The Story of O: The Dominance of Organisms as a Soil-Forming Factor From an Integrated Geologic Perspective and Modern Field and Experimental Studies

摘要

Geological and neoichnological evidence demonstrates the dominance of organisms through their life histories and behaviors as a major soil-forming factor since the Late Ordovician (-460 million years of Earth history). Continental deposits since thattime preserve an abundance of paleosols that contain a great variety of trace fossils (i.e., krotovina) of microbes, plants, and animals. Trace fossils produced by animals preserve the burrows, nests, tracks, and trails that are intimately associated with a range of sedimentary and pedogenic structures indicative of immature to mature soil development in fluvial, alluvial, lacustrine, and eolian depositional systems. Neoichnological studies of organisms—field and experimental research on their tracemaking activity—in terrestrial environments confirm their tremendous influence on sediment mixing, soil formation, and soil turnover. Burrowing animals displace sediments by diffusive (mm-scale particle movement) and advective (cm- to m-scale particle movement) methods via a combination of carrying, pulling, pushing, raking, breaking or cutting, and forcing that result in traces. These traces have distinct three-dimensional shapes and volumes that are repeated in space and time, resulting in soil formation. Many of these traces have changed little through 100's of millions of years of evolution based on comparisons between modern and ancient animal traces.