Final answer:
The changes that happened to the features on some faces can refer to a variety of processes, such as aging, natural weathering, or technological reinterpretations that alter our perception of these features.
Step-by-step explanation:
In the provided texts, these changes are discussed about different phenomena: the discoloration and tan lines on a masked figure's face, the highly debated 'Face on Mars' observed in NASA's Viking mission photographs, varying facial features on death masks, the weathering and loss of paint on ancient marble figures, and a literary reference to a facial mark. For example, the re-examination of the 'Face on Mars' with higher resolution imaging disproved earlier interpretations of a 'face' and showed natural geological formations instead. Similarly, traces of paint on marble figures indicate that they had once been painted to give features like eyes, mouths, and hair, which have since faded or worn away.