In this episode Brian Cox visits South East Asia's 'Ring of Fire'. In the world's most volcanic region he explores the thin line that separates the living from the dead and poses that most enduring of questions: what is life?

Amidst the rich natural history of the United States, Professor Brian Cox encounters the astonishing creatures that reveal how the senses evolved.

The universe is almost entirely devoid of life. Earth, the planet we call home, seems to defy the laws of physics. It is teeming with life in all colours, shapes and sizes. No-one knows for sure how many different species are alive right now, our best guess is close to 8.7 million

In this episode, Brian travels around Australia to explore the physics of the size of life. Beginning with the largest organisms on our planet, a forest of giant eucalyptus trees, he then takes to the seas to get up-close with an ocean giant - the great white shark.

As far as we know, there is only one place in the universe on which life has taken hold - Earth - but for how much longer will this distinction remain? Astronomers are on the brink of finding other worlds the same size as Earth and the same distance from their star.