What is the minimum depth required to identify new parent material when assessing lithology?

To identify new parent material when assessing lithology, the minimum depth required is 25 cm. This depth ensures that the soil profile penetrates sufficiently deep to observe significant changes in material properties. At this depth, you can clearly differentiate between the existing soil materials and any underlying parent materials that may influence the soil's characteristics.

In soil assessment, understanding the lithology, or the physical and chemical properties of the parent material, is crucial for soil classification and interpretation. This depth allows for an adequate assessment of changes that can indicate a shift in the material, which is essential for accurate soil analysis and management. Observations made at shallower depths may not capture the complete picture of the soil's development and composition.

The other options, while they represent varying depths, do not provide the minimal threshold required for a reliable identification of new parent material in terms of accepted soil assessment practices.