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Learning Target~ I understand that Earth’s surface is constantly changing.
“Rocks and Weathering,” Chapter 2 section 1 of Earth’s Changing Surface
Different Mountain Landscapes
* Sierra Nevada Mountains (~10 million
years old)
* Appalachians (~250 million years old)
What is weathering?
* The younger mountains are rocky and steep, with many
peaks rising 3,000 meters above sea level.
* The older mountains are more rounded, with gentler
slopes, and covered with soil and plants. Their highest
peaks are less than half of those in the Sierras.~ they’ve had
more time for weathering to wear away jagged edges.
Weathering is the process that breaks down rock and
other substances at Earth’s surface.
Weathering breaks rocks into smaller and smaller pieces.
What causes weathering?
What is erosion?
heat
cold
water
ice
chemical reactions
Erosion is the removal of rock particles by wind, water,
ice, or gravity.
Erosion happens when sediments are moved from one
place to another.
***Weathering and erosion work together
continuously to wear down and carry away
the rocks at Earth’s surface.***
These forces are always in action. Every second. Right
now, rivers and ocean waves are tearing rocks down and
moving sediment all over the world. All. The. Time.
Uniformitarianism
The principle that same processes
that operate today operated in the
past.
Mechanical weathering~ physically breaking
rocks into smaller pieces.
Caused by~
* freezing and thawing~ ice wedging
* release of pressure
* plant growth
* actions of animals (including humans)
* abrasion: grinding away of rock by sediment carried by
water ice,wind, or gravity
Ice wedging
Water seeps into cracks in rocks.
Water expands when it freezes.
Ice acts like a wedge, making cracks wider and deeper.
Slow processes
Mechanical weathering works slowly. But over very long
periods of time, it does more than wear down rocks.
Mechanical weathering eventually wears away whole
mountains.
Chemical weathering breaks down rock
through chemical changes.
The causes of chemical weathering include the action of
water, oxygen, carbon dioxide, living organisms and acid
rain.
Rocks are made of minerals. Reactions with chemicals can
break down some minerals. (Hannibal crossing the Alps.)
Chemical and mechanical weathering work
together.
Chemical weathering creates holes or soft spots in rock, so
the rock breaks apart more easily.
Figure 3
Weathering and Surface Area
As weathering breaks apart rock, the surface area
exposed to weathering increases. The total volume (and
mass) of the rock stays the same even though the rock is
broken into smaller and smaller pieces.
Sketch Diagram (simple but clear, with labels)~
Causes of Chemical Weathering
* Water
* Oxygen
* Carbon Dioxide
* Living Organisms
* Acid Rain
* Water is the most important cause of chemical
weathering. Many minerals will dissolve in water over
time.
* Oxidation (rust) breaks down minerals containing iron.
Rust makes rock soft and crumbly and gives it a red or
brown color.
* Carbon Dioxide (CO2) dissolves in water (including
rainwater and in the ocean), making a weak acid called
carbonic acid. It easily weathers rocks such as marble and
limestone. (Too much is bad for ocean creatures, too.)
* Living Organisms, like plants and lichens, produce weak
acids; plant roots also cause mechanical weathering.
Acid Rain causes very rapid chemical
weathering. (The Gargoyles of Notre Dame)
Burning fossil fuels (coal oil, and gas) pollutes the air with
sulfur, carbon, and nitrogen compounds. They react with
water vapor in clouds, forming acids, which fall as acid
rain.
Rate of Weathering is determined largely by
the type of rock and the climate the rock
lives in 
Type of Rock~
* Some minerals dissolve easily in water and weather
more quickly than those that do not.
* Permeable rocks have tiny air spaces that allow water to
seep in (increasing dissolving and ice wedging).
Human Activities
Climate~ refers to the average weather conditions in an
area. Weathering occurs faster in wet climates (chemical
changes as well as freezing and thawing). Chemical
reactions occur faster at high temperatures. Chemical
weathering occurs more quickly where the climate is both
hot and wet.
Burning fossil fuels increases acid rain.
Construction projects break up rock formations and
reshape land.
Math~ Analyzing Data
“Which Weathered Faster?” p. 44
This set of questions is your homework. Yes, all of them.
Write a complete heading and use IQIA (Include the
Question In the Answer) for credit.
Key Concept Question, p. 45
1c. Over millions of years, how do
weathering and erosion change a mountain
made of solid rock? Use one or more
complete sentences and a labeled diagram.
This will be tomorrow’s entry task.