How does the C Horizon form?
A. Rainwater washes clay and minerals from the A horizon to the C horizon.
B. Plant roots weather pieces of rock.
C. Plants add organic material to the soil.
D. Bedrock weathers, and rock breaks up into soil particles
I think its A
Actually, the correct answer is D. Bedrock weathers, and rock breaks up into soil particles. The C horizon, also known as the parent material, is formed when bedrock undergoes weathering and breaks down into smaller soil particles. This process can be slow and facilitated by physical, chemical, and biological weathering agents such as temperature changes, ice expansion, and the action of plant roots. The other options you mentioned describe processes involved in the formation of other soil horizons, such as the A and O horizons.
To determine the correct answer, let's analyze the options provided:
A. Rainwater washes clay and minerals from the A horizon to the C horizon.
This option refers to the movement of materials from the topsoil (A horizon) to the subsoil (C horizon) through the process of leaching. Leaching occurs when rainwater or irrigation water drains through the soil, carrying dissolved clay and minerals with it. Therefore, option A is not correct in terms of how the C horizon forms.
B. Plant roots weather pieces of rock.
This option suggests that plant roots play a role in weathering pieces of rock, which can contribute to the formation of soil. While the weathering of rock is an important aspect of soil formation, it primarily occurs in the upper layers of soil (A and B horizons). Therefore, option B is not correct regarding the formation of the C horizon specifically.
C. Plants add organic material to the soil.
This option points out that plants contribute to the formation of organic material in the soil. Organic material, such as decaying plant matter (e.g., leaves, roots), can accumulate and enrich the upper soil layers (A and B horizons). However, the C horizon is typically comprised of weathered parent material that has undergone minimal organic enrichment. Therefore, option C is not an accurate explanation for the formation of the C horizon.
D. Bedrock weathers, and rock breaks up into soil particles.
This option suggests that the C horizon forms through the weathering of bedrock, where rock gradually breaks down into soil particles. Over time, physical and chemical weathering processes act upon the bedrock, resulting in the formation of the C horizon. This option aligns with the general understanding of how the C horizon is formed and is thus the correct answer.
Therefore, the correct answer is D. Bedrock weathers, and rock breaks up into soil particles.