The Critical Zone

Lesson 8 Introduction


Thus far through the course, we have focused on one of the state factors of soil formation: climate. (We have also studied how water specifically contributes to this process.) Now we turn our attention to the other state factors. In this unit on geology and landforms, we will consider and discuss three of the remaining four natural state factors of soil formation: parent material, topography, and time.

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Modern soil profile developed on Eocene paleosols and sediments, Malakoff Diggins State Park, California.
Credit: Tim White, 2004.

Parent material is obviously a critical component of the pedogenic system and the Critical Zone—all the other state factors of soil formation act upon the parent material to create soil, and thus the original, unweathered composition of the parent material plays a unique role in the weathered product. In Lesson 8, you will learn (review) basic concepts of geology to remind you that rocks and sediments have widely ranging textures and compositions formed in a wide range of environments. These variations, in turn, can affect soil formation and Critical Zone processes.

The landforms and topography of a region control a variety of Critical Zone processes. You will learn in Lesson 8 that the plate tectonic setting plays a first-order role in determining the topography of a site and thus in determining whether soils develop and accumulate or are subject to erosion. In addition, the geologic setting determines other aspects of environmental control on the Zone. As you study Lesson 8, consider the following questions: Can unique depositional environments consist of characteristic landforms? If so, what can those landforms show us about Critical Zone processes? Do soils developed on unique landforms have unique characteristics? What is the slope and aspect of a site and how do these relate to solar heat budgets and vegetation?