Supercontinent: Ten Billion Years in the Life of Our Planet (4 page)

On a planet like ours, orbiting a sun that itself will one day die and bring geological time to an end, nothing is for ever. The deep time with which geologists conjure every day will – as our space explorer from Betelgeuse discovered – wipe away all traces of everything, including us. And when geological time does come to an end, the even deeper time of the cosmologist will erase all traces of everything.

Since the universe began, 13.7 billion years ago (plus or minus 0.2 billion), stars like our sun have been forming, burning and blowing up, their nuclear fusion furnaces making progressively heavier
elements
out of hydrogen, the simplest and most abundant atom. We and our rocky planet are made from substances composed of those heavy elements (carbon, oxygen, nitrogen, sulphur, iron, silicon) thanks to long-vanished stars. So even the immense lifespan of the Earth has a context in which it seems small. At this scale everything must go.

Think about what this means. Perhaps once, orbiting those lost stars that made the immortal atoms that build your body, there may have been some planets, perhaps like ours, on which there may have been life; life that may have become sentient, and that may have
developed
civilizations far beyond ours. We cannot possibly know this for sure; but there has been time, since the universe came into being, for it all to have come and gone – more than once. The only traces now left of those possible worlds may be those atoms in you, formed in the stellar explosions that banished whole histories to oblivion and wiped the slate clean. And one day, when there are no more days, that will be precisely all that’s left of us too.

But not yet. Although Earth is about 4700 million years old at the moment, it is actually a galactic youngster. The universe was already 9000 million years old when the Earth started to form from cosmic dust and debris. Earth’s lifespan is determined by the Sun, which will
engulf our world in its death throes. So not only do we know how old Earth actually is, we also know (because we understand how long it will take the Sun to exhaust its fuel) how old the Earth will get. From this we can say that our planet has passed her middle age but still has a way to go: perhaps five or six times longer than the entire period that complex life has lived on her surface.

We began with a glimpse just a little way into our planet’s (and
perhaps
our species’) future, a mere 200 million years or so, by which time the next supercontinent will have formed. Apart from giving some sense of the immensity of the time with which we will be
dealing
, I hope it illustrates another central point of the supercontinent story; and that is how building imaginary worlds stirs passions.

Imagined worlds, both past and future, embody assumptions that affect our vision of ourselves, our past and future, our identity, our prospects. As human beings, our own species and what might happen to it lies at the heart of most of our thinking. The unsettling thing about the universe is the fact that within it our existence has no importance; and the unsettling thing about science is that it reflects that. The effect has come to be called the ‘progressive dethronement’ of Man. Science attempts to find out how things really are, rather than (for example) to frame myths to explain things away while at the same time flattering our vanity by putting humans at the centre of everything. When geology rebuilds the lost worlds of nature, the assumptions it employs put no weight upon human beings’ mental comfort.

Building lost worlds, now scientifically the domain of geologists, has been with us a lot longer than geology, which as a scientific
discipline
is barely two centuries old. Lost worlds as an idea reach back to the earliest of our planet’s explorers, who speculated about
continents
that may have once existed, or might still exist, somewhere, beyond or under the sea. Wondering what lies over the horizons of the
deep oceans and deep time is no dry pursuit, through the centuries it has held the power to embody dreams, hopes and fears – of idyllic pasts and futures, of nationhood, myth and legend – even of God and divine purpose. And in the mêlée of history the two have often become confused as scientific ideas about possible ‘lost worlds’ have escaped the domain of science and taken on new life as myth.

After 1492, travellers’ tales began to feed rumours of lost continents. The great world map
Typus Orbis Terrarum
, published in Antwerp in 1570 by Abraham Ortelius (1527–98), fossilized many of these ideas into a kind of reality. As well as a host of fictitious islands in the South and North Atlantic, Ortelius depicted massive unknown
continents
covering the (then unvisited) North and South Poles. These were the first lost continents to be endorsed by something we might recognize as ‘science’. And you can’t miss them.

Ortelius was the son of an Antwerp merchant and started
illustrating
maps at the age of twenty. He was no traveller himself; he preferred the information to come to him. Dictionaries of scientific biography have traditionally been rather sniffy about the ‘uncritical’ Ortelius, because he collected all the information available to him about what people thought the world was like, and naturally much of it was wrong. Now, this fusion of the known with the asserted, the rumoured and the traditional, is precisely what is most fascinating about his ‘theatre of the world’.

‘Terra septemtrionalis incognita’
(‘Unknown northern land’) it says across the top of the map, and
‘Terra australis nondum cognita’
(‘Southern land not yet known’) across the bottom. These unknown polar lands, especially the southern one, almost dwarf the known
continents
of the world. Although
Terra australis
occupies the site of the
then undiscovered continent of Antarctica, it is very much larger. Even though it is
incognita
, Ortelius does record a few details. Facing the Cape of Good Hope, for example, he writes ‘
Psittacorum regio’
, and goes on to explain how, ‘according to the Portuguese’, this great southern continent is inhabited by giant parrots.

At one point, in a strange coincidence with geological reality, the parrot-infested
Terra australis
reaches out to touch South America at Tierra del Fuego. Antarctica was indeed once joined to South America across Drake Passage, the region of ocean floor studied by Roy Livermore. Antarctica only became today’s frozen continent about thirty million years ago when that link was broken and the
circumpolar
current (which isolates Antarctica from the heat of the world ocean) finally shut the freezer door.

Ortelius did not invent these continents from nothing. The idea of a great southern continent began life as an ancient Greek notion of a ‘counter-Earth’ ‘balancing’ the known continents of the Northern Hemisphere, and named by Hipparchos of Rhodes (190–125 BC), who coined the term ‘Antichthon’ for it. Hipparchos even speculated that Sri Lanka might represent this southern continent’s northernmost extremity, thus joining a long line of writers, from ancient Tamil poets to modern geologists, to embroil the southern extremities of the Indian subcontinent in stories of lost lands: real, imaginary and somewhere in between.

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.

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?

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
was 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.

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.