2. Rocks on the Earth’s surface undergo changes in appearance and composition

3. Weathering: changes in rock material exposed at surface 1.Mechanical- physically changing rock into smaller pieces without changing its composition 2.Chemically- breakdown of rock by changing its chemical composition

4. What is the difference between physical and mechanical weathering?

6. Types of Mechanical Weathering 1. Exfoliation - process where sheets of rock peel or flake away

7. Example of exfoliation:

8. Types of Mechanical weathering 2. Ice wedge- occurs when water seeps into rocks and freezes Types of Mechanical Weathering

10. Ice wedging

11. Types of Mechanical weathering 3. Biological activity- the activity of organisms, including plants, burrowing animals, and humans that weather away rock Types of Mechanical Weathering

12. How do we see weathering here?

13. Weathering by sandmartins nesting in cliff

14. Types of Mechanical weathering 4. Abrasion- collision of rock with one another resulting in breaking and wearing away. Types of Mechanical Weathering

15. Abrasion takes place in many environments: –fast-moving streams –beaches subject to storm waves –desert environments with high winds –beneath glaciers that are loaded with fragments of rock.

16. How can we see weathering here?

17. How can we see weathering here

18. What about this beach?

20. Types of Chemical Weathering 1. Hydrolysis: Change in composition of minerals when they react with water

21. Feldspar combines with H 2 O to form a common clay called kaolin

22. Types of Chemical Weathering 2. Carbonation – When some minerals come in contact with carbonic acid, they form a new product Types of Chemical Weathering

23. Stalactites caused by carbonation Limestone is eaten away by acid and deposits as it drips from ceiling of cavern

24. Types of Chemical Weathering 3. Oxidation – When metallic elements combine with oxygen Types of Chemical Weathering

25. Oxidation = rust!

26. Is rust a physical change or a chemical change? Why?

27. Types of Chemical Weathering 4. Acid Precipitation “acid rain” Types of Chemical Weathering

29. 5. Plant acids – plants secrete acids that erode away the rock Types of Chemical Weathering

30. Lichens and mosses grow on rocks and secrete weak acids that dissolve the surface

32. Regolith A layer of weathered rock fragments covers much of the Earth’s surface

33. Regolith

34. Soil part of the regolith that supports plant growth Complex mixture of minerals, water, gases, and remains of plants and animals

35. Which do you think comes first – the soil or the regolith? Why?

36. Soil Composition has 4 major components: –mineral matter –organic matter (humus) –water –air

37. Composition of Soil:

38. Humus Dark, organic material, remains of animals and plants

39. Humus:

40. What do you think will affect the texture of soil? How?

41.  Soil Texture Loam (a mixture of all three sizes) is best suited for plant life. Texture refers to the proportions of different particle sizes. - Sand (large size) - Silt - Clay (small size)

42. CLAY

43. SILT

44. SAND

45. Soil Texture

46. source of the mineral matter in soil The most important factors in soil formation are: (1) parent material

47. (2) Time The longer a soil has been forming, the thicker it becomes. Important in all geologic processes (3) Climate Greatest effect on soil formation

48. (4) Organisms Furnish organic matter to soil Organisms influence the soil's physical and chemical properties.

49. Soil profile : A cross-section in which the layers of the soil and bedrock can be seen Each layer is called a horizon. In fully developed soil, there are three horizons

50. Pull out your diagram to label First Layer O (Organic) material like decaying leaves, animals, and bacteria.

51. A horizon (topsoil) mixture of organic matter and small rock particles B horizon (subsoil) contains minerals and clay

52. C horizon (regolith) partially weathered bedrock

53. Bedrock

56. Various forces move weathered fragments of rock away from where the weathering happens

57. Soil Erosion – process by which the products of weathering are moved.

58. Soil Erosion 1.occurs world wide and is normally a slow process 2.ordinarily, new left-over soil forms about as fast as the existing soil erodes 3.However, unwise use of the land and unusual climatic conditions can upset this natural balance

60. Accelerated Soil Erosion 1.unwise farming and ranching methods increase soil erosion one example is clearing trees another example is furrows plowed in land

63. Constant erosion reduces the fertility of the soil by removing the A horizon, which is rich in humus (unable to grow crops)

64. contour plowing: soil is plowed in circular bands that follow the shape of the land

66. strip cropping: crops are planted in alternate bands

67. How do you think contour plowing and strip cropping help to prevent erosion?

68. Contour cropping of corn, alfalfa and wheat.

69. terracing: construction of step- like ridges that follow the contours of a sloped field

70. crop rotation: farmers plant one type of crop one year and a different type of crop the next year

71. Besides controlling erosion, what is another benefit of crop rotation? (Hint- what do we find in the soil?)

72. Gravity and Erosion Gravity, through its downward pull, causes rock fragments to move down inclines mass movement is the movement of fragments down a slope

73. rockfall: the fall of rock from a steep cliff is the most rapid can be from tiny fragments to large boulders

75. landslide: sudden movement of masses of loose rock and soil down the slope of a hill

76. mudflow: the rapid movement of a large mass of mud

77. slump: downhill movement of a large block of soil under the influence of gravity

79. creep: extremely slow downhill movement of weathered rock material

81. erosion of mountains: weathering and erosion wear down rugged peaks to rounded peaks and gentle slopes Rocky Mountains Appalachian Mountains