Unit 7 Day 2
Soil Formation
Objective
1 Explain the process of soil formation to include key
terminology: soil horizon, soil profiles, humus and
leaching.
Enduring Understandings
Weathering, erosion, and
are
interrelated processes that form a cycle of forces that
wear down and build up the Earth’s surface.
Soil is formed from the
of
rocks and organic activity.
Soil Formation
Soil is an important
. It is
essential to life on Earth. Without soil we would not
have land based plants and numerous other vital
organisms
Many
such as fungi,
bacteria, and insects begin to live in these broken pieces
and add nutrients through life processes.

is the decaying organic
matter that mixes with the rock particles to make soil
Development of Soil
Soil is the loose organic covering of
and
overlying the bedrock of Earth’s surface
Soil Types
The composition of the parent bedrock determines
the type of soil formed as well as the length of time it
takes to form. The process generally takes a very long
time
It can take hundreds of years for only
of
soil to form
Soil does not necessarily remain in the same place.
Soil is the result of
and . .
weathering and biological
activity over very long periods of time
The soil forming process begins with the weathering
of solid bedrock breaking it into
The agents of
and
can move
soil and the materials that make it from place to place
Residual soil is soil that is located above its parent
material

soil is soil that has
been moved away from its parent bedrock to a new
location
The soil in
soils
is mostly transported
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Horizon O
Soil Profiles
An important feature for any area of land is it’s
.
. This can be found by
digging a hole in the ground to expose the layers that
make up the local soil
Horizon B forms under the A layer and contains
and holds many of the .
that have been washed down
from above

is the process of
minerals washing out of the topsoil into the lower
layers
The soil horizons form in the order from
to make up the soil profile.
Soil Profile is the
of
soil layers
Not all horizons are present in a given soil!
Soil Horizon
Soil Horizon is
or
zone within a soil profile
 In terms of soil texture, soil type usually refers
to the different sizes of mineral particles in a
particular sample. Soil is made up in part of
finely ground rock particles, grouped according
to size as sand, silt and clay. Each size plays a
significantly different role.
1. The size of the three particles that make up soil
are broken down by size
2. Gravel is the largest of soil particles
3. Sand is the next largest of soil particles
4. Silt is the middle size of soil particles
5. Clay the smallest of the soil particles
Horizon C is the layer just above the
.
and is the least developed soil.
Horizon A is the top layer and is the most developed
soil and contains the most
materials
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