Chapter 4 Weathering and Soil Formation

Weathering breaks down rocks into smaller pieces 1. Mechanical weathering 2. Chemical weathering

Mechanical weathering produces physical changes in rocks: Ice wedging Pressure release-causes rock to expand, cracking and leading to exfoliation Exfoliation-process in which layers of exfoliation rock gradually break off. Plant root growth Abrasion-wearing down by friction, the rubbing of one object or surface against another

Chemical weathering Breakdown of rocks by chemical reactions that change the rocks composition (what it is made of) Water (dissolving) Rusting

Weathering occurs at different rates Surface area-the more exposed area, the faster the break down of rock (chemical) Rock composition ex: Granite compared to limestone Climate: chemical weathering occurs in wet, hot areas faster than cold, dry regions Mechanical weathering caused by freezing and thawing

Weathering and organic processes form soil Soil- a mixture of weathered rock particles and other materials Humus-decayed organic (living things) in the soil

Soil formation is affected by: Rock in an area Climate: tropical, desert, temperate, artic Landforms: mountains and valleys Plant cover: provide organic matter Living organisms: microorganisms and animals Time

Soil composition Soil horizon-a layer of soil with properties that are different than the layers above and below it Soil profile- soil horizons in a specific area

Soil Properties Texture-determined by size of weathered rock particles it contains Color-most comes from iron and humus Pore space-the spaces between the particles Chemistry-minerals and organic nutrients

Human activities Soil is a valuable resource for humans 1. Farming-soil loss and overgrazing results in desertification- expansion of desert in areas where natural plant cover has been destroyed 2. Construction and development 3. Mining Strip mining Open pit

Soil conservation Crop rotation Conservation tillage Terraces Contour plowing Windbreaks