Question

__ 1. Which layer in the diagram below contains the most organic material?
A. A B.B C.C D. the bedrock  
_____ 2. How is soil created from rock?
A. physical weathering without chemical weathering

B. chemical weathering without physical weathering

C. erosion without weathering

D. weather without erosion



_____ 3. Which of the following is not a major factor in soil
formation within Collin County. *Hint-Which factor is
uniform throughout the county.)

A. Time

C. Relief
B. Climate

D. Parent material

____ 4. Approximately how many years does one centimeter of topsoil take
to form?
A. 100 – 400 years
C. 1000 – 4000 years
B. 10 – 40 years
D. 10,000 – 40,000 years

_____ 5. Which of the following is found in the greatest % in soil?
wA. Mineral matter
B. Organic matter
C. Water
D. Air
_____ 6. Which layer of a soil profile forms first from the bedrock?
A. A horizon
B. B horizon
C. C horizon
D. humus

7. For the soil profiles below, label the horizons (A, B, or C) and the parent material
in each of the soil profiles using the spaces provided next to each image.

Answer 1

Here are the answers with short explanations. For question 7 I don’t see the images — please upload or describe them and I’ll label the horizons and parent material.

1. A — A horizon (topsoil).
Explanation: The A horizon contains the most organic material (humus mixed with mineral matter).

2. D — weather without erosion.
Explanation: Soil forms by weathering (physical and chemical breakdown of rock). Erosion moves material but isn’t required to form soil in place. (The question uses “weather” where it means “weathering.”)

3. B — Climate.
Explanation: Within a single county climate is essentially uniform, so it’s not a differing factor in local soil variation. Time, relief (topography), and parent material vary and are major factors.

4. A — 100–400 years per cm.
Explanation: Typical natural soil formation rates are on the order of centuries per centimeter.

5. A — Mineral matter.
Explanation: Mineral particles make up the largest percentage of most soils (roughly ~45% by volume in a typical idealized soil).

6. C — C horizon.
Explanation: The C horizon is the least-weathered layer derived directly from the parent rock and forms first above the bedrock.

7. I don’t have the soil-profile images. If you upload them (or describe colors, texture, depth, rock fragments), I will label each horizon (A, B, C) and identify the parent material. Quick ID hints:
- A horizon: dark, organic-rich, surface layer.
- B horizon: lighter, denser subsoil with accumulated clays/oxides, may be reddish or yellowish.
- C horizon: weathered parent material, few roots, many rock fragments; transitions to unweathered bedrock (parent material).