Final answer:
A ground rod in perpetually moist earth has low resistance due to the ease of ion movement in the moist medium, resulting in decreased resistance.
Step-by-step explanation:
A ground rod that penetrates perpetually moist earth will have a fairly low resistance. Soil moisture is a key factor that affects electrical conductivity. In an environment where the soil is perpetually moist, ions which carry electric charges can move more easily through the medium. This results in a slight decrease in resistance. By comparison, do note that resistances can range significantly based on the material and conditions. For instance, specific insulators can have very high resistances, and materials like copper have very low resistances. Additionally, superconductors are capable of having no resistance at all.