All of the Earth's systems — including life — are intimately connected.
The Earth's Biosphere: Evolution, Dynamics, and Change
- Vaclav Smil
No object in the Solar System is more enigmatic than our own familiar planet. At least four of its attributes stand out as unique, as far as we know. The slow mill of tectonics pumps the rocks around from the deep Earth to the surface and back; two-thirds of the planet is covered with liquid water; the atmospheric composition is far removed from thermodynamic equilibrium; and, most stunning of all, there is abundant life — a biosphere. We feel that these remarkable attributes are intimately connected, but are poorly informed about these relations and by what principles the system evolved. Earth dynamics, in particular the role of life, is hot stuff at present, Earth system science and geobiology being examples of new disciplines specifically concerned with this problem. So Vaclav Smil's overview of what we know about the biosphere is timely.
To those reading Nature today, it may come as a surprise that only a few decades ago Earth dynamics was overwhelmingly considered as resulting from purely physicochemical interactions. Even Edward Suess, who coined the term 'biosphere' in 1875, thought of life as basically independent of the rest of the planet. In retrospect, it seems as though the geologists first had to settle the more basic aspects of their subject before they could concentrate on the intricacies of geobiology.
This may explain why the Russian scientist Vladimir I. Vernadsky, who had already set the stage for modern geobiology in the first half of the twentieth century, could be ignored for so long in the Anglo-Saxon part of the world. It is one of the great merits of Smil's book that it puts this record straight. The volume opens with a vivid description of Vernadsky's eventful life and career, stressing the enormous achievements of this great scientist. The Earth's Biosphere may be read as an update of Vernadsky's key book The Biosphere, which only appeared in English as recently as 1998 (Copernicus Books, translated by D. B. Langmuir).
The subject is immense, encompassing the present state of life and its environment, as well as the history of the system over almost 4 billion years. To deal with a field of this complexity, two options are open. One can either try to organize the different aspects around a single vantage point, or just give a kaleidoscopic description of the state of our knowledge. The first approach has the advantage of coherence and perspective. Things fall into place and there is an argument that one can agree with or not. James Lovelock's book on Gaia (The Ages of Gaia: A Biography of Our Living Earth, Norton, 1988) is an example. It is easily accessible even to a lay audience and, although the message has been criticized, the book has sparked a vivid interest in a systems approach to the Earth and to global geobiological feedbacks.
Another example is S. A. L. M. Kooijman's Dynamic Energy and Mass Budgets in Biological Systems (Cambridge University Press, 2000; 2nd edition), which presents a theory of biological organization at the level of the individual organism. Based on a very limited set of assumptions, this theory has a high predictive value and covers an amazing variety of natural phenomena. The ambition is to extend the organismal models to the molecular, ecological and eventually global levels of organization.
Smil's book is closer to the descriptive end of the scale. It covers almost the full range of relevant subjects, while many of the actual relationships between them remain open-ended. Discussions of the physical aspects of the system include the generation and output of energy by the Sun, plate tectonics, oceanic and atmospheric current systems and global climate. Biological subjects include molecular processes, organismal biology, ecology and global phenomena. Thus there are passages on basic molecular-biological concepts and the origin of life, metabolic pathways, microbial ecology, and biogeochemical cycling. The global dimension includes discussions on the deep hot biosphere and biospheric mass and productivity. The book ends with the impact of civilization on the biosphere.
The above is only a selection, and the whole text becomes a bit of a pot-pourri. I feel that this not only reflects the author's jumpy mind, but also the state of the art. Nevertheless, the book offers updated reviews of many of these subjects, and most of its statements are well documented by the long list of references. This by itself is a major achievement, for which all those interested in the biosphere should be grateful.
In addition to presenting the broad overview, Smil indulges in a wealth of salient and often entertaining details. Did you know that a sperm whale can dive more than 2,000 metres deep, holding its breath for over an hour? Or that in 1973 a jet collided with a huge vulture at an altitude of over 11,000 metres? The book is replete with such petites histoires. These are welcome, of course, but point to a lack of organization underlying Smil's less systematic approach. At times I felt somewhat overwhelmed by the abundance of facts, observations, theories and details. This impression was strengthened by the uneven style of writing. Some parts read like a newspaper, whereas others are in the dry style of professional reviews. I recommend several rounds of rigorous reorganization before the next edition goes into print.
With the present focus on Earth system science and geobiology, there is a pressing need for good introductory textbooks. Although I do not think that Smil's volume is sufficiently systematic to qualify for a first students' introduction to this burgeoning field, it will certainly be of great use to a more advanced audience with a general curiosity in biospheric matters. Smil conveys the thrill of exploring the unknown planet we inhabit. His enthusiasm and the broadness of his interest are infectious.