Soil, Soil Formation, and Soil Layers Mr. White 6th Grade Earth Science

Warm Up Based 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.

It takes 500 years to replace 1 inch of topsoil! Fact You Should Know It 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

Sand Feels: Gritty Rough Rock Particle Size: Large We can see it with our eyes

Silt Feels: Powdery Soft Occurs: Chemical weathering of rock Particle Size: Smaller than sandy particles

Clay Feels: Hard when dry Sticky when wet Rock Particles Small Packed Close together

Loam Composed of sand, silt, and clay Feels: Best for growing crops 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.