ABSTRACT
Soils currently contain almost three times as much carbon as does the atmosphere in both organic and inorganic forms. Under arid to semihumid climatic conditions, the dissolution of primary carbonates followed by recrystallization with transpiration-derived CO2 leads to the formation of pedogenic (secondary) carbonates that usually migrate downwards into the soil column. Pedogenic carbonates exist in several forms and, in toto, comprise 30%–40% of the world's soil carbon inventory. Determining the history of a soil begins with optical examination of its structure/morphology. While this starts with the use of a hand lens or eye loupe, much more can be learned by examining thin sections of it with the aid of a petrographic polarizing light microscope. A fundamentally different way to perform isotopic ratio determinations is based on the fact that infrared spectra are generated by the electrons within multiatomic species shifting between different quantized vibrational/rotational energy levels.
