In the fourth episode, leading landscape photographer Peter Eastway follows in the footsteps of Frank Hurley – the pioneering Australian photographer on Shackleton’s expedition to the south a century ago – to capture the wilderness and wildlife of Antarctica and South Georgia.

For the last 40 years, the photographer Sebastião Salgado has been travelling through the continents, in the footsteps of an ever-changing humanity. He has witnessed some of the major events of our recent history; international conflicts, starvation and exodus. He is now embarking on the discovery of pristine territories, of wild fauna and flora, and of grandiose landscapes as part of a huge photographic project, which is a tribute to the planet's beauty". Sebastião Salgado's life and work are revealed to us by his son, Juliano, who went with him during his last travels, and by Wim Wenders, himself a photographer.

In the National Geographic tradition of powerful natural-history images and storytelling, this film reveals once-invisible dimensions of nature that are filled with beauty and wonder-and hold secrets crucial to our survival. It shines a fascinating spotlight on objects and events that escape the naked eye every minute of every day. Visually stunning and rooted in cutting-edge research, the film blends high-speed and time-lapse photography, electron microscopy and nanotechnology.