GY 111 Lecture Notes
D. Haywick (2008-09)
GY 111 Lecture Note Series
A) What is soil?
B) Typical soil profile(s)
C) Soil Types
Reference: Press et al., 2004, Chapter 7; Grotzinger et al., 2007, Chapter 16 p 373-384
A) What is Soil?
As we discussed last time, rocks exposed at the surface of the Earth are subject to physical and
chemical weathering. Given sufficient time and a suitable climate (hot and wet is best for
chemical weathering; cold and wet is best for physical weathering), even the most resistant rock
will be reduced to a shadow of its former self.
The product of weathering will ultimately be sediment (the major ingredient of sedimentary
rock); however, we reserve the term “sediment” for material that is moved from its place of origin
(i.e., the place where weathering is occurring), to some
(i.e., a place where
sediment is collected). In situ weathering of rock may leave a layer of weathered residue atop the
rock. If the residue is more or less broken bits of rock which was primarily the result of physical
weathering, we generally refer to it as
If the rock has been physically and chemically
weathered and if there is an appreciable amount of organic material, it is better to refer to the
Soil is the most important Earth resource that we have (with the possible exception of water and
as one smart ass student said "air"). Without soil, we would not have potatoes, lettuce, peas, corn,
bread, beef, chickens, trees etc. Life without potatoes would be pretty tough. It is for this reason
that soil conservation is taken so seriously. In the past, we had many serious experiences with
soils erosion (the Great Dust Bowl of the early 20
Century is but one example). Today,
agricultural practices are better and soil erosion by wind is not as much of a problem; however,
water runoff as a cause of soil erosion is still a major concern.
B) Soil Profile(s)
Soils are complex, but they all more or less share one important characteristic. They are layers.
Soil scientists (usually agricultural geographers) recognize 3 or 4 layers (properly termed
) within most soils. The following cartoon summarizes a typical