Since the Earth's creation 4.5 billion years ago, the planet has been struck by a series of catastrophes-each pushing life to the edge of extinction. Again and again, dinosaurs found themselves victims of these catastrophes, but from each disaster came new life. While a dominant species was wiped out, hardier creatures survived and thrived, moving into the vacuum left by the extinction. In turn, these gigantic creatures took over the planet until they fell victim to yet another mass extinction. The Earth's history is rife with prehistoric disasters that have molded the planet and changed the course of evolution. Each disaster took another leap forward on the evolutionary trail from single-celled bacteria to dinosaurs to humankind itself. Without this series of events, neither mankind nor any of the life we see around us would be here today.