Mechanical Weathering The chemical and physical process that break down rock at the Earth’s surface Erosion The process by which water, ice, wind or gravity moves weathered rock or soil Uniformitarianism The geologic principle that the same geologic processes that operate today operated in the past to change the Earth’s surface Mechanical Weathering The type of weathering in which rock is physically broken down into smaller pieces Abrasion The grinding away of rock by other rock particles carried by water, ice or wind

The process that breaks down rock through chemical changes Ice Wedging Process that splits rock when water seeps into cracks, freezes and expands Chemical Weathering The process that breaks down rock through chemical changes Oxidation A chemical change in which a substance combines with oxygen and forms rust Permeable Characteristic of a material that is full of tiny connected air spaces that water can seep through Soil The loose weathered material on the Earth’s surface in which plants can grow

Bedrock Humus Fertility Loam Soil Horizon The solid layer of rock beneath the soil Humus Dark colored organic material in soil Fertility A measure of how well soil supports plant growth Loam Rich fertile soil that is made up of about equal parts of clay, sand and silt Soil Horizon The layer of soil that differs in color and texture from the layers above and below it

A thick mass of grass roots and soil Topsoil Mixture of humus, clay and other minerals that for the crumbly topmost layer of soil Subsoil The layer of soil beneath the topsoil that contains mostly clay and other minerals Litter The loose layer of dead plant leaves and stems on the surface of the soil Decomposer Soil organism that breaks down the remains of organisms and digests them Sod A thick mass of grass roots and soil

Natural Resource Dust Bowl Soil Conservation Contour Plowing Anything in the environment that humans use Dust Bowl The area of the Great Plains where wind and erosion caused soil loss during the 1930’s Soil Conservation The management of soil to prevent its destruction Contour Plowing Plowing fields along the curve of the slope to prevent soil loss Conservation Plowing Soil conservation method in which dead stalks from the previous year’s crop are left in the ground to hold the soil in place

Crop Rotation The planting of different crops in a field each year to maintain the soil’s fertility