Supercontinent: Ten Billion Years in the Life of Our Planet

by Ted Nield

  Ortelius’s great map, and the Thesaurus Geographicus that he published six years later, start us off on the story of vanished supercontinents. It is barely ten years, in fact, since historians realized that Ortelius was also the first to speculate, from the fit of the opposing shores of the Atlantic, that this ocean may have arisen by the horizontal displacement of its bordering continents. Supercontinents and continental drift were born twins.

  Not until 1994, in a paper in the British scientific journal Nature by a US historian of science, James Romm, did Ortelius finally get the credit he deserved. In the 1596 edition of his Thesaurus Geographicus Ortelius speculated about Plato’s allegorical ‘lost world’ of Atlantis, which by that time was widely regarded as a piece of true history. He went on to make two scientific breakthroughs. He noted how the opposing shores of the Atlantic were congruent, and he then speculated about how some catastrophe might have separated them. He concluded that if Plato was to be regarded as accurate history, then his work should be reinterpreted in terms of lateral dislocation of the opposing continents, rather than subsidence.

  They say the best place to hide information is in a library, and of all the books in a library the most secure are encyclopaedias. So it was that Ortelius’s insight lay buried for four centuries as a single entry in a huge, outdated and unread work of reference.

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  ICE AT THE EQUATOR

  History warns us … that it is the customary fate of new truths to begin as heresies and to end as superstitions.

  THOMAS HUXLEY, 1878

  Bouverie Street is a short and rather drab offshoot of Fleet Street in London. Number twenty-seven, which later was to become the office of a newspaper and of its editor, Charles Dickens, was originally built by William Blanford to house a small manufacturing business as well as himself and his wife. She bore him two sons, William Thomas and Henry Francis Blanford. Both became geologists and, like many others of their generation, pursued their life’s work in India, work that would lead them to make the wild surmise that Southern Hemisphere continents were once united.

  William, born in 1832, was the elder by two years. He would live twelve years longer than his younger brother, dying in 1905 covered with scientific glory: Fellow of the Royal Society and President of the Geological Society of London. And in a world obsessed with priority, it is William who is generally credited with being the first to notice the striking geological similarities between rocks of the now widely separated southern continents and draw attention to a conundrum that would puzzle geologists and biologists for the best part of a hundred years.

  As red spread over the world map, sons of England sought their fortunes – financial, military and scientific – among the Empire’s furthest reaches. And as geologists were off studying the rocks of these distant lands, a new species of biologist (the biogeographer) began mapping the distribution of animals and plants across the known world. It was not long before scientific London began to receive reports of some odd patterns that demanded explanation.

  These patterns, in the distribution of rock types, in the fossils they yielded to the hammer, and in the living things that grew above them, boiled down to two basic and very puzzling facts. Some things that were very similar to one another were being found much farther apart than their similarity would suggest possible; while other things, utterly different in character, often cropped up much closer together than their dissimilarity should demand. Every scientist who added another fact to this mounting body of evidence instinctively knew that this was important. But what was it telling them?

  King coal

  The annus mirabilis for the Blanford brothers was 1856. David Livingstone was returning triumphantly to Britain after his coast-to-coast exploration of the ‘dark continent’ of Africa. In Germany’s Neander Valley the first fossils of another species of human being, Homo neanderthalensis, were being unearthed. And in India the Blanfords were surveying coal-bearing rocks in the eastern state of Orissa.

  The brothers had arrived in India after being offered posts at the country’s nascent Geological Survey by its Superintendent, Dr Thomas Oldham. Unfortunately, Oldham had neglected to tell anyone about either appointment, so, when the Blanfords landed in the late summer of 1855, nobody in Calcutta was expecting them. Oldham was away in the field. The Survey had no offices. They were stranded.

  By one of those absurd pieces of chance that sometimes attend the fortunate traveller, amid the hurly-burly of one of the biggest cities on the planet, the hapless brothers ran into a fellow staff member of the Survey, William Theobald. There were no telegraphs and the posts were very slow, so it was December before they finally met their new boss on his return.

  The Blanfords had not wasted their time, filling the intervening months with excursions to the Raniganj coalfield and the study of Hindustani. And less than another month elapsed before Oldham dispatched them, with Theobald, on their first proper job. They were sent to examine and report on a coalfield near Talchir (Talcher), some sixty miles north-west of Cuttack, an important provincial town in Orissa.

  The Talcher coalfield, today part of a company called Mahanadi Coalfields, still boasts reserves of 35.78 billion tonnes. It feeds several local power plants operated by India’s National Thermal Power Corporation, the country’s biggest generating company. What the Blanfords found, as well as coal, was evidence that before it had been deposited, in what they presumed to be lush, steaming tropical swamps, India had apparently suffered a massive Ice Age.

  The telltale deposits lay at the base of a two-kilometre-thick series of sedimentary rocks rich in coals and plant fossils. Underneath these coal-bearing rocks lay another unit, the Talchir Formation. This consisted mostly of sandstones and shales; but at its very base, lying on top of an eroded and grooved ancient land surface, was a highly unusual deposit. Many boulders, some larger than a man, lay embedded in a matrix of fine mudstone. The curious thing about this was the coincidence of huge boulders with fine mud. No beach, river or seabed accumulates a deposit like that. Apart from volcanic mudflows (which this was not, though many in years to come would claim it was) only one known natural agent was powerful enough to have moved the boulders and yet also was capable of depositing them together with fine mud: a glacier.

  Glaciers are extremely powerful erosive agents, gouging out their U-shaped valleys and breaking up the rock walls into debris of all sizes from boulders as big as buses to rock dust as fine as flour. And when glaciers melt and retreat, all the material carried by the slowly moving river of ice is dumped together. The result is called, appropriately, boulder clay, or sometimes till. And a fossilized till, one turned into rock by age and pressure, is a tillite.

  Looking more closely at the boulders, it is possible to see scratches that also betray the action of ice, which grinds each piece of debris over its neighbour with huge force. It is also likely that many of the boulders have travelled hundreds (even thousands) of kilometres, and a careful comparison with a geological map can help you work out the direction in which the ice moved.

  But, as we shall see many times in the story of reconstructing supercontinents, it is not always easy to admit what the rocks are telling you when your mind refuses to believe it. This is what makes the Blanfords’ conjecture so amazing today. The two young men returned to Calcutta and submitted their first report to their boss. In it they said they had discovered unequivocal evidence that ice sheets once covered what is now tropical India. The intellectual toughness that this betrays is matched only by the fact that their boss appears to have believed them.

  By no means everyone was convinced. It simply seemed impossible. Even as late as 1877 the recorded discussions of a paper given to the Geological Society of London by the younger Blanford are full of disbelief. But by that time the same boulder bed had been traced beyond Talchir throughout a wide area of Bengal and the Central Provinces. By 1886, when the elder Blanford read another paper at the Society, boulders bearing those unequivocal scratches had been found. There wa
s no longer any room for serious doubt. The Blanfords had been right all along. Somehow, all those millions of years ago, there had indeed been sea-level ice at twenty degrees of latitude.

  Explaining how this could be so became no easier in the decades following the discovery. A similar boulder bed (now named the Dwyka Formation) had been discovered at the bottom of a similar succession of rocks bearing similar fossils in South Africa. Henry Blanford had already suggested that these were the same as the glacial deposits he and his brother had first seen in India. Moreover, as early as 1861, the frequently absent Mr Oldham had tentatively correlated the Talchir boulder bed with one he had seen on a visit to Australia. These, too, had cropped up all over the country, from Queensland in the north through Sydney to Wollongong in the south, and in the Blue Mountains in the west. This troublesome glaciation, which seemed impossible enough even when confined to India, now appeared to have spanned the Equator and covered half the globe.

  Further investigations were throwing up bigger questions than they were answering. Could the Earth perhaps even have tilted on its axis, as Oldham had suggested? And what was the precise age of the glaciation? The fossils of Southern Hemisphere rocks were being described bit by bit; but they were very different from the better-known fossils of the Northern Hemisphere. It was like trying to navigate by the southern stars knowing only the boreal constellations. Maybe this glaciation had coincided with one of the mass extinctions that had already been recognized in the fossil record. Was there a connection? Nobody could be sure, but everyone had an opinion about why so many similar rocks, with their identical fossils, were found so widely scattered across the continents of the Southern Hemisphere, and how a glaciation could occur at the Equator.

  Looking back at the lives of geologists from these heroic days makes one doubt that Victorians were made from the same stuff as we are. William Blanford worked for twenty-seven years in the Indian Survey, during which time he travelled and mapped widely, not only within the subcontinent but through Afghanistan and what was then Abyssinia and Persia. He retired from the Geological Survey at fifty and bought a house in Kensington. He married, settled into London’s scientific scene and began his second career.

  W. T. Blanford had already been elected a Fellow of the Royal Society in 1874. Before him now lay many years of office-bearing, not only at the Geological Society of London but also at the Royal Geographical Society and the Zoological Society of London. During his travels Blanford had noticed many things that puzzled him about the living world, and his retirement offered him the chance to complement his geological work by researching more fully the distribution of species across the subcontinent that had been the main interest of his life.

  In 1890 Blanford wrote the following words, which have since turned out to be even truer than he knew: ‘all who recognise how intimately the story of the Earth is bound up with that of its inhabitants will have little doubt that the present distribution of animals and plants is of the highest geological importance, and that the existence of particular forms of living beings in continents and islands is the result and the record of the history of those areas and of their connexions with each other [italics added].’

  Presidential addresses to the Geological Society have often been long, but few rival the fifty-four pages of the Society’s Quarterly Journal that are occupied by Blanford’s second; and few Presidents (even including that of zoological luminary Thomas Henry Huxley, exactly twenty years before) had quite the nerve to deliver one so completely non-geological. But this was probably deliberate. Geologists had to be made to take biogeography seriously.

  Grand tours

  Biogeography had come into its own as the great trading empires of the West had fanned out across the globe, taking their naturalists with them. A small army of botanizers and hunters, including many eminent scientists, set off to find, draw, paint, capture, skin, stuff and in some cases send back their captives alive for the fascination of the London public. They also returned home with new ideas, ideas that would break first on London and quickly overwhelm the world with their significance.

  Charles Darwin had his eyes opened as the gentleman-naturalist companion to the captain of the Beagle. For the man who would be his champion, the less genteel Thomas Henry Huxley, the experience was to be a spell in Her Majesty’s Navy aboard a leaky frigate called HMS Rattlesnake. As the young ship’s surgeon on his first job, Huxley was forced to inhabit a cramped berth, frequently awash, and to watch his shipmates die of injuries and fevers he had no medicine to cure. Science was feeling the spur of Empire.

  Another of the great biogeographers of the nineteenth century, Philip Lutley Sclater (1829–1913), sailed for the Americas in 1856. In the course of his travels over the next decades he was not only to cover most of the USA but also many of the continents linked geologically by those boulder beds and plant fossils (including Argentina, Australia and India) and, crucially, the lands of the Malay Archipelago. He was also the first modern scientist not only to propose but also to name a hypothetical vanished supercontinent.

  After he returned to London, Sclater’s career was worthy and long. For forty-four years he held the influential post of Secretary to the Zoological Society of London. But he made his mark as an original thinker just two years after leaving on his first great trip, by triumphantly dividing the living world into six great realms defined by distinctive assemblages of animals, realms that are still recognized today. As an ornithologist first and foremost, Sclater began with the birds, Class Aves as zoologists have it.

  His paper to the Linnean Society on birds’ global geographical distribution became an instant classic. He soon began to incorporate other animals into his scheme, and twenty years later wrote a review in the popular and influential monthly periodical Nineteenth Century in which he recounted the curious distribution patterns of the lemur.

  Lemurs are primates, grouped together broadly as Lemuriformes. They are less closely related to humans than monkeys or apes are, and much more ancient in evolutionary terms. As defined today, they are limited to Madagascar and the Comores, where they have diversified into fifty-five species and subspecies, including the mouse and dwarf lemurs, the true lemurs, sportive lemurs, the woolly lemurs and the ghostly aye-aye, the nocturnal grub-eater with one modified long finger that it uses to winkle its prey out of wood.

  At the time Sclater was writing he used a broader classification of lemurs than our modern one, including similar, related primate groups found in southern India and Sri Lanka and the scattered islands of South-East Asia. The pattern he found recalled the one geologists were puzzling over with their boulder beds and plant fossils. Lemur-like primates had a scattered distribution that didn’t make sense. One could believe, for example, that lemurs might cross the strait between Africa and Madagascar on rafts. But was it likely that these little creatures (or their common ancestors) could cross all the way to Sri Lanka and the Malay Archipelago, traversing the Equator and thousands of miles of ocean, or float there on rafts washed from distant shores?

  It was 1864 when Sclater first published his proposed solution to the problem, in a paper called ‘The Mammals of Madagascar’ in the Quarterly Journal of Science. He wrote:

  The anomalies of the Mammal fauna of Madagascar can best be explained by supposing that … a large continent occupied parts of the Atlantic and Indian Oceans … that this continent was broken up into islands, of which some have become amalgamated with … Africa, some … with what is now Asia; and that in Madagascar and the Mascarene Islands we have existing relics of this great continent, for which … I should propose the name Lemuria!

  Lemurs could not have swum between these far-distant places – they must have walked – so there must have been land.

  Sclater was not the first scientist to suggest a lost southern continent to explain biological (or geological) anomalies. Geoffroy St Hilaire (1772–1844), a French natural historian, had suggested one in the 1840s, having also noticed the peculiarities and Indian affinit
ies of Madagascar’s animals. What Sclater did, however, was give his creation life by naming it. This enabled his ‘Lemuria’ to escape from the world of science and enter common knowledge. Lemuria, a place that never really existed, began to rise to the status of an Atlantis, to enter into myth and inhabit that same strange hinterland of half-truth. By the 1880s the idea of Lemuria had become well entrenched in the literature. The ghost had entered the machine.

  Toeing the line

  Another travelling naturalist whose story intersects with ours at this point was Alfred Russel Wallace (1823–1913). Though later critical of invoking sunken continents as a way of explaining biogeographic provinces, at first he eagerly adopted Sclater’s Lemuria in his writings, believing that the giant vanished continent must have extended from ‘West Africa to Burma … South China and the Celebes’.

  Wallace is mainly remembered today for hitting upon natural selection as the driving force of evolution independently of Darwin. This is the great Welsh naturalist’s other great claim to fame. Unlike Sclater and the geologists (who noticed things that were too far apart to be so similar), Wallace’s breakthrough came when he began to notice certain animal species that were too different to be so close together.

  As you sit in a small beachside café in Padangbai, Bali, waiting for the Lombok ferry to arrive at the jetty on the southern headland, you look out at the palm-covered arms of land that enclose the bay, the fishing canoes drawn up on the sand, their great outriggers and prows painted like crocodile jaws, and you can make out your destination quite easily. Mysterious Lombok stands, densely wooded, against a pale horizon. Its classic cone shape tells you that you are looking at Mount Rinjani, Lombok’s 3727-metre volcano. In fact, though, you are looking only at its top half, and missing completely all of the southern, low-lying part of the island. It lies below the horizon, hidden by the curvature of the Earth.