Supercontinent: Ten Billion Years in the Life of Our Planet

BOOK: Supercontinent: Ten Billion Years in the Life of Our Planet
10.79Mb size Format: txt, pdf, ePub
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‘The four dimensional complexities of our happy little planet – “earth’s immeasurable surprise” – are made elegantly accessible by Ted Nield in this truly exceptional book. At least until the next major discovery it deserves to become the standard work, ideal for students of the subject, and hugely enjoyable to those for whom the world remains an
unfathomable
enigma’ Simon Winchester

 

 

‘Ted Nield tells the fascinating story of how the world has been made – and re-made – through billions of years of geological time. Geology underpins everything, yet the history of the continents on which we live has remained almost neglected. Nield has put this right with his
imaginative
and dynamic account of the movements of plates, and the assembly of the familiar world from an unfamiliar past’ Richard Fortey

 

 

‘As a geologist turned science journalist, editor and provocative blogger, Ted Nield has a complex view of life and science. His skills as a writer successfully convey in
Supercontinent
the recent exciting work in
grand-scale
geoscience … To handle it without oversimplification or getting lost in a maze of detail is no small accomplishment. I know of no other attempt to reduce the complexities of the relevant primary literature to the confines of a single popular-science book’
Nature

 

 

‘Entrenched in daily life, we all crave a little perspective: in
Supercontinent
we find more than a little, as Ted Nield takes us into the vistas of “deep time”’
Financial Times

 

 

‘Both informative and entertaining. He has thought well outside the
academic
box, touching on a huge diversity of topics … lively and stimulating’
Science

SUPERCONTINENT

Ten Billion Years in the Life of Our Planet

TED NIELD

 
 

GRANTA

The mind must believe in the existence of a law, and yet have a mystery to move about in.

JAMES CLERK MAXWELL

 
ACKNOWLEDGEMENTS
 
 

For particular help with this book and with previous writings of mine that have contributed to it, I gladly acknowledge the following
persons
(who are, of course, in no way responsible for remaining omissions and errors, for all of which responsibility rests with me).

Professor Philip Allen, Professor Mike Benton, Ms Vivianne Berg-Madsen, Professor Kevin Burke, Dr Tony Cooper, Professor John C. W. Cope, Professor Charles Curtis, Professor Ian Dalziel, Dr Wolfgang Eder, Professor Michael Ellis, Professor John Grotzinger, Dr Gordon Herries-Davies, Professor Paul Hoffman, Mr Robert Howells, Dr Patrick Wyse Jackson, Dr Werner Janoschek, Dr Sven Laufeld, Dr Roy Livermore, Dr Bryan Lovell, Dr Joe McCall, Professor Mark McMenamin, Dr John Milsom, Professor Eldridge Moores, Dr Bettina Reichenbacher, Professor John J. W. Rogers, Dr Mike Romano, Professor Mike Russell, Dr Gaby Schneider, Professor Chris Scotese, Professor Dick Selley, Professor Bruce Sellwood, Professor Dr Klaus Weber, Dr Jeffrey Huw Williams, Mr Simon Winchester and Dr Rachel Wood. My special thanks go to those in this list who critically read parts of the book in manuscript.

I should like to acknowledge the Geological Society of London for its enlightenment in encouraging private enterprise among its
employees
; but I also owe an immense debt to the Society as a Fellow. Fellowship has provided me with invaluable access to one of the great geological libraries of the world; and to the services of my colleague, Wendy Cawthorne. Wendy, like all the best Assistant Librarians, assists in finding the things readers ask for, but then goes the extra mile to find the things they actually need.

The idea for this book came to me very early one happy summer morning in 2003, among the chestnut trees of Vallée Française, Lozère, France. I made the first outline in a letter I was writing to my dear friend since student days, Professor Mike Ellis, now at the US National Science Foundation. Had he and I not been corresponding in this old-fashioned way since he selfishly removed himself to the other side of the Atlantic, I might never have begun this project. I also thank my editor, George Miller at Granta, who took me to lunch and made editorial suggestions that greatly improved the text.

I should pay homage to the late and great Professors Janet Watson and Mike Coward of Imperial College, London. They never taught me in the strict sense, but after reading their work as a
student
I eventually met Janet and came to count Mike as a friend. In this group must also be numbered Dr Rod Graham (still vigorously extant), who did teach me, but who has since, I hope, forgiven me.

To all I owe my sense of awe at their achievements in untangling the rocks of the Precambrian. I must also acknowledge two more of my personal giants, the late Professors Derek Ager and Dick Owen, both of whom taught me by example that the most complicated
science
ought to be explicable in language everyone can understand: a lesson that stood me well in my subsequent career as a science journalist.

I hope that this book will be seen as one long homage to all those great geologists whom I have met over the years and who have helped me. I lay no claim to having seen further, but in the thirty years that have passed since I began studying Earth science, too many giants have offered me their shoulders as footstools for me to be able to acknowledge them all by name. However, for the
dedication
of this book I would like to single out my fellow members of the Management Team of the International Year of Planet Earth, with whom discussions on the way that Earth sciences benefit
society
in general have played a major role in the development of this book.

Most of all, my thanks go to my wife Fabienne, who has continued to provide that without which nothing would be possible.

Ted Nield

FOREWORD
 

BIG CRUNCH

 

Different living is not living in different places

But making in the mind a map.

STEPHEN SPENDER

 
 

The drifting continents of the Earth are heading for collision. Two hundred and fifty million years from now, all landmasses will come together in a single, gigantic supercontinent. It already has a name (in fact, it has three) even though human eyes will, in all probability, never see it.

That future supercontinent will not be the first to have formed on Earth, nor will it be the last. The continents we know today – Africa, the Americas, Asia, Australia, Europe and the Antarctic – are
fragments
of the previous supercontinent Pangaea, which gave birth to dinosaurs, and whose break-up was first understood barely a century ago, in 1912. Yet 750 million years before Pangaea formed, yet another one broke up; and before that another, and so on and on, back into the almost indecipherable past. The Earth’s landmasses are locked in a stately quadrille that geologists call the Supercontinent Cycle, the grandest of all the patterns in nature.

Men and women have been imagining lost or undiscovered
continents
for centuries. For early mapmakers they filled in gaps, forming a bridge from the uncertain to the unknown. Nineteenth-century zoologists and botanists speculated about sunken lands to explain odd distributions of animals and plants. Early evolutionists peopled their hypothetical lost lands with the ancestors of mankind. Fringe religions adopted them and embattled minority cultures latched on to them to bolster their myths. All had one thing in common: the basic human urge to understand and make sense of the world.

Today geography has no room for lost continents. The world is ringed by satellites that reveal no undiscovered country. But lost
continents
have found, at last, a true science of their own. This book is about how that science emerged and how Earth scientists are using the most modern techniques to wring as much information as they can out of the oldest rocks on Earth and predict what the next
supercontinent
will look like.

Supercontinent Earths, salvaged from oblivion or projected into the future by today’s geologists, share one thing with all the lost
continents
that were ever dreamt of, whether by other scientists, mystics or madmen. All lost lands truly exist only in one place: the human mind, the only eye that can see through time.

But why should we care? We human latecomers evolved a mere six million years ago, halfway through the present cycle, when today’s moving continents were barely a few hundred kilometres from where they are now. And if what we understand of other species can be applied to ours, there is very little chance that humans will survive the 250 million years that will pass before a new supercontinent assembles.

Yet the supercontinents of modern geology are no exotic fruit from some esoteric branch of science. Their discovery began with an innate urge to explore; it was boosted by the spur of Empire in the
nineteenth
century as science reached out through the third dimension to map the world and its living things. It continued as the patterns of today were seen to hold meaning for their evolution through the fourth dimension, time. And as the human mind has reached out it has also drawn together.

Without science the Earth could not sustain us in anything like our present numbers. Our continued life on the planet that gave rise to us will depend upon our ability to use our science to protect and feed ourselves in the face of what threatens us (chiefly ourselves). Understanding the Supercontinent Cycle is nothing less than finally knowing how our planet works. This can be to our benefit – we have, after all, made it thus far – or our detriment.

If scientific knowledge had been properly deployed many, perhaps most, of the quarter of a million people who died around the Indian Ocean on Boxing Day 2004 could have been saved. The knowledge that makes that possible is the same knowledge that reconstructs
landscapes
that washed into oblivion hundreds of millions of years before our species existed.

London, 2006

PART ONE

 
MOVING IN MYSTERY
 
 

1

 
LOST WORLDS
 
 

Far out in the uncharted backwaters of the unfashionable end of the Western Spiral Arm of the Galaxy lies a small unregarded yellow sun. Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue green planet …

DOUGLAS ADAMS

 
Novopangaea – a science fiction
 

A blue planet hangs in space. You have seen many planets as you have searched the cosmos for signs of life far from your own small planet somewhere in the vicinity of Betelgeuse. But as you approach this one, something about it impresses and excites you. It’s the third planet from an unremarkable star, and the largest of the rocky inner ones. But as you approach it from below the plane of the ecliptic, it shines like an opal, streaked with white.

The galaxy is full of the common oxide of dihydrogen that appears to cover this planet, but almost everywhere else it is a solid. Here it exists as a liquid and there are traces of its vapour in the atmosphere. The liquid phase can only exist within a very small range of
temperatures
; temperatures you, as a space explorer, expend a lot of energy maintaining inside your craft. Yet here these equable conditions seem to cover the entire planet. There isn’t even an icecap at the pole, where the temperatures should be at their lowest. It is almost inconceivable that a planet’s temperature should be so constant over its entire
surface
. It must be that the deep atmosphere is trapping the star’s heat, and then, with the help of the ocean, spreading it around.

Above the glowing blue ocean, especially over its equator, are streaks of white. Cloudy curlicues and spiralling weather systems track like miniature galaxies across the hemispheres. At first it all looks chaotic, but on your long approach, heading towards the planet’s southern pole, you have time to study time-lapse images. Suddenly the apparent chaos starts to make sense. The clouds’
movements
are indeed complex, but do describe a sort of ragged mirror symmetry about the planet’s equator. What seemed like chaos now looks more like order: the atmosphere is convecting in six great cells arranged symmetrically about the equator.

The planet’s moon is unusually large, though to an experienced space traveller little else is unusual about this satellite. No heat
regulation
there; with no atmosphere to distribute energy, temperatures can swing wildly through almost 300 degrees from sunlight to shade: quite normal for a space rock struck by starlight. A satellite as big as that must set up a tidal bulge in the ocean by the force of its gravity; you will be able to detect that once you are in orbit and can train your altimeter on the ocean surface.

Already, using the spectrometer to analyse the light reflecting from the planet, you have detected, amid the dominant nitrogen signature gases like carbon dioxide, and the gas phase of dihydrogen oxide (which will also help to trap heat and keep the planet warm). Methane is there too, and does the same job.

The unusually tall oxygen spike piques your interest, but just as you are thinking about that, something momentous distracts you. Your ship is now pulling level with the planet’s equator. Perhaps because the clouds had drawn all your attention you had missed it at first, but now you see that this is not a liquid-covered world after all. There, below, is a single, gigantic landmass. You can see it clearly, because the clouds obligingly part over it; few penetrate far beyond its coastline. As the hours go by you watch the landmass unroll as you enter a fixed equatorial orbit.

It sits mostly in the Northern Hemisphere, covering perhaps 30 per cent of the planet’s total surface area. It is dry. Immense white and beige deserts occupy nearly all of it. Three ranges of mountains, low, desolate and worn down with age, stand out amid the dune seas and endless dazzling playas. Dry, wiggling canyons feed the arid interior wastes, dying into vast plains of white from which expanses of blown sand stretch far away beyond the shimmering mirages of the horizon.

Most spectacular, apart from this terrifying barren waste, is the continent’s southern coast, maybe twelve or fifteen thousand
kilometres
long. It lies at a slight angle to the equator and crosses it near its southern end before taking a dogleg and heading back, reaching even greater heights, to the north-west. This entire coast presents a cordillera of jagged peaks up to eight thousand metres high (perhaps nearer ten thousand at its eastern end) punching into the cold upper atmosphere and capped with white. These mountains are young, active, still growing. There are volcanoes too. One of them is
erupting
now, its plume of ash sweeping offshore like a thin veil, carried by the winds of the topmost atmosphere. This planet’s surface is moving, geologically active; the planet is alive inside, powered by heat generated continuously by radioactive elements, so that the whole crust seethes like the scum on a boiling pot. As the largest of the rocky planets in this system, it is big enough not to have cooled down and died like the others, even after nearly five thousand
million
years.

What excites you perhaps more than anything as a space explorer are the colours you can see at the coast of the supercontinent,
especially
where those coasts cross the tropics. The interior is parched; but the point at which the driest area comes closest to the ocean is behind the range of towering mountains on the south-east coast. Here the weather systems that sweep inshore stand little chance of breaching those massive battlements (even though some of those systems are thousands of kilometres across, with wind speeds of over three
hundred
kilometres per hour).

But on the diametrically opposite north-west coast things are
different
. Here, where prevailing westerlies make landfall, streamers of cloud obscure the land for thousands of kilometres. Beneath them, from time to time and around the edges of the cloud blanket, you detect a livid green stain. Other, narrower areas on the
supercontinent’s
coasts are green too, peeping out occasionally from the fringe of coastal clouds. This is the eureka moment. The oxygen spike! That huge ocean, and those coastal regions where moisture falls as rain, are teeming with living things.

You have just topped the greatest scientific discovery by any member of your species since it first began to look up towards the stars. You have found another place in the universe where matter
lives
. You knew it must be possible. Some said probable. Growing numbers believed it inevitable. But would – indeed,
could
– anyone ever
find
such a place? Given the distances of space, would it be possible to travel to such a world? And then even if, somewhere else in that limitless abyss, matter had become imbued with life, would it necessarily
coincide
with yours? For there was another abyss to consider: the abyss of time.

The universe is like a post-apocalyptic town: there appear to be other houses, but only yours is currently inhabited. Maybe all those other living worlds were marooned not only by impossible and untravellable distances, but also by
duration;
lost in time as well as space. Now you have an answer. You have found a neighbour alive.

You learn as much as you can about this precious place from orbit, but the next thing on your mission directive is to check if any among those living things down there is sentient. But you already know the answer to this question. Sentient life becomes civilization in a
geological
instant, and the chances of finding the first living planet at just that tiny moment between the evolution of an intelligent being and its
ability
to build cities and get power from atoms are too small to imagine. There are no satellites orbiting. There are no transmissions. This planet hangs in space like a great unseeing eye. There is no civilization down there. The creatures that may swim in its seas, or fly through its air, wander those forests or cling to its fertile coasts are dreaming their innocent world, unaware of anything beyond it, or that over them all, your shadow has now fallen. It is a kind of paradise. You envy it.

But hunches are not enough. Rules are rules and the manual says you have to check, run tests, write reports. From your vantage point, with your instruments, you can now scan the surface of this planet’s landmass in precise detail, centimetre by centimetre. If there is (or was) a civilization down there, you will find it. Even if some extinct creature had built something, or carved the sacred images of its great leaders into some granite mountain, you will see it.

You begin the scans, which eventually will be assembled in a
computer
that will remove all the obscuring clouds; but you know this is hopeless. If the absence of transmissions tells you there’s nothing intelligent there now, the planet’s reflected light tells you there was probably
never
anything there. Sentient life quickly learns the secrets of matter and makes power from atoms. That process creates forms of matter that never exist in nature and which take millennia to decay away to nothing. Even on an active planet like this one, with
weathering
and erosion and deposition and a seething crust that renews and recycles itself, these substances endure. They are the only truly
lasting
products of civilization.

You scan the arid surface of the supercontinent for radioactive
isotopes
of the most insoluble elements with the longest half-lives. You find some: Thorium 232, and Uranium 235 and 238. But these all occur naturally. There is nothing more. If there ever had been an advanced civilization on this planet it must have vanished more than 100,000 years ago, though this does not yet depress your
archaeologist
, because the surface scans are not finished.

Much of the land surface is dry. Physical traces of civilization might have survived for more than 100,000 years, a great city perhaps, or some massive monument hewn from living rock, whose outline would still be visible. But even after you have assembled in your memory banks a complete inventory of every valley, mountain and hill on this supercontinent, the archaeologist finally admits defeat. Now only the geologist is interested in the possibility. But looking for fossils is something you cannot do from a spaceship.

As the weeks go by, you turn (with little real enthusiasm but because the mission directive says you must) to the planet’s moon. You have seen so many other bodies like it, a dull, cratered space rock, dry, dead, circling for ever, its inert surface open to space, almost unchanging from its earliest violent days of heavy meteorite
bombardment
.

Yet here you are in for a surprise. Almost immediately your
preliminary
scans of the surface turn up real and unequivocal evidence of advanced civilization. At six separate sites you identify the remains of landing craft, transportation vehicles, transmitters, a seismic array. Another enormously significant revelation for your mission. Not only is your home world no longer the only living planet in the universe; you know now there have been other space explorers; and what is more, they have passed this way.

Subsequent archaeological research on the lunar artefacts reveals the trail to be a little cold, however. As the moon is clearly not itself a living planet, you can check out one of the alien spacecraft. Landing some way off and approaching with care, you see it and, most
exciting
of all, the footprints around it. They still look as though they arrived yesterday: unequivocal evidence of alien beings with
spaceflight
capability. Your archaeologists take samples of the spider-like landers, from each of which an escape module once blasted into space. Clearly the six visitations to this moon were made by the same beings, at more or less the same time. But when?

The answer is not long in coming; microscopic examination of the metal surfaces reveals that they are pitted with billions of tiny
micrometeorite
impacts. From their density, and what you know about the rate of influx of such tiny objects, you work out that these visitors – whoever they were – must have left for the last time 200 million years ago. But there’s a nagging question. Why would these travellers come to this moon, and not to the much more interesting planet?

Perhaps, despite the lack of any trace of them there now, these beings had come
from
the planet?

You ask your geologist, who has been studying the planet’s single continent and its volcanic mountain chain. From what she now knows of the planet’s crust and how it moves, even if some civilization of 200 million years ago had completely covered that same planet in cities and then wiped itself out in some gigantic global nuclear holocaust, nothing – not even the faintest trace of some unnatural radioisotope – would now remain on the surface. What is more, if those vanished beings were to be brought back today, they wouldn’t recognize the world below as theirs. At the speeds at which the planet’s crustal plates move, even with all the land locked together in a great
supercontinent
, she can be certain that 200 million years ago the planet looked nothing like this. Perhaps then there were once many smaller, separate continents, all scattered about like islands in the ocean.

The geologists begin to write a research proposal to break the
mission directive and visit a living world for the first time, spurred on now by the possibility of finding fossils of a vanished sentient race that may have developed space flight before vanishing completely. Now the only trace of them and their culture could be six short visits they had made in their heyday to their dead, unchanging moon,
lasting
in all not much more than 300 hours.

And who knows what they would find if they got permission? Maybe those alien explorers are in for yet another shock. Perhaps those fossils that they discover of a small, forked creature would look very familiar – just as the footprints on the moon had done. Perhaps the space visitors from a small planet in the vicinity of Betelgeuse would find themselves meeting their ancestors. Perhaps they would discover themselves to be one lost tribe within a galactic diaspora that had saved the human species from inevitable extinction on a home world to which it had now, for the first time, returned.

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