Book excerpt: Planet Earth is middle-aged. Science has worked hard to piece together the story of the evolution of our world up to this point, but only recently have we developed the understanding and the tools to describe the entire life cycle of a planet. Ward and Brownlee, a geologist and an astronomer respectively, combine their knowledge of how the critical sustaining systems of our planet evolve through time with their understanding of the life cycles of stars and solar systems, to tell the story of the second half of Earth's life. The process of evolution will essentially reverse itself: life as we know it will subside until only the simplest forms remain. Eventually, they too will disappear. The oceans will evaporate, the atmosphere will degrade, and, as the sun slowly expands, Earth itself will eventually meet a fiery end. --From publisher description.