Which type of earth has the lowest resistivity?

Marsh has the lowest resistivity compared to the other types of earth mentioned. This is primarily because marshy soils are often saturated with water, which significantly enhances their conductivity. The presence of water allows for the easy movement of ions, leading to lower resistivity. In contrast, clay, sand, and rock typically have higher resistivities. Clay can retain water, but its tightly packed particles can impede the movement of ions, making its overall resistivity higher than that of marshy soil. Sand, while somewhat porous, lacks the saturation that characterizes marsh and does not conduct electricity as effectively. Similarly, rock tends to have high resistivity due to its solid structure and lack of water content. Thus, marsh stands out as the ideal option due to its wet, conductive nature.