Processes that Shape the Earth. WEATHERING: the process that breaks down rock and other substances at Earth’s surface EROSION: the movement of rock particles.

Processes that Shape the Earth

WEATHERING: the process that breaks down rock and other substances at Earth’s surface

EROSION: the movement of rock particles by wind, water, ice, or gravity - or – the process by which natural forces move weathered rock and soil from one place to another.

**Weathering and erosion work together continuously to wear down and carry away the rocks at Earth’s surface.

HowStuffWorks Videos "Erosion"

**There are 2 kinds of weathering – mechanical and chemical.

MECHANICAL WEATHERING: the type of weathering in which rock is physically broken down into smaller pieces.

**Mechanical weathering breaks rock into pieces by freezing and thawing, release of pressure, growth of plants, actions of animals, and abrasion.

Abrasion - grinding away of rock by rock particles carried away by water, ice, wind, or gravity

ICE WEDGING: the process that splits rock when water seeps into cracks, then freezes and expands

CHEMICAL WEATHERING: the process that breaks down rock through chemical changes

•Water – most important chemical weathering agent – dissolves rock•Oxygen – oxygen in air mixed with iron and water causes rust in rocks, just like on metal•Carbon Dioxide – causes carbonic acid •Living Organisms – roots from plants produce weak acids that slowly dissolve rock around the root•Acid rain – pollution from burning coal, oil, and gas for energy reacts chemically with water in the clouds, forming acids which can fall in raindrops as acid rain. This causes very rapid chemical weathering.

**Chemical weathering produces rock particles that have a different mineral makeup from the rock they came from.

Agents of Chemical Weathering:

**The most important factors that determine the rate at which weathering occurs are type of rock and climate.

PERMEABLE: Characteristic of a material that is full of tiny, connected air spaces that water can seep through

**Permeable rock weathers easily, especially chemically.

SOIL: the loose, weathered material on Earth’s surface in which plants can grow

**Soil forms as rock is broken down by weathering and mixes with other materials on the surface.

**Soil is a mixture of rock particles, minerals, decayed organic material, air, and water.

•The decayed organic materials are called humus, which is a dark-colored substance that forms as plant and animal remains decay.

SOD: the thick mass of tough roots at the surface of the soil that keeps the soil in place and holds in moisture

BEDROCK: the solid layer of rock beneath the soil

SOIL HORIZON: a layer of soil that differs in color and texture from the layers above or below it

**Horizon A is made of Topsoil.

TOPSOIL: a crumbly, dark brown soil that is a mixture of humus, clay, and other minerals.

**Horizon B is often called subsoil.

SUBSOIL: usually consists of clay and other particles washed down from the A horizon, but little humus.

**Horizon C contains only partly weathered rock.

**Soil is one of Earth’s most valuable resources because everything that lives on land depends directly or indirectly on soil.

**Soil is a renewable resource that can be found wherever weathering occurs, but it takes a long time.

HowStuffWorks Videos "The Ecosphere: Succession and Soil

Formation"

DUST BOWL: The Dust Bowl included western Oklahoma and parts of the surrounding states. Wind blew dry particles of soil into great clouds of dust that traveled thousands of kilometers. (Dirty Thirties – Dust Bowl lasted from 1930-1938)

HowStuffWorks Videos "American Grasslands: The Dust Bowl"

**Plowing removed the grass from the Great Plains and exposed the soil. In times of drought, the topsoil quickly dried out, turned to dust, and blew away.

SOIL CONSERVATION: the management of soil to prevent its destruction.

1.contour plowing – the practice of plowing fields along curves of a slope

2. conservation plowing – disturbs the soil and its plant cover as little as possible.

SEDIMENT: material moved by erosion

**Deposition occurs where the agents of erosion lay down the sediment. Deposition changes the shape of the land.

**Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surface.

MASS MOVEMENT: any one of several processes that move sediment downhill.

**Mass Movement can be fast or slow.

HowStuffWorks Videos "How

Mudslides Work"

**Gravity is the force that moves rock and other materials downhill.

RUNOFF: water that flows over the ground surface rather than soaking into the ground

FLOOD PLAIN: the flat, wide area of land along a river.

ALLUVIAL FAN: a wide, sloping deposit of sediment formed where a stream leaves a mountain range. It is shaped like a fan.