7) topsoil
8) subsoil
9) parent material/weathered rock
10) bedrock
11) humus = the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms
12) organic layer (very top)
13) crop rotation, contour plowing, no-till farming
It washes it away. Soil erosion is caused by water or wind. Both affecting top soil. Thus washing it away.