Forces that Shape the Earth Chapter 5, lesson 4

 Weathering: the breaking down of rock into smaller pieces by natural process  Ice  Moving Water  Vegetation

1. PHYSICAL  Breaking down of rock by physical movements  Water  Plants  Animals  Frost wedges into cracks and expands  Moving water carries pieces of rock  Plants root under rocks and grow  Animals burrow and bring pieces underground

2. CHEMICAL  Breaking down of rock by changes in its chemical composition  Oxygen VS iron  Acids  Rocks contain iron which reacts with oxygen in the air  Oxygen and iron make rust, which makes the rock less strong than it was before  Carbonic acid, or acid rain, can wear away at natural limestone

 Erosion is the picking up and removing of rock pieces  Deposition is the dropping off of particles in another location  Wind contributes to erosion  Carries small particles in the wind  Shapes sand dunes  Water contributes to erosion  Freezing and thawing changes landscape  Melting snow affects soft rocks

 Flowing water is a major cause of erosion  When the river slows down, some of the particles are deposited as sediment, or loose pieces of rock  This can cause the river to meander, or curve

 Gravity and glaciers are other agents that cause erosion  Glaciers form when more snow falls than it can melt  When ice sheets are about 100 meters thick, it begins to fall downhill  When it falls, it takes loose pieces of land with it  This mixture of land pulled loose by glaciers is called till  These deposits take the form of a ridge or mound, called a moraine

 Weathering results in loose rock pieces which become a part of soil  Soil: a mixture of weathered rock, air, water, living things, and humus  Humus: material made of decayed plant and animal remains  Bacteria, fungi, worms, and insects all contribute to the formation  When plants or animals die, their remains enrich the soil and develop layers called soil horizons

 Minerals in soil cannot be replaced, it must be conserved  Soil can be ruined by…..  Growing too many plants Or the same plants many years in a row  Dumping waste in soil  Paving over land  Building dams