Chapter 8 Notes
Weathering is the process that breaks down rock and other substances at Earth s surface
Factors that contribute to weathering Heat Cold Water Ice O 2 & CO 2 in the atmosphere
Examples of weathering Rust Peeling paint
Examples of weathering Cracking sidewalks Potholes
Erosion is the removal of rock particles by water, wind & ice or gravity
Weathering breaks rocks into smaller pieces and erosion takes those pieces away
Mechanical Weathering Chemical Weathering
Mechanical Weathering is caused by physically breaking rocks into smaller pieces
Causes of Mechanical Weathering Freezing Ice Wedging: process where wedges of ice in rocks widen and deepen cracks
Release of pressure
Plant growth
Animals
Abrasion: grinding away of rock by rock particles carried by erosion
Chemical Weathering is the process that breaks down rock through chemical changes
Action of water = dissolves rock
O 2 (Oxygen Gas) = oxidation (rust)
CO 2 = dissolves in rain water and forms carbonic acid
Living organisms = plants grow and produce a weak acid
Acid Rain = compounds from burning fossil fuel to mix chemically with rain to form acid
Mechanical weathering breaks rock and makes more surface area for chemical weathering to take place
Rate of weathering affected 2 ways Rock type More permeable allow more water to seep inside
Climate Mechanical weathering occurs faster in wet climates Chemical weathering occurs faster in hot temps Weathering occurs more rapidly in a warm rainy climate
The graph shows the rate of weathering for two identical pieces of limestone that weathered in different locations. (1) What does the x-axis of the graph represent? (2) What does the y-axis of the graph represent?
(3) How much thickness did Stone A lose in 1,000 years? How much thickness did Stone B lose in the same period?
(4) Which stone weathered at a faster rate? (5) Since the two identical pieces of limestone weathered at different rates, what can you infer caused the difference in their rates of weathering?
Soil is the loose weathered material on the earth s surface Main ingredient: bedrock Bedrock: solid layer of rock beneath soil
Rock particles Minerals Humus: dark colored substance that is plant and animal matter decay Water Air
Fertility of Soil: measure of how well the soil supports plant growth
Depends on size of individual soil particles Largest: Gravel Sand Silt Clay
Texture is important for plant growth Clay holds too much water Plants drown
Sandy soil drains quickly Plants die from too little water
Loam: best type of soil for growing plants Soil that is made of equal parts of sand and clay
What two materials make up the major portion of this soil?
Soil forms as rock is broken down by weathering and is mixed with other materials on the surface.
Soil Horizon: a layer of soil that differs in color and texture from the layers above and below it.
Horizon A: Topsoil which is a crumbly dark brown soil mixture of humus, clay, other minerals
Horizon B: clay and other particles washed down from horizon A Also called subsoil
Horizon C Only weathered rock
Climate Soil formation quickly forms in a warm rainy climate Type of rock Limestone forms soil more quickly
Climate Thick soil: Moderate Temp Plants Grassland soil is different from forest soil
Soil Composition rocky sandy clay
Make humus (formed from decomposition) Litter: a loose layer of dead plant leaves and stems on the surface of the soil.
Decomposer: organisms that break down the remains of organic material Bacteria Worms Fungus Small animals
Mix soil Makes space for air and water
Soil Conservation: The management of soil to prevent its destruction
Contour plowing farmers plow their fields along the curves of a slope.
Conservation plowing: farmers disturb the soil and its plant cover as little as possible
Crop rotation: a farmer plants different crops in a field each year.