Can a Time Capsule Outlast Geology?

A ridiculous but instructive thought experiment involving deep time, plate tectonics, erosion and the slow death of the sun

- BY PETER BRANNEN ILLUSTRATIONS BY FEDERICO TRAMONTE

STUFF IS OLD WHERE I LIVE, in greater Boston. Clapboard houses that list with age bear plaques touting the former residence of the town cordwainer or victualler. The gravestones, worn rough by New England winters, also stand crooked, bearing similarly outmoded biblical names—a Lemuel here, an Ephraim there. Old, too, are the local churches where many of these souls were commended to the great hereafter.

As for the building material that makes up these churches, well, that's a little bit older still. Roxbury puddingstone, the mottled rock quarried nearby and used for much of the old church masonry in Boston, formed 600 million years ago in violent submarine landslides off the coast of a barren volcanic microcontinent that had been rifted off Africa. This upheaval happened so long ago in the course of the perpetual wandering of continents that the whole thing took place somewhere near the South Pole. The sediments hardened to rock, then hitched a ride across a bygone ocean as part of a traveling tectonic plate before being sutured onto the rest of equatorial North America some 140 million years before the first dinosaur evolved.