1. Chapter 2 Section 2 Pages 48 - 54
How Soil Forms
Chapter 2 Section 2
Pages

2. Objective: Describe the composition of soil & explain
how it is formed, and recognize the soil horizons.
Soil is formed as rock is broken down by weathering and
Mixes with other materials on the surface.
Soil: The loose, weathered materials on Earth’s surface,
In which plants can grow.
Bedrock: The solid layer of rock beneath the soil.
Soil is a mixture of rock particles, minerals, decayed
Organic material, air and water
Humus: Dark colored substance that forms as plants &
Animal remains decay.

3. Fertility of Soil: A measure of how well the soil supports
plant growth. Rich in humus = high fertility
low in humus = low fertility
Loam: Soil that is made up of equal parts clay, sand and
silt.
Soil forms as rock is broken down by weathering and
mixes with other materials on the surface. Soil is
constantly being formed wherever bedrock is exposed.
Soil Horizon: Layer of soil that differs in color and
texture from other layers.
Topsoil: A crumbly, dark brown soil that is a mixture of
humus, clay and other minerals. (A Horizon)

4. Subsoil: Consists of clay and other particles washed
down from the A horizon, but has little humus.
(B horizon)
C horizon: Partly weathered rock.
Scientists classify the different types of soil into major
groups based on climate, plants, and soil composition.
Prairie Soils: Form in cool dry climates of grasslands;
Topsoil is thick and rich in humus.
Mountain Soils: Topsoil is often thin because cold temps
slow chemical weathering and erosion causes soil loss.

5. Some soil organisms make humus, the material that
makes soil fertile. Other soil organisms mix the soil and
make spaces in it for air and water.
Litter: As plants shed leaves, they form a loose layer
called litter.
Humus forms is a process called decomposition. As
decomp occurs, organisms that live in soil turn dead
organic material into humus.
Decomposers: The organisms that break the remains of
dead organisms into smaller pieces and digest them with
chemicals. (Fungi, bacteria, worms, etc.)