Earth Science: Soil: Layers and Composition
Exploring soil horizons, particles, and living things in soil
Earth Science: Soil: Layers and Composition
Exploring soil horizons, particles, and living things in soil
Earth Science - Grade 4-5
- 1
A soil profile is a side view of soil from the surface down to the rock below. Name the top layer of soil and describe one thing usually found there.
Think about the layer where most grass and plant roots grow.
The top layer is called topsoil. It often contains humus, plant roots, small animals, and minerals that help plants grow. - 2
Put these soil layers in order from the surface down: bedrock, topsoil, subsoil, organic layer.
The correct order is organic layer, topsoil, subsoil, and bedrock. The organic layer is closest to the surface, and bedrock is the deepest layer listed. - 3
What is humus, and why is it important in soil?
Humus comes from once-living things such as leaves, roots, and dead insects.
Humus is decayed plant and animal material in soil. It is important because it adds nutrients and helps soil hold water for plants. - 4
A student finds dark, crumbly soil with many roots and earthworms. Which soil layer is the student most likely observing? Explain your answer.
The student is most likely observing topsoil. Topsoil is usually dark, has humus, contains many roots, and supports living things such as earthworms. - 5
Soil is made of several parts. List four things that can be found in healthy soil.
Think about both nonliving parts and living things in soil.
Healthy soil can contain mineral particles, humus, water, air, and living organisms. Any four of these parts are correct. - 6
Sand, silt, and clay are soil particles. Which particle is the largest, and which particle is the smallest?
Sand is the largest soil particle, and clay is the smallest soil particle. Silt is in between sand and clay in size. - 7
A sample of soil lets water pass through very quickly and feels gritty. Is it likely to have more sand, silt, or clay? Explain your answer.
Large spaces between particles allow water to move through more easily.
The soil is likely to have more sand. Sandy soil has large particles, feels gritty, and lets water drain through quickly. - 8
A sample of soil holds water for a long time and feels sticky when wet. Is it likely to have more sand, silt, or clay? Explain your answer.
The soil is likely to have more clay. Clay has very small particles that pack closely together, so it can hold water and feel sticky. - 9
Loam is often good for growing many plants. Explain why loam is useful for plant growth.
Good plant soil needs both water-holding ability and spaces for air.
Loam is useful because it has a balanced mix of sand, silt, and clay. It can hold some water and nutrients while still allowing air and extra water to move through. - 10
Look at this soil profile: the top layer is thin and dark, the middle layer is light brown, and the bottom layer is solid rock. Identify the middle layer.
The middle layer is subsoil. Subsoil is usually below topsoil and often has less humus but more small rock pieces and minerals. - 11
Why do many plant roots grow mostly in topsoil instead of deep in bedrock?
Compare loose soil with solid rock.
Many plant roots grow mostly in topsoil because it has more nutrients, water, air, and space for roots. Bedrock is solid rock, so roots cannot grow through it easily. - 12
A jar test shows three layers after soil settles in water: heavy sand at the bottom, silt in the middle, and clay near the top. Why does sand settle first?
Sand settles first because its particles are the largest and heaviest. Larger, heavier particles sink faster than smaller particles in water. - 13
Explain how worms and tiny organisms help make soil healthier.
Think about decomposers and soil tunnels.
Worms and tiny organisms help break down dead plants and animals into humus. Worms also mix and loosen soil, which helps air and water move through it. - 14
A hillside has very little plant cover. After a heavy rain, muddy water runs down the hill. What soil problem is happening, and how could plants help reduce it?
The soil problem is erosion. Plants can help reduce erosion because their roots hold soil in place and their leaves slow down falling rain. - 15
Draw or describe a healthy soil profile with at least three labeled layers. Include one detail about what is found in each layer.
Start at the surface and move downward.
A correct response should include at least three labeled layers, such as organic layer, topsoil, subsoil, and bedrock. The organic layer may have leaves, topsoil may have humus and roots, subsoil may have minerals and small rocks, and bedrock is solid rock.