Adam Sedgwick was a priest and scholar. Roderick Murchison was a retired soldier. Charles Lapworth was a schoolteacher. It was their personal and intellectual rivalry, pursued on treks through Wales, Scotland, Cornwall, Devon and parts of western Russia, that revealed the narrative structure of the Paleozoic Era, the 300-million-year period during which life on Earth became recognisably itself. Nick Davidson follows in their footsteps and draws on...