Which three statements about soil formation are true? – The composition of soil depends largely on the composition of the parent rock. – The chemical composition and structure of soil remain constant for millennia. – Soil becomes less fertile when it is mixed with decaying organic matter. – Strong roots of shrubs and trees hold onto soil and protect it from erosion. – Soil formed from local rock is residual soil, and soil formed from distant rock is transported soil.
The Correct Answer and Explanation is:
Correct Statements About Soil Formation:
- The composition of soil depends largely on the composition of the parent rock.
- Strong roots of shrubs and trees hold onto soil and protect it from erosion.
- Soil formed from local rock is residual soil, and soil formed from distant rock is transported soil.
Explanation:
Soil formation is a dynamic and complex natural process that results from the interaction of five key factors: parent material, climate, organisms, topography, and time. Over time, rocks break down into smaller particles through weathering processes, and these particles mix with organic matter to form soil.
Firstly, the composition of soil largely depends on the parent rock, also known as the parent material. This rock provides the mineral content of the soil. For example, soils formed from granite tend to be sandy and well-drained, while those formed from basalt may be clay-rich and fertile. The mineral composition, texture, and structure of the parent rock significantly influence the characteristics of the resulting soil.
Secondly, strong roots of shrubs and trees help anchor the soil. These roots physically hold soil particles together and create a network that reduces the risk of soil being washed or blown away. This natural defense against erosion is essential in preserving soil depth and fertility, especially on slopes or in areas with heavy rainfall or wind.
Thirdly, residual and transported soils differ based on their origin. Residual soil forms directly over the bedrock from which it derives and remains in place. In contrast, transported soil is carried from its place of origin by agents like water, wind, glaciers, or gravity. This soil often settles in valleys, floodplains, or low-lying areas and may differ significantly in composition from the underlying rock.
The other two statements are incorrect. Soil does not remain chemically unchanged for millennia; it evolves continually under environmental influences. Also, mixing soil with decaying organic matter increases, not decreases, its fertility by enriching it with essential nutrients.
