1. EQ: What is chemical and mechanical weathering?
Rocks and Weathering
EQ: What is chemical and mechanical weathering?

2. Weathering
Weathering – process that breaks up rocks and other substances at the Earth’s surface
Two types of weathering, mechanical and chemical
Heat, cold, water, ice, oxygen and carbon dioxide contribute to weathering
Erosion – movement of rock particles by wind, water, ice or gravity

3. Mechanical Weathering
Mechanical weathering – rock is physically broken into smaller pieces
Caused by heating and cooling, freezing and thawing, growth of plants, actions of animals, and abrasion
Abrasion- grinding away of rock by rock particles carried by water, ice, wind or gravity
Works slowly , over long periods of time. Eventually wears away whole mountains

4. Mechanical Weathering
Ice wedging
Occurs in cold climates
Water seeps into a crack in the rock, freezes (expands)and thaws (contracts) repeatedly
This process expands the rock slowly and pieces crack off

5. Chemical Weathering
Chemical Weathering – process that breaks down rock through chemical changes.
Agents are water, oxygen, carbon dioxide, living organisms, and acid rain
Produces a different mineral makeup from the rock they came from
i.e. – granite begins with minerals of feldspar, quartz and mica. After chemical weathering, granite changes feldspar to clay

6. Chemical Weathering
Creates holes or soft spots in the rock allowing it to break apart more easily
Chemical and mechanical weathering often work together.
Mechanical weathering breaks apart rock
This process exposes more surface area of the rock to chemical weathering

7. Five agents of Chemical Weathering
Water – most important agent of chemical weathering. Wears away rock by dissolving the rock, mixing it uniformly to make a solution
Oxygen – combines with iron in the presence of water. This is oxidation. Causes rust. This process makes the rock crumbly and gives it a red or brown color

8. Five agents of Chemical Weathering
Carbon Dioxide – found in our air. Dissolves in water and forms a weak acid called carbonic acid. Weathers marble and limestone
Living organisms – as plant roots grow they produce a weak acid that slowly dissolves rock around the roots
Acid Rain – cause is burning fossil fuels that pollute air with sulfur, carbon, and nitrogen compounds. The compounds mix with cloud vapor to form acid.

9. Rate of Weathering Two factors that determine the rate Type of Rock –
Depends on the minerals that make up the rock
Is the rock permeable – full of tiny, connected air spaces that allow chemicals to seep through it
Climate
Average weather conditions of an area
Hot and wet climates weather rock more quickly

10. Class Work and Homework
Fill In What did I learn Confused Say Rock Shake Page G46 Read pages G 40 – G 45, #’S 1-5