Soils - past and present

摘要

'Lying at the interface of the geosphere, biosphere and hydrosphere, soils occupy a central place in ecosystems, and because of this they are sensitive and detailed indicators of past and present environments.'The soils that cover much of the Earth's land surface support the growth and development of virtually all terrestrial life. The fertile alluvial soils near the Tigris and Euphrates rivers allowed the ancient civilizations of Mesopotamia to flourish. Natural flooding of these soils led to continual replenishment of nutrients and made possible a reliable and abundant food supply. However, degradation of these same soils through the, gradual accumulation of soluble salts reduced their capacity for food production and contributed to the decline of this once prosperous region. The importance of fertile soils for human welfare is perhaps most evident today in Africa, where the highly weathered and nutrient-poor soils of the region con-tribute to famine that occurs all too frequently in this continent.The importance of soil for the sustenance and prosperity of human societies may be direct and obvious, as illustrated above, or it may be subtle and indirect, as in the case of ancient soils whose influence has been passed down through geological time. For example, the fertile soils that nurtured the development of higher plants during the Carboniferous Period made possible the growth of lush and expansive forests, the fossilized remains of which were used to fuel the Industrial Revolution. These same fossil deposits are a primary energy source in many parts of the world even today.