A Crack in the Edge of the World (10 page)

Most important, the sides of this fissure are not moving away from each other—they are not spreading as they would be if this were the point of the plate junction. At least, the movement is nothing like the one that is occurring sixty miles east of this line, sixty miles closer to the capital city of Reykjavík. It is there that geophysicists now believe a spreading ridge exists—and most specifically at a place to which I had been that sixties summer. I had visited it not because of any great interest in its topography but because it was where Iceland's ancient parliament had first met more than a thousand years before.

The parliament was called the Althing, and it sat for many years, from the tenth century until the thirteenth; then Iceland entered into a treaty with Norway and for a while lost its independence. The Althing met in a natural rocky amphitheater northeast of where the present capital lies, at an old town called Thingvellir that is a shrine to all Icelandic people. The structure can be reached by traveling—as I had done—a road that runs along the western edge of a lake called Thingvallavatn. It now turns out that this road, which passes through a canyon cut through cliffs of layered basaltic rock, follows exactly the spreading center of the ridge. For the canyon is cut not by a river but by a series of faults, caused by the two sides of the canyon pulling away from each other, with the valley floor between dropping down because its supports have been stolen from it.

The cliffs on the east of the canyon are in Europe; those on the west are American. They are pulling apart at a rate of about one-tenth of an inch every year; and the floor between the cliffs—where the roadway runs today and where I drove back in 1965—is dropping at about the same rate.

This, then, is the true eastern edge of the North American Plate, and I had indeed stood there forty years before, perhaps with a foot on both it and on its Eurasian Plate neighbor, even though I didn't know it at the time. I was pleasantly intrigued when I realized that one of the world's first structures made to house the fledgling idea that later evolved into a form of rudimentary democracy had been sited, centuries ago, at the very edge of one of the world's most crucially important geological pivot points. Synchronicities between geology and
expressions of humans' physical achievements are legion, of course—roads and railways run along valleys, cities tend to be built at river crossings or by estuaries, national boundaries follow mountain chains. But few are the coincidences, so far as I know, between the underpinnings of the earth and the foundation of ideas; and I found it elegant and satisfying to imagine Iceland as a place where this seems to be true. Not least, perhaps, because of its reciprocal: that a wealth of ideas of quite another kind is being produced at the other end of the same plate, in California. Tectonic plates may have more of an effect on those who inhabit their livelier parts than anyone cares to notice.

FROM SURTSEY
we had to head west, first across the Denmark Strait to Greenland and then on down to Newfoundland. As we did so, the rocks that composed the landscape became steadily older, and the real character of the plate started, in spectacular fashion, to assert its identity and personality.

Not that this aging of the rocks was dramatically apparent at first. Our icebreaker rammed its way slowly, steadily, and very noisily across the strait, punching leads in the floes for three full days before finally emerging below the curtain wall of tall and embrasured black cliffs with which the East Greenland coast is fortified. We knew a fair amount about these cliffs, and the nunataks, the black mountains that speared through the ice cap behind. We knew they were basalt, the same fine-grained frozen lava that made up the canyon walls that rose beside Thingvellir, and we knew that they were older, though in the geological scheme of things only marginally so. Those back at Surtsey were brand-new—rocks of the entirely modern Holocene Epoch, which we had seen being fashioned before our eyes. Those in the cliffs above the Althing, on the other hand, were a little older—the simple fact of their solid existence being proof of that—by a few million years (comparing the amount of the decay products of rubidium and strontium and other once-radioactive-marker elements would easily give an accurate figure). And the rocks here in Greenland were older still—perhaps 30 million years old, maybe a little more. They were nowhere near as old as rocks in the island's center—but these were buried beneath miles of ice and for now were barely visible. The East Greenland basalts merely hinted at the age of things to come.

But the East Greenland basalts interested us for another reason, when we first went there in the mid-sixties. Back then no one could be certain that the continents were spreading apart—and only a scattering of well-connected scientists had any idea of the existence of such entities as tectonic plates—but there was, nonetheless, a widespread feeling that the continents might not always have been where they were today. At the beginning of the century Alfred Wegener had said that a phenomenon he called continental drift had occurred, and that
what we think of as a solid earth was not solid at all. These ideas, though they were for decades derided by many in the scientific establishment, were in later postwar years tempting some believers to look for evidence that might prove that Wegener was right—the continents had moved. The apparent “fit” across the Atlantic—the bulge of Brazil looking as though it might fit handily into the bight of West Africa, for example—was proving impossible to ignore. And so student expeditions galore were being sent out from sixties Britain around the world, often organized for reasons of biological or anthropological inquiry that had nothing, ostensibly, to do with the possibilities of continental movement; the expedition leaders, however, were taken aside before setting sail and politely asked if they would mind keeping a weather eye open for any compelling evidence, for any jigsaw puzzle pieces that looked as if they might fit.

The expedition that we took to the Blosseville Coast, as it was called, of East Greenland was just one such search for evidence: We were there to examine the basalts in a very specific way, to try to establish if there was indeed anything about their makeup that might suggest, conclusively, that their position had shifted in the 30 million years since they had poured and oozed and erupted out of the ground. So we spent several weeks taking core samples of the rocks, which we looked at back in the laboratories in Oxford. When we compared the direction of the magnetism in the tiny crystals of hematite, which had frozen themselves into the basalt like microscopic compasses at the very moment they were laid down, we proved, in what came to be our own private (if small)
Eureka!
moment in the affirmation of tectonic plate theory building, that the Atlantic Ocean had indeed become fifteen degrees of longitude wider at this point
*
during the 30 million years since the basalts were laid down. Greenland had moved westward during those years—whether it had shifted or drifted, been shoved or pulled, or accelerated away we could not tell. But those little
magnets told us incontrovertibly that it had moved, and the way was now left open to others to explain why.
*

There were other Greenland rocks nearby that were fascinating, too, and that remain a subject of much study still (in a way the basalts do not, as their story is now familiar to everyone in the geological community). These were located about a hundred miles farther south, close to the community of Angmagssalik: They are to be found in what is generally known as the Skaergaard Layered Igneous Intrusion, and constitute one of the more remarkable geological phenomena known.

When they were first spotted from the deck of a ship, all on board thought, seeing the horizontal layers that were such a prominent feature, that they were sediments, like sandstones, with bands showing traces of the history of the period when they were deposited. But when geologists clambered ashore they quickly discovered that the rocks were not sedimentary at all but in fact volcanic—which was shocking, to say the very least. And these volcanic rocks had the outward appearance of having been laid down, instead of having been spurted out of a volcano, which was something that had never been seen before. Fieldwork began in earnest, and eventually it was discovered that the layering had been the result of a pod, or a lens, of trapped volcanic magma having been allowed, thanks to a coincidence of unusual circumstances, to cool very slowly indeed—to cool so slowly as to allow all the heavier crystals and minerals that formed during the cooling to sink downward, and all the lighter minerals and crystals to float upward, until the moment when the rock froze, or solidified, and layers were locked into place for all eternity. There are, for example, places where crystals of chromium salts have floated down to one particular place in the pluton—the tear-shaped body of rock, a mile or so in circumference—to form a layer of chromium so solid and metallic and thick that when hit by a hammer it rings.

Geologists from the world over visit the Skaergaard—and its two sister intrusions, one known as the Stillwater, in western Montana, and the other in the bushveld in South Africa. To see it is a compulsion common to many, to be there, to marinate oneself in its millions of unsolved chemical and physical mysteries. For an igneous geologist—the kind of scientist whom I have long thought of as an inquirer into a science of an elemental purity, a figure largely unbothered by the baser concerns of commerce—there is perhaps no more hallowed a place than the Skaergaard. Reputations have been won and lost there, theories have advanced and retreated like the glaciers that spill down to the sea. To the outside world the place is little known (and it was very little known indeed back in the sixties), but today if one whispers names like Kangerlugssuaq and Basistoppen and Aputiteq and Mount Wager (named after the Oxford professor, mine for a while, who first worked on it) in certain corners of university common rooms around the world, men in beards and wearing oiled-wool sweaters and corduroys will nod knowingly and smile.
*

Curious and interesting though the Skaergaard is, its relevance to the North American Plate and, by extension, to the mechanics of the San Francisco Earthquake might seem just a little tenuous. It is not tenuous at all, however, and for two reasons.

The Skaergaard, it turns out, sits at the base of a four-mile-thick layer of basalts; during the millions of years that the Atlantic has been opening, untold trillions of cubic feet of lava have spewed from vents in what was then the center of Iceland, depositing on each spreading side layers of basalt that are miles and miles thick. But it is not quite so
important for this story to know what lies on top of the Skaergaard. More important is what the intrusion itself lies on—and it so happens that it rests on top of two layers of rock, each of which, crucially, is of much, much greater age.

It sits first on a massively thick layer of sediments, filled with fossils, that was laid down in Cretaceous times, as much as 145 million years ago. These Cretaceous sediments in turn sit on a basement of rocks—highly contorted schists and gneisses, formerly made up of an entire spectrum of more recognizable sedimentary and igneous rocks but now hopelessly contorted under the influence of intense pressure, extreme heat, and eons of time—that are so ancient that some scholars of radiochemical-dating techniques believe they are the oldest in the world. It was the rocks of the Isua Formation in West Greenland that had, until 2002, been positively dated at 3,500 million years old, thus claiming the record; the fact that more recent studies have said a group of rocks at Porpoise Cove on Hudson Bay in Canada is 350 million years older still—before that the earth seems to have been an inchoate blob of hot gases and slithery supermelt—does not make the central question posed by the rocks' existence any less relevant.

And that question is: How is it that such very old rocks lie cheek by jowl with an array of rocks of relatively recent age? What mechanism allowed the world's youngest country of any extent—which is what Iceland is—to stand directly beside an island that has within its geological suite some of the oldest rocks on the planet? How did it happen—and why, for that matter?

Ever since 1915, when the quietly charming and tragically misunderstood German Alfred Wegener—a meteorologist, an explorer, and a pipe-smoking theorist of the first water—proposed the idea that the continents had not always been where they are today, there has been a grudging familiarity abroad with five hitherto entirely unfamiliar
words: Panthalassa, Gondwanaland, the Tethys, Pangaea, and Laurasia. All of these words entered the language at Wegener's urging, though the first had been invented in the late nineteenth century by an Austrian polymath named Eduard Seuss, who thought continents floated and sank, popping up out of the abyssal dark on the command of some heavenly genie. Seuss, regarded by his supporters as an early seer of the science of geology, wrote an impenetrable four-volume book,
The Face of the Earth
, setting out his theories.

Wegener's basic notion, vaguely familiar in a back-of-the-mind kind of way today, held that there had at some stage on our planet been the one huge supercontinent, Pan-
gaea
, which was surrounded by the vast proto-sea, Pan-
thalassa
. Part of this continent then foundered or split up or in some other exotic way broke apart to leave behind an immense scattering of bodies of land, of which Gondwanaland
*
—an assemblage that contained today's India, Madagascar, Australia, southern Africa, and Patagonia—is the best known, together with a sea that surrounded the remaining continental islands and that Seuss was moved to call, after an ancient Greek sea giant, the Tethys.

This basic model has survived ever since. The birth of the plate tectonic theory has done little to dampen the enthusiasm for the story of Pangaea, and it is now reckoned with some certainty that such a supercontinent did indeed exist between about 200 and 300 million years ago. Its plates did indeed break up more or less as Wegener surmised and, in doing so, formed mountain ranges and oceans, many of which still exist today. Movement is still going on: The Atlantic widens, Australia shifts northward, plates hurtle slowly toward Alaska, the Pacific folds and buckles itself beneath California. This much is certain: Its processes are complex and its effects dramatic and often catastrophic.