Ghosts in absentia

One of the books that changed my perception of the world is The Open Sea, Part 1, by the marine biologist Sir Alister Hardy. He had set out to write one book about the sea, but found that there was so much to say about the world of the plankton that it took up a whole book (he then had to write another book about everything else). It’s now more than half a century old, and yet this hidden world remains marvellously evoked by his words, and by the antique black and white photographs and line drawings. Coming to this as a palaeontologist, it was eye-opening. I was aware that in the strata, one normally only finds the remains of those forms of life that had some hard parts to fossilize. Bones, teeth, shells—and in the case of the acritarchs, chitinozoa and graptolites, their tough organic casings and homes. I knew that there had been other soft-bodied things out there of course, but alas these don’t register often enough on the radar of the geologically programmed. So the sheer variety and exuberance of this world, revealed in those pages, took me by surprise. The remains of some of this life, within the pebble, lie somewhere within the amorphous black carbon that gives this object its dark colour, and in some of the subtle chemical signals of the rock itself. Parts of the hidden Silurian sea are beginning to be decoded from this unpromising material, and the stories emerging—fragmentary, ambiguous, tantalizing— sometimes have surprising uses. Tow a fine-mesh net behind a ship for a few minutes, as Hardy did as a working scientist, and then examine its contents with a microscope, and a small fraction of this world is revealed—enough to reveal its almost boundless diversity. There are microscopic plants, the base of the food chain: the diatoms, for instance, single-celled algae with a silica skeleton that looks like a tiny ornate hatbox; the coccolithophores, even smaller algae with a bizarre calcium carbonate skeleton made of overlapping shield-like discs, and the dinoflagellates, too.