The Great Extinctions
What Causes Them and How They Shape Life

For over a century geologists have tried to identify and understand the processes responsible for the complex history of species extinction. This search has become even more important over the last decade as human populations and human technology may now rival sea-level change, volcanic eruptions, and asteroid impacts as extinction mechanisms. The Great Extinctions explores the history of that search, its subjects, its controversies,

its current conclusions, and the meaning of those conclusions for our efforts to preserve the Earth’s current biodiversity. It explains what extinction is, what causes it and whether it can be prevented.

In total some 1,000—3,000 million species are estimated to have appeared during Earth’s history, yet only 12.5 million currently exist today. This means that the overwhelming majority of species that have ever lived are now extinct. Contrary to popular conception, species extinction is as natural a process as species evolution but the rate of extinctions in the geological past has not been constant. On at least five occasions in Earth’s history extinction intensities have spiked well above the normal levels and there’s even evidence to suggest that these levels have changed over time. Examining extinction over geological time, The Great Extinctions compares past geological extinction events and uses them to predict what is likely to happen in the future.