BOOK REVIEW
In Search of Permian Perpetrators
Richard Twitchett
Extinction: How Life on Earth Nearly Ended 250 Million Years
Ago. Douglas H. Erwin. x + 296 pp. Princeton University Press,
2006. $24.95.
Life on Earth has had a bumpy ride. The past half-billion years have
witnessed a number of biotic crises of varying magnitude and impact.
Probably best known is the end-Cretaceous cataclysm during which the
dinosaurs, among other species, died out. However, the most severe
event of this type occurred toward the very end of the Permian
period, a little more than 250 million years ago, long before the
first dinosaurs scampered about: Every ecosystem on Earth was
devastated, from tropics to poles, from deep ocean to desert plain.
Nine out of every 10 species disappeared forever. It took 100
million years for global biodiversity to return to preextinction
levels. The cause of this catastrophe? We are still not completely certain.
The end-Permian event is currently attracting more scientific
attention than ever before. Barely a week goes by without
publication of a new scientific article on the subject, and we are
at last closing in on the truth of what happened to our planet so
long ago. This paleontologic detective story, the patient study
required to solve it, and the frustrations, excitement and red
herrings generated in the process are all detailed by Douglas H.
Erwin in his wonderful new book, Extinction.
Erwin begins his tale in Utah, neatly explaining the severity and
importance of the end-Permian crisis by taking the reader on a short
field trip to some classic localities that give us
"before" and "after" snapshots of the event. He
then goes on to explain the layout of the book: It is "written
as a mystery story." And indeed, it's a very readable one. The
obvious strengths that make it so—the clarity of the writing,
the relaxed style, the neat mixture of scientific fact and amusing
personal anecdote—come to the fore very early. The mystery
begins not with the scene of the crime, or a discussion of the
evidence, as one might expect, but with a description of the
suspects: the list of possible causes.
This is followed by another field trip, this time to South China,
and a review of some of the key research projects Erwin was involved
with in the mid-to-late 1990s, which demonstrated for the first time
the pattern and rate of extinction. Again, the anecdotes and asides
help keep the reader's interest and provide nice little insights
into the character of the author and his colleagues. Included in
this section is the best explanation of the methods, biases,
problems and absolute necessity of geological dating that I have
ever read!
Finally we get back to the mystery story proper, with a discussion
of what groups actually went extinct. Here Erwin missed an
opportunity. In his first book on the end-Permian event, The
Great Paleozoic Crisis: Life and Death in the Permian
(Columbia University Press, 1993), he described in great detail the
extinction patterns of all fossil groups. Since then, there has been
a tremendous advance in our understanding of the fossil record,
particularly with the publication of new, larger databases of fossil
diversity and descriptions of many more species. It would have been
nice if Erwin had explored in this new book how the extinction plots
of 1993 have changed. But instead he skims over many of the groups
affected, and some he doesn't even touch on. For a fuller (though
slightly out-of-date) picture, readers should consult his earlier book.
Next Erwin recounts a field trip to South Africa and examines some
of the recent advances made in studies of the extinctions on land,
with particular reference to the vertebrates. He discusses the
vertebrate fossil record and explains how a literal reading of
fossil ranges, if it fails to take into account the relationships
between the different species, can lead to a false picture of the
severity of the extinction. This is a fundamental concept—one
that affects all fossil groups, not just vertebrates, and all
events, not just the end-Permian crisis. Almost certainly
paleontologists have overestimated the magnitude of diversity loss
during all past biotic crises through reliance on a literal reading
of the fossil record.
Then Erwin briefly returns to the subject of the oceans to discuss
Permian marine ecosystems. Here I came across my favorite typo: The
coal beds that lie beneath the volcanic Siberian Traps and may be a
source of light carbon dioxide mysteriously morph into
"extensive Siberian cola beds"—which would almost
certainly be a great source of CO2! Next comes a roundup
of the evidence and a whittling down of the list of suspects to . .
. ah! but I won't spoil it for you!
Then Erwin briefly describes the patterns of postextinction
recovery, summarizing some very recent work. The book concludes with
a nice, succinct account of how the end-Permian event fits into the
evolutionary history of the biosphere and what lessons—if
any—we can draw from it that might apply to the present-day
biodiversity crisis. Notes, a comprehensive reference list and an
index follow.
Overall, Extinction is a very enjoyable read and a worthy
follow-up to The Great Paleozoic Crisis. It provides a
thoroughly up-to-date account of the causes of the end-Permian event
and the developments in the field since 1993 as seen through the
eyes of one of the key players. Here and there Erwin is able to put
his hands up and admit he was wrong (the sign of a first-class
scientist), but in truth Extinction leaves the reader with
the (accurate) picture that here is a scientist whose work has
significantly advanced our understanding of the greatest extinction
event known to science.
Recently, I had the good fortune to bump into Erwin at a conference.
I asked him what aspect of the end-Permian problem he was going to
tackle next and was somewhat surprised when he answered that he is
moving on to other fields of research. "I've said all I want to
say [on the subject]," he confessed. I sincerely hope he'll
change his mind, as there are few others who have worked so hard and
long on this problem. If Extinction really is his last word
on the end-Permian event, then this readable and scholarly account
is a fine way to bow out. I recommend it to all.