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The Earth's Biosphere: Evolution, Dynamics, and Change

Posted on: Thursday, 24 June 2004, 06:00 CDT

THE EARTH'S BIOSPHERE: EVOLUTION, DYNAMICS, AND CHANGE Vaclav Smil, 2002, 346 pp., $32.95, hardbound, The MIT Press, ISBN 0-262- 194472-4

This is a book about everything that matters on Earth. Vaclav Smil paints this portrait of the living Earth with a holistic synthesis approach, and with many references to the historical development of scientific knowledge of life and its environment. He does this by drawing from a vast spectrum of diverse sources, from cosmology all the way to molecular biology and everything in between. Smil's "biosphere" is the space where life-forms exist. Thus, he uses the term in a more inclusive way than is common in the atmospheric sciences: it contains the troposphere, soils, all bodies of water, and, of course, all life-forms on Earth. Smil's motivation for writing this eclectic piece of work is indicated in the preface: "One of the principal reasons for the rejuvenation of scientific syntheses (which used to make up such a large part of nineteenth- century science) is the growing realization that the very survival of modern civilization is inextricably tied to the fate of our environment, to changes in the Earth's biosphere. And anybody with even the most basic understanding of the environment realizes that in order to minimize the impact on the biosphere modern societies need integrated, multidisciplinary studies that inform by the breadth of their syntheses."

Vaclav Smil is Distinguished Professor of Geography at the University of Manitoba, Canada. He is a Fellow of the Royal Society of Canada, and in 2001 he received the Award for Public Understanding of Science and Technology from the American Association for the Advancement of Science. He has written seventeen books, with translations in many languages, principally on energy production and management and its impact on the environment and agriculture. While reading The Earth's Biosphere, I tried to guess what discipline of science is Smil's intellectual home, but I quickly realized that this is a futile question: as pointed out in his Royal Society citation, he is a true polymath, a person of much and varied learning.

The Earth's Biosphere has the look of a coffee-table book and is written in a sophisticated style. Yet it is not light reading, mostly because of its sheer density of information. To pack everything that matters about life into nine chapters and an epilogue, within just over 270 pages of text (the rest is references, appendices, and indexes) is a formidable task that does not allow for descriptive loitering. Smil starts out with a history of the concept of the biosphere. He attributes the roots of modern biospheric science to the Russian bio-geo-chemo-physicist Vladimir Vernadsky( 1863-1945). In reference (or perhaps reverence) to Vernadsky, chapter 1 contains an extensive biography, and each chapter starts out with a quotation from Vernadsky's principal work, Biosfera (Vernadsky 1926). Rooted in the nineteenth-century fledgling thermodynamics, and the traditional view of the natural world as a composite of disparate spheres, the modern term biosphere transcends these divisions, and biospheric science synthesizes the traditional disciplines with the objective to understand the dynamics of the global environment. Chapter 1 ends by emphasizing the role of satellite monitoring in our ability to see the biosphere evolve over time, and to see how its various components interact to form a global whole.

The actual portrait of the biosphere starts in chapter 2, with an overview of life's cosmological origins and the coevolution of the biosphere and its life-forms. Why are all life-forms carbon based? What are the physical and chemical conditions in which life evolved? Is life the result of chance or necessity? These are questions that are critically reviewed in this chapter. Chapter 3 showcases and celebrates biodiversity and its resilience in the face of various degrees of disturbance, from changes in solar luminosity over billions of years to catastrophic asteroid impacts and their aftermath. The chapter also summarizes the discovery of biodiversity and the various historical and contemporary attempts to organize and categorize it.

The survey of solar radiation and Earth's radiation balance in Chapter 4 is closer to home for atmospheric scientists. For the specialist it holds nothing new, but it is an accurate and concise summary of the basics. If, in analogy, this holds true for other subject areas covered in the book, it may serve in testimony of its quality. At the intersection between solar energy and the biosphere, Smil spends some time to discuss the energy efficiency of photosynthesis at various scales. In contrast to the maximum theoretical photon efficiency of 27%, the actual global-scale efficiency is only 0.2%. While this discussion illuminates the importance of scale in considerations of energy or mass-flow processes, it comes across as overly reductionist to treat the light- use efficiency of photosynthesis as the only juncture between solar energy and the primary production of phytomass. By driving the circulation of the atmosphere and oceans at a variety of scales, and by enabling the hydrologic cycle, solar energy literally sustains the climates in which plants grow and extends the range of many biomes far beyond what their limits would be without those circulations. Unfortunately, this is only hinted at in a short paragraph a little earlier in the chapter. Of course, it would be rather difficult to summarize these climate processes into a simple energy efficiency for the biosphere, and thus this criticism may not be entirely fair. The fact remains, however, that the book is unfortunately rather narrow in its treatment of biosphere- atmosphere interactions, confined mostly to the biogeochemical cycling of carbon, nitrogen, and other biologically important trace elements. Chapter 4 closes with a summary of Earth's endogenic heat production and the influence of plate tectonics on the evolution of the biosphere.

Biogeochemical cycles are the topic of chapter 5. About a quarter of the chapter is devoted to the water cycle and ocean circulation, followed by the global cycles of carbon, nitrogen, sulfur, phosphorus, calcium, silicon, and iron. For each of these elements, Smil provides schematic diagrams of major reservoirs and the pathways between them. An overview of relevant chemical reactions is given in an appendix.

Chapter 6 describes the spatial and physical domain of the biosphere and how organisms have adapted to life in the extreme reaches of this domain. Included here are (e.g.) discussions of exposure to UV light, and the residence times of bioaerosol. Smil describes the adaptation strategies of birds to sustain their high metabolic rate in the low pressure (and low oxygen level) of high altitudes, and how marine mammals rise to the double challenge of oxygen supply and high pressure in deep dives. If anyone is still in doubt about the adaptability of life-forms to extreme environments, the description of life in soils and the fact that a live bacterium was found in a borehole of 4000-m depth, or that tiny arthropods have survived exposure to temperatures as high as 151C and as low as 3 K, should be a cure.

Chapter 7 is devoted to the question of how much living biomass our planet sustains and what the turnover rate, or net primary productivity (NPP), is. One remarkable, and alarming, result of such estimates is shown in figure 7.2: "the zoomass of domesticated land animals, dominated by cattle, is now at least twenty times larger than the zoomass of all wild vertebrates." Estimates of global annual NPP have appeared for nearly 150 years. Given the immense effort in observation and modeling of NPP, it is at first surprising that the earliest NPP estimate (by Justus von Liebig in 1862, at about 63 Gt of C/year) is right in the midrange of satellite-based model estimates performed in the 1990s. However, this correspondence should not indicate that von Liebig was particularly accurate, nor should it be taken as demonstrating lack of progress to answer this question. It is simply a result of the overwhelming spatial and temporal variability of ecosystems and the formidable difficulty to account for it in global integrations of NPP or related fluxes.

In Chapter 8, Smil surveys the "grand patterns" of life's functioning and organization, whereas chapter 9 describes the influence on these patterns and their disruption caused by human action, much in excess of the magnitude and rate of environmental modifications incurred by any other species. The biochemical unity of life's structures was described in chapters 2 and 3, but, as Smil aptly writes, the "underlying commonalities extend far beyond the molecular, cell, and tissue levels." Despite their astonishing diversity, most species are "organized in a limited number of basic patterns ranging from small-scale plant communities to continent spanning Monies" and governed by highly predictable regularities. These quantifiable regularities include "the quarter-power scaling of animal and plant metabolism that applies across an entire range of body sizes and metabolic pathways." Arguments of scale and similarity are pervasive also in the context of life span and \population dynamics. Of course, the principle of scale invariance for many processes rings familiar to atmospheric scientists, but it is perhaps unexpected to find it in a discussion of empirical biometrics. The second part of chapter 8 describes the extent and characteristics of some of the most important biomes. It closes with an evocative discussion on the ubiquity of symbiotic coevolution, in the face of the much more well-known "survival of the fittest" principle, and the potential role of diversity and biocomplexity played as key determinants of biomass productivity, ecosystem stability, and resilience. Seeing that the loss of biodiversity may well be the most profound effect of human-induced global change, this discussion is an excellent lead-in to chapter 9, where anthropogenic change is the focus.

Thus far, relatively simple organisms such as cyanobacteria and photosynthesizing algae, or carbonate sediment forming plankton are likely the all-time champions of biogenic global environmental change. However, these organisms have retained most of their fundamental characteristics over at least hundreds of millions of years. In contrast, human evolution has been short, but its success (measured by the proliferation of the species) is impressive. In chapter 9, Smil suggests that this "remarkable evolutionary achievement is also the most worrisome of all problems immediately facing the biosphere." He reviews current knowledge, ignorance, and uncertainty about the global or continental scale issues of acid rain, fossil fuel burning and the enhanced greenhouse effect, biomass burning, species invasion, and industrial agriculture, and discusses their potential effects on climate, on society, and on the long-term integrity of the biosphere. Smil asks: will these effects be "just ephemeral perturbations that will leave peculiar traces in the sedimentary record but will not fundamentally alter the natural course of the biosphere's development? Or will they amount . . . to a major derailment . . . of human aspirations as they undercut the very biophysical foundations of our existence?" Smil does not offer an answer to these questions, but I suspect that these two possibilities are not mutually exclusive.

In the epilogue, Smil speculates on what could happen, what could be done, and what should happen to the emerging problems we have with "our" biosphere. He joins others in suggesting that the future cannot be determined by science alone. The choices we face are not primarily technological, but political and, ultimately, moral ones.

The main text is followed by a number of useful appendices with charts and summaries of relationships and data presented in the text. The rich body of literature references to both historical landmark works and up-to-date developments is perhaps one of the greatest strengths of the book, true to its encyclopedic breadth. Although all figures and illustrations are only in black and white, they are of high quality and I considered them very useful. In many cases, references to internet sites are given, where full-color versions or other similar illustrative material may be found.

This is an impressive book. I see it as a very useful resource on everything even remotely linked to the biosphere. I expect that I will refer to it often in my teaching, or to provide "big-picture" context references for my research work. However, at close inspection, there are some inconsistencies and lapses that are perhaps inevitable in a synthesis work of this scale, but that can be very confusing or misleading. For example, figure 7.8 shows a relationship between daily growth rate and body mass of various mammals and invertebrates. The way this relationship is presented in the text does not match the figure at all. According to my best interpretation of the text, a buffalo with a mass of 500 kg could grow by 50 kg each day, but according to the figure (where body mass is mislabeled as weight), that buffalo would grow by only 0.1 g in a day. Here, and in some other places, clarity appears to have fallen victim to brevity, with small inconsistencies throwing a spanner into the works. In contrast to many passages in the book, where fairly specialist relationships or processes are brushed over and assumed to be known by the reader, Smil goes into some detail to explain the properties of a power law (p. 202), curiously without mentioning that it is a power law. In chapter 5, carbon, nitrogen, and sulfur are labeled as "doubly mobile elements," but unfortunately the reader is left without an explanation of what "doubly mobile" refers to. A search on Google.com interestingly uncovered references to this term only in other works by Vaclav Smil. In one of these, there was at last a hint to what is meant: "the three elements enter not only into a huge variety of water soluble organic and inorganic compounds but . . . they also form stable atmospheric gases"; so: mobile in both air and water. The need to hunt for this term is not uncharacteristic for this book. Indeed, one of the most sorely missing components in this polyscientific text is a comprehensive glossary. Because the text abounds in often avoidable jargon expressions from all subdisciplines of biospheric science, but is lacking in explanations and definitions, the subject index is only partially successful as an orientation tool. Readers of this book are advised to keep a good dictionary of science handy, or ensure access to an internet search engine.

The shortest paraphrase of the contents of this book that I can think of is "an annotated discussion of the state of biospheric science." I experienced the reading of it as hard work. But now that I am done, I think I need to read it again.

-HANS PETER SCHMID

ECHOS

"One glanceat a book and you hear the voice of another person, perhaps someone dead for 1000 years. To read is to voyage through time."

-Carl Sagan, astronomer and writer (1934-96)

REFERENCES

Vernadskii, V. I., 1926: Biosfera (The Biosphere). Scientific Chemico-Technical Publishing, 146 pp.

Hans Peter Schmid is an associate professor in the Atmospheric Science Program, Department of Geography, and director of the Institute for Research in Environmental Science, at Indiana University, Bloomington. His research interests are in biosphere- atmosphere interaction and experimental boundary layer- and micrometeorology.

Copyright American Meteorological Society May 2004

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