Atlantic (5 page)

At first this land was represented by little more than the appearance of countless huge supervolcanoes, each separated from the other so that their clusterings might have looked from the air like the chimneys of a planet-sized industrial complex, giant marine mountains that belched out choking clouds of smoke and spewed thousand-mile-long puddles of thick black lava. Eventually these isolated volcanoes managed to vomit out so much new rock that they started to coalesce, and some of these coagulating masses became more or less stable, such that they could be thought of in aggregate as
landmasses.
Some long while later, these landmasses formed into even larger bodies of land that could fairly be described as
protocontinents.
And thus did the defining present-day characteristic of our planet—an entity formed of continents and seas—have its beginnings, although the process of reaching a configuration that looked anything like today’s world was infinitely slow and involved a fantastic complexity. The making and unmaking of a multidimensional topography is only now beginning to be understood.

The earth in its early days may have been both water and land, but it was a scalding and wretched place. It spun on its axis much more rapidly than today: once every five hours the sun would rise, though had any inhabitants been around they would not likely have seen it through the vast clouds of ash and smoke and fire and noxious gas. If the skies ever cleared, the planet below would have been scourged by unfiltered pulses of ultraviolet radiation and gamma rays, making the surface hostile to almost everything. And the newly made moon was still so close that each time it swept around in orbit, it raised great acid tides that would inundate and further corrode such continents as existed.

But some continents most certainly did exist. Today’s geological record contains the relict remains of half a dozen or so identifiable former bodies mighty enough to be as continents. Their remains have been dispersed by billions of years of planetary restlessness: no longer is any one of these early bodies intact. All that is left is a collection of stratal shards and sunderings that can be dated from at least three billion years ago, and which are now scattered to places as otherwise unconnected as present-day Australia (where parts of this earliest of continents are to be found) and Madagascar, Sri Lanka, South Africa, Antarctica, and India.

The detective work needed to piece together the original continents is prodigiously difficult. Yet it has become possible, by looking carefully 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 landmass 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 honor 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 recognizable, 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 northeast to southwest. 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 Iapetus, for the mythical figure known by the ancient Greeks as the father of Atlas. The Iapetus Ocean, long since dry, and now seen at its spectacular best in the sandstones and deepwater gray limestones in northern Newfoundland that memorialize its existence, was the precursor, the father or mother, of the true and eventual Atlantic Ocean.

•  •  •

The modern and recognizable 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 Popocatépetls, 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 northward and southward, and splintering and smashing the earth for scores of miles downward into the crust.

Some 195 million years ago,
Pangaea
began to break up, and the first tonguelike extension of the Panthalassan Ocean (center) began to seep into the narrow but widening gap between America and Europe, and in time between Africa and South America too. The Atlantic was being born: it would exist for 440 million more years.

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 tons 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 prying 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 opened up only a crack, like a door cautiously ajar: but this 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 Iapetus 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 vacation 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. Afterward 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 realized 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 Paleozoic 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 realized by researchers in 1988, were of exactly the same age as the rocks in places like Grand Manan, in eastern Canada. This discovery, which I was 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, dikes, 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 dikes 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.