Sealab 2021

Life in the mountains is the focus of this episode, which explores the geologic and volcanic forces that have shaped the land. Animals that have had to adapt to the special survival challenges of high-altitude life are featured, including rare footage of three big cats: a mountain lion, snow leopard and puma. Also, bar-headed geese migrate over the Himalayas.

Fresh water, which is so vital to life, makes up only three percent of the water on the planet. This episode follows the course of high-mountain streams as they flow into rivers and then on to the sea. Among the animals featured are huge flocks of snow geese in flight, swimming monkeys, giant salamanders and Amazon river dolphins. Footage also focuses on fresh-water otters in Lake Baikal, caiman and piranhas in the Pantanal, Indian otters and Nile crocodiles.

Cave systems around the world are home to geologic features and creatures that remain largely unknown to many people. Millions of bats support an entire ecosystem at Deer Cave in Borneo thanks to their droppings, while caves in certain parts of Indonesia are home to swiftlets that make nests out of saliva. Also featured are blind salamanders in Thailand, massive crystals in New Mexico and snottites in Mexico.

Deserts cover one fifth of the planet and they are spreading. In the Gobi Desert in Mongolia, Bactrian camels eat snow instead of drinking water, while guanacos in Chile's Atacama Desert survive by licking dew off cactus spines. Also featured are a short-lived blooming of flowers in Death Valley and the struggles of elephants and a lion to find food in Namibia.

Accessible fresh water is surprisingly scarce at the two poles, adding greatly to the challenges faced by the creatures living in the Arctic and Antarctica. As the ice ebbs and flows with the change of seasons, killer whales team up on a hunt and a polar bear is forced to travel a great distance in search of food. Also, emperor penguins spend a long winter in Antarctica and beluga whales and narwhals feast on Arctic cod.

Covering up to a quarter of the earth's surface, grasslands support vast herds of animals, from East Africa's plains and West Africa's Sahel to the grasslands of Mongolia and the plains of Papua New Guinea. Among the animals featured are white-eared kob in the Sudan, golden eagles hunting on Russia's steppes and antelopes in South Africa.

Plants take center stage in this exploration of coniferous and deciduous forests. These seasonal forests cover vast tracts of temperate regions, such as the endless forests of Siberia, Tasmania and large areas of Eastern Europe. Among the animals that call these woodlands home are Siberian tigers, red pandas, wolverines, lynx, mouse lemurs. cicadas and European wolves.

The rain forests, so critical to the health of the planet, are home to an amazing number of animal and plant species. That leads to intense competition between animals for food. Footage includes jaguars on the hunt in the Amazon, gibbons traversing the canopy and flying frogs mating.

Spectacular storm photography from above and below the water is among the highlights of this exploration of the shallow seas, where coral reefs and fishing grounds lie. Massive shoals of fish act like magnets for predators such as sharks and whales. Also featured is the epic journey of a humpback whale and her calf from the tropics to polar seas.

The vast expanses of the world's oceans are home to some of the largest and strangest creatures on Earth, such as blue whales and vampire squid. Also featured are dolphins, manta rays, oceanic white tips, lanternfish, tuna, whale sharks and petrels.

The making of the sprawling, ambitious series is documented. The show took three years to produce and required 2,000 days in the field and 71 cameramen filming across 204 locations in 62 countries.