1. External Forces That Shape Our Planet Presentation created by Robert L. Martinez Primary Content Source: World Geography by McDougal Littell Images as cited. http://www.ers.usda.gov/Briefing/AgAndEnvironment/background.htm http://www.uvm.edu/~inquiryb/webquest/fa08/jlfisher/worksheets.html

2. Weathering refers to physical and chemical processes that change the characteristics of rock on or near the earth’s surface. www.csulb.edu

3. Weathering occurs slowly over many years and even centuries. http://www.ask.com/wiki/Wind_erosion

4. Weathering processes create smaller and smaller pieces of rock called sediment. Sediment is mostly identifiable as either mud, sand, or silt, which is very fine particles of rock. kohalacenter.org http://www.pubinfo.vcu.edu/masc/photos-2003-04/photos-2003.htm

5. Processes that break rock into smaller pieces are referred to as mechanical weathering. skywalker.cochise.edu/wellerr/students/green-sand/project.htm

6. Mechanical weathering does not change the composition of the rock, only its size and shape. For example, when ice crystals build up in the crack of a rock, they can actually create enough pressure to fracture the rock into smaller pieces. http://kayty.glogster.com/glog-8007/

7. All sorts of agents can break apart rocks. Frost and even plant roots dig into crevices in the rock, splitting it. http://www.flickr.com/photos/42386373@N05/4173374526/

8. Human activities like road construction or drilling and blasting in mining, are also mechanical weathering forces. http://gpssystems.net/tag/chilean-mine-disaster/

9. Eventually, the smaller broken material will be combined with organic material to become soil. http://greenspade.com/how-to-collect-a-soil-sample

10. Chemical weathering occurs when rock is changed into a new substance as a result of interaction between elements in the air or water and the minerals in the rock. http://www.shendapack.com/2011/04/27/chemical-weathering/

11. Decomposition, or breakup, can happen in several ways. Some minerals react to oxygen in the air and begin to crumble. That is when iron rusts, for example. http://www.qub.ac.uk/geomaterials/weathering/causeway/geologicalsuccessiol

12. When sulfur and nitrogen oxides mix with water, acid rain is formed. The increase of acid rain in the 20 th century is believed to be speeding up some decomposition. http://www.cvgs.k12.va.us/research/final/sresch02/eevans/lit reviw.htm

13. The location and the climate in which the rocks are located have a great deal to do with how rocks decompose. http://www.aralam.com/html/geology.htm

14. Climates that are warm and moist will produce more chemical weathering than do cool dry areas. http://www.qwickstep.com/search/chemical-weathering-examples.html

15. Rocks in cold dry and hot dry areas generally experience more mechanical weathering than chemical weathering. http://geoimages.berkeley.edu/GeoImages/Johnson/Landforms/RocksWxing/ChemicalWxingGranitel

16. Erosion occurs when weathered material is moved by the action of wind, water, ice, or gravity. http://www.grundfos.com/service-support/encyclopedia-search/erosion-corrosion

17. For erosion to occur, a transporting agent, such as water, must be present. Glaciers, waves, stream flow, or blowing winds cause erosion by grinding rock into smaller pieces. http://www.flickr.com/photos/40079018@N08/3810438780/

18. Material moved from one location to another results in the lowering of some locations and increased elevation in others. http://www.uvm.edu/~inquiryb/webquest/sp09/mbeattie/Erosion by wind.html

19. For example, water might carry topsoil from a hill into a river and gradually cause the river to become more narrow. http://savethesheyenne.org/erosion.htm

20. Erosion in its many forms reshapes landforms and coastal regions, as well as riverbeds and riverbanks. http://www.dinsdale.co.uk/regeneration_water_courses.cfm

21. One form of water erosion occurs as water flows in a stream or river. http://www.sandhillstaskforce.org/Photo_Essay/Temp_sandhills_photos

22. The motion picks up loose material and moves it downstream. The greater the force of water, the greater the ability of the water to transport tiny rock particles, or sediment. http://www.thefrancisgallery.com/photosn2.php

23. Another form of erosion is abrasion, the grinding away of rock by transported particles. The heavier the load of sentiment, the greater the abrasion on the banks and riverbed. ://geology.about.com/od/geoprocesses/ig/mechweathering/abrasion

24. A third eroding action of water occurs when the water dissolves chemical elements in the rock. The composition of the rock changes as a result. http://pulse.pharmacy.arizona.edu/9th_grade/culture_cycles/earth_science/erosion.html

25. Most streams erode both vertically and horizontally, that is, the valley cut by a stream gets deeper and wider, forming a V-shaped valley. http://www.aegweb.org/i4a/pages/index.cfm?pageid=4083

26. As the water slows, it drops the sediment it is carrying. When a river enters the ocean, the sediment is deposited in a fan-like landform called a delta. http://geographyfieldwork.com/CrowdedCoasts.htm

27. Wave action along coastlines also changes the land. Waves can reduce or increase beaches. http://www4.ncsu.edu/eos/users/c/ceknowle/public/chapter12/part1.html

28. Sediment deposited by wave action may build up sandbars or islands. Wave action is so powerful that in some locations, it erodes about three feet of beach per year. http://www.geograph.ie/photo/369272

29. For some unfortunate people, a beach house with an ocean view may end up in the ocean as a result of wave action erosion. http://www.learnnc.org/lp/editions/cede_sealevel/366

30. In many ways, wind erosion is similar to water erosion because the wind transports and deposits sediment in other locations. http://oceanworld.tamu.edu/resources/environment-book/aeoliantransport

31. Wind speeds much reach 11 miles per hour before fine sediment can be moved. The greater the speed of the wind, the larger the particles moved. http://www.omafra.gov.on.ca/IPM/english/soil-diagnostics/erosion

32. Dust storms are capable of carrying as much as 6,000 tons of sediment per cubic mile of air. As the wind slows, the sediment is dropped. http://www.pssac.org/SoilTeachingUnit/daytwo.htm

33. Depending on the type of windborne sediment, new landforms, such as sand dunes miles from seashores and rocks sculpted into fantastic forms, may be produced. http://www.phototravels.net/egypt/egypt-v/egypt-v-072.html

34. Deposits of loess, windblown silt and clay sediment that produce very fertile soil, are found across the world. In northern China, for example, the deposits are several hundred feet deep. http://www.pbase.com/dougsherman/image/93270863

35. Extensive areas of loess are found in the Mississippi Valley in the United States and in the grasslands of Argentina. http://www.igsb.uiowa.edu/browse/loeshill/loeshill.htm

36. A glacier is a large, long-lasting mass of ice that moves because of gravity.

37. Glaciers form in mountainous areas and in regions that are routinely covered with heavy snowfall and ice.

38. In mountain regions, glaciers move downslope as a result of gravity.

39. Glaciers such as ice caps and ice sheets move from the highest point on land toward the lowest point. http://newglobalwarmingeffects.com/2009/11/16/disappearing-arctic-ice-caps/

40. Glaciation is the changing of landforms by slowly moving glaciers. As a glacier moves, several types of erosion occur. http://web.arc.losrios.edu/~borougt/GlaciationDiagrams.htm

41. Rocks caught underneath the glacier are ground into finer and finer particles. Some particles are so small that they are called rock flour, which is one component of soil. http://ana20cristina.blogspot.com/2009/03/gif-letras-numeros-y-simbolos-en-rombos_4508.html

42. Massive glaciers also cut U- shaped valleys into the land. http://ed101.bu.edu/StudentDoc/current/ED101sp09/sandra06/Valley.html

43. On top of or within the ice are other rocks carried by the glacier. When the glacier melts, these rocks are left behind. http://serc.carleton.edu/details/images/22149.html

44. Rocks left behind by a glacier may form a ridge or a hill called a moraine. Moraines can be found on the sides, down the center, or at the leading edge of a glacier. http://oceanworld.tamu.edu/students/iceage/iceage1.htm

45. Inside or under the glacier may be tunnels formed by running water. These tunnels fill up with sediment dropped by the water. http://www.ens-newswire.com/ens/jul2010/2010-07-08-01.html

46. When the ice melts, it leaves a long snakelike ridge called an esker. Sometimes blocks of ice are trapped in the sediment. They melt slowly and leave behind a dent or a depression in the ground. http://robinsonroom.blogspot.com/2010/06/glacial-features-photos.html

47. These depressions are called kettles. The kettles may be filled with water forming a small lake. http://geology.about.com/od/glaciers_ice/ig/glacier-pictures/kettles

48. Weathering and erosion are a part of the process of forming soil. Soil is the loose mixture of weathered rock, organic matter, air, and water that supports plant growth. http://www.mysciencebox.org/soilanalysis

49. Organic matter in the soil helps to support the growth of plants by providing needed plant food. http://www.gardeninginfozone.com/organic-matter-for-the-garden

50. Water and air share tiny pore-like spaces in the soil. When it rains, the pores are filled with water. As the water evaporates, drains away, or is used by the plants, the pores are filled with air. http://www.flickr.com/photos/dirkvdw/3752985815/

51. The texture of the soil, the amount of organic material called humus, and the amount of air and water in the soil all contribute to the soil’s fertility, its ability to nurture plants. http://www.earthfort.com/products/supplies/denali-gold-humus