system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do they still find ancient footprints/campfire ashes preserved after thousands of years?
gpt
Something walked in mud, mud dries hard during dry spell. Then it can get covered with more mud but the impression is still there.  Eventually it the top layers can erode away leaving the footprint.  Campfires may have been in caves or overhangs which protect from the elements.