With spring finally starting to show its face, we're thinking about everything that's green and growing. But as Yvonne Baskin shows in Under Ground: How Creatures of Mud and Dirt Shape Our World, we'd be nowhere without that most overlooked of substances: dirt. In the first chapter, she introduces an amazing world that holds two-thirds of the planet's biodiversity, from gigantic fungi to ancient microbes that can live in boiling hot springs or under sheathes of polar ice. After reading it, you'll never think "plain as dirt" again.