Rocks and Weathering
Which mountain range is older?
The Sierras are rocky
and steep, higher
than the
Appalachians.
The Appalachians are
more rounded and
gently sloping, and
are covered with soil
and plants.
Which mountain range is older?
The Sierras formed
within the last 10 to
20 million years
ago.
The Appalachians
formed more than
250 million years
ago.
Q: How can you tell that the Sierra
Nevadas formed much more recently
than the Appalachians?
How is Earth's surface shaped?
1. Weathering- the process that breaks down
rock and other substances at Earth's surface.
2. Erosion- the transportation of sediment by
wind, water, ice, or gravity.
weathering vs. erosion video
Q: What is the difference between
weathering and erosion?
The principle of uniformitarianism
-an assumption that the same processes that
operate today operated in the past.
Two Types of Weathering
MechanicalWhen rock is
physically broken
into smaller pieces.
Keep the same
chemical
composition.
ChemicalThe process that
breaks down rock
through chemical
changes.
Is this the cause of mechanical or
chemical weathering?
Plant growth
Is this the cause of mechanical or
chemical weathering?
oxidation
Is this the cause of mechanical or
chemical weathering?
weak acid from plant roots or lichens
Is this the cause of mechanical or
chemical weathering?
freezing and thawing
Ice wedging
1st - water seeps into cracks of rocks
2nd- water freezes
3rd - water expands when it freezes and
breaks rock
Is this the cause of mechanical or
chemical weathering?
pressure release
The causes of mechanical weathering
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•
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•
•
freezing and thawing
release of pressure
plant growth
actions of animals
abrasion
The causes of chemical weathering
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•
•
•
•
water dissolves minerals
oxygen combines with iron in the presence
of water forms rust (oxidation)
carbon dioxide dissolves in water to form
carbonic acid
living organisms- root tips and lichens can
form weak acid
acid rain is formed when pollutants combine
with water vapor
What determines how fast
weathering occurs?
• surface area
• type of rock
• climate
Increasing the surface area of rock
increases the rate of a chemical
reaction
Q. Which type of stone weathers
faster?
granite
marble - dissolves in acid,
and is more permeable
Climate
Weathering is faster in hot and wet climate.