told about while sitting sunning myself in a rooftop bar in the coastal town of Essaouira, led geologists on a huge Easter egg hunt around other Atlantic coastal countries for more basalts of the same antiquity. A series of expeditions in the 1990s found scores of outcrops - sills, dykes, flood basalt sequences - all in enormous abundance, which showed almost certainly just what had been going on a little over two hundred million years ago.
The outcrops were all over — four million square miles of lavas, covering parts of what in time would become four continents: in North America they ranged along the Appalachians from Alabama to Maine, and then well beyond up into Canada and along the shores of the Bay of Fundy; in South America they were found in Guyana, Surinam, French Guiana, and, most impressively, throughout the Amazon basin of Brazil; in southern Europe they were detected in France; and in Africa there were swarms of sills and dykes found not only in Morocco but in Algeria, Mauritania, Guinea, and Liberia. And all these puzzle pieces had alignments and ages and proximities that positively shouted their intimate geological connections and their probable common origin.
The average age of their deposition eventually came in with some accuracy: most of the basalts had been laid down or extruded or blown into the sky 201.27 million years ago, a figure computed with an error either way of only perhaps three hundred thousand years. Some discrepancy exists between the age of the basalts on what would be the eastern side of the region — in North Africa, especially — and those in what would become North America: the American basalts seem older. This discrepancy has led to an impassioned debate over whether the volcanoes led to the extinction of so much of the flora and fauna, since that massive wiping-out - when huge numbers of amphibian species vanished, leaving environmental niches perfectly suited for the arrival of scores of Jurassic dinosaur types - occurred around 199.6 million years ago. Would volcanoes, however almighty, have their principal biological effect almost two million years later? It seems a little improbable — but some laboratories are still trying to link the two events, not least because it makes for a more dramatic, and anthropomorphically comprehensible, story.
The great continent unzipped, though not like a fly on a pair of trousers. It was an inelegant, jerky process, rather like watching a camel getting to its feet, with one part of the ocean opening, then another far away, then a portion of the middle, then another section in the distance, and then back to the middle again. The first waves of water washed the shores of eastern Canada and northwest Africa as they pushed apart from each other, almost at the very beginning of the Jurassic, 195 million years ago. This was the first true moment of the Atlantic Ocean’s life.
Twenty million years on, the process of sea-floor spreading got under way in earnest, in the middle of the sea — like two unrolling carpets, or two unspooling conveyor belts running away from each other from a vague submarine midpoint. The bottom of the sea started to split open, and its two halves began to diverge, the continents on either side shifting steadily apart. West Africa shifted itself about three hundred miles away from South Carolina; Mali moved a couple of hundred miles off Florida; there was a large stretch of wide-open ocean around where the Windward Islands would eventually be, and then a gap of almost a thousand miles opened between Liberia and Venezuela. In this midsection a body of seawater as large as today’s Mediterranean was created, and yet unlike the rather stable-sized Mediterranean, this body only continued to get bigger.
By 150 million years ago, continuing a Canaveral-style countdown, Greenland5 had begun to pull away from Norway, and Iceland began to be built up from deep down in the sea. (The spectacular eruption that began in the spring of 2010 from Ey-jafjoll, an Icelandic volcano that had been quiet for the previous two centuries, and which disrupted air traffic across northern Europe with its immense swathes of high-altitude volcanic dust, is part of the process of building up. Surtsey, an entirely new island born just a few miles away in 1963, may have provided somewhat clearer evidence of the steady swelling of Iceland, but Eyjafjoll produced much more lava, even if most of it was blasted high into the sky.)
At the same time the shallow waters off the northern parts of the British Isles had deepened, and serious wave-tossed oceanic expanses now separated Ireland from Labrador. By ten million years later, Guinea, the Gambia, Senegal, and Sierra Leone had pulled relentlessly away from the coastlines of the putative Guyana, Surinam, and French Guiana, which would occupy a similar dependent position in South America. Hitherto they had been in the same place: five hundred miles of ocean now separated them.
By the early Cretaceous, 120 million years back in time, the conveyor-belt-unrolling-carpet mechanism that was now evidently driving the entire process — for there was to be no further dramatic volcanism to complicate matters - had an apparent source: the Mid-Atlantic Ridge had been formed. This linear bulge in the seabed, its centre fissured and faulted and alive with submarine volcanoes, would play a vital role for the rest of the ocean’s history. It was the place where new crustal material would be belched out of the inner earth, where the ocean floor to the east and the west of it would spread out and away, and where islands — a long string of them, the Azores, the Canaries, St. Helena, Fernando do Noronha, Tristan da Cunha, a jagged line stretching from Jan Mayen in the far north to Bouvet Island, 9,200 sea miles away to the south6 - occasionally poked their peaks above water level, only to be pushed away in their turn to end up, remote and mostly unpeopled, in the new ocean’s farther reaches.
And still the opening went on. Fifty million years more, and the north and middle portions now began to create and separate the southern coasts of Africa and South America. There was at first another sudden outbreak of volcanic activity - flood plains of basalt poured from numberless vents. But then separation began down here, too, though it is still not clear if this was connected with the volcanic spasm. And here the process did indeed look like the unzipping of a fly, and it was accomplished with similar speed. It was an opening up that rippled southwards, one coastline following hard on another. Nigeria stripped itself away from Brazil. The valleys that would one day house the Congo on one side and the Amazon on the other snapped apart. The flood basalts of the southern edge of Pangaea separated into two: on one side the enormous Etendeka Traps, which would come to lie in southern Africa — and over the edge of which the Victoria Falls now cascade - and on the other the Paraná basalts of Argentina, currently home to the sprawling spray curtains of the falls the Guarani called big waters, the Iguazu.
And then in a final protracted frenzy of tearing, all of eastern Patagonia wrenched itself away from Angola, and the flatlands that were then off Cape Horn freed themselves from their geological embrace of what is now Namibia and the South African cape, and swept away to become the foothills of the southern Andes.
This was all accomplished at a remarkable speed, for though in the north matters unfolded in a somewhat leisurely fashion, down south they raced almost breathlessly. The Atlantic coastlines that had once been welded together between the bulge of Brazil and the armpit of Africa - the apparently natural fit that led nineteenth century figures like Alfred Wegener to think out loud that continents might once have moved apart, thoughts that condemned him to live in near-universal and near-perpetual ridicule - had managed in a scant forty million years to spring five thousand miles apart from one another. The sea in these parts must have opened up at rather more than four inches a year - infinitely more rapidly than the separation that took place up in the brisk waters of the North Atlantic, and more than three times the rate at which the ocean continues to spread wider today.
And that movement has never ended. The outline of the Atlantic Ocean that we know today was fixed perhaps ten million years ago, and though to us and our cartographers it appears to have retained its boundaries, its coastlines, and its “look” ever since the days of Columbus and Vespucci and the great German map of Martin Waldseemüller that first defined it, it has been changing, subtly and slightly, all the time. Coastlines in the east continue to advance, those in the west to retreat. Things fall apart: the centre cannot hold. The Mid-Atlantic Ridge continues to disgorge untold tonnages of new ocean floor; some of it appears above the water’s surface
