Justin Rowlatt discovers how phosphorus may have held evolution back for a billion years. How plants first colonised the land - precipitating an ice age in the process. And why volcanoes have both rescued and almost wiped out life on the planet, thanks to the carbon dioxide they emit.

Anjali Goswami of the Natural History Museum takes Justin on a tour of the big five mass extinction events in the fossil record over the last half billion years. But could we humans be adding a sixth one to the list? Tim Lenton of Exeter University explains why he thinks lowly lichen may have turned the Earth into a snowball. And Graham Shields of UCL tells us why we should all hug a volcano, even if one does occasionally wipe out 95% of all life on Earth.

Producer: Laurence Knight

Image: Tyrannosaurus Rex looking up at an incoming meteor (Credit: Detlev van Ravenswaay / Science Photo Library) Show less