Extinction

How Life on Earth Nearly Ended 250 Million Years Ago. Condition: Very Good. The Permian-Triassic extinction, some 250 million years ago, was the greatest of the mass extinctions that have struck the Earth, but its cause is still unclear. In Extinction Smithsonian paleontologist Douglas Erwin offers an account of what we know about that extinction and the various theories for its cause. His starting point is the contrast between the diverse fossils of the Late Permian and the barren strata of the Early Triassic.