Footprints on the Moon will outlast us all

The Moon has no atmosphere. Without air there is no wind, without water there is no rain, and without either there is none of the erosion that erases every trace on Earth within a few years. That is why the Apollo astronauts' footprints are still pressed into the lunar dust, as crisp as the day they were made.

This is not a guess: NASA's LRO probe has photographed the landing sites from orbit, and in the images you can make out the descent modules, the instruments, and even the dark little trails the astronauts left as they walked back and forth.

The only thing that will wear them down is the achingly slow rain of micrometeorites, which will take millions of years to blur them. Think about it: the most durable monuments humanity has ever built are not on Earth. They are footprints.