Walter Alvarez 1997, Princeton University Press, pp. xii + 185, hardback, ISBN 0-691-01630-5. £18.95.

This book is a concise popular account of the story of the K/T meteorite hypothesis written by one of the main protagonists. As it shows the K/T debate has moved on rapidly in the last few years. The hypothesis that a meteorite impact was responsible for the Iridium in boundary clays has been essentially vindicated by the discovery of the Chixculub Crater and associated Tsunami deposits around the Caribbean. At the same time improvements in stratigraphy mean that the maximum likely duration of the boundary clay has declined from millions to thousands of years (Herbert et al. 1995) and that the extinction levels of marine and non-marine faunas have been shown to be coincident with each other and with the iridium layer (within most peoples margin of error). Given this, vaguely interested observers of the K/T debate may begin to wonder what it is about now. The answer is given in the first and last chapters of this book.

The first chapter is a journalistic rendering of the current hypothesis of what happened when the 10km meteorite, or comet, hit the earth at around 30 km per second. The cataclysmic scenario of fireballs, ash induced darkness and acid rain contains numerous details which need to be refined and tested in the light of the detailed record of change, and perhaps equally important non-change across the boundary. The number of unanswered questions still easily exceeds the amount we do know about this extraordinary episode. In addition any palaeobiologist would want to start serious debate over assertions such as that without the meteorite the Mesozoic fauna and flora would have essentially persisted to the present day. Similarly estimates that 50% of all extant genera went extinct at the K/T boundary are at best contentious. Recent analyses of faunal change across the boundary (e.g. Macleod et al. 1996) provide little support for either assertion.

At the other end of the book the extraordinary evidence for correlation of flood basalts with mass extinction is outlined. The coincidence of the Deccan Traps and the K/T boundary might reasonably be dismissed as simply a hundred to one coincidence. However, work showing that the even larger Siberian Traps coincide with the Permo-Triassic extinctions (Renne et al. 1995) lengthens odds on the double coincidence to at least ten thousand to one. There is apparently a lack of any sensible mechanism for explaining this coincidence, but as we all know in geology that is an extremely dangerous line of argument.

So intensive research and productive controversy is liable to continue to surround the topic of mass extinctions for a considerable period. Nonetheless, it is timely to reflect on the development of the K/T controversy since the first exposition of the meteorite hypothesis, by Alvarez et al. (1980). Walter Alvarez as one of the prime participants in the story may not be the most objective witness but can bring a unique perspective to the tale. This he does admirably in the main part of this book which concentrates on his personal trail from study of the Gubbio boundary clay as an offshoot of geomagnetic research to identification of the Chicxulub crater as the source of the iridium. Along the way he weaves in a popular description of how geology works and some philosophising on catastrophism vs uniformitarianism.

Understandably Alvarez avoids the contentious fine detail of the fossil record – and forams are almost the only microfossils mentioned; he does give nice cameo descriptions of Jan Smit and Isabella Premoli Silva though. Given this I am not in a good position to comment on how accurate the content is but I did not notice any obvious howlers and felt that he dealt fairly with conflicting opinions and gave a fair balance of coverage between the different disciplines. The main value of the book for a micropalaeontologist is that it provides a very readable account of the multidisciplinary activity related to the K/T boundary debate.

As suggested by the title, the book is written as a lively piece of popular science for a general audience. It is a short book, 150 pages of main text set in a large font on small pages, so nothing is explained in detail. However, a careful use of endnotes means that the book is fully referenced and an excellent introduction to the scientific literature on the subject. It is slightly irritating having the basis of biostratigraphy explained in words of one syllable, but it broadens the accessibility, and similar explanations of techniques such as neutron activation analysis are rather more welcome to a micropalaeontologist. I found it an excellent read and would strongly recommend it to anyone with an interest in the K/T debate or in the history of science as it provides much food for thought on both topics, if not authoritatative analysis. It also could easily form the basis for student projects or indeed a course on geology for non-geologists.

References

Alvarez L.W., Alvarez W., Asaro F. & Michel H.V., 1980. Extraterrestial cause for the Cretaceous-Tertiary extinction. Science, 208, 1095-1108.

Herbert T.D., Premoli Silva I., Erba E. & Fischer A., 1995. Orbital chronolgy of Cretaceous – Paleocene Marine Sediments. In Berggren W.A. et al. (eds.) Geochronology times scales and global correlation, SEPM Special Publicaton No. 54, 81-93.

MacLeod N. and 21 others. The Cretaceous-Tertiary biotic transition. Journal of the Geological Society of London, 1254, 265-293.

Renne P.R., Zhang Z., Richards M.A., Black M.T., and Basu A.R., 1995. Synchrony and causal relations between Permian-Triassic boundary crises and Siberian flood volcanism. Science, 269, 1413-1416.

Jeremy Young, Department of Palaeontology, Natural History Museum, London SW7 5BD.