The correct answer is option 2: Sedimentary rock.

Sedimentary rocks are formed from the accumulation and compaction of particles such as sand, clay, and organic matter. Over time, these particles settle and are cemented together, forming sedimentary rock layers. These rocks can then weather and erode, contributing to the creation of upper soil.

Option 1, Igneous rock, is incorrect. Igneous rock is formed from the solidification of magma or lava and does not directly contribute to the formation of upper soil.

Option 3, Metamorphic rock, is also incorrect. Metamorphic rock is formed from the transformation of existing rock types due to high heat and pressure. While it can indirectly contribute to the formation of soil through weathering and erosion, it is not the primary source of upper soil.

Option 4, Biological degradation, is also incorrect. Although organic matter can contribute to the formation of soil, it is not the significant quantity in the formation of upper soil.