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Aim: How do soils form?
I. Soil – mixture of weathered rock
and organic remains that usually
covers bedrock.
A. Formed as a result of both
physical and chemical weathering
1. Physical – breaks solid rocks into
smaller particles (example – bedrock
is broken down into regolith)
2. Chemical – changes hard minerals into softer
3. Burrowing animals help mix materials
B. Soil Horizons (profile) – soil with three
distinct layers
1. “A” Horizon (topsoil) – upper layer
that is rich in dark colored organic
remains (humus). Contains water, living
animals (worms,burrowing animals),
bacteria, and air.
2. “B” Horizon (subsoil) – poor in organic
material but enriched by minerals that
have been leached out of horizon “A.” May
contain magnesium and calcium carbonates.
3. “C” Horizon (regolith) – composed of broken up
bedrock in various stages of decomposition and
weathering. It sits upon unweathered, solid
Soil Profile
C. Climate is the main factor affecting type
of soil
1. Soil Types
a. Arctic – has thin soil due to lack of
b. Forest – very humid and is not very fertile
c. Grassland – can support grass but not trees
d. Desert – dry and contains very little
e. Tropical – formed in high temperatures and
abundant rainfall