Atlantic: A Vast Ocean of a Million Stories. Simon Winchester

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СКАЧАТЬ at the ages and structures of such rocks, to come up with at least an approximate sequence of events that led to the formation of today’s Atlantic Ocean and the continents that now border it.

      It is a sequence featuring the dozen or so continents and seas that have come into existence, briefly or for aeons, over the planet’s life. The lineage commences with the arrival of the world’s first continental body: a mighty, two-thousand-mile long land-mass shaped much like the silhouette of a monstrous albatross, which formed itself and hoisted itself above the boiling seas some three billion years ago. Today’s geological community has given it a suitably sonorous and memorable name: it is known, in honour of the Chaldean birthplace of Abraham, as the supercontinent of Ur.

      The remains of other ancient continents have been discovered since the finding of Ur, and they have been given names reflecting either the national pride of those living where they lie, the classical education of the explorers who discovered them, or the realities of modern global politics. They are names mostly unfamiliar beyond the sodalities of geology: Vaalbara, Kenorland, Arctica, Nena, Baltica, Rodinia, Pannotia, Laurentia. They are names that define bodies either as small as present-day Greenland, or as immense as present-day Asia. They were bodies constantly in motion, constantly changing their shape, topography, and position.

      Over immense stretches of time, during periods of scourging heat and colossal physical forces, they all shifted themselves slowly and in stately fashion around the surface skin of the planet. Sometime they collided with one another, creating what are now ancient and much-flattened mountain chains. More often than not, they broke apart in a series of slow-motion explosions, events that took millions of years to play out. The shards of their ruin then banged and ricocheted their way around the earth, reordering themselves and occasionally recombining with one another, as though the planet’s surface were covered with the pieces of some enormous jigsaw puzzle that was being operated by an unseen and none-too-bright giant. And all the while, the spaces between the continental bodies were filled with the seas — being constantly shape-shifted and divided up and redivided and configured into bodies of water that were each recognisable, from about one billion years ago, as true and proper oceans.

      By Cambrian times, some 540 million years ago, one of these oceans was starting to have a familiar look to it. When it first appeared, its shape was inconsequential - it was merely very big. But during the Ordovician period, it started to become fairly narrow, vaguely sinuous, no more than a thousand miles wide, like a great river coursing across the world from north-east to south-west. That is to say - it was in appearance not altogether unlike the North-Atlantic-to-be.

      And because it washed the shores of what would in time become the east of North America and the northwest of Europe, so this supposed Ordovician sea was given the name that it should by rights bear. It was called lapetus, for the mythical figure known by the ancient Greeks as the father of Atlas. The lapetus Ocean, long since dry, and now seen at its spectacular best in the sandstones and deepwater grey limestones in northern Newfoundland that memorialise its existence, was the precursor, the father or mother, of the true and eventual Atlantic Ocean.

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      The modern and recognisable world began to come about some 250 million years later - 250 million years ago, indeed - during the end of the Permian and the beginning of the Triassic eras. It was a process that got under way when four of the original protocontinental jigsaw pieces collided and formed themselves into the one supercontinent that has since managed to achieve wide familiarity: the great body known as Pangaea. This vast entity contained every piece of Permian real estate that then existed on the globe. Its name alone says this was one land that comprised all of the world’s land, and it was surrounded by one sea - Panthalassa - that was all of the world’s sea.

      Out of these two bodies - one water, the other land - today’s Atlantic Ocean would be made. The process began with a long era of spectacular volcanic violence, one of the planet’s most violent episodes in its entire recent history. Soon thereafter there was a mass extinction of life forms, both at sea and on the land; and then finally Pangaea started to break apart, and the new ocean started to form. The extent to which these three events were connected has been debated at length - especially over whether the vigorous volcanic activity caused both the extinction and the breakup — but these events did occur, and within relatively short order.

      The volcanic period was so comprehensively and terrifyingly violent, so generous in its extent and so profound in its consequences that it must have felt as though the entire world were ripping itself apart. A gigantic series of explosions started to cannonade around the central core of Pangaea. Thousands of mighty volcanoes, first thousands of Heclas, and then in time thousands of Krakatoas, or Etnas or Strombolis or Popocate-petls, pushed themselves up and out of the countryside and started to spew fire and magma thousands of feet into the air. A ceaseless round of unbearably huge earthquakes began to shake and shatter the planet, trending along a roughly delineated line that ran for hundreds of miles northwards and southwards, and splintering and smashing the earth for scores of miles downwards into the crust.

      Even if the immense universal continent of Pangaea had not yet broken up, it certainly had started to weaken and groan with the weight and weariness of its own long existence. The world was witnessing the beginnings of a brief and yet merciless series of spasms of tectonic mayhem that started tearing the world’s one stretch of land into pieces, from end to end.

      And water began to seep into the growing gap between the two halves of Pangaea that were beginning to form. The tiny weasel-tongue of water that laid down sediments that are found in today’s Greece turned into an almighty spigot: trillions upon trillions of tonnes of seawater started to rush inward from it and from the feeder-waters of the surrounding Panthalassan Ocean. In doing so - by beginning the process of prising apart, levering open, wielding a tectonic crowbar — this potent combination of volcanoes, earthquakes, and lots and lots of water started the making of a brand new ocean. It only opened up a crack, like a door cautiously ajar: but it was a process that would continue, and then accelerate and proceed without let-up, for scores of millions of years, right up to the present day. The resulting ocean had been paternally prefigured by the lapetus two hundred million years before. This tiny filigree of seawater that was fast rising between the newly made volcanic cliffs of what are now Nova Scotia and Morocco was the first small-scale indication of the coming birth of the Atlantic.

      • • •

      The volcanoes lasted for only a few-score thousand years (though some say as much as two million) but their pulses were so violent and the amount of magma they disgorged was so prodigious that the cliffs and mountain ranges that today stand as memorial are awesomely impressive.

      I took a family holiday in 1975 on the Canadian island of Grand Manan in New Brunswick, a short distance from where Roosevelt took his summer’s ease on Campobello. We spent happy afternoons investigating the tide pools at Southwest Head, a high cape from where only the Atlantic could be seen, misty and cold, endlessly stretching to the south. Afterwards we walked home to watch the huge Fundy tides at Seal Cove, and on the way passed by a curious assortment of pure white boulders that sat incongruously at the top of a cliff composed of sheer columns of a dark brown rock. The boulders, deposited by glaciers, were called the Flock of Sheep. But it was the brown rock below them, a columnar basalt, that has most intrigued geologists -ever since, in the late 1980s, it was realised that they were quite similar in appearance and probable age to another huge pile of basalts, in a mountain range in Morocco.

      I went to these mountains, the High Atlas, when I was researching a different aspect of this book. I had no idea then of their connection with the Grand Manan rocks, nor did I know until I started to ask around. For although Morocco is known for its Palaeozoic as well as its Jurassic and Cretaceous fossils, the Atlas mountains have large outcrops of basalt, too - layers of volcanic rocks sandwiched between the sedimentary rocks, which, it was realised by researchers in 1988, were of exactly the same age as the rocks in places like Grand Manan, in eastern СКАЧАТЬ