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Chapter 8 Big Question Mechanical weathering Mechanical weathering is the type of weathering in which rock is physically broken into smaller pieces. The causes of mechanical weathering are Freezing and thawing Release of pressure Plant growth Actions of animals Abrasion – grinding away of rock by rock particles carried by water, ice, wind, or gravity Chemical weathering Chemical weathering is the process that breaks down rock through chemical changes. The causes of chemical weathering are Water Oxygen Carbon dioxide Living organisms Acid rain The most important factors that determine the rate at which weathering occurs are the type of rock Permeable rock weathers chemically at a fast rate because the rock is full of tiny, connected air spaces that allow water to seep through it. the climate. Big Question The loose, weathered material on Earth’s surface in which plants can grow. Soil is a mixture of rock particles, minerals, decayed organic material, water, and air. Big Question As rock is broken down by weathering and mixes with other materials on the surface. Soil is constantly being formed wherever bedrock is exposed. A soil horizon is a layer of soil that differs in color and texture from the layers above or below it. The A horizon is made up of topsoil – a crumbly, dark brown soil that is a mixture of humus, clay, and other minerals. The B horizon, often called subsoil, usually consists of clay and other particles washed down from the A horizon, but little humus. The C horizon contains only partly weathered rock. Big Question into major groups based on Climate Plants Soil composition They are Tundra soils Northern forest soils Prairie soils Mountain soils Southern forest soils Desert soils Tropical soils Big Question It is a natural resource. Soil is one of Earth’s most valuable natural resources because everything that lives on land, including humans, depends directly or indirectly on soil. The value of soil is lost when soil loses its fertility and when topsoil is lost due to erosion. Soil conservation is the management of soil to prevent its destruction. Soil can be conserved through Contour plowing Conservation plowing Crop rotation