Aim: How do soils form? I. Soil – mixture of weathered rock and organic remains that usually covers bedrock. A. Formed as a result of both physical and chemical weathering 1. Physical – breaks solid rocks into smaller particles (example – bedrock is broken down into regolith)

2. Chemical – changes hard minerals into softer ones 3. Burrowing animals help mix materials B. Soil Horizons (profile) – soil with three distinct layers 1. “A” Horizon (topsoil) – upper layer that is rich in dark colored organic remains (humus). Contains water, living animals (worms,burrowing animals), bacteria, and air.

2. “B” Horizon (subsoil) – poor in organic material but enriched by minerals that have been leached out of horizon “A.” May contain magnesium and calcium carbonates. 3. “C” Horizon (regolith) – composed of broken up bedrock in various stages of decomposition and weathering. It sits upon unweathered, solid bedrock.

Soil Profile

C. Climate is the main factor affecting type of soil 1. Soil Types a.Arctic – has thin soil due to lack of moisture b.Forest – very humid and is not very fertile c.Grassland – can support grass but not trees d.Desert – dry and contains very little vegetation e.Tropical – formed in high temperatures and abundant rainfall