The Indian Ocean is the third largest body of water on Earth at more than 6,000 miles wide and covering 13% of the world's surface. It is home to 5,000 species of fish, many of which only exist in the Indian Ocean. But it is also an ocean under threat from global issues such as over-fishing and climate change, which make this an ocean on the edge.

In Bhutan, Palin finds himself back in the land of yaks for a last look at the high Himalaya. Trekking to Chomolhari base camp he meets a nomad with a penchant for yak songs before heading down to Paro to witness the Buddhist festival or Tsechu. In a bar in Thimphu, he discusses reincarnation and the pursuit of happiness with Benji and Khendum, two of the king's cousins, and en route to Bangladesh is taken by Benji to see the rare black-neck cranes. On his journey south through Bangladesh, Michael visits the ship-breaking beaches of Chittagong and grid-locked Dhaka. He meets a man who made a fortune in Birmingham in the poultry business, and a woman who lends money only to women. On a 1920s paddle steamer he is serenaded with the words of Bengal's Shakespeare, and he completes his epic Himalayan journey aboard a fishing boat that carries him out into the Bay of Bengal and a westering sun.

The extraordinary wildlife, culture and history of this immense, fascinating ocean and its myriad islands are revealed in stunning detail. With its coral reefs, turquoise lagoons and dramatic oceanic atolls, the South Pacific is the archetypal paradise. It is still relatively healthy and teeming with fish, but it is a fragile paradise. International fishing fleets are taking a serious toll on the sharks, albatross and tuna, and there are other insidious threats to these bountiful seas. We look at what is being done to preserve the ocean and its wildlife.

Sir David Attenborough reveals the findings of one of the most ambitious scientific studies of our time - an investigation into what is happening to our oceans. He looks at whether it is too late to save their remarkable biodiversity. Attenborough explores some of the ways in which we are affecting marine life - from over-fishing to the acidification of sea water. The film also uncovers the disturbing story of how shipping noise is deafening whales and dolphins, affecting their survival in the future.

From the makers of Walking With Dinosaurs comes an epic and entertaining new exploration of early life on Earth, revealing that before the age dinosaurs, a succession of fantastical animals and plants ruled the planet. A time when a two-ton predatory fish came on land to hunt, when four-metre sea scorpions sliced sushi in the shallows and when just one species of lumbering reptile represented 80 per cent of all life. For the first time, this special two-hour presentation uncovers and recreates these creatures and the bizarre world they inhabited.

For the animals in the polar regions, autumn means dramatic battles and epic journeys. Time is running out - the Arctic Ocean is freezing over and the sea ice is advancing at 2.5 miles per day around Antarctica. Polar bears gather in large numbers on the Arctic coast as they wait for the return of the ice. Soon, tempers fray and violent sparring contests break out. Meanwhile 2,000 beluga whales head for one special estuary, a gigantic 'whale spa' where they will thrash their snow-white bodies against the gravel and exfoliate. Inland, the tundra undergoes a dramatic transformation from green to fiery red. Here, musk ox males slam head-first into each other with the force of a 30mph car crash as they struggle to defend their harems. Frisky young caribou males play a game of 'grandma's footsteps' as they try to steal the boss's female. Down in Antarctica, Adelie penguin chicks huddle together in creches. When a parent returns from fishing, it leads its twins on a comical steeplechase - sadly there's only enough for one, so the winner gets the meal. Two months later and the chicks are fully feathered apart from downy Mohican hairdos - they're ready to take their first swim - reluctantly though, as it seems penguins are not born with a love of water! And with good reason - a leopard seal explodes from the sea and pulls one from an ice floe, a hunting manoeuvre that has never been filmed before. As winter approaches and everyone has left, the giant emperor penguin arrives and makes an epic trek inland to breed. The mothers soon return to the sea leaving the fathers to hold the eggs and endure the coldest winter on earth.