Short publications
PEDOLOGICAL AND PALAEOECOLOGICAL ASPECTS REVIEWED INA critique of Phanerozoic climatic models involving changes in the CO2
content of the atmosphere. By A.J. Boucot and J. Gray. In: Earth Science
Reviews,
The reason that this book-length (159 pp) discussion of climatic models
for the geologic past is reviewed here is that about half of its content
deals with chemical and microbiotic weathering processes and their effects
in soils from ancient rock surfaces to current rhizosphere characteristics.
Judging from the title and the keywords, it would not normally attract
soil scientists, though it is actually one of the more detailed reviews
and discussion of the evolutionary history of the rhizosphere, of microbiotic
weathering effects as controlled by environmental factors, of microbial
desert crusts, temperature effects and more. Factors controlling soil organic
and inorganic carbon sequestration and preservation are also treated but
in less detail. It is a nice example of the function and impact of pedology
in paleoecology. Hence it is valuable to soil biologists, soil ecologists,
paleopedologists and weathering processes specialists, who will find here
references to many useful publications. There are some 750 references.
The purpose of the authors Art Boucot and the late Jane Gray (both from Oregon) , is to present an alternative model of climatic change to the geochemically based model of Robert Berner from Yale, most widely cited in the literature. They point out that such models of ancient and past climates need to take into account and be validated by actual field evidence paleoecological and paleopedological. The documentation which they have assembled and reviewed indicates shifting climatic temperate gradients from pole to equator, varying both in time and intensity, not in accord with those postulated by Berners model based on past pCO2 reconstructions. They consider the geological field data more reliable and a better proxy indicator than other reconstructions of past climates. Hence indirectly they also cast a suspicion on the current global climate change models which invariably rely mainly on the recent atmospheric pCO2 variations. Though it deals with a wide range of different topics, the discussion is suitably organized, but it is not easy reading. Vascular plants are here called tracheophytes and hence soil rock/microbiotic interactions become pre-tracheophyte effects. The role of the rhizosphere is well reviewed and that the rhizosphere in temperate forest soils occupies only a relatively small volume of the total soil is pointed out. The role of varying precipitation quantities is hardly touched upon. In summary, the review is highly recommended to all pedologists and soil ecologists, whether interested in past or current processes cum effects. For me a process oriented pedologist - it will become a valuable reference to the understanding of terrestrization and early soil forming processes, whether now or in the past. Dan H. Yaalon Institute of Earth Sciences, Hebrew University Jerusalem 91904, Israel
Down to earthWhy soil and soil science matters. By Dan H. Yaalon, NATURE, vol. 407, p. 301, 2000. (www.nature.com) Â 2000 Macmillan Magazines Ltd
Any ancient religions recognized the importance of soils, and their customs evolved into a spiritual attachment to the life-giving Earth. But surprisingly, ancient and classical scholars did not study the nature of soil. Early scien-tists also ignored it. For instance, the famous naturalist Alexander von Humboldt (17691859), a founder of plant geography, never compared the soils of the several con-tinents on which he studied the distribution of plant species. This attitude still crops up frequently. The Fontana History of the Envi-ronmental Sciences (1992) contains no men-tion of soils as a branch of environmental science, although other Earth sciences are included. Is soil just dirt, too commonplace for mention or study? I am a pedologist an Earth scientist focusing on the origin and distribution of soils in relation to the history of landscapes. We have much to learn about non-arable soils, and must try to integrate our knowl-edge into a holistic view of the Earths dynamics and biogeochemical transformations.Soils are economically and socially important. They can even have beauty: the soil scientist Hans Jenny (18991992) was enchanted by the soils depicted in paintings. To paraphrase Leonardo da Vinci: why do we know more about distant celestial objects than we do about the ground beneath our feet? New ideas about the nature and origin of soils emerged only in the second half of the nineteenth century. V. V. Dokuchaev (1846 1903) and E. W. Hilgard (18331916), both mineralogists and chemists by training, recognized in their soil surveys that climate, vegetation and substrate were all important, and saw the importance of soil horizonation the development of different layers of soil parallel to the surface in representing and elucidating a landscapes history. Dokuchaev had imperial backing in Russia, and several distinguished followers; Hilgard, although a respected university professor in the United States, was not favoured by the establishment. An opportunity to promote his ideas was lost when J. W. Powell and he failed to establish a geologicalagricultural (soil) survey in the US Geological Survey. Language barriers hindered communication between soil scientists, and the spread of knowledge was painfully slow, even after the new Russian pedogenetic ideas were presented at world exhibitions and translated. Gradually, topographical and biological effects, and the duration of soil-formation processes were all recognized as equally important factors in soil evolution. It took more than one generation before C. F. Marbut (18631935) included the concepts of external and internal environmental effects on pedogenesis in the influential US Department of Agriculture soil survey, established by Milton Whitney in 1899. When Jenny submitted his now-classic book on the five soil-forming factors and the quantitative approach to single-factor soil-forming func-tions, it was at first rejected for publication. It took five years before the book was eventually published in 1941. The importance of soils as a life-support system and in the production of food and fibre was duly recognized. There were spectacular achievements, helping to feed the ever-growing population. Nowadays, most of the 50,000 soil scientists work in agronomic institutes, studying the composition and dynamics of soils in ever greater detail.Yet less than 5% of the global agricultural research budget goes on soil research. The use of soils in road building, construction, ceramics and the cement and aluminium industries is another area where a basic knowledge of soil and landscapes is important. Technological institutes promote this study, which is anchored in ancient practical applications. Soils teem with life. The Nobel laureate Selman Waksman (18881973) isolated streptomycin from soil biota, and the preservation of pedodiversity and biodiversity may aid similar research in the future. Also, it seems plausible that biological evolution was influenced and constrained by the properties of the soil environment, an attractive field of unexplored research. For Earth scientists, ancient and buried soils are one of the better proxies for reconstructing past climate and the development of the landscape. But it is as the transformer, regulator, buffer and filter of water, nutrients and other dissolved and dispersed compounds that soils are most important to humankind a focal and connecting link between the biogeochemical cycles of the Earth and the dynamic atmospheric system. In the conceptual wiring diagram of the International GeosphereBiosphere Program the soil system, especially its carbon dynamics, is the central link between the physical climate and biogeochemical systems. It is therefore a major route to understanding and predicting the effects of human actions on the Earth. Dan H. Yaalon is at the Institute of Earth Sciences, Hebrew University, Givat Ram Campus, Jerusalem 91904, Israel. |