Extinction by Erwin Douglass

Extinction

Erwin, Douglas H. Extinction.Princeton: Princeton University Press, 2006.

Author Douglas H. Erwin is Senior Scientist and Curator in the Department of Paleobiology at the Smithsonian's National Museum of Natural History and an External Faculty Member of the Santa Fe Institute. This book addresses the end-Permian mass extinction, one of several mass extinctions that have been found in the history of life on earth. This particular instance occurred some 250 million years ago, and the cause is unknown. The author seeks in this book to explore the nature of this mass extinction and to consider what might have been the cause, looking at the evidence from around the world and offering an analysis to answer the questions raised.

Erwin describes the evidence of the Triassic as found in rocks in China, Europe, and Utah. He concentrates on Utah and the ay the Triassic era is sen in the landscape and the rocks. Some narrow bands show fossils, and one area shows the evidence of the Permian period, the last profusion of life before the extinction that occupies this book. Some twenty million year separate the rich fauna preserved in West Texas and the dry and very different fossils found in Utah. Erwin notes that there were two great disasters between these periods, so that some 82% of genera and half of all marine families disappeared, with plants and animals on land almost completely eliminated, only to rebound in a few tens of millions of years. Many suggestions have been made as to what triggered this massive loss of life, with suggestions made by geologists, physicists, evolutionary biologists, and complexity theorists. There are many events known from the Permo-Triassic interval, which complicates finding the cause. Erwin also notes that making a decision on this subject requires knowing how rapidly the extinction took place, and this is not known. Establishing the duration is critical and he addresses this issue in the book.

Erwin sets out clearly the nature of the chapters in the rest of the book, beginning with an explanation of the issue and some of the evidence found, then considering what is known about the first extinction during this period (which had little long-term impact), and then the larger and catastrophic extinction at the end of the Permian era. This extinction altered the ecosystems so they never recovered, and it is this extinction that occupies the author throughout this book. Some of the possible explanations are considered. Erwin introduces some of the possible causes and the evidence found by geologists and paleontologists, examining the evidence that can be used to test the hypotheses that have been put forward. Erwin also reports on his own investigations as part of a team including geologists from China who have been examining the Permian extinction. Here, the author also introduces the complexity of the fossil record and the evidence of an abrupt shift in the carbon cycle, an idea he applies to other parts of the world to show its importance as an analytical tool. Erwin also considers the history of thinking on this issue before considering the specific fossil evidence from South Africa, documenting the extinctions near the Permo-Triassic boundary.

The author also begins by considering some of the other mass extinctions that took place at a much earlier date, in part to see what caused those extinctions in order to see if the same causes applied to the Permian extinction. The evidence from the extinction at the K-T boundary (between the Cretaceous and the Triassic) has been much analyzed because of the discovery of higher deposits of iridium from that period. Iridium is found primarily in meteors or in some volcanic explosions, and so the higher levels have caused many to see the extinction of the dinosaurs as caused by a large meteor crashing into the earth and depositing iridium around the world on the same geologic level. Another substance found at the site of extinctions has been fullerenes, which can be produced by lightning strikes, forest fires, and meteorite impacts. Some evidence exists for an impact around the time of the Permian extinction, but the author says this is inconclusive at this time.

Some of the solutions have been quite exotic, such as the suggestion that a mass of weakly interacting massive particles (WIMPS) at the earth's core emerged to cause genetic damage and increased rates of cancer. This is highly speculative and uses an idea from physics that has not been verified as yet. Some geologists believe that slow processes could be the explanation rather than a sudden catastrophe, such as increased volcanism leading to climatic change and the emission of certain gases into the atmosphere. There is more evidence possible for this sort of change, though again, a final determination would also depend on knowing the rate of change involved, something that is not currently known. The possibility that continental drift and accompanying changes in the earth's biota is another class of explanations, and the author examines this as a reason and finds it possible but uncertain. A drop in sea level could also bring about such a change, with the drop being attributable to climate change.

A more complex explanation addresses a supposed change in the carbon cycle, showing that at the Permo-Triassic boundary, there was a large volume of organic carbon added to the oceans and atmosphere. Erwin investigates this sort of change and draws on the work of geochemists and others, leading to the view that the sudden drop in sea level could have released methane, triggering a change in carbon isotopes and creating global warming and extinction.

The chapter on the author's "South China Interlude" shows the results of his investigations in China and the geology of that region and what it shows at different levels. The widespread discovery of marine rocks in the area offers good evidence of some of the changes taking place at the Permo-Triassic boundary, along with the sea fossils such as trilobite from the same era. Erwin notes how this work in china revived interest in the Permo-Triassic boundary and produced new ideas and new theories to be tested further. Some of the evidence supports one of the existing theories or another, some suggest a completely different idea, and some have yet to be incorporated into any theory.

After presenting and analyzing the evidence for the extinction, Erwin considers much more briefly the evidence for the revival that followed, noting how species came back to the fore soon after the extinction, as is shown in the fossil record. The world that emerged after the extinction was very different from the one that existed before the extinction. The mass extinction clearly had much to do with shaping this new world and with the changes that came about as a result, producing a similar but different diversity in the species now thriving in this new system. This change also meant new living strategies for different species, with considerable diversity noted for the species in the sea.

The discussion in this book covers the topic well and gives the reader a good idea of the sort of evidence being gathered, ways in which scientists find and analyze this evidence, the theories developed to explain the evidence, and how these theories are then tested by other scientists and by new evidence. Erwin provides extensive source data so the reader could examine some of the other work in this area and read the scientific papers on which Erwin relies. Erwin presents his argument in a clear manner, beginning by explaining the nature of the chapters to come, then by developing the nature of the problem, noting his own investigations into the matter and then by considering the various theories and how they do or do not fit with the data gathered. The discussion of the various theories is especially interesting for what it shows about the way scientists think and how they can be as speculative as anyone else in the formative stages of their thought, though after that, proof is required.