Why do we and our wildlife live where we do? A fresh look at the 'postcards' left from the pole to pole journey which the British Isles has made over the past 3 billion years, answering why our wildlife lives where it does today. On this journey Britain-to-be passed through the Tropic of Cancer, the Tropic of Capricorn and the Equator, before it came to rest in its current position. Like any globetrotter it collected mementoes of that journey, reflecting the environments it passed through: the deserts, the steamy swamps, the drownings under the sea or under the ice. It is these 'postcards from the past' that Anna Grayson goes in search of.