Introduction A Personal Note

At the age of 12 or 13, I read a J. B. S. Haldane book on the natural sciences, which I discovered in my uncle's library. Haldane mentioned some of the Russian work on the biological role in weathering (probably Polynov or one of his students). I had forgotten about all this until I became interested in this subject again as an adult. I have not yet found the Haldane volume mentioned, but those early researchers felt, doubtlessly influenced by Vernadsky's thinking on the subject, that weathering was basically a biological phenomenon and would be much slower without life present. Having grown up in an "old left" household in the 1950s in Brooklyn, I discovered the Marxist classics in a hidden space below the family television. Reading Engels's Dialectics of Nature strongly impressed me. Burning the top of my dresser with chemistry experiments and collecting minerals, insects, and plants occupied my childhood. I probably passed Stephen Jay Gould on my monthly pilgrimage to the mineral hall at the Museum of Natural History (the dinosaur exhibit was on the way). I majored in chemistry at Stuyvesant High School and geochemistry at City College of New York and Brown University, where my graduate research was on excess argon in the Stillwater Complex and degassing models of the Earth. I did a term paper on Vernadsky and biogeo-chemistry as a senior in Alexander Klots's (the author ofA Field Guide to Butterflies) biology class in the spring of 1964.

This book is an outgrowth of research that I have been pursuing for the past 15 years, since I first felt the powerful heuristic influence of Lovelock's 1979 book on Gaia. The concept of Gaia strongly resonated with my sense that spheres of nature interacted dialectically in the Engelsian sense, that is, emergent phenomena arise from the interactions of the parts (the whole's systems and subsystems; for a lucid exposition of a modern dialectics of na ture, see Levins and Lewontin 1985). The whole, Gaia, evolves as the parts (organisms and ecosystems) themselves evolve. The Gaian interactions to be discussed in this book include those among life, climate, weathering, hydrology, and crustal/impact history. This book will present in a systematic way the developing theory for a biotically mediated regulation of Earth's temperature over geologic time, the first order determination of the history of climate. The emphasis is on long-term geologic trends, not the short-term perturbations that have received so much media attention (e.g., the anthropogenic greenhouse effect).

The first third of the book (chapters 1-3) will introduce my theory of biospheric evolution followed by the Gaia concept and its evolution in the 1980s and 1990s. The biogeochemical cycle of carbon and the silicate-carbonate climatic stabilizer will then be discussed. This stabilizer entails the dependence of the chemical weathering rate (the sink for atmospheric carbon dioxide) on global temperature. A key question raised here is the crit-icality of life to the operation of the stabilizer. Is climatic stabilization an emergent property of the Earth's biosphere, in the context of changing solar luminosity and other abiotic factors?

The second third (chapters 4-6) will present a systematic exposition of the weathering process, including recent research on its biotic enhancement, and a model for understanding the habitability of the Earth over geologic time. The evidence for biotic enhancement of weathering includes experimental and field studies that need to be significantly expanded. This section will include discussion ofthe abiotic factors affecting climatic evolution, such as tectonics and the carbon geodynamic cycle, as well as their possible biotic mediation.

The last third of the book (chapters 7-11) will present a reinterpretation of the surface temperature history of the Earth. A much warmer Precambrian Earth surface is supported by a diverse body of evidence, implying a high present biotic enhancement of weathering consistent with our earlier estimates (two orders of magnitude, though probably not three). A geophysio-logical theory of the coevolution of life and the biosphere itself, entailing a progressively changing biotic enhancement of weathering, will be presented. The implications of these results to evolutionary biology and to bioastron-omy (the search for life elsewhere in the universe) and a theory of the self-organization of the Earth's biosphere will be discussed. One startling conclu sion emerges: microbial evolution in the Precambrian was constrained by the surface temperature, indicating that the major events in biotic evolution were forced by the physical context for self-organization. A concluding chapter will summarize the main conclusions and raise a research agenda for diverse fields of science ranging from geochemistry to biology.

:: LIFE, TEMPERATURE, AND THE EARTH

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