Futures

The pebble is on the beach, once more, unmarked by its brief contact with human sentience. Almost unmarked. The fingerprints that it lightly bears will, however, be washed away by the next tide. It has a long future, still, but probably not as a pebble—though quite how long it remains as a pebble may well depend on human action. Not on immediate, direct human action—whether it is scooped up by a digger and converted into concrete for a sea-front esplanade, for instance, or even collected as a souvenir by some passing tourist. Either of these fates should cause only a brief deflection from its long-term future (the esplanade is, after all, only a cliff to be attacked by the elements, while beach souvenirs are soon discarded). A larger perturbation of its trajectory more probably hinges on wider human effects—but more of that anon. We might assume, first, that nature runs its course. A pebble on a beach, its natural environment, is changing all the time. Not long ago, it was part of a slab of slate in a cliff, then it briefly became an angular chunk of rock, before the waves and water smoothed it down. They are still smoothing it, wearing away at it, making it smaller. Even the contact with human hands probably removed a grain or two. A pebble has the appearance of permanence, but it is not permanent. How long does it take to wear down a pebble? This can happen astonishingly quickly. Even over a single tide, being washed backwards and forwards by every incoming wave, a pebble can become detectably lighter—by less than one tenth of one per cent, admittedly, but that weight difference can easily be measured using modern electronic scales. Over a season, on an exposed part of the coast, a pebble can lose between a third and a half of its mass. The rates will vary—on a stormy day the banging of pebbles against each other can produce distinct percussion marks on their surfaces, while on a calm day the attrition rate will drop markedly. Night and day, though, the pebble is disintegrating.