Supercontinent: Ten Billion Years in the Life of Our Planet (18 page)

When the geophysical evidence finally came, much of it was derived from the ocean basins, where nearly everyone had always thought the answers about continental drift would eventually be found, and where
geophysicists such as Tanya Atwater and others eventually found it. Particularly fruitful was a technique that used sensitive ship-borne instruments to map out the magnetization of the ocean bottom. These surveys discovered that the ocean floor is magnetized in stripes created by rocks of either normal or reversed magnetic polarity. In the mid-1960s it came to be realized that this pattern was created when basalt lava, erupting at the mid-ocean ridges where ocean floor is made, became magnetized according to the prevailing magnetic field. Then, as the ocean floor moved away on either side of the spreading centre, new lavas welled up to take their place.

When, as it sometimes does, the Earth’s magnetic field flipped and the north magnetic pole sat at the south geographic pole, all
subsequent
lavas would then be magnetized in the ‘reversed’ sense – until the field decided (for reasons that are even today not fully
understood
) to flip back. Ocean floor, which was oldest near the continents and youngest near the mid-ocean ridges, acted like a recording tape, setting in stone the history of magnetic reversals that had happened since the ocean basin began opening, and creating two ‘bar code’
patterns
of ridge-parallel magnetic stripes, one the exact mirror image of the other.

Ship-time is notoriously expensive, and once again it was war that provided the rationale for oceanic magnetic surveying. The reason was simple enough. If you want to detect submarines using
magnetometers
, you need to see them against a known background. As that research was just beginning, Henno Martin and Hermann Korn would listen to their radio, powered by a truck battery charged by a wind-powered generator, passing the long desert evenings making biltong by their campfire. Martial music and disturbing news from Berlin were a constant reminder of what they were escaping; and long into the night they wondered about the fate of humanity.

It must have seemed odd to Martin to see the drift theory, which he and Korn’s researches had long supported, finally receiving its
geophysical
blessing as a result of research that would never have been carried out had it not been for the very thing that brought humanity its darkest hour. The uncomfortable truth remains that, while science should never be taken as a reason to indulge in it, nothing in human history has done more to improve our understanding of the past and future of our planet than fear of our fellow beings.

Although science is a supercontinent and its citizens participate in a collective enterprise, it remains a human enterprise, subject to most of the faults to which humans fall victim. For this reason the desire to honour heroes is probably as strong among scientists as it is among generals and admirals; but the nature of the enterprise makes it more difficult, even when the motives are entirely blameless.

Science mostly honours heroes out of a genuine sense of
admiration
and respect, and two kinds of scientific advance tend to get names attached to them. Most are grand hypotheses, but some are objective discoveries, the equivalent of new mountains or other
features
of the landscape. These objective discoveries are easier to deal with (though politically no less fraught). There is no mistaking Mount Darwin, for example, in Tierra del Fuego, Chile, which received its name on 12 February 1834 from Captain Fitzroy, the
captain
of HMS
Beagle
, in honour of the expedition naturalist’s twenty-fifth birthday.

Darwin’s theory of evolution by natural selection, however, is often referred to in the twin names of Darwin and Wallace, to give credit to Alfred Russel Wallace, who sketched the same idea (and, crucially, the driving mechanism) in February 1858, the year before Darwin published
The Origin of Species.
Wallace was seized by the same idea as Darwin while recovering from a malarial attack in a beach hut at Dodinga, on the almost unexplored island of Gololo (Halmahera) in the Moluccas. The enforced rest gave him the respite from collecting that he needed for more theoretical thoughts. Darwin, meanwhile, had been most of the time at home in Kent since returning to England from the
Beagle
voyage, wrestling with natural selection, and how to present it to the world, for the best part of two decades.

Scientists usually mean nothing but well by seeking to honour their heroes, yet this will to elect them to the pantheon of the gods so often embroils everyone in acrimonious, futile disputes that an impartial observer may reasonably wonder why the habit persists. As we shall have more to say about the chemical elements later, let us take this example from the world of chemistry, where there is no greater honour than to have one of them named after you.

In 1997 a long-running and acrimonious dispute over the naming of the element seaborgium (atomic number 106) came to an end. It was the first time an element had been named for a living scientist (Nobel Prize-winner Glenn T. Seaborg, co-discoverer of plutonium). The naming of elements and other chemical substances is the job of a body called the International Union of Pure and Applied Chemistry (IUPAC), of which all national chemical societies around the world are members. Each member state pays its dues according to a complex formula, and the nation that paid most to IUPAC was the USA. It
was from this quarter that pressure to name element 106 after Glenn Seaborg, Professor of Chemistry at the University of California at Berkeley, principally came.

The US lobby held that a venerable IUPAC rule banning the naming of elements after living scientists had already been broken in the case of einsteinium (element 99), discovered in 1952 in the debris of the thermonuclear explosion at Eniwetok Atoll. It is probably true that IUPAC would have fallen over itself to name an element after ‘the world’s greatest scientist’, rules or no rules. However, as IUPAC pointed out, the finding was not published until 1955, by which time the great sage had died. So there was no precedent.

Considering the case for ‘seaborgium’ dismissed, IUPAC proposed that element 106 be named for Ernest Rutherford. Rutherford was the New Zealander who (with others) worked out the structure of the atom and the nature of the various radioactive emissions and who was also the first to realize that radioactive decay could be used to
determine
the age of the Earth. But the Americans kept up their pressure.

In the end, by virtue of its enormous financial clout, the USA got its way over element 106, which officially became seaborgium in 1997 and Seaborg lived a further two years to savour the crowning triumph of his career.

If naming
things
can cause such problems, it is easy to imagine the difficulties associated with the attribution of
ideas
. Almost every idea has occurred before to someone else, and often long ago, when nobody realized how important it was (like the mapmaker Ortelius and
continental
drift). To take another example: geology’s central doctrine of uniformitarianism, which allows geologists to interpret the past by
reference
to the processes going on around us today, is usually said to have arisen in the late eighteenth century with the Scots geologist James Hutton. However, it could be said to have been around since at least 55
BC
, when the philosopher-poet Lucretius wrote: ‘the movement
of atoms today is no different from what it was in bygone ages, and always will be. Things that have regularly come into being will continue to come into being in the same manner; they will be and grow and flourish so far as each is allowed by the laws of nature.’

And as for atoms, they go back all the way to Epicurus (341–270
BC
), whose school helped lay the intellectual foundations for modern science. If you read original sources, you soon discover that in fact nearly all science’s relevant ideas have been there right from the
beginning
, like jigsaw pieces waiting for someone to see where they fit.

As we shall see, geologists soon came to grasp the idea of
supercontinents
older than Pangaea, ones that broke up and re-formed, again and again, deep in Earth history. Finding a scientist after whom to name the Supercontinent Cycle shows how hard it is to single out
individuals
for honours in science’s cooperative venture. We shall attempt the choice from three men, in reverse chronological order of their entry into the story: John Tuzo Wilson, John Sutton and John Joly.

All through van der Gracht’s volume of proceedings from his New York symposium, Wegener’s critics make one point constantly. If ‘a Pangaea’ really had existed, why did it wait so long before breaking up? Rollin T. Chamberlin of the University of Chicago asked: ‘What was happening throughout most of geological time? Why did the
continents
remain coalesced only to become fragmented very recently?’ David White of the US National Research Council agreed: ‘How could it happen that conditions favouring the sliding of the continents to the four corners of the earth did not come about until, geologically speaking, almost yesterday?’ Joseph Singewald of Johns Hopkins University pointed out: ‘The forces called upon by Wegener were operative in pre-Carboniferous time, as in post-Carboniferous time.’
Why then should they only have become effective right at the end of our planet’s long life story?

In his lengthy summing-up, the symposium’s convener nailed this point right away. There was a logical flaw in the argument, he said. Wegener did not talk about any continental drift that may have
happened
before Pangaea formed because ‘the relevant facts are too little known’. It was not legitimate to infer that continental drift had not operated before Pangaea just because the theory’s author had not chosen to address the issue.

Touché
… But what may have begun as the response of a
quick-witted
lawyer on behalf of his absent client soon took on the form of a crucial scientific idea, another truly wild surmise. Perhaps supercontinents were indeed, like so much else in nature, cyclic. Even in van der Gracht’s symposium, one of the very earliest records of a public discussion of drift theory, geologists were hinting at previous phases of continental drift
before
Pangaea. Wegener’s book had set out the story of only the most recent episode in a process that perhaps stretched back into the depths of geological time. Drift did not need to be a mysterious one-off, incompatible with uniformitarianism and endlessly repeating histories.

Let us return for a moment to the carpenter’s bench, and the way the lasagne that was squeezed in the vice to create the mountain range we called the Lasagnides stuck partly to both jaws when the vice was reopened. What would happen next? The answer of course is that new sediments will accumulate in the gap of the open vice (perhaps, on this occasion, a helping of
melanzane parmigiana
), which then become squeezed in turn to create a new range of mountains, the Melanzanides, sitting in roughly the same orientation as its predecessors.

The spatial coincidence of old and new mountain ranges, noted by Swiss geologist Emile Argand as early as 1824, is readily explained in modern, plate-tectonic terms of continental blocks splitting apart again along the sutures that were created when they last collided. And so it was that, as the era of plate tectonics was just dawning, the cyclic nature of continental rifting, oceanic expansion, followed by
subduction
and contraction and finally collision and mountain building, was explained by one of the greatest geologists of the
twentieth
(and perhaps of any) century, the ‘benign cyclone’, John Tuzo Wilson (1908–93) of the University of Toronto.

In some Huguenot history of geology, pride of place would have to be conceded to Alex du Toit, but ‘Tuzo’would run him a close second. He was born in Ottawa to John Wilson, a Scottish engineer, and an adventurous mountaineering woman called Henrietta Tuzo, whose ancestors had crossed the Atlantic and landed in Virginia at about the same time as du Toit’s people had been heading south.

Tuzo was one of those charismatic, larger-than-life people whose entry into a room caused heads to turn and conversations to stop. Your eyes went to him; you felt your spirits lifting. His school in Ottawa had made him head boy, and he kept the position for the rest of his life. With his resonant voice he compelled your attention and persuaded you – often against your will – that he was not only right about this but also pretty much right about everything (which, by and large, he was). A positive man, not given to regrets, he would have been brilliant, you felt, at whatever career he had followed, especially, perhaps, politics; and as though to show off his wide-ranging facility, he was also a published expert on antique Chinese porcelain. But global tectonics was his passion, and the plate-tectonic revolution was made for him. It was also very largely made
by
him.

Tuzo had not always been right. Originally a devotee of the
contracting
-Earth hypothesis, he became a convert to drift as he was
entering his fifties (by which time he had been Professor of Geophysics at the University of Toronto for a decade). Swiftly
recanting
his former views, Tuzo saw the way the Earth’s mountain belts were often superimposed upon one another, and set about explaining it in terms of plate tectonics. In a classic paper published in
Nature
in 1966 and titled ‘Did the Atlantic close and then re-open?’ he addressed the coincidence of the modern Atlantic with two mountain ranges called the Caledonides in Europe and the Appalachians in the USA. It was the very first time the new plate tectonics had been extended back to the pre-Pangaean Earth.  

These two mountain ranges are really one and the same – except that they are now separated by the Atlantic Ocean, which cut the range in two at a low angle when it opened between them. At one time the two belts had been joined, end to end, Caledonides in the north, Appalachians in the south; and the collision that had created them was one event among many that built the supercontinent Pangaea. Indeed, the matching of the now separated halves of this once-mighty chain provided Wegener with one of his key ‘proofs’ – part of his
geological
matching of opposing Atlantic shores.  

As van der Gracht pointed out on his behalf, Wegener did not
speculate
about how his Pangaea had come together. But as the new plate tectonics emerged from studies of the ocean floor and began to revitalize drift theory, the time was ripe to see the break-up of Pangaea as part of a bigger process. Professor Kevin Burke of the University of Houston, Texas, recalls that on 12 April 1968 in Philadelphia, at a meeting titled ‘Gondwanaland Revisited’ at the Philadelphia Academy of Sciences, Wilson told his audience how a map of the world showed you oceans opening in some places and
closing
in others. Burke recalls: ‘He therefore suggested that, because the ocean basins make up the largest areas on the Earth’s surface, it would be appropriate to interpret Earth history in terms of the life cycles of
the opening and closing of the ocean basins … In effect he said: for times before the present oceans existed, we cannot do plate tectonics. Instead, we must consider the life cycles of the ocean basins.’ This key insight had by then already provided Wilson with the answer to an abiding puzzle in the rocks from either side of the modern Atlantic.

Nothing pleased Tuzo more than a grand, overarching framework that made sense of those awkward facts that get thrown aside because they don’t fit – ideas that philosopher William James dubbed the ‘unclassified residuum’. Geologists had been aware since 1889 that within the rocks forming the Caledonian and Appalachian
mountains
– that is, rocks dating from the early Cambrian to about the middle Ordovician (from 542 to 470 million years ago) – were fossils that fell into two clearly different groups or ‘assemblages’. This was especially true for fossils of those animals that in life never travelled far, but lived fixed to, or grubbing around in, the seabed. By analogy with modern zoology, the two assemblages represented two different faunal realms, just like those first described on the modern Earth by Philip Lutley Sclater and Alfred Russel Wallace.