Soil

6th gradeEarth Science

Howard Middle School

Soil Soil is defined as the layer of

unconsolidated material found at the earth’s surface.

Soil thickness varies from a few millimeters (mm) to several meters (m).

Soil Thinner soils can indicate a very young soil

or a place where soil has been removed by water, wind, gravity, or animal activity.

Composition

Weathered mineral particles Dead and living organic matter Dissolved substances

Composition The type of soil that exists in an area is

influenced by five major factors: Local climate Topography Rock types Organisms (especially plants) Amount of time the soil has been developing

Classifying Soils In general, soils are classified based on the

proportion of organic material and the different-sized particles—sand, clay, and silt—that they contain.

Inorganic and Organic Components The size and type of the inorganic

components of a soil are determined mostly by the local rock type and terrain.

The type and amount of organic material is influenced mostly by climate (temperature, sunlight, and precipitation).

Dead and Living Organic Material Dead organic material is particularly

important because it contains a readily accessible source of necessary nutrients.

Living organic material helps aerate the soil and decompose the dead material.