Soil is classified by grain size.
Name them from largest to
Sand – largest
Clay - smallest
S6E5 – Students will investigate the scientific
view of how the earth’s surface is formed.
.h Describe soil as consisting of weathered
rocks and decomposed organic material.
MYP Unit Question: How does land change?
Area of Interaction: Environment
Learner Profile: Caring and Principled
Learning Target: I’m learning how rocks
weather because they eventually turn into soil.
Work Session: Weathering Notes
Bellringer: Cleopatra’s Needle
Closing: Summarizing Statements
Cleopatra’s Needle in NYC
Three ancient Egyptian obelisk were originally erected in the Egyptian city
of Heliopolis around 1450 BC. Around 1891, the Egyptian Government
moved them to London, Paris, and New York City in return for funding the
Panama Canal. In September 2013, the Egyptian government threatened
to remove the NY obelisk if precautions were not taken to prevent it from
Process by which rocks are
broken down physically or
There are two types of weathering:
Mechanical and Chemical
If it’s in BLUE, write it down.
1. Mechanical Weathering
Rock is physically
(something hitting it)
broken down into smaller
Causes of Mechanical
1. Ice (ice wedging – freezing and thawing)
2. Wind - Abrasion (the grinding of rock by other rock
carried by wind, water, gravity, or ice.)
3. Water - Abrasion
4. Gravity - Abrasion
5. Plants and Animals - burrowing
a. Ice Wedging–freezing and thawing of
Ice gets into the cracks of rocks, freezes
and spreads the rock apart.
b. Wind Abrasion
Abrasion is the grinding and
wearing away of rock surfaces
through the mechanical action
of other rock or sand particles.
c. Water Abrasion
Rocks and pebbles roll along the
bottom of swiftly flowing rivers, they
bump into and scrape against each
other. The weathering that occurs
eventually causes these rocks to
become rounded and smooth.
d. Gravity Abrasion
When rocks fall on one another they exert forces on
each other as they tumble down a mountainside.
Larger rocks break into smaller rocks.
e. Plant Roots
As the plant grows the
expanding root becomes so
strong that the crack widens.
Eventually, the entire rock can
e. Animals burrowing
When the animals burrow in the ground, they break up
soil and loosen rocks to be exposed to further
2. Chemical Weathering
Rock breaks down through
What are the agents (causes) of
Agents of Chemical
1. Water (dissolves rock)
2. Air (oxidation from oxygen = rust)
3. Carbon Dioxide (carbonic acid in caves)
4. Living Organisms (produce acids like lichens)
5. Acid Precipitation (rain, snow, sleet, or hail with acid from
a. Water - water weathers rock by dissolving it.
• Oxygen in the air reacts to the
metal causing it to oxidize.
• The product of oxidation is rust.
• Water speeds up the process.
c. Carbon Dioxide
• CO2 dissolves in rain water and creates
• Carbonic acid easily weathers limestone
d. Living Organisms
Lichens that grow on rocks produce weak
acids that chemically weather rock
e. Weak Acid
In certain places groundwater contains weak acids, such as carbonic
or sulfuric acid. These acids react with rocks in the ground, such as
limestone and forms caves.
Features of Karst: Sinkholes
Features of Karst: Caves
Features of Karst: Disappearing
e. Weak Acid (continued)
2) Acid Precipitation
(hail, sleet, snow, rain)
What affects the rate rock
Type of Rock
Mineral composition – some minerals dissolve
faster than others.
Permeable rock weathers easily because
made of small air pockets.
Climate (average weather condition)
Wet, high climates = faster weathering
Dry, cool climates = slower weathering
Closing: “Tell Me”
“Tell me” what type of weathering is
occurring in each image (mechanical or chemical).