High above Earth's surface David Attenborough floats weightless, showing that without gravity the world would be a chaotic place. Seen from space huge cloud patterns sweep across the globe. But some species like spiders, ski-diving frogs, gliding squirrels, birds and bats have overcome the force of gravity to fly through the air.

David Attenborough examines the borders between land and water, and the life that thrives there - from the sticky mud of an English estuary and its bird and insect life to the more numerous life in the tropical mangrove forests.

He looks at the fish that hunt out of water, the world's largest reptile, the turtles that come ashore to breed in Costa Rica and the seven-foot-long leatherback turtle that can be found in Malaysia.