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. weathering 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?
A. 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

1. A — the A horizon (topsoil) contains the most organic material.

2. D — weathering (both physical and chemical) converts rock into soil; weathering is the key process.

3. B — Climate. (Climate is fairly uniform across Collin County, so it does not explain local soil differences there.)

4. A — about 100–400 years per centimeter of topsoil.

5. A — Mineral matter (soil is mostly mineral particles by percent).

6. C — the C horizon (the weathered parent material) forms first from bedrock.

7. I don’t have the images, so I can’t label those specific profiles. If you upload the profiles or describe them I will label the A, B, C horizons and name the parent material. Quick identification tips you can use now:
- A horizon: dark, organic-rich top layer (topsoil).
- B horizon: lighter or more compact subsoil where clays, iron oxides, or carbonates accumulate (often denser, reddish or rusty stains).
- C horizon: partially weathered rock/fragmented parent material, little biological activity.
- Parent material: identify by texture and fragments — e.g., loess (windblown silt, very uniform fine texture), alluvium (rounded/sorted layers, deposited by water), glacial till (mixed sizes unsorted), or residual bedrock (weathered pieces of underlying rock like limestone, shale, granite).

If you upload the soil profile images, I’ll label each horizon and name likely parent material.