Supercontinent: Ten Billion Years in the Life of Our Planet

by Ted Nield

  In other words, oceans can open and close, like a carpenter’s vice, more than once. Imagine that you open a vice, put the carpenter’s lunch (cold lasagne) into it and squeeze it tight. The lunch will ooze out and up, forming a mountain chain, which we shall call the Lasagnides. You then leave it until the lasagne has gone hard before opening the vice again. By now agents of erosion – mice – have scoured the once mighty Lasagnides back to bench level; but their roots, within the vice itself, remain. If you now reopen the vice to start the process again, some of those old Lasagnide remnants will stick to one jaw and some to the other; but the vice reopens along the same basic line. That is how you get some parts of the same mountain chain in Europe and others in America.

  This is the second way to form a supercontinent; one that splits the landmass only to replace the pieces roughly where they were before. Supercontinent theorists call this introversion. Any would-be modeller of the next supercontinent faces this crucial question: will the Atlantic go on expanding and become a new ‘world ocean’ through extroversion, or will it eventually, like some tail-eating Leviathan, destroy itself by introversion? Roy sees no reason why the Atlantic should not continue to open; though other ‘preconstructions’ beg to differ, and for them the next supercontinent looks quite different from Novopangaea.

  One preconstruction of the next supercontinent, created by Professor Chris Scotese of the University of Texas at Arlington, assumes that the Atlantic will one day close again. I put this idea to Roy Livermore. ‘What Scotese is saying is that subduction is starting up in the Caribbean and the trenches of the Scotia Sea, and that these will propagate.’ It is true; although the western half of the Atlantic Ocean’s floor is welded tight to the eastern seaboards of North and South America, there are some places (in the Caribbean and between South America and Antarctica) where there is subduction. Livermore’s research centres on the Scotia Sea area, however, and he doesn’t see subduction there propagating up the eastern coast of South America. ‘There is rapid subduction in these places, but it is tending to propagate eastwards,’ he says. In fact, that eastward propagation is what makes Drake Passage resemble the pierced armour plating. What has passed between the two headlands is a narrow slice of ocean floor.

  ‘Plus, it’s still a moot point in geophysics as to how you start subduction off. How you do this at a passive margin, where the ocean crust is welded to the continent edge, is really not clear. Around the Pacific you already have well-established subduction zones that have been going on since the Permian. Why would they turn off ?’

  Livermore shifts his attention to the preconstruction he made for 100 million years hence, halfway to Novopangaea. ‘To show how continents can rift,’ he says, ‘I have taken the liberty of opening up a new rift in here …’ and his pen follows a new seaway connecting the Indian Ocean with the North Atlantic. ‘We know the East African Rift is active, so we propagate that into the future by opening a small ocean. East Africa and Madagascar have moved across the Indian Ocean to collide with Asia; Australia has already collided with South-East Asia.’ South of what is now India a mountain chain has arisen along a new subduction zone. And just south of it lies a familiar landmass, in an unfamiliar position. It is Antarctica. ‘I don’t believe Antarctica is going to stay at the pole,’ he says. ‘I want it to come north. Every other fragment of Gondwana has done that, piece by piece, and in the future Antarctica will; but only if it’s dragged north by a subduction zone.’

  Meanwhile the Pacific continues to shrink. North America and South America begin to wrap around the coasts of Asia. Australia has already collided with Japan and stuck. North America collides first, and South America sweeps around to consume the last vestiges of the Pacific and finally form Novopangaea.

  Tales of Hoffman

  Livermore is only the latest of a number of distinguished geologists to speculate about how today’s continents might eventually recombine. The first to do so was Paul Hoffman. He called his future supercontinent, an amalgam of America and Asia, Amasia.

  Much has been written about Paul Hoffman, and such accounts usually begin by remarking that he was the first on the scene. Writer and palaeontologist Richard Fortey has written: ‘If expertise is defined as knowing more and more about less and less, I am at a loss to describe what it is to know more and more about more and more, but that is the Hoffman condition.’

  One of the leading geologists of our age, Paul Hoffman is a man of whom stories are told. With his tanned, ascetic head, flashing eyes, mane of white hair and flailing, wiry arms, he has never been known to take prisoners. One geologist who has worked with him put it to me succinctly when he said, with a smile and a shake of the head: ‘Paul is one hell of a scary dude.’

  Hoffman is now Sturgis Hooper Professor of Earth Sciences at Harvard University. Much of his career, however, was spent at the Geological Survey of Canada. As one of the foremost thinkers on how plate-tectonic processes form supercontinents, and on how it might be possible to reconstruct supercontinents before Pangaea, Hoffman was also the first to write about the supercontinents of the future.

  He, like Roy Livermore, thought that the Atlantic could well continue to expand and that we might be now in the middle of a process of continental extroversion (turning Pangaea inside out). He presented his idea at the 1992 Spring Meeting of the Geological Society of America in Montreal. ‘The Americas are swinging clockwise about a pivot in NE Siberia,’ he wrote in his abstract. ‘They seem destined to fuse with the eastern margin of a coalesced Africa+Eurasia+Australasia, instituting the future supercontinent “Amasia”.’

  Hoffman used this pioneering preconstruction as a means of explaining something he believed about how supercontinents had formed and broken up in the deep past: the process of extroversion, turning old supercontinents inside out. He never published a map of Amasia, though in essence it might have looked something like Livermore’s Novopangaea. However, he did give it a name, and a good one.

  Amasia is often referred to by Earth scientists as shorthand for an extroverted resolution to the current pattern of Pangaea’s break-up; but the concept received relatively little media coverage and so never really escaped into the wider world. Not so, however, Chris Scotese’s projection, based on the opposite assumption, that the Atlantic will one day close back on itself. This creature definitely got out. And like all supercontinents whose names run amok, it has attracted the attentions of some strange and mystical colonizers.

  Pangea Ultima’s creator, Professor Chris Scotese, is a bear of a man with a big beard and a big smile. He has been involved for much of his career in reconstructing the continental positions in the past – a subject called palaeogeographic reconstruction – and in the Paleomap Project, an amiable, eccentric, homespun (and award-winning) website, www.scotese.com.

  Scotese has produced a series of palaeogeographic atlases since he was an undergraduate at the University of Illinois in Chicago. His first were published as miniature ‘flip books’ in the 1970s and computer animations in the 1970s and 1980s. While a graduate student in the University of Chicago and the Paleomagnetic Laboratory at the University of Michigan, he and his supervisors published a series of maps that uniquely combined plate tectonics, palaeomagnetism and palaeogeography. These early publications of the Paleogeographic Atlas Project were the first to illustrate, through the emerging understanding of plate tectonics, how ocean basins and continents have evolved over the past 542 million years of Earth history.

  Scotese’s work did not hit the media, however, until 2000, when the NASA publicity machine published an interview with him about his work on the Paleomap Project. Attention focused on his ideas about the next supercontinent.

  ‘We don’t really know the future, obviously,’ he told NASA science writer Patrick Barry at the time.

  All we can do is make predictions of how plate motions will continue, what new things might happen, and where it will all end up. The difficult part is the uncertainty in new behaviours. If you’re travelling o
n the highway, you can predict where you’re going to be in an hour; but if there’s an accident or you have to exit, you’re going to change direction. And we have to try to understand what causes those changes. That’s where we have to make some guesses about the far future 150 to 250 million years from now.

  Among those predictions: Africa is likely to continue its northern migration, pinching the Mediterranean closed and driving up a Himalayan-scale mountain range in southern Europe. Of that everyone seems certain. Australia is also likely to merge with the Eurasian continent. ‘Australia is moving north, and is already colliding with the southern islands of South-East Asia. If we project that motion, the left shoulder of Australia gets caught, and then Australia rotates and collides against Borneo and south China – much as India did 50 million years ago – and gets added to Asia.’

  So far Scotese’s vision works out very similar to Livermore’s and Hoffman’s. But his Pangea Ultima forms differently from Amasia or Novopangaea. Scotese believes subduction will start up on the west side of the Atlantic. The Mid-Atlantic Ridge is then eventually pulled into the Earth. The widening stops and the Atlantic begins to shrink.

  Late Permian, 258 Ma

  Paleogeographic maps by C. R. Scotese, PALEOMAP Project, University of Texas at Arlington (www.scotese.com)

  Eocene, 50 Ma

  Scotese told reporters in 2000: ‘Tens of millions of years later, the Americas would come smashing into the merged Euro-African continent, pushing up a new ridge of Himalaya-like mountains along the boundary. At that point, most of the world’s landmass would be joined.’ The result, however, is very different from Hoffman’s Amasia or Livermore’s Novopangaea. It looks like what it is: Pangaea reformed.

  Modern World

  Late Permian, Eocene and today’s world maps, showing the break-up of Pangaea according to modern research. © 2002, C. R. Scotese, Paleomap Project.

  As a result of the news coverage generated by the NASA story, the name Pangea Ultima is now out there in the wider world in a way that Amasia never was. But there is something slightly wrong with its name. Scotese has called it ‘ultima’ because, as his website proclaims, ‘it will be the last supercontinent to form’. But in reality the next supercontinent is just that. Whether Pangea Ultima, Amasia or Novopangaea, the next supercontinent will break up in turn and many other supercontinents will form again before the Earth is destroyed. Perhaps a better name might have been Pangaea Proxima.

  Long, long ago in a galaxy far, far away

  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.

  Here be parrots

  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 incog
nita, 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.