When Martin Kunze was 13, he was on vacation with his parents in Spain, and at a beach next to the Mediterranean, did what kids sometimes do out of curiosity and boredom while their parents apply sunscreen and read and kibitz about the other tourists: He started digging a hole in the sand. The process intrigued him. About two feet down, fresh water started filling the hole from underneath. There was a plastic bottle his parents had brought with them, and on a childish lark, Martin took a piece of newspaper and jotted his name, number, and address on it in German with a message: If you find this, please contact me. “I put this into the bottle, and put it into the ground, hoping that some beautiful girl would find it in the next year,” Martin says.

He waited and waited. “I never forgot this,” he says. Years passed, then decades. No beautiful girl called out of the blue. Then, something astonishing happened. Three years ago, more than 30 years after Martin had buried the bottle, a dog-walking retiree from the area, after having the note translated for him, contacted Martin's parents, who were still at the same scribbled address, saying he'd found the bottle and read the note inside.

Martin, who is now 50, says it was probably the bottle's vintage and shape that helped it get found. What amazed Martin, though, was that someone had taken the time and effort to call after all those years, because of the jottings on a scrap of newspaper. It was all so simple, really, a naive impulse on a beach, a missive fired from the past to the future, and now from the future back to the past. And for Martin Kunze, who'd by then gone from being a scrappy boy with a curious mind to a shaggy university student with a passion for ceramics to a middle-aged father of five kids whose urgent mission these days has become the construction of an enormous time capsule meant to survive for thousands of years, it was also affirming. He had imagined a beautiful girl, and the pensioner from Spain had imagined someone on the other end of the message, too. Who was the sender, and the receiver, and what was each looking for?

“Some communication through time,” says Martin now, “some kind of contact.”

If you were to build your own time capsule, what would you want people—or alien beings—a million years from now to know about us? That we were loving, or warmongering, or dopes strung out on memes and viral videos? That we flew to the moon and made great art, ate Cinnabons (that we measured at 880 astonishing calories), and committed atrocities? How could you begin to represent these times, as lived by nearly 8 billion people? And what would give you, of all people, the right to tell the story?

After these questions would come another wave of more logistical ones. Assuming the capsule was found, how would it be translated into the language of the future, whatever that language might be? And what materials could be employed that might last that long? And how could you lead a future race of beings to the capsule itself, assuming our planet might be buried under ice or oceans of red sand by then?

It's this very vision of an earth one million years from now that changed Martin Kunze's life forever. About ten years ago, he read a book called The World Without Us, by Alan Weisman, a thought experiment in how quickly things on our planet will deteriorate once humans have been eradicated. Weisman imagines New York City's Lexington Avenue as a sudden river, unmanaged petrochemical plants spewing toxins like Roman candles, then with the passage of real time, neighborhoods becoming overgrown wildlands and houses moldering beam by beam until eventually there's nothing but the incoherent ruin of us left behind: the flooded Chunnel, the slow erosion of Mount Rushmore, all of our horrific plastic nurdles swimming the seas. Most importantly, the book points out that ceramics, which are not unlike fossils, stand the greatest chance of living on as they already have from previous ancient civilizations.