The ride, through mountain passes and the contorted passages through vales of rock, was spectacular. But then the landscape flattened to a desert, populated by what the old Afrikaners called fynbos, a mixed, complex flora of shrubs and bushes. It was spring, here in the southern hemisphere, and the desert — sheltered by its encircling mountains from the acid rain and climate shifts suffered by most of the world’s land masses — was putting on a show, red white and yellow flowers of every shape.

At last, though, even the fynbos submitted to the logic of the climate, and only aloe and cacti relieved the panorama of rocks and sky.

At a village called Touws River — abandoned now — they came upon the first Karroo rocks: squat black mudstones, sitting atop the younger Cape sands. Henry knew that the mudstones had been dumped from icebergs, floating on the surface of the polar ocean that had once covered this land, an ocean four hundred million years gone.

Jane stared out the window, with that mix of patience and intelligent interest that had always characterized her, and the low, smoky sun picked out her old melanoma scars.

Ten years. And still, every day they were granted seemed like a bonus to him, a new gift.

Henry drove on, and the rock grew more complex.

In a lifetime of geology Henry had never been here before, to this high-veldt plateau that covered two-thirds of South Africa. It was a large, empty place, devoid of human history, unpopulated save for a few scattered towns and farms — most of them abandoned now — crossed only by the immense road between Cape Town and Johannesburg. But to geologists and palaeontologists this land of sandstones and shales, piled up into the tablelands the Afrikaners called koppies, was one of the Earth’s greatest storehouses: a thousand-mile slab of sedimentary rock that was the best record on Earth of land-animal evolution.

The Karroo had always been, for Henry, a place for the future, to visit before he got too old, or died. Now he was forty-five, though he felt a lot older, but the future was self-evidently running out.

So here he was, before it was too late.

They stopped near a large koppie, and clambered stiffly out of the car. It was still morning, and the air was blessedly cool; Henry found himself surrounded by cactus and aloe and wild flowers.

Henry and Jane didn’t speak; their routine, working together, was long enough established by now.

Henry shucked off his antique Air Jordan trainers and pulled on his heavy field boots. He smeared sunblock on the exposed flesh of his arms, legs and face. He donned his broad-brimmed hat, pulled on his oxy-resp and dust and humidity filters — his spacesuit, as he thought of it — and he attached his digital Kodak to his chest bracket.