 The part of dirt that will support life
 Found all over the world
 Not all soil is the same
 Oceans and deserts have sandy soil whereas swamps have
soil that is very muddy
 Soil is divided into four parts
 Water  Found in pore spaces
 supplies the moisture and nutrients for root systems
 Air  Found in pore spaces
 source of carbon dioxide and oxygen for plants and animals
 Mineral Matter All the sediments that make up most of the
soil
 Organic Matter (Humus)
 is the decayed matter from dead animals and plants that supplies
nutrients to soils through its ability to retain water
 Soil is made through the weathering and erosion of
rocks
 Five factors that determine the soil types:
 1. Climate (most important factor)
 Warm, wet climates encourage all types of weathering and
have thicker soil
 Dry, cool climates have thin, poor soil
 2. Parent Material
 The sediments in the soil from an original rock (the parent
rock) that was weathered
 The harder the parent rock, the less sediments you will have
in the soil (hard rocks don’t weather as easily)
 3. Time
 The longer rocks have to weather, the thicker the soil in that
area
 4. Organisms
 Plants are the main source of organic humus in soil
 Microorganisms and fungi will decompose the dead “stuff”
into nutrients for animals and plants to use
 5. Slope
 On steeper slopes
 erosion increases, the soil gets very little water and is very thin
due to the gravitational pull (downward)
 Flatter areas
 Erosion decreases, soil gets plenty of water and is generally
thicker
 Soil is not the same throughout
 Changes as you go down from the top to the crust
 Soil Profile: The layers of soil
 Four layers:
 A-Horizon, B-Horizon, C-Horizon, and the Unweathered
Parent Material (UPM) also known as the crust of the Earth
 Top layer of the soil
 Contains majority of
nutrients for the plant’s
roots
 Many roots, bugs, and
burrowing animals are
found in this layer
 Mostly made of humus,
water and air
 Mostly made of clay and




water
Lacks sufficient air because
the pore spaces are filled
with water that has trickled
down
Roots from older trees
reach down in to this layer
and get water supplied
Hard packed clay
Not many bugs or smaller
creatures found here
 Mostly made of weathered
parent material (smaller to
larger sediments)
 Only the deepest roots will
reach down here and get
the available water
 Very rocky
 Few if any animals or bugs
because they cannot dig
through the rocks
 This should be solid
bedrock to some
weathering towards the
top of the layer.
 No air and very little
water
 No animals due to lack of
air and water
 Refers to the proportions of different particles sizes
found in all soils
 Categories are based on the percentages of sand, silt
and clay
 The different textures can be found on a diagram
called the soil triangle