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 being struck by a meteorite 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 describes some of the most recent destructive disasters of volcanic origin in the history of our planet, including Krakatoa and Yellowstone National Park.A large part of the book is devoted to relating humorous stories about the scientists behind the research and discoveries and their sometimes eccentric behaviours. Bryson also speaks about modern scientific views on human effects on the Earth's climate and livelihood of other species, and the magnitude of natural disasters such as earthquakes, volcanoes, tsunamis, hurricanes, and the mass extinctions caused by some of these events.The book contains several factual errors and inaccuracies. Some of these have arisen because new discoveries have been made since the book's publication, and some classifications have changed. For example, Pluto has been reclassified as a dwarf planet, and the universe is not going to stop expanding, it is speeding up.