1. Weatheringand Soil Formation

2. Rocks and Weathering

3. What is weathering? Weathering- is the process that breaks down rock and other substances at Earth’s surface. Air, water, weather & living things work to wear rocks down.

4. Types of weathering:Types of weathering: –Mechanical weathering –Chemical weathering

5. Mechanical Weathering Mechanical weathering- a type of weathering in which rock is physically broken into smaller pieces.

6. Agents for Mechanical Weathering: 1.Freezing & thawing of water – Ice Wedging  water expands when it freezes  When water gets into a crack in rock and then the temperature drops to the freezing point, the water (ice) expands inside the crack, breaking the rock.  This is called ice wedging.

7. Ice Wedging

9. Agents for Mechanical Weathering: 2. Release of Pressure

10. Release of Pressure

11. Agents for Mechanical Weathering: 3. Growth of plants – roots of plants begin to break rock apart as they get bigger.

12. Growth of Plants

13. Agents for Mechanical Weathering: 4. Actions of animals – some animals make tunnels, which can cause rocks to break since they are weakened.

14. Actions of Animals

15. Agents for Mechanical Weathering: 5. Abrasion – over time particles of sand and water begin to tear away at the rock, breaking it down.

17. Chemical Weathering Chemical weathering- i i i is the process that breaks down rock through chemical changes. Chemical weathering changes the mineral content of the rock

18. Agents for Chemical Weathering: 1. Water – the most important chemical weathering agent. It dissolves the rock. 2. Oxygen – causes oxidation (rust), which weakens and softens rock. 3. Carbon Dioxide (CO2) – mixes with water to form carbonic acid which eats away at marble and limestone.

19. 4. Living organisms – As plant roots grow they make a weak acid, which over time, dissolves rock. 5. Acid rain – eats away at rock.

20. Chemical Weathering

22. The Rate of Weathering is Determined by: 1. The type of rock – t– t– t– the minerals that make up rock determine how fast it weathers 2. Climate

23. The Rate of Weathering If a rock is permeable (has holes, which allow water to filter through it) will speed up the rate of weathering. Both chemical and mechanical weathering occur faster in wet and hot climates.

24. Remember... Erosion is the movement of sediment Deposition is laying down of sediments

25. Soil Formation and Composition

26. What is soil? Soil- is the loose, weathered material on Earth’s surface in which plants can grow.

27. Soil forms in layers as rock is broken down by weathering and mixes with other materials on the surface.Soil forms in layers as rock is broken down by weathering and mixes with other materials on the surface. Soil is a mixture of rock particles, minerals, decayed organic material, air, and water.Soil is a mixture of rock particles, minerals, decayed organic material, air, and water.

28. The type of rock particles and minerals in soil depends on: 1.T he bedrock that was weathered to form the soil. 2.T he type of weathering. **Chemical weathering can change the mineral content.***

29. Humus- a dark-colored substance that forms as plant and animal remains decay. Humus is rich in nutrients and helps plants grow.

31. Soil Texture Soil is classified by the size of the rock particles in it. Sizes (from BIG to small): 1. GRAVEL 2. SAND 3. SILT 4. clay

33. Soil Formation Soil forms layers called horizons. Soil horizon- is a layer of soil that differs in color and texture form the layers above or below.

34. Soil Horizons Horizon A – topsoil / Humus Horizon B – subsoil Horizon C – partly weathered rock Bedrock – solid layer of rock beneath the soil

38. Living organisms mix soil and add organic materials to form humus. (fungi, protists, bacteria, and worms, plants)