The Critical Zone

Summary and Final Tasks


In this lesson on soils, you read about soil formation, the description of soils, and the classification of soils in the United States into twelve soil orders. You also considered the effects of soil erosion on the Critical Zone and how the distribution of the twelve soil orders might relate to the five state factors of soil formation. By now you should understand that soil is a complex material composed of mineral and organic matter, formed by competing processes associated with climate, biota, parent material, topography and time. Soil exists in the overlapping realm between the atmosphere, hydrosphere, lithosphere, and biosphere. It is classified according to need: a geologist studying soil formation rates may have a very different view of soil compared to an engineer building a superhighway or an agronomist trying to understand soil fertility for crop management. Furthermore, due to the increase in human activity on Earth, soil erosion mostly exceeds soil formation rates, thus soil should be viewed as a finite resource that is rapidly being depleted. Finally, you should be well aware that soil maps are available for most of the United States and that they can be very useful, if not critical, for land-use planning and decision making.

With this firm background, throughout the course I want you to remember and contemplate the outstanding question in Critical Zone science, which was introduced in a Lesson 1 reading (Brantley et al. p. 11): can a unified approach be developed to characterize environmental conditions and mechanisms that produce different soil types?

Reminder—Complete all of the lesson tasks!

You have finished Lesson 2. Double-check the list of requirements on the Lesson 2 Overview page to make sure you have completed all of the activities listed there before beginning the next lesson.

Tell us about it!

If you have anything you'd like to comment on or add to, the lesson materials, feel free to share your thoughts with Tim. For example, what did you have the most trouble with in this lesson? Was there anything useful here that you'd like to try in your own classroom?