The Address Book: Our Place in the Scheme of Things. Tim Radford

However assimilated one tries to be, however aware of the history, geography and romance of the new location, one remains a stranger in one’s adopted country, and at the same time one becomes a stranger in one’s place of birth. That may not present a disadvantage: people who never leave a place never really understand where they are. Those of us who change places, who migrate, perhaps get the best of both worlds. It was a commonplace of 1950s fiction that young people set off to find themselves: to find out who they really were. When you migrate, you find out who you are not; you can be at ease, and secure, and part of a community, but you also discover that you are never quite at home.

      Chapter Three

       The County A Piece of Chalk

      Underfoot, the turf is short, rabbit-bitten and studded with tiny flowers with names that read like fragments of an unassembled poem: eyebright, silverweed and bird’s-foot trefoil; wild thyme, yellow wort and scarlet pimpernel. To the right and left, nearer the woods, and standing much higher, are more wildflowers: hemp agrimony, self heal, woundwort, centaury, rosebay willow herb, wild parsnip, viper’s bugloss and thistles that smell like spilt honey. Among them flutter the butterflies: my wife, the expert, identifies comma and peacock, red admiral, large and small tortoiseshell.

      We are deep in the Cretaceous, in a shallow valley or bottom between two of the Sussex Downs, and everything about me is a lesson in the making of a county. The rock underneath our feet is a soft, porous form of calcium carbonate called chalk, and it extends into the Earth’s crust for hundreds of metres. This chalk represents ancient life: each microscopic brick in this prodigious earthwork was once a tiny little planktonic alga called a cocco-sphere that flourished in the hot, sunlit seas that marked the Cretaceous period, which lasted for about eighty million years and ended sixty-five million years ago. Creatures similar to these still live in the tropical waters, well below the surface, but within the region that light can penetrate. They still use sunlight and the weaponry of photosynthesis to build tissue by absorbing carbon dioxide dissolved in seawater; they still bloom, replicate and die, and their tiny remains still fall slowly through the darkening waters, to settle on the deep seabed and become part of the abyssal ooze that cloaks the hard basalt of the ocean floor. The remains – bones seems the wrong word, because a cocco-sphere is a little assembly of tiny scales or plates, shaped into an orb – are called coccoliths. It isn’t hard to imagine a great, warm ocean under sunny skies; it isn’t hard to imagine the light flickering diffusely through the relatively still water far beneath the waves; it isn’t hard to imagine microscopic plants slowly forming, hijacking energy from this filtered sunlight to construct themselves, molecules at a time, from material dissolved in the waters around; it isn’t hard to imagine many of them being eaten by zooplankton or consumed by fish which would in their turn be devoured by larger predators. It isn’t hard to imagine that enough would survive to die naturally, and begin the long, slow fall into the darkness below.

      It isn’t hard to imagine any of these things; it is however hard to imagine such things happening for eight, or eighteen, or eighty million years. People who tick off generations in twenty-five-year spans, who expect to die at around the time their grandchildren are ready to reproduce, who count national history in centuries, who measure the history of civilisation in millennia, simply cannot absorb the immensity of a time span measured in tens of millions of years.

      Algal plankton are not visible to the naked eye. Their mortal remains are even smaller. What kind of dusting would invisible skeletons leave on the ocean bottom, and how fast would this dust assemble? Under the pressure of more and more invisible skeletons raining down, to create at first a protective layer, and then a blanket, and then another blanket, and then the submarine equivalent of an eiderdown, and then another eiderdown, and then a mattress, at what stage would the cumulative, smothering weight finally crush the bottom-most layers of this soft, yielding bed into rock? How long would it take to make what now represents a centimetre of chalk, a cylinder of which a teacher might once have used to inscribe history on a blackboard, or in exasperation might once have thrown at an inattentive pupil (something that teachers used to do)?

      Suppose it took a thousand years to make one centimetre of this undisturbed, impacted submarine dust. In 100,000 years, there would be a metre of chalk. In a million years, there would be ten metres of chalk. The chalk of the Sussex Downs extends for five hundred metres, and nobody can possibly know how much of this chalk has already been eroded: washed or blown or scraped away by rain, wind and ice, or scoured away by advancing and receding seas. The white cliffs of Dover in Kent and the Seven Sisters of Sussex are a work in progress: in the progress of demolition rather than construction, as the Channel tides and tempestuous waves driven by seasonal gales tear away at their basements, and bring down the fabric above. But as long as they endure, the cliffs stand as testament to warm seas, sunny skies and a world occupied by strange creatures.

      The Cretaceous period was one in which there was almost no ice or snow, except on the highest mountains. Forests grew in Antarctica, and on the north slopes of Alaska. Dinosaurs grazed, hunted, reproduced and died far within the Antarctic Circle. Sea levels were far higher than today: sometimes hundreds of metres higher. The chalk exposed in the iconic white cliffs of southeastern England is only a small fraction of all the chalk there is to be found: there is chalk beneath, and occasionally exposed at the surface of, Yorkshire, and East Anglia, and France, and Germany, and much further, too. Darwin’s bulldog, Thomas Henry Huxley, in a famous essay on ‘A Piece of Chalk’, pointed out that

      it runs through Denmark and Central Europe, and extends southward to North Africa; while eastward, it appears in the Crimea and in Syria, and may be traced as far as the shores of the Sea of Aral, in Central Asia. If all the points at which true chalk occurs were circumscribed, they would lie within an irregular oval about three thousand miles in long diameter – the area of which would be as great as that of Europe, and would many times exceed that of the largest existing inland sea – the Mediterranean.

      But this vast bedrock-in-the-making, this shelf of calcareous substrate, cannot have been submerged for the whole of the Cretaceous. Below the chalk lies greensand from the same geological period, a muddy sediment that speaks of entirely different conditions: of a huge, wandering delta landscape, of marsh, meanders, oxbow lakes and seasonally flooding rivers that would dry up and exist only as trickles, built up by silt from the mountains further inland, and then occasionally swept away again as the sea invaded, leaving its signature in the form of raised beaches.

      These beds, too, extend hundreds of metres downwards: their rock is now the Weald of Kent and Sussex, and they represent a long overture, a prelude, a period of marsh and mudflat, water meadow and tidal estuary, beach, dune and delta. Through this well-watered, fertile silt stalked iguanodon and baryonyx, and above them flew pterosaurs. Elsewhere in the world, Tyrannosaurus rex was already on the prowl; ichthyosaurs and plesiosaurs hunted in the shallow seas. So the Cretaceous period is marked by episodes of high and low water, of violence and movement. The modern world had begun to take shape: the Atlantic had begun to open, and Africa had begun to close in upon what would become the Mediterranean, to start pushing up the Alps. The extended ripples of that impact would gently uplift the chalk and shape the contours that would one day become the Downs, and the sediments that would form the Weald. Western Europe might be partly or entirely submerged, but at intervals fragments of Britain and Brittany must have been visible high above the waves: Wales was a rocky island, and so was something that would one day become Cornwall. The Pennines stood proud, and there was once an East Anglian massif – yes, marvel at the mountains of Norfolk, now at sea level and sooner or later to be submerged – that towered above the submerged Wessex basin. This exposed rock was sheathed not just with the implacable green of fern and cycad and moss: it sported splashes of bright colour. Vegetation had begun to change, and with it the fauna of fields and forests.

      The ancestors of modern butterflies and moths, the first ants, the first aphids, grasshoppers and gall wasps appeared during the Cretaceous, and so did the first flowering plants. The grasses will not emerge for aeons, but petals, pistils and pollen have begun to evolve and flowering plants to speciate in precise step with a new generation of pollinators, predators and scavengers. Chalk flowers such as eyebright and scarlet pimpernel have their roots in the Cretaceous, metaphorically as well as literally, and the comma butterfly is a kind of lepidopteran punctuation mark in a long story that begins