Perilous Planet Earth places our present concern about the threat to Earth from asteroids and comets within an historical context, looking at the evidence for past events within the geological and historical records. The book looks at the way in which prevailing views about modes of global change have changed dramatically over the years. It also considers the way in which catastrophic events are now seen to have influenced the course of evolution in the distant past, as well as the rise and fall of civilizations in more recent times. Professor Palmer argues that the better we understand our past, the greater the likelihood that we will be able to take appropriate action to preserve our civilization for the future.