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Resetting the clock,
This review is from: Extinction: How Life on Earth Nearly Ended 250 Million Years Ago (Hardcover)Any scientist who opens [and closes!] a book by saying "We [I] don't know!" is worthy of your attention and respect. Too many others have taken up a theme and defended against all comers. Erwin's examination of the catastrophic close of the Permian Age is complete, admirably researched and exquisitely written. Within its pages, this work examines the various ideas on the massive loss of life 250 million years ago. These days, not to have heard of an meteor's killing off the dinosaurs 65 million years ago suggests you've lived hidden in a cave for a generation. Erwin opens with a brief overview of that event, reminding us that extinctions, particularly "impact events", have loomed large in discussions of the history of life ever since Walter and Luis Alvarez proposed the idea.
It's easy to rattle off the numbers: when the dinosaurs "went West", perhaps 75% of life was also extinguished. When the Permian ended, over 95% of living things disappeared. Erwin asks: "How do we know this? What life forms disappeared? Did they all go at the same time? How long did it take to recover?" Most important, of course, "What killed them off?" Instead of dull statistics, Erwin asks the important questions. Acknowledging that "Triassic rocks are boring", he explains why this is so. Fossils are scarce is the obvious answer, but why they are missing is his quest. With most of his attention focussed on ocean life, he details what causes shifts in benthic populations. The seas rise and fall - for a variety of reasons. Glaciation takes up sea water and leaves continental shelves high and dry. Oceans need to "turn over" an oxygen supply. What is the result of that failing? Carbon, with its various isotopes, passes through life selectively. Tracing that path provides insights into where it's been - and where not. When did the Siberian "traps" form? How much lava spewed from that rift, and what other products did it bring along or destroy? Finally, is there evidence that Earth was pelted by another bolide to provide an easy answer to all those questions? That reply is almost surely negative.
Erwin would like to couch this narrative as a detective story, but it doesn't really work. There are too many victims - unless you count life as one entity. There is also a phalanx of detectives all trying assiduously to solve the case. If you thought there were too many cooks spoiling the broth, wait until you meet this mob. Nearly all of them have an agenda and they have a disturbing tendency to trumpet a single tune. Erwin should have portrayed them as an orchestra, with himself as conductor. Van Kariajan would go emerald with envy. Each investigator supplies a theme, striving for a solo performance. Erwin cautiously assesses the tune, fits it nicely into a grander theme and produces a symphony instead of a cacophony. It's quite a performance. To keep himself from the sin of hubris, he points out his own flaws in a previous effort. The strain wasn't discordant, but the composition needed refinement.
Erwin fastidiously acknowledges his contributors. Jack Sepkowski comes in for deserved accolades, as do Bruce Rubridge, Yugan Jin and many others. Their methods, results and further work - including that incomplete but "promised" - are given a full hearing. Even those whose suggestions are highly suspicious, such as Luann Becker's Bedout "crater" are given a respectful hearing. Nobody's work is chastised or rejected. "We need more investigation" is the running theme of Erwin's account. The reason the ongoing search is important lies in understanding what is happening around us today. Are we, in Dave Sepkowski's words a "Dead Clade Walking"? Or can we glean enough information from the rocks to find the means to succeed through the extinction we seem to be part of - and likely creating? The "95%" means life had to restart the clock after the Permian. There were a few "Lazarus species" that re-emerged after the cataclysm. Will the human species manage to revive itself when so much life around us has been decimated? No more pertinent question confronts us. [stephen a. haines - Ottawa, Canada]