EVOLUTION OF THE CRITICAL ZONE BASED ON THE TRACE FOSSIL-PALEOSOL RECORD OF CONTINENTAL LANDSCAPES THROUGH TIME (Invited Presentation)

The critical zone is the thin, heterogeneous veneerfrom the top of the canopy to the bottom of groundwater aquifersthat results from the complex interactions between rock, soil, water, air, and organisms in a dynamic system that shapes the Earth’s surface. This zone is significant as it regulates the natural habitat and determines the availability of life-sustaining resources (National Research Council, 2001), and varies depending on the biophysicochemical conditions that shape those landscapes. The archive of the critical zone is preserved in the pedogenically modified sedimentary deposits containing trace fossils as proxies of plants and animals as well as pedogenic features that comprised those ancient landscapes in geologic record. The critical zone of today’s landscape and its different environmental, topographic, latitudinal, and climatic expressions is the result of nearly four billion years of evolution, which is preserved in the archives of the geologic record. Though there are body fossils of the plants and animals that once lived in those ancient landscapes, they are best represented by their in siturecord in paleosols. These trace fossilsare three-dimensional structures and volumes that record the presence of plants and animals in space and time as single individuals or multiple generations of individuals and social groups. Their combined activities destroyed the original sedimentary fabrics deposited upon the landscape and built and destroyed pedogenic fabrics and voids, playing distinct roles in the nutrient cycling via their work as producers, herbivores, carnivores, detritivores, and saprovores. The work of terrestrial and aquatic organisms, in particular, shaped the critical zone through time as ecosystem engineers, adapting and evolving to the various physicochemical conditions of those landscapes as did their roles in the detritivore-dominated nutrient cycling system.