Why does soil erosion matter?

Question: 

What is soil erosion and why does it matter?

Answer: 

Soil erosion is the movement of soil particles down and from sloping land. These moving soil particles reduce soil productivity and degrade water quality.  Soil erosion thins and can completely remove topsoil, the soil layer richest in organic matter and plant nutrient concentration. These lost nutrients must be replaced for crop production purposes, adding extra cost in addition to lost crop yield potential.