Geology Reference
In-Depth Information
The very top of a soil profile is the O horizon, composed of
humus:
a layer of fluffy, air-filled sediments
mixed with high amounts of carbon resulting from decaying plant materials. Below that is the A horizon,
which still has high levels of organic material but contains more mineral sediments than the O horizon.
Below the A horizon is the B horizon, a layer of sediments with very little organic material and high
amounts of weathered mineral sediments. At the bottom of the soil profile is the C horizon, made of
weathered bedrock sediments with no organic materials. Below the C horizon is solid bedrock.
Soil classification, or the naming of different types of soil, is extremely complex. The scientific names
of soil types try to describe the bedrock that is being weathered, as well as the climate (tropical and
wet, or dry like a desert) and the stage of development the soil is currently in.
Okay, maybe the whole thing isn't quite that simple. In this section I describe the pro-
cesses that create sediment particles from existing rock, how the transportation of sedi-
ment particles changes their shape and size, and how those characteristics are used to
classify
(categorize) different sedimentary rocks.
Weathering rocks into sediments
Rocks at the earth's surface are
weathered,
or changed by contact with water, heat,
wind, ice, and other natural processes. Everything exposed to the “weather” (water,
wind, and so on) is weathered; you may notice that anything you leave outside for a long
