Six billion people live on earth, but we share the planet with trillions of other life-forms, ranging from bacteria to whales. They make up life's infrastructure and are in effect the underpinnings of human existence. Life counts shows why we must preserve this biodiversity: if we don't, scientists predict, the earth may lose the ability to support its inhabitants within the next fifty years. Through color illustrations and narration, readers learn that each animal on earth--whose numbers are greater than our galaxy's stars--as well as each plant and each microbe, plays a role essential to the life of the planet and, in surprising ways, human economies and health. The authors weigh scientist's and international governments' best ideas on how we can protect these living things and hence our world. Life counts: a worldwide balance sheet is part of the larger Life Counts Project, designed to raise awareness across the globe of the importance of the world's biodiversity.