He buckled on the old leather of his field gear and picked up his hammer and chisel, all of it worn smooth by hundreds of days of sun and rain.

The familiar ritual, which for Henry long predated the coming of the Moonseed, was a great comfort to him. It was a prelude to the greatest pleasure of his working life, which was field work. The nature and objectives of the work had changed, but the pleasure he took in it hadn’t.

Jane knew him well enough now to let him be, to relish this moment.

So he walked into the desert, looking for fossils.

The ground was full of so much detail it would be easy to miss the fossils; the trick was to train the eye and brain to filter out the noise and pick out the key signs. But right now, he didn’t know what those signs would be. Bones, of course, but would they be white or black? Crushed or whole? In the sandstone, river bed deposits, or the shale, silt and mud deposited by ancient floods, now metamorphosed to rock?

It took a half-hour before he began to see them: fragments of bone, protruding from the rock. He recorded their location with the Kodak; the camera was tied into the GPS satellites so the location and context of the specimens were stamped on their images. He scooped up the fragments, unceremoniously, and stuffed them in a sample bag.

As the day wore on, and his eye grew practised, he found more impressive samples. Bones of ancient amphibians, two hundred and fifty million years dead. The tiny skeletons of two burrowing proto-mammals, his earliest ancestors, white and delicate, embedded in a dark silty matrix. Here, peering ghoulishly out of a layer of flat sediment, was the skull of a dicynodont, a low-slung, pig-like animal a couple of feet long, covered with fur and sprouting impressive tusks.

He tried to imagine what it must have been like here, a quarter of a billion years ago.

But right now there was no time to study, classify, identify, deduce. For now, all Henry could do was to collect the raw data.

Geology and palaeontology had always been a race against the predations of weathering and human expansion.

As Earth’s upper layers wore away, ancient bones were exposed, removed from their quarter-billion-year storage, and, in a relative flash, eroded or frost-cracked to dust. Humans could only hope to collect a handful of these ancient treasures before they evaporated like dew.

Now, of course, that time pressure had gotten a lot worse.

He came at last to a new layer of rock, a coarse brown sandstone which overlay the black shales below.

The upper bed was almost devoid of fossils.