Theng, B. K., Tate, K. R., Becker-Heidmann, P. (1992): Towards establishing the age, location, and identity of the inert soil organic matter of a spodosol. Z. Pflanzenernaehr. Bodenk. 155 (3): 181–184.
An interlayer clay-organic complex has been isolated from a near-surface horizon of a recent Spodosol from New Zealand. Treatment with hydrogen peroxide selectively removed the organic material attached to external clay surfaces. The radiocarbon age of the treated complex, determined by accelerator mass spectrometry, was 6716+/-524 years B.P. Since this value refers to the interlayer organic species which has been completely protected against microbial attack, and contamination by “young” carbon, it may be regarded as the “true” age of the soil, that is, the starting point of humus formation and pedogenesis. The interlayer organic carbon comprised approximately 13 percent of the total carbon in the soil horizon.
We propose that a biologically inert organic matter (IOM) fraction may be isolated from most soils as this fraction is commonly associated with clay-size particles. Evidence is also accumulating to indicate that IOM is dominantly composed of polymethylenic structures, probably derived from natural waxes, and aliphatic biopolymers present in protective layers of vascular plants.