Rate of Weathering and Soil Formation Ch. 10, section 2 and 3

Rate of Weathering Depends on: Climate Shape or composition of the rock Elevation

Differential weathering When softer, less weather resistant rock wears away leaving harder, more weather resistant rock behind Devils Tower: softer rock is gone, leaving harder rock tower

Shape of the rock The more surface area exposed, the faster it weathers: sugar activity: grains dissolved faster than the cube

Climate Chemical weathering happens faster in warm, wet climates: heats speeds up reactions, and oxidation happens more Mechanical weathering happens faster in cold, wet climates: ice wedging and frost action

Elevation Elevation is how far ABOVE sea level something is. The higher the elevation, the more wind, rain, ice a rock is exposed to.

What is soil? Soil is mineral fragments (sediment), organic material (humus), water and air that contains enough nutrients for plants to grow. Parent rock=Bedrock Why? The “parent rock” breaks down into little pieces (mom and babies) The bedrock is what breaks into pieces

Soil Properties Soil texture Soil structure Soil fertility: can it support life? Soil pH Soil Horizons: layers in the profile

Soil Texture Based on the proportions of soil particles How much silt, sand, clay particles it has Loam is made up of equal parts of sand, silt, and clay

Horizons Humus: the organic material in soil Decayed plants and animals Provides the nutrients to the soil O horizon-Litter (grass, twigs, etc. A horizon-Topsoil (humus, small sediment, dark brown) B horizon-subsoil (very little humus, larger rocks, light brown) C horizon-weathered parent (chunks of rocks, no humus) R horizon-Bedrock(solid rock)

Soil in different climates Tropical Rain Forest-lots of humus but poor in nutrients because of leaching Deserts-less weathering because of no rain, very little topsoil, dry, salty Temperate forest/Grassland: where we are, very fertile, lots of humus and topsoil, rich in nutrients Arctic-cold means less decaying, slow weathering, less soil

What is the ‘perfect’ soil? Loam- it contains equal parts of sand, silt and clay, plus lots of humus.