Journal of Petrology | Volume 43 | Number 10 | Pages 1985-1986 | 2002
© Oxford University Press 2002
BOOK REVIEW |
Convection Made Easy, Mantle Convection in the Earth and Planets, by G. Schubert, D. L. Turcotte and P. Olson. Cambridge University Press, Cambridge. Paperback: ISBN 0 521 79836 1, £49.95, $74.95. Hardback: ISBN 0 521 79837 X, £140, $200.
In the final chapter of this monumental survey of our present understanding of convection in the Earth and planetary interiors, one finds a list of major questions (160 questions in 13 categories) that provides a relatively concise insight into how these authors approach their task of surveying such a huge subject. In discussing these questions, many of which remain either unconstrained or controversial, the authors round out their overview of the many diverse streams of evidence that have been brought to bear in building an understanding of the convection system in the mantle.At 940 published pages, few will read this book from cover to cover, but it will provide an invaluable resource to many, as a source book that explains and summarizes so much of the relevant literature in a field that is notoriously difficult to come to grips with, if only because of the sheer volume of published work. The book works on two levels: as a research resource, starting with Chapter 15 and using it to guide directed forays into earlier parts of the book, or as an introduction to the subject, starting with Chapter 1 and following the conventional route. The first five chapters or so provide a textbook-style summary of the history of the subject, a review of plate tectonics, the evidence of global structure from seismology, and detailed summaries of the thermodynamic theory and the evidence for a viscous mantle. The approach with this material is reminiscent of that used in the classic reference Geodynamics by Turcotte and Schubert, but the focus here is specifically on aspects relative to convection, and the view is updated and extended, taking into account the evidence that has come to light in the two decades since publication of that book. These chapters would serve well as a primary reference for a postgraduate or senior undergraduate course on physical geodynamics.
The next three chapters develop the mathematical side of convection theory, starting from the basic conservation principles and proceeding to a full statement of the equations for a range of approximations and coordinate systems. Linear stability theory and boundary layer theory as two of the major tools of the convection theorist are explained in detail. Non-linear approximations starting from the Lorentz equations lead to a discussion of the chaotic nature of convective systems. Explanations of mean field theory and weakly non-linear stability are also included. These chapters will provide an invaluable reference to anyone who actually wants to do convection calculations. And for those who simply want to use and understand the results that arise from other people's calculations, contained herein are answers to vexing questions such as: what is the Boussinesq approximation anyway?
The subsequent section (Chapters 9–13) is probably that which will be of most interest to readers of this journal. At the risk of not doing justice to these chapters, this section might be described as a comprehensive summary of the many papers published during the past three decades that use numerical simulation as a research tool to address specific questions about the mantle convection system. However, I think that the authors achieve here more than just a summary. The selection of material and the text provide a clear path through the thicket, explaining why results may be significant. Clearly they have not included everything, but their judgment will satisfy most. The original sources cited in this section probably account for most of the references cited in the 76 pages of the bibliography, a useful resource in its own right.
This section is divided into chapters with the themes of: 2D calculations, 3D calculations, hotspots and plumes, chemical geodynamics, and thermal history of the Earth. Subduction seems to find its niche in the first two of these chapters. The approach with each of these subjects is a systematic description of the principal results that are described in the primary references. This description is supported well by the choice of figures, often reproduced from those primary references, including a liberal selection of colour plates grouped in separate sections of the book.
Although the authors state: ‘the eventual goal of numeric modelling is to provide a complete picture of the flow within the Earth's mantle’ the point that comes clearly out of these chapters is the value of systematic focused experimentation, whether it be using laboratory apparatus or computer programs. The value in ‘numerical modelling’ (a much abused term) is not in the construction of a model, but in its application via systematic experimentation designed to explore and describe how a complex system such as convection in the mantle depends on assumed parameters and properties. A second point that emerges clearly from these chapters is the difficulty of pinning down definitive answers to questions that might appear on the face of it to be simple, for example, the degree to which mantle convection occurs (or has occurred) in separate layers.
Also evident in these chapters is the degree to which experimentation using computers has supplanted that using tanks and analogue materials in the past two decades. Many of the specific questions listed in the final chapter cannot easily be addressed by tank experiments, but they are susceptible to numerical investigation if errors can be controlled. If I have one minor misgiving about the presentation of this material, it is that it is easy to lose sight of the fact that the accuracy of such calculations is often taken for granted. Benchmark studies involving multiple independent groups have become an essential element in the validation of numerical experiments.
The penultimate (and longest) chapter before the concluding summary is concerned with the subject of convection in the interiors of other planets, with focus particularly on the terrestrial planets and the Jovian satellites. This chapter in its own right is a significant contribution to the planetary community, but our understanding of the other planets draws heavily of course on the understanding of our own planet developed in the preceding chapters.
Can convection be made easy? Probably not, but I think that publication of this book makes it much easier to get into the subject and build an overview of it than it has been in the past. All whoa re working in this field will welcome its appearance.
- G. A. Houseman
- School of Earth Sciences, University of Leeds
- School of Earth Sciences, University of Leeds
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