Just over 250 million years ago, during the Permian Period, life on Earth came as close as it has ever come to being wiped out. The Permian extinction may be the greatest murder mystery in the history of the world. Whatever happened back then killed off more than 55 percent of all families on Earth, including about 96 percent of marine species and 70 percent of terrestrial vertebrate species. Ancient ecosystems were so severely disrupted that it took millions of years for them to be restored.

Researchers once thought that this "great dying" took place over a long time. But new fossil data suggest that it took no more than 200,000 years. In geological terms, that's a short time. Look for clues in this chapter as to what could have killed so many different forms of life. Then, solve the mystery.