Among the most striking and startling features of the Earth are its immense craters and hidden underground passageways. Created instantly by huge meteoric impacts or gradually by the erosion of solid rock, these features reveal the varied geologic processes that have shaped our Earth, forming its craters, caverns and canyons.Starting with the Earth"s early geologic history when the planet was bombarded by asteroids and comets, geologist Jon Erickson details historic impacts and their geologic aftereffects, from disastrous earthquakes and volcanoes to the possible cause of dinosaur extinction. Erickson examines the formation of caves and caverns, including ice caves, limestone caves and natural bridges, as well as the formation of the Earth"s major basins. The author also explains erosion"s part in the creation of canyons, both on land and under the sea. He analyzes the underground causes and effects of explosive geologic forces such as volcanic eruptions and earthquakes, as well as catastrophic ground failures and landslides, and concludes with a look at some of Earth"s more unusual geologic depressions, among them potholes, sod pits and lave lakes.The text is illustrated throughout with more than 100 photos, maps and line drawings, and includes tables listing information on major meteoric impacts (and dangerous near-misses), volcanism and mass extinction, locations of the world"s ever-growing deserts, dimensions of deep-ocean trenches and more.