Lecture 3

The pedosphere, where the worlds ofrock (the lithosphere), air (theatmosphere), water (the hydrosphere),and life (the biosphere) all meet. The soilas interface can be understood at manydifferent scales. At the kilometer scale (a),soil participates in global cycles of rockweathering, atmospheric gas changes,water storage and partitioning, and the lifeof terrestrial ecosystems. At the meterscale (b), soil forms a transition zonebetween the hard rock below and theatmosphere above—a zone through whichsurface water and groundwater flow, andin which plants and other living organismsthrive. A thousand times smaller, at themillimeter scale (c), mineral particles formthe skeleton of the soil that defines porespaces, some filled with air and some withwater, in which tiny creatures lead theirlives. Finally, at the micro- and nanometerscales (d), soil minerals (lithosphere)provide charges, reactive surfaces thatadsorb water and cations dissolved inwater (hydrosphere), gases (atmosphere),and bacteria and complex humusmacromolecules (biosphere). (Diagramcourtesy of R. Weil)