Regolith or soil? An ongoing debate
Richard Huggett
Abstract
Definitions of soil and regolith abound, the traditional view seeing soil as the top part of the regolith. Leighton (1958) claimed that soil and regolith are the same thing. Definitions of soil arising from research on soil and regolith in extraterrestrial, Precambrian, and some human-made settings tends to reinforce this view. Over the last two decades, the work of some researchers, including whole-regolith pedologists, has reinforced the case for Leighton’s claim, suggesting that soil and regolith are indeed the same and form pedo-weathering profiles. This view partly reflects a growing realization that the substratum plays an important role in some soil-forming processes, and should be included in soil classification schemes. The regolith-or-soil debate also applies when looking at soil in the contexts of the Earth System and the Critical Zone, both of which stress the connections between unweathered rock, weathered rock, fluid flows, and biological activity at local, regional, and global scales. It is unlikely that the debate will end: realistically, research on the whole-regolith pedological studies, including those that tackle wider links with the Earth System, will accompany pedological studies that focus on the solum and soil-forming processes within it, although they will assuredly inform each other; and, even though a case is made for regolith and soil being the same thing, it is will doubtless spark disagreement.