Soil & Weathering
Weathering
 The breakdown of materials of Earth’s crust
into smaller pieces.
Mechanical Weathering
 Process by which rocks are broken down into
smaller pieces by external conditions.
 Types of Physical weathering
 Frost wedging
 Plant roots
 Friction and impact
 Burrowing of animals
 Temperature changes
Frost Wedging
Plant Roots
Friction and Repeated Impact
Burrowing of Animals
Temperature Changes
Questions
Chemical Weathering
 The process that breaks down rock through
chemical changes.
 The agents of chemical weathering
 Water
 Oxygen
 Carbon dioxide
 Living organisms
 Acid rain
Water
 Water weathers rock by dissolving it
Oxygen
 Iron combines with
oxygen in the presence
of water in a processes
called oxidation
 The product of
oxidation is rust
Carbon Dioxide
 CO2 dissolves in rain water and creates
carbonic acid
 Carbonic acid easily weathers limestone and
marble
Living Organisms
 Lichens that grow on rocks produce weak
acids that chemically weather rock
Acid Rain
 Compounds from burning coal, oil and gas react
chemically with water forming acids.
 Acid rain causes very rapid chemical weathering
 Acid rain has the same ph level as tomato juice
Soil
 What is soil?
 Loose mixture of
weathered rock,
organic matter, water,
and air
 Is chemically and
physically different
from parent material
Soil Horizon
 Soils have distinct
zones that roughly
parallel land surface
Horizon Layers
 Typical soil profile
 O horizon -- dark organic
matter
 A horizon -- contains some
organic matter but many
minerals are removed from
this layer; Lighter-colored
than O
 B horizon -- contains
decomposed rock such as
clay, iron oxides, calcite; may
be red, yellow, or tan
 C horizon -- slightly altered
parent material
Soil Horizons in Archaeology
Ashland, home of Henry Clay
Soil Horizon 
Can you see the layers?
Monticello, VA
Can you figure out the layers?
Which is horizon O, A, B, & C?
Erosion
 The process by which water, ice, wind or
gravity moves fragments of rock and soil.
Water Erosion
 Rivers, streams, and runoff
Ice Erosion
 Glaciers
Wind Erosion
Mass Movements
 Landslides, mudslides, slump and creep
landslide clip.mpeg
POP QUIZ TIME!!
 You may use your notes
POP QUIZ TIME!!
 What is mechanical weathering?
POP QUIZ TIME!!
1 What are the two types of weathering?
POP QUIZ TIME!!
1 What are the two types of weathering?
2 Acid rain is which type of weathering?
POP QUIZ TIME!!
1 What are the two types of weathering?
2 Acid rain is which type of weathering?
3 Iron combines with what 2 things to form
rust?
POP QUIZ TIME!!
1 What are the two types of weathering?
2 Acid rain is which type of weathering?
3 Iron combines with what 2 things to form
rust?
4 Frost wedging & animal burrowing are
which type of weathering?
POP QUIZ TIME!!
1. What are the two types of weathering?
2. Acid rain is which type of weathering?
3. Iron combines with what 2 things to form
rust?
4. Frost wedging & animal burrowing are
which type of weathering?
5. Which horizon has dark, organic matter?
POP QUIZ TIME!!
What are the two types of weathering?
1. mechanical & chemical
2. Acid rain is which type of weathering?
1. chemical weathering
3. Iron combines with what 2 things to form rust?
1. oxygen & water
4. Frost wedging & animal burrowing are which type of
weathering?
1.
1.
mechanical
Which horizon has dark, organic matter?
5.
1.
Horizon O