Seven Worlds, One Planet

Antarctica - a land of survivors enduring the most hostile conditions on Earth. 98% of the mainland is covered by ice on which virtually nothing can live. Even the sea freezes over, but the Weddell seal manages to survive here by keeping its breathing holes open by using its teeth to grind away the ice. Below the sea ice, conditions have been stable for millennia. Life has flourished and diversified. Starfish, sea spiders and three million predatory worms carpet the ocean floor, and sea anemones feast on ocean giants. Islands on the fringes of the continent are free of sea ice, far more hospitable and crowded. Huge colonies of king penguins cover the land, and four-tonne elephant seals fight for territories on the beach. The abundance of life found here is down to the incredibly rich ocean surrounding the continent. The strongest currents in the world whip up nutrients to the surface that feed Antarctic krill. Numbering an estimated 400 trillion, their combined weight is greater than any other species in the world. Humpback whales round them up using sophisticated feeding techniques, and gentoo penguins escape the jaws of leopard seals and orcas to reach the open ocean and feed on them. On rare occasions krill swarm in baitballs measuring kilometres across, where they are feasted on by thousands of penguins, seals, albatross and fin whales. Antarctica was only discovered 200 years ago, but humans have had an enormous impact in that time. The whaling industry killed over 1.5 million whales here, taking many species to the brink of extinction. But since the ban on commercial hunting in 1986, whales are making a remarkable come back. In addition, the Antarctic treaty is exemplary in demonstrating that countries from around the world can unite to protect wildlife. However, due to climate change, the Southern Ocean is warming and sea levels are rising. Perhaps more worrying is that a warming of the coldest region on earth will have profound effects on global weather patterns. Although Antarctica is far away, what happens here will affect all of us.

Asia is the largest and most extreme continent on our planet, stretching from the Arctic Circle in the north to the tropical forests on the equator. The animals here face the hottest deserts, tallest jungles and highest mountains found anywhere on Earth. But the continent has not always looked like this. These extreme worlds were created when India collided with the rest of Asia 30 million years ago, shaping the continent as we know it today. Animals here have adapted to the extreme environments in almost unbelievable ways. In the frozen lands of the Kamchatka peninsula in Russia, bears seek out active volcanoes - despite the dangers. And on the Siberian coast, a remarkable spectacle appears for a few weeks during the summer - tens of thousands of walruses haul themselves on to a beach in one of the largest gatherings of mammals seen anywhere in the world. In China, mysterious blue-faced monkeys walk upright through some of the least-explored forests on Earth, whilst the baking deserts of Iran are home to what has to be the world's most bizarre snake. On the barren plateaus of India, garishly coloured lizards fight like miniature kung fu masters as they try to find a mate before they die. The south of the continent couldn't be more different. When India collided with Asia, the Himalayas were formed. These mountains blocked clouds, helping to create the monsoon. Heavy rains fell and tropical forests, full of life, developed to the south. Here, baby orangutans learn to climb the tallest jungle trees on the planet and a female Sumatran rhino - one of the rainforest's rarest inhabitants - sings a mournful and haunting song. Will anyone return her call? These forests - home to thousands of incredible species - are in danger of being lost forever. Under threat from deforestation and human development, today the largest continent on Earth is running out of space for its wildlife.

South America - the most species rich continent on Earth. From the bone-dry deserts of the Atacama, where penguins weave their way through a minefield of snapping sea lions, to the lush cloud forests of the Andes, where Andean bears scale 30-metre trees in search of elusive fruits, South America is full of the unusual and ingenious. In the far south of the continent, predators prowl the jagged Patagonian landscape. Underneath vertical spires of rock, a mother puma must draw on all her experience and strength to bring down a formidable prey. Guanaco, a relative of the camel, are three times her weight and able to fling a puma in the air. East of the Andes lies the world's largest rainforest, the Amazon. To stand out from the crowd here, male blue manakins have developed elaborate and comical dance routines. Poison dart frogs have unique ways to protect their young. Fathers carry their tadpoles piggy-back style to individual pockets of water throughout the forest, but must remember where they hid each one. Precious clay-licks attract rainbow-coloured flocks of macaws and butterflies, all desperate to lap up the precious salts. In southern Brazil, freshwater springs bubble up crystal clear. Piraputanga fish cruise through the turquoise waters following capuchin monkeys feeding overhead. Fruit dropped by the primates makes an easy meal for the fish until giant anacondas send the monkeys scrambling for safety. The hungry fish resort to leaping athletically from the water, snatching fruit directly from the branches. The rainforests of South America are under threat. A few small patches of Colombian forest are the last remaining refuge of one of the world's rarest monkeys. Cotton-top tamarins flit through the treetops hunting down insects, a wild shock of white hair on the top of their heads. Great dusky swifts fly dangerously close to the spectacular Iguazu falls - then mysteriously disappear.

Australia, a land cast adrift at the time of the dinosaurs. Isolated for millions of years, the weird and wonderful animals marooned here are like nowhere else on Earth. The Daintree, one of the world's oldest tropical forests is home to the most dangerous bird on earth, the cassowary. A dinosaur-like bird standing six feet tall, they are formidable but their success is down to how well a father cassowary can carefully protect his tiny stripy chicks. The wombat, a tough short-legged marsupial, roams Australia's mountain ranges surviving freezing snowstorms. In the hot gum tree forests is a newly discovered predator with a bizarre courtship ritual, and on the wide, open grasslands the dingo, Australia's elusive and much persecuted wild dog, hunts kangaroos to provide food for its pups. Life in Australia is tough and getting tougher. Since its isolation, the continent has been rapidly drifting north, getting hotter and drier - turning the forests and grasslands to dust. Over 70% of Australia is now arid land. In the sun-scorched red centre, reptiles rule the desert. Giant perentie lizards patrol the dusty land in search of smaller lizards to eat, and weird thorny devils drink using only their skin. At watering holes, huge flocks of wild budgerigars bring a splash of bright colour. This island continent now lies so far north it is surrounded by warm, clear tropical waters, and here coral reefs thrive. They are home to a kaleidoscope of tiny colourful fish and the largest number of shark species in the world. Once every 10 years or more, thousands of sharks gather creating an amazing spectacle. But Australia's animals face a challenge as a result of humans. More species of mammals have been lost here than anywhere else on the planet. An extensive site containing thousands of extraordinary ancient carvings is all that remains of some. But on a secret offshore island, the enigmatic and rare Tasmanian devil, a pugnacious marsupial predator, has one of its last strongholds.

Sir David Attenborough explores the continent of Europe - a crowded continent transformed by mankind. From the rare and elusive wolves to the almost-extinct Iberian lynx, this continent needs protection to ensure a future for its wildlife.

More than any other continent, North America is defined by extreme weather and seasonal change. For animals that live here this poses great challenges, but for those with a pioneering spirit it can also offer great rewards. In Canada's Yukon, winter can be brutal - up to six feet of snow can fall in a single day. But lynx have found a way to survive where others cannot, pushing farther north than any other cat species on earth. To catch a meal, they must outsmart quicker and more nimble prey, the aptly named snowshoe hair. With no east-west mountain range crossing North America, Arctic air can flow unimpeded as far south as the southern swamps, locking alligators into a blanket of ice and forcing manatees to flee in search of warmer water. Spring arrives rapidly, covering the Rocky Mountains in a riot of wildflowers and turning frozen creeks into raging torrents. In the streams of Tennessee, male chub fish go to great lengths to attract a mate, moving thousands of stones to build rock pyramids over a metre high. When temperatures are just right, the forests of Mississippi come alive with the spectacular glow of millions of fireflies illuminating the night. On the central prairies, summer brings formidable weather. Warm air from the Gulf of Mexico meets Arctic air head-on, resulting in tornados. Spinning across the Great Plains at speeds of 300 miles per hour, these are the fastest winds on earth. Prairie dogs take evasive action, and it's not just tornados they're avoiding. American badgers slink through the long summer grass on the hunt for burrowing owls and unsuspecting prairie dog pups.