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6th Grade Chapter 2
Transcript of 6th Grade Chapter 2
Weathering and Erosion Weathering Geologist categorize rocks into 3 categories:
Sedimentary, Igneous, Metamorphic Rock Cycle- Changing of a rock Weathering- Process of breaking down rocks Mechanical weathering- breaks rocks into smaller and smaller pieces.
Chemical weathering- transforms rocks into new substances Temperature, water, wind, and plant and animal life all contribute to mechanical weathering. Mechanical Weathering Frost wedging, frost action, frost heaving Exfoliation and abrasion Abrasion sometimes creates unusual rocks formations called
hoodoos. Plants and animals contributing to weathering of rocks:
Roots may grow in the cracks of a rock.
Fires, floods, and other catastrophic events can cause mechanical weathering. Anything that breaks a rock into smaller pieces is physically weathering that rock. The most common type of chemical weathering:
oxidation and reaction of acids Chemical Weathering Oxidation- When oxygen in air combines with iron and iron oxide (rust) forms
Reaction of acids- When rain carries chemicals from the air onto surfaces below. One of the most common chemical compounds produced by fossil fuels is sulfur dioxide. Rain containing sulfuric acid, carbonic acid, and other chemicals is stronger and weathers rocks much more quickly than rain containing carbonic acid alone- Acid Rain Weathering forms many kinds of caves.
chemical weathering forms limestone caves or caverns. Caves Stalactites- Hang from ceiling and look like stone icicles.
Stalagmites- "Grow" up from the ground as a result of dripping of dissolved calcite. Spelunkers- People who explore caves. The loose material at the surface of the earth. Soil Humus- the small particles, along with water, air, and decayed organic particles that make up the soil. Soil Particles Pedologist- Scientist who studies soil Pedologists generally separate soil into 3 basic sizes: Sand,
Clay, Silt Sand- Largest particle
Rough, grainy feel
Do not fit tightly together
Drains quickly that it doesn't retain water
for plants to grow Clay- Smallest particle
100,000 clay particles = 1 sand particle
Dry= smooth texture
Holds nutrients and water well
Particles hold close so little air gets through Silt- Tiny, yet larger than clay
Dry silt feels like flour
Allows water and air to mix in soil Soil texture is very important to farming.
The composition and fertility of the soil depend on the climate. Soil horizons
Topsoil (A Horizon)
Subsoil (B Horizon)
Bedrock (R Horizon, regolith) Agents of Erosion Erosion Weathering produces small particles called sediment When weathered material moves from one location to another, erosion takes place. Weathering breaks down rock, but erosion moves the broken-down material one place to another. Primary force behind erosion is gravity
Other factors of erosion are called agents of erosion Deposition occurs when wind, water, or ice drops sediment
and rocks in a new location. Usually sediment drops according to its weight; as a result depositions have a layered look. Mass movement, or mass wasting, occurs when gravity moves rocks and sediments Soil Creep, Earth Flow, Mud Flow, Rockslide, Avalanche