Download Unit 4: Soil Profiles Activity Regents

Name ___________________________
Date _______________
ES period ________
Mr. Landsman
Examining Soil Horizons and Profiles
Soil begins to form as rock material weathers into smaller pieces. Some of their fragments are
also chemically weathered to become different minerals or dissolve in water. Organic matter, which
comes from the remains of plants and animals, is also added at or near the surface. As time passes, the
weathering process changes rock at deeper and deeper levels. The thin layer of soil that first formed
becomes thicker and thicker. The soil-forming process continues to move downward with time.
Eventually, different layers or zones become noticeable. Such zones are called HORIZONS, while the
entire arrangement of horizons is known as a soil PROFILE. Each zone or horizon within the profile
has its own distinct characteristics.
Stage 1: Parent, or un-weathered rock is exposed to the atmosphere and hydrosphere.
Stage 2: Broken and weathered rock closely resembles (is a lot like) the parent or original rock from
which it came. This zone is sometimes referred to as the C Horizon.
Stage 3: The layer that forms at or near the surface, which contains organic matter (humus), is called
TOPSOIL and is often dark in color due to the high content of dead stuff. It is known as the A
Horizon.
Stage 4: In mature soils, a third (and last) layer forms beneath the topsoil and is often brown or
reddish-brown in color. It is referred to as the B Horizon. This layer contains minerals that were
leached from the topsoil layer.
A mature soil profile may take centuries to form at a rate of about 250 years per centimeter of depth.
Mature soil profiles may be hundreds of centimeters thick.
Carefully examine the four diagrams. Using the text above and your review book, complete the activity
as described below.
1. Describe the difference between a soil profile and a soil horizon.
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2. On the diagram sheet, label the soil horizon illustrated in each of the four diagrams.
3. In stage 4, how thick is each soil horizon in centimeters?
A)______________ B)______________ C)_______________
4. How long would it take for the full soil profile (Horizons A, B, and C) to form in stage 4?