Earth Science: Soil: Layers and Composition Worksheet

Question 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.

Accepted Answer

The top layer is called topsoil. It often contains humus, plant roots, small animals, and minerals that help plants grow.

Question 2

Put these soil layers in order from the surface down: bedrock, topsoil, subsoil, organic layer.

Accepted Answer

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.

Question 3

What is humus, and why is it important in soil?

Accepted Answer

Humus is decayed plant and animal material in soil. It is important because it adds nutrients and helps soil hold water for plants.

Question 4

A student finds dark, crumbly soil with many roots and earthworms. Which soil layer is the student most likely observing? Explain your answer.

Accepted Answer

The student is most likely observing topsoil. Topsoil is usually dark, has humus, contains many roots, and supports living things such as earthworms.

Question 5

Soil is made of several parts. List four things that can be found in healthy soil.

Accepted Answer

Healthy soil can contain mineral particles, humus, water, air, and living organisms. Any four of these parts are correct.

Question 6

Sand, silt, and clay are soil particles. Which particle is the largest, and which particle is the smallest?

Accepted Answer

Sand is the largest soil particle, and clay is the smallest soil particle. Silt is in between sand and clay in size.

Question 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.

Accepted Answer

The soil is likely to have more sand. Sandy soil has large particles, feels gritty, and lets water drain through quickly.

Question 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.

Accepted 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.

Question 9

Loam is often good for growing many plants. Explain why loam is useful for plant growth.

Accepted Answer

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.

Question 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.

Accepted Answer

The middle layer is subsoil. Subsoil is usually below topsoil and often has less humus but more small rock pieces and minerals.

Question 11

Why do many plant roots grow mostly in topsoil instead of deep in bedrock?

Accepted Answer

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.

Question 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?

Accepted Answer

Sand settles first because its particles are the largest and heaviest. Larger, heavier particles sink faster than smaller particles in water.

Question 13

Explain how worms and tiny organisms help make soil healthier.

Accepted Answer

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.

Question 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?

Accepted Answer

The soil problem is erosion. Plants can help reduce erosion because their roots hold soil in place and their leaves slow down falling rain.

Question 15

Draw or describe a healthy soil profile with at least three labeled layers. Include one detail about what is found in each layer.

Accepted Answer

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.

Earth Science: Soil: Layers and Composition

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