Soil, Soil Formation, and Soil Layers

Mr. White6th Grade Earth Science

Warm UpBased on our discussion of weathering, erosion, and

deposition…how do you think soil is formed?

What is soil?Soil is the loose, weathered material on the Earth’s surface in which plants

can grow.

Why is Soil Important?•All living things need minerals.•Plants get minerals from soil.•Plant-eating animals get the minerals from the plants that they eat.•We get minerals from the plants and animals that we eat.

Soil Formation• Over many years, weathering and erosion will cause

the formation of soil. • 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.

Rate of Weathering• The most important factors that determine the rate at

which weathering occurs are the type of rock, surface area of the rock, and climate .• Type of Rock• Minerals will determine the rate.• Permeable rocks (full of tiny air spaces) weather faster.

• Climate:• Weathering occurs faster in wet climates and higher

temperatures.

Fact You Should KnowIt takes 500 years to replace 1 inch of

topsoil!

What Determines Soil Type?• Color• Texture (size of particles)• Porosity (ability to hold water)

What are the Different Soil Types?

There are over 70,000 different types of soil in the United States. They have:• Different colors• Hold more or less water• Different size of rocks in them• Different minerals

Soil Types in the U.S.• Tundra Soils• Northern Forest Soils• Prairie Soils• Mountain Soils• Southern Forest Soils• Desert Soils• Tropical Soils

Soil Particle Sizes

SandFeels: • Gritty • RoughRock Particle Size:• Large• We can see it with our eyes

Silt

Feels:• Powdery • SoftOccurs:• Chemical weathering of rock • Particle Size:• Smaller than sandy particles

ClayFeels: • Hard when dry• Sticky when wet Rock Particles• Small • Packed Close together

Loam • Composed of sand, silt, and clay• Feels:• Soft • Crumbly

• Best for growing crops • Lots of nutrients

What is the point?Sand, silt, clay, and loam all describe the textures of soil

and are one of the characteristics used to identify different soil types.