Which type of evidence is primarily physical in nature?

The choice of footprints left in the ground as the correct answer highlights the essence of physical evidence in search and rescue scenarios. Physical evidence refers to tangible, observable items that can be analyzed and measured. Footprints provide crucial information, such as the direction a person was heading, their weight, and sometimes even specific details about their footwear, which can help searchers determine the lost person's identity and movements.

In contrast, eyewitness accounts, although valuable, are subjective and rely on individuals’ memories and perceptions, which can vary widely in accuracy. Documented behaviors of the lost person and environmental changes are more abstract; they may provide context but do not involve definitive physical items that can be directly observed or analyzed. Thus, footprints exemplify physical evidence by being concrete indicators of past presence and activity in an area, making them invaluable in SAR operations.