Topsoil: This is the uppermost layer of soil which has high concentrations of organic matter and microorganisms. It's like your skin - protecting what's underneath while providing nutrients.
Sedimentation: This refers to the process by which eroded material is transported and deposited by wind, water or ice. It’s similar to how sand might collect at one end when you tilt your sandbox.
Desertification: This term describes land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors including climatic variations and human activities. It's like your sandbox becoming a desert because you've lost too much sand.