Extinction: How Life on Earth Nearly Ended 250 Million Years Ago

Some 250 million years ago, the earth suffered the greatest biological crisis in its history. Around 95% of all living species died out — a global catastrophe far greater than the dinosaurs' demise 65 million years ago. How this happened remains a mystery. But there are many competing theories. Some blame huge volcanic eruptions that covered an area as large as the continental United States; others argue for sudden changes in ocean levels and chemistry, including burps of methane gas; and still others cite the impact of an extraterrestrial object, similar to what caused the dinosaurs' extinction.

Extinction is a paleontological mystery story. Here, the world's foremost authority on the subject provides a fascinating overview of the evidence for and against a whole host of hypotheses concerning this cataclysmic event that unfolded at the end of the Permian.

After setting the scene, Erwin introduces the suite of possible perpetrators and the types of evidence paleontologists seek. He then unveils the actual evidence — moving from China, where much of the best evidence is found; to a look at extinction in the oceans; to the extraordinary fossil animals of the Karoo Desert of South Africa. Erwin reviews the evidence for each of the hypotheses before presenting his own view of what happened.

Although full recovery took tens of millions of years, this most massive of mass extinctions was a powerful creative force, setting the stage for the development of the world as we know it today.

"The last time Earth experienced a mass extinction, some 65 million years ago, at the end of the Cretaceous period, there is little doubt about what happened. A humongous meteor slammed into the Yucatan Peninsula, incinerating everything around for thousands of miles. Plumes of vaporized rock blanketed the planet in a layer of thick ash, blocking the sun and choking off photosynthesis. The entire global... Washington Post Book Review (read the entire Washington Post review) ecosystem virtually collapsed in a geological eye-blink.

Though the dinosaurs might find it crass to say so, the late Cretaceous cataclysm that did them in was a planetary bad hair day compared to the mass extinction that occurred some 250 million years ago, at the end of the Permian period. The Permian event is probably the closest that life on Earth ever came to being completely extinguished. Around 95 percent of marine species and 70 percent of terrestrial vertebrates were wiped out — a greater percentage of the Earth's species than the next two largest mass extinctions combined. The break in the fossil record at the Permian boundary is so severe that 19th-century geologists saw it as evidence of two completely separate creations of life.

Just what caused this apocalypse is one of science's great unsolved riddles. Over the years, a cottage industry of Permian speculators has pointed the finger at just about every conceivable culprit. The list of indicted suspects includes — take a deep breath — plate tectonics, volcanoes, glaciation, a meteor, a supernova, a massive methane burp from the depths of the sea, oxygen-deprived oceans, an overly complex global ecosystem that collapsed under its own weight and, most fantastic of all, a buildup of cancer-inducing dark matter in the Earth's core. Dream up a way of killing off life on Earth, and chances are some reputable scientist has already proposed it as a cause of the Permian extinction.

Douglas H. Erwin, a Smithsonian paleobiologist and one of the leading experts on the Permian extinction, has meticulously sifted through the evidence for each of these hypothetical culprits. His accessible new book, 'Extinction' — written, it seems, both to persuade his colleagues and to educate a lay audience — is told from the perspective of a forensic scientist trying to piece together a quarter-billion-year-old crime scene from an impossibly scant body of clues. It unfolds as a sort of geological mystery story.

An extraterrestrial impact, like the one that killed off the dinosaurs, is perhaps the most attractive hypothesis, one favored by many scientists because it's both elegant and plausible. But no one has ever found the telltale signs of impact — a spike in iridium (a metal rare on Earth but common in meteorites) and shocked quartz crystals — that are present in rocks dating back to the Cretaceous extinction. Unlike the meteor that annihilated the dinosaurs, whatever killed off the Permian fauna apparently left no smoking gun.

But it left some suggestive pieces of circumstantial evidence. The Permian extinction happens to have coincided with the million-year-long eruption of the Siberian flood basalts, one of the most massive volcanic events in the last 600 million years. Those eruptions spilled magma across an area larger than the continental United States — in some places as deep as six kilometers. It's hard to say what volcanism on that scale would do to the planet or what might have caused it, but the large amounts of dust and carbon dioxide vented into the atmosphere would probably have created a very unpleasant environment. The problem facing geologists is how to distinguish cause from coincidence.

The Permian also happens to have coincided with the formation of the massive supercontinent Pangea. Species that had previously existed in isolation suddenly had to compete against one another, and, according to one theory, this competition forced much of the planet's biodiversity out of business. Other scientists speculate that the formation of Pangea could have severely affected the global climate. Proximity to water moderates the weather, which means that a supercontinent with vast, landlocked spaces would have had nasty seasons — think Siberia, but much, much worse. But nasty enough to knock out most of the life on Earth?

For a long time, scientists assumed the Permian extinction was a drawn-out affair. Recently, however, a consensus has emerged that the extinction probably occurred in two waves, separated by about 10 million years, and that the second, more brutal wave probably happened over no more than 180,000 years and possibly much faster — practically a split second in geological time.

The speed of the extinction would seem to rule out gradual processes like plate tectonics as the culprit, but with the Permian extinction, it's hard to rule out anything. The mystery is too deep, the evidence too scarce, the plausible causes too many. Unlike some of his colleagues, Erwin is humble enough not to pretend to know what happened at the end of the Permian. His whodunit ends the way it begins — not with a conviction but a question mark.

Joshua Foer is working on a book about the science of memory.

" Reviewed by Joshua Foer, Washington Post Book World (Copyright 2006 Washington Post Book World Service/Washington Post Writers Group)
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"Erwin has spent his professional life searching for clues...and this book is his invitation to amateur paleontologists to join in his sleuthing." Cleveland Plain Dealer

"Theories and mysteries can be dispelled with good data from the geologic record, and Erwin...offers an authoritative account of the search for these data and for the cause of the extinction. Extinction provides a great reference for researchers and the interested lay reader alike." Andrew M. Bush, Science

"Douglas Erwin's geological mystery story is engrossing.....The book ends with Erwin warning that the Earth is arguably entering another mass extinction period, this time unnatural and man-made. And this time the destruction may well be total." Sunday Age

"The author...explain[s] what this paleontological, as well as geological, evidence can tell scientists about the dramatic and deadly shift in the Earth's environment." Science News

"Extinction — written, it seems, both to persuade his colleagues and to educate a lay audience — is told from the perspective of a forensic scientist trying to piece together a quarter-billion-year-old crime scene." Joshua Foer, Washington Post Book World

"Although framed in terms of hypotheses and their tests, Erwin's story unfolds as a gripping who-done-it for the ages." Andrew H. Knoll, Harvard University, author of Life on a Young Planet

"Douglas Erwin blends careful scholarship and graceful prose in this authoritative elucidation of Earth's greatest mass extinction. Although framed in terms of hypotheses and their tests, Erwin's story unfolds as a gripping who-done-it for the ages."--Andrew H. Knoll, Harvard University, author of "Life on a Young Planet"

"Douglas Erwin is the world's leading expert on the end-Permian extinction. This book will be the standard reference on this crucial event in the history of life. It is a wonderful example of science in action."--Richard Bambach, Virginia Tech

"This book provides an up-to-date review and critical appraisal of all we know about the end-Permian mass extinction, a subject that has drawn much popular attention. Complementing its solid scholarship, its friendly style enables educated general readers to get to grips with all the current debates."--Paul Wignall, University of Leeds, author of "Mass Extinctions and Their Aftermaths"

"In conversational prose, Douglas Erwin provides a useful roadmap to a complex scientific subject--an up-to-date treatment of the end-Permian extinction."--Michael J. Foote, University of Chicago

Douglas H. Erwin is Senior Scientist and Curator in the Department of Paleobiology at the Smithsonian National Museum of Natural History and an External Faculty Member of the Santa Fe Institute. He began researching the end-Permian mass extinction in the early 1980s and has traveled many times to China, South Africa, and Europe seeking its causes.