What might be a sign of heat exposure on exposed bones during a fire?

A change in color and mass is a significant indicator of heat exposure on exposed bones during a fire. When bones are subjected to high temperatures, such as those produced in a fire, their composition undergoes a transformation. This can result in hues shifting from their natural bone color to shades of gray or even black, depending on the temperature and duration of exposure. Additionally, prolonged heat exposure can lead to a reduction in mass due to the combustion of organic materials within the bone, contributing to its altered appearance.

The other options address aspects that may not accurately reflect the effects of extreme heat on bones. For example, while the development of cracks and fractures can indeed occur under certain circumstances, the primary and most observable changes from heat exposure tend to be in color and mass. The presence of soot and ash is more commonly associated with soft tissues rather than bone, and retention of the original color would suggest that the bone was not exposed to significant heat, which does not align with the scenario described.