Soil

Soil

What is Soil??

Soil's component is a mixture of weathered rock, rock fragments, decayed organic matter, water, and air.

About half the volume of soil is solid materials. The other half is liquids and gases. Weathering breaks rocks into smaller pieces. These fragments, however, do not become good soil until plants and animals live in them. 

Multiple Choice

About how much of soils volume is made up of solid material?

• all

• a quarter

• half

• none

Multiple Choice

What is the other half made up of?

• dead animals

• rocks

• gases and liquids

• plasticlike material

Multiple Choice

Does broken down rock material make good soil?

• yes

• no

The Organic Part of Soil

 Plants and animals add organic matter to rock fragments. Organic matter is the remains of something that was once alive.

Organic matter in soil includes leaves, dead insects, and waste products of animals. As living things die and fall to the ground, organisms that live in the soil decompose these materials for food.

The Inorganic parts of soil

The term inorganic describes materials that have never been alive. Mechanical and chemical weathering of rocks into fragments forms inorganic matter in soil. Scientists classify the soil fragments according to their sizes. Rock fragments can be boulders, cobbles, gravel, sand, silt, or clay. 

Inorganic soil continued....

 Larger rock particles have larger pores between them. Sand particles are larger than silt, so sand drains more easily than silt because sand has larger pores. The smaller particles in silt store more water in the soil.

Multiple Choice

Which holds more water?

• large particles

• smaller particles

Decomposition

Decomposition changes once-living material into dark-colored organic matter. This matter helps hold water and plant nutrients in the soil

Soil Formation

Not all soils are the same. The five factors of soil formation determine the type of soil that forms. These five factors are parent material, climate, topography, biota, and time

Parent Material

Parent material is the starting material of soil. It is the rock or sediment that weathers and forms the soil. Soil can develop from rock that weathers in the same place where the rock first formed. This rock is called bedrock. Wind and water can also carry away the rock particles and form soil in a different location. The particle size and type of parent material determine the properties of the soil that develops. 

Multiple Choice

What two things determine the property of the soil created?

• the particle weight and climate

• the particle size and type of parent material

• the particles biota and topography

• the particle color and shape

Climate

Climate is the average weather of an area. Some examples of climate are the amount of precipitation and the daily and average annual temperatures. Soil can form rapidly if the parent material is in a warm, wet climate. Large amounts of rain can speed up the weathering of rock. Warm temperatures speed up weathering by increasing the rate of chemical changes. Weathering rates also increase in locations where freezing and thawing occur.

Topography

Is the land where you live hilly or flat? If it is hilly, are the hills steep or gentle? Topography is the shape and steepness of the landscape. The topography of an area determines what happens to water that reaches the soil surface. For example, in flat landscapes, most of the water enters the soil. In steep landscapes, much of the water runs downhill and doesnt have time to seep into the soil

Biota

A variety of organisms, from rodents to bacteria, live in soil. Biota (bi OH tuh) is all of the organisms that live in a region. Biota helps speed up soil formation. Most soil organisms decompose organic matter. Mature soils form over thousands of years as plants, animals, and other processes break down bedrock and subsoil.

Time

Weathering constantly acts on rock and sediment. As a result, soil forms constantly, but slowly. Soil is still young after a thousand years. Mature soils develop layers as new soil forms on top of older soil

Multiple Choice

Soil formation happens

• quickly

• slowly