Imagine alien visitors arriving on Earth in the remote future. What evidence may they find to tell them intelligent beings once thrived here? What fragments of our cities, dams and factories may be detectable in, say, 100 million years' time? It is a simple but intriguing thought experiment that is explored, to some effect, in this neat little geological entertainment.

The crucial point, says the author, is that the remains of humanity's handiwork will be pitifully hard to discern. "Once a geological age or two has passed, there will be nothing but the odd bone or gold ring to say that we were ever here," he tells us.

Now that might seem strange. After all, we still dig up plenty of 100-million-year-old dinosaur bones today. However, those ancient animals thrived for tens of millions of years. By contrast, Homo sapiens has lasted around 100,000. By that reckoning, we are a bunch of Johnny-come-latelies.

To stress this point, the author points to the example of the Grand Canyon. "In the mile-deep chasm, the strata span 1.5 billion years. Measured on such a scale our own species span would fit into a layer just three inches thick, while our industrial record should be confined to just one-hundredth of an inch," he adds. Not much room for manoeuvre there.

The problem, adds Zalasiewicz, is that the planet's constantly shifting geology will, inevitably, crush and bury every one of our greatest creations, our skyscrapers, motorways, bridges, churches and temples. Tectonic trashing, then, is to be the fate of most of humanity's handiwork.

Not all will be lost, however. Odd clues will emerge when seismic activity will push up a slice of petrified city. "Here there will be metres-thick layers of rubble, of outlines of tunnels and pipes, of giant middens of rubble and waste." That, then, will be our legacy. It is not much of a memorial. Indeed, by contrast, Ozymandias did well with a couple of headless trunks of stone.