Lava tubes on the moon, thought to have been created some 3.5 billion years ago, are undisturbed by geologic process, Kokh explains. For storage purposes, they represent the ultimate cool, dry place.

"They offer the most, if not only, safe place in the entire solar system to archive all the records of human civilization and culture where we can be confident they will be safe and undisturbed for hundreds of millions of years to come," Kokh told SPACE.com.

While saying he is "not one who believes the universe is crowded with intelligent civilizations," Kokh does figure there must be some smart beings out there. And if those beings ever visited Earth, perhaps long ago, and were looking for a place to leave a note, a lunar cave would have been the intelligent choice.

"These [lava tubes} have integrity over billions and billions of years," he said. On Earth, nothing lasts in the face of weather and geologic processes.

In addition to records about their own civilization, Kokh wonders if intelligent visitors might have left a record of Earth as they found it, "an enormous encyclopedia about ourselves that no amount of scholarship and research could ever reveal."

If members of the Artemis Society had their way, we'd find out. The organization promotes establishing a permanent, self-supporting exploration base on the moon, from which a human colony would ultimately develop.