We often think that it's ice, fire or other elements that have forged and transformed the earth, but there is a force that has been just as powerful in changing Earth's fate - plants.
This episode tells the story of the astonishing moment in Earth's distant past, when almost the entire planet froze - a glistening 'Snowball Earth' in the dark void of space.
In Inferno, we explore one of the darkest periods in Earth's history: the worst mass extinction the planet has ever seen, when as much as 90% of all species died, 252 million years ago.