When Life Nearly Died: The Greatest Mass Extinction of All Time by Michael J. Benton, Thames and Hudson, London, 2003; 336 pages, ISBN 050005116x, hardback, $29.95.
Comet and meteor impacts, "snowball" earth, sudden mass extinctions -- earth scientists today seriously discuss such scenarios, testifying to the return of catastrophism after a 150-year reign of uniformitarianism, the theory that all past geological events should be explained only by the processes we see acting around us now. Dr. Benton, Professor of Vertebrate Palaeontology and Head of the Department of Earth Sciences at the University of Bristol, takes us from Victorian scientists who identified the first fossil reptiles and rock strata, through the fall of catastrophism in the 1830s, to its eventual return in the 1980s. Writing in a clear style laced with humor and anecdote, he lays out the evidence supporting the various changing theories about the extinction of prehistoric life, including present controversies. Putting a very human face on geology and paleontology through biographical sketches of scientists over the years, as well as descriptions of his own activities, he emphasizes the way scientists work, the data that is and is not available, and the collegial process of arriving at and rejecting theories. As James Lovelock remarks on the jacket, this "splendid book brings back to Earth Science a sense of adventure. . . . It is both a wonderfully good read and a valued reference."
Dr. Benton's special interest is the mass extinction at the end of the Permian period, currently dated at 251 million years ago, when an estimated 90% of all species on land and sea became extinct. He examines the more thoroughly studied extinction of the dinosaurs 65 million years ago and the evidence that has led scientists to accept that the earth has been struck by large extraterrestrial objects several times, including an asteroid 65 million years ago. Whether this event caused the extinction of the dinosaurs or merely contributed to it is not yet settled, though widely accepted. The study of meteor craters and confirmations of the impact 65 million years ago, at first rejected by most geologists and paleontologists, reestablished the respectability of catastrophism.
Focusing on the Permian extinction, he reveals how recent much of the vital data is. In fact, only in 2000 did scientists select the particular example of rock strata, in southern China, that serves as the internationally recognized boundary point or division between the Permian and Triassic periods. Mapping this boundary and the strata above and below it worldwide is an ongoing collaborative process taking place in far-flung parts of the globe -- particularly China, Russia, Italy, Iran, Pakistan, Kashmir, Greenland, North America, and South Africa. These rocks and their fossils give information about the order and types of events, climate changes, and a detailed record of the disappearance and appearance of life forms. Not until 1995 could scientific methods date the rocks accurately enough to reveal the time span involved, and therefore the extinction's relative suddenness. The weakness of paleontology, the author points out, "is short time-scales, where the error bars on age estimates may exceed the time intervals in question. So, no one can say whether the end-Permian crisis lasted for one day or a few thousand years" (pp. 302-3).
The diverse Permian land and marine ecosystems are described, along with the bleak state of life worldwide at the beginning of the Triassic; and "the astonishing finding from all the current work is that perhaps the end-Permian crisis was actually more severe for life on land than for life in the sea. This is a striking turn-around from the view of only 15 years ago, that essentially nothing out of the ordinary had happened on land at all" (p. 219). How could this dramatic event have been overlooked?
Looking back to the state of understanding of the end-Permian crisis in 1970, or 1980, or even 1990, we can easily point to errors of judgment. Why were palaeontologists and geologists then so blind to the truth? (Can we be sure we have the truth now?) They were looking at the biggest crisis in the history of life and of the Earth and they didn't see it. They must have been deluded, or incompetent, or both. Not so. It is hard for scientists, just as for anyone else, to throw off everything they have been taught. And when the evidence is somewhat intangible, it is understandable if scientists err on the side of caution. -- p. 252
Current theories accounting for the end-Permian extinction include a meteor impact, massive volcanic activity in Siberia, and the sudden release due to global warming of gas hydrates (newly discovered crystalline solids that collectively trap massive amounts of pressurized carbon-rich gases, such as methane). Laying out the evidence of all factions, he explains why he believes the predominant factor was volcanic activity, while emphasizing that all the evidence is far from in.
The book concludes by considering the lessons such extinctions may hold for us during what is sometimes characterized as the "sixth mass extinction," due to human intervention. Undogmatic in approach throughout, the author ends by saying that:
When I was beginning my career, I felt that scientific research was a line of work that led to ever greater complexity. As one accumulated information about how the Earth works, all the simple questions would be answered. Then the questions would have to become more intricate and harder to solve.
But the unanswered questions are as big and as simple as you could wish for . . . How diverse is life? How does the world react to human intervention? What will happen in the next 100 years? Where did life come from? How resilient is life to crisis? -- pp. 304-5
-- Sarah Belle Dougherty
(From Sunrise magazine, August/September 2003; copyright © 2003 Theosophical University Press)