilous waters of the world's largest wetland.

The Cave of Swallows in Mexico is a 400m vertical shaft, deep enough to engulf the Empire State Building. The Lechuguilla cave system in the USA is 193km long with astonishing crystal formations. Caves are remarkable habitats with equally bizarre wildlife. Cave angel fish cling to the walls behind waterfalls with microscopic hooks on their fins. Cave swiftlets navigate by echo-location and build nests out of saliva. The Texas cave salamander has neither eyes nor pigment. Planet Earth gets unique access to a hidden world of stalactites, stalagmites, snotites and troglodytes.

Around 30% of the land's surface is desert, the most varied of our ecosystems despite the lack of rain. Saharan sandstorms reach nearly a mile high and desert rivers run for a single day. In the Gobi Desert, rare Bactrian camels get moisture from the snow. In the Atacama, guanacos survive by licking dew off cactus spines. The brief blooming of Death Valley triggers a plague of locusts 65km wide and 160km long. A unique aerial voyage over the Namibian desert reveals elephants on a long trek for food and desert lions searching for wandering oryx.

The Arctic and Antarctic experience the most extreme seasons on Earth. Time-lapse cameras watch a colony of emperor penguins, transforming them into a single organism. The episode reveals new science about the dynamics of emperor penguin behavior. In the north, unique aerial images show a polar bear swimming more than 100km. Diving for up to two minutes at a time. The exhausted polar bear later attacks a herd of walrus in a true clash of the Titans.