The Planet in a Pebble, By Jan Zalasiewicz

The very stone one kicks with one's boot will outlast Shakespeare." So laments Mr Ramsay in To the Lighthouse, whose author, Virginia Woolf, had originally plumped for Plato in the novel's manuscript. With his fascinating brief study of the aeons encapsulated in a slate pebble washed by the waves on a Welsh beach, the geologist Jan Zalasiewicz finds so much more than books in babbling brooks or sermons in stones. It is soon evident that the years between the acts of a Greek philosopher and Jacobean playwright are a mere instant.

For Zalasiewicz, who speaks so readily in terms of millions of years that for him a late-running train can never be a vexation, that pebble provides a palm-reading of the universe. Even though "the pebble, while nicely representative of the Earth's upper crust, is - along with the rest of the Earth and the inner planets - cosmically unrepresentative." Whereas the universe "is mostly hydrogen and helium", the pebble and the earth it rests on "is oxygen and silicon and iron and suchlike heavy elements".

As he elaborates, "this cosmic otherness of the pebble needs explaining. and before even that, there is the question of the ultimate origins of the atoms within our fragment of slate. For their birth has been extraordinary, and their journey has been unimaginably long".

Starship Zalasiewicz is continually illuminating as he describes, often humorously, all that found its way into the pebble, such as a scant drop of oil or hint of uranium, as the atoms coalesced and separated on the voyage out from the molten core; as the seabed changed and the continents separated.

Meanwhile, the earth gained its vital magnetic field, dependent upon that core. Its melting, due over the next billion years, means that the magnetic field, evident in the pebbles's sedimentary particles, will vanish. That will leave this planet as vulnerable to solar wind's cosmic radiation as Venus and Mars have been.

Zalasiewicz is as sympathetic to bearded Victorians as he is to our other ancestors, the plankton, whose close study by Sir Alister Hardy 50 years ago inspired much of his own enthusiam. Almost as a parenthesis, he remarks that "microbes then, as now, ruled the world". Although ever alert to climate change, he finds a certain hope for energy within the methane solidified by the sea bed's weight.

Never has Wales - even in Francis Pryor's recent hefty The Making of the British Landscape - appeared as cosmic as it does here. Not least in an ending way beyond Plato, Shakespeare and Mrs Woolf, as the sun implodes and our earth, that pebble and all, is reduced to dust borne across the universe - perhaps to come up against boots unknown.