Bryson describes graphically and in layperson's terms the size of the universe and that of atoms and subatomic particles. He then explores the history of geology and biology and traces life from its first appearance to today's modern humans, placing emphasis on the development of the modern Homo sapiens. Furthermore, he discusses the possibility of the Earth's being struck by a meteor and reflects on human capabilities of spotting a meteor before it impacts the Earth, and the extensive damage that such an event would cause. He also focuses on some of the most recent destructive disasters of volcanic origin in the history of our planet, including Krakatoa and Yellowstone National Park.