Supercontinent: Ten Billion Years in the Life of Our Planet (30 page)

But now things were different and soup was on the menu. Life had turned on itself for the first time, and the selection pressure this imposed accelerated the origin and the extinction of new acritarch species. The spiny, heavily armoured and relatively short-lived forms of the post-snowball world are nothing less than the first tooth and claw marks of nature’s new order.

A little later, at around 580 million years ago, we find the first unequivocal animal fossils, in the form of a beautifully preserved clusters of cells representing embryos of an animal (though we cannot say what sort), in the mid to upper parts of the Doushantuo Formation of southern China. Not long afterwards the first trace fossils – those telltale marks made by animals moving across and through the sediment – first appear, in rocks no younger than 558 million years old, in the Verkhovka Formation of north-west Russia.

The period we are speaking of is called the Ediacaran, now officially named for the remarkable forms over which Mark McMenamin and many others have been puzzling. The Ediacarans were part of this new evolutionary order, but although some may have evolved into animal forms that are still around us today, others (perhaps, who knows, those photosynthesizing animals in McMenamin’s vision of the Ediacara Garden), after first trying sheer size as an evolutionary refuge against the mounting pressures against them, finally succumbed. They succumbed to the destruction of the algal lasagne they rested on and ended up as lunch for those voracious new predators that, tiring of soup and lasagne, moved on to the meat course.

There is one final line of evidence for life’s sudden dash to complexity after the snowballs, suggesting that these climatic crises were indeed what set the process off. That evidence is found inside the molecule of life itself. DNA, the molecule that carries the genetic codes and governs our growth and development by regulating the process whereby amino acids build proteins, is vast; yet it is a lot vaster than it needs to be, since large tracts of every organism’s genome have no known function. Because they are not expressed in the biology of the organism, they are not subject to natural selection like other areas of the molecule.

Natural selection is often thought of as what ‘changes’ organisms, but this is only true if something in the environment is changing, disturbing the equilibrium. Under stable conditions, natural selection is a strongly conservative force that keeps things the way they are and makes sure that things that aren’t broke
don’t
get fixed. But those areas of the DNA molecule that are not expressed biologically are able to mutate freely without impairing an organism’s evolutionary ‘fitness’. Biologists have found that, left to its own devices in this way, this so-called ‘junk’ DNA mutates at a rate that (over geologically long periods of time) is constant enough to be used as a clock (though it has to be regulated by reference to a good fossil record).

Despite what the film
Jurassic
Park
would have you believe, very little DNA is preserved in the older fossil record, and the further back you go, the less survives. So if you want to use DNA to date events that took place more than 500 million years ago, finding DNA from those times is not an option. But fortunately there’s no need; we can look at the DNA of different groups of
living
animals (sponges, worms, molluscs etc.) instead. Then we can combine what we know about the rate at which the DNA clock ticks, with a statistical expression of the difference between the junk DNA sequences of sponges,
worms or molluscs, to work out how far back we would have to extrapolate these in order to make the different groups’DNA look the same. The result should be the point in time at which the groups’ evolutionary paths diverged, and it should be confirmed by the fossil record. On the supercontinent of science, everything must fit together. The molecular biology of today’s animals confirms the fact that they are all related, that some groups split before others and that every living thing is the product of its unique history: a history that dates back billions of years and ultimately makes us one with the stars.

To confirm whether the snowballs and the Supercontinent Cycle might have been responsible for creating complex life, the crucial evolutionary divergence that we want to date is the one that gave animals the power to move purposefully, even
through
sediment (burrowing), to ingest material, process it in a gut and expel excrement. For these were the developments that changed nature for ever and finally dug up the Garden of Ediacara. This evolutionary event was all to do with how the tissues of animals became organized and differentiated in the embryo.

Sponges are simple multicellular animals, but they are little more than balls of barely differentiated cells. Jellyfish, on the other hand, are two-layered animals. This allows them to move, albeit in a rather undirected way, as they drift with currents or to move away from harm (they hope) when warned by their rudimentary sense organs. They have an outer layer of cells and an inner one, separated by a springy, gelatinous mass. Muscles around a jellyfish bell contract against the springiness of this mass, which bounces back into shape when they relax, allowing the swimming cycle to start again.

But the next development in the history of embryology was crucial because it created animals with
three
layers of tissues, the middle layer developing from the jelly-like stuff as it became invaded with cells. Moreover, the embryos of the new three-layered animals developed a
method of ‘turning in’ on themselves. First, the embryonic ball of cells became hollow, to create the body cavity. A fold in the outer layer then developed, forming a pouch on the inside. This became budded off along most of its length, but remained connected to the exterior by a single pore that developed into, literally, the fundamental opening: the anus. The mouth developed later, at the opposite end. You can see this evolutionary process re-enacted every time a human embryo develops today, and it is the reason why you have a body cavity filled with tubular guts.

Three-layered animals were a giant leap. The outer layer gave skin, nerves, ears and eyes. The middle layer gave rise to muscle, bone and the circulatory system; while the inner layer created the digestive, glandular and respiratory systems. Worms, snails and humans all have this same basic organization. Having three layers meant having more cells per unit volume, and separating the digestive tube from the body wall created problems of transport. Oxygen needed to be brought in, and wastes and nutrient carried out. All this required ducts, circulation systems and respiratory mechanisms that simpler animals didn’t need because they could live by absorption alone.

Above all, three-layered animals were directed by sense organs concentrated at a head end, and their muscles enabled them to move in more or less any direction in active pursuit of food. The mouth, being also at the head end, was the first thing to arrive at the food source, ingesting what it found, filling the gut with a mixture of food particles and sediment. Burrowing and grazing modes of life were born; and as a result, trace fossils started to appear in the fossil record, and the fine, undisturbed laminations of Lasagne World became rare as the Garden of Ediacara went under the plough.

According to the molecular clock, the first three-layered animals, complete with heads and nerves and muscles and guts, should have appeared about 580 million years ago, which places this evolutionary
event right in the middle Ediacaran (630–542 million years); just after the Marinoan snowball had melted, after its cap carbonate had been safely deposited, and the climate had settled down again. What is more, 580 million years also turns out to be the date when fossils of the Ediacaran animals, though already doomed, became abundant enough to be preserved in non-exceptional circumstances. And all this took place barely forty million years after the last of the two major Neoproterozoic white-outs came to an end.

As scientists are fond of pointing out, correlation need not imply causation; but to many, these convergences are too consistent and too numerous to be meaningless coincidence. If true, the correlation between the origin of complex life and the end of major snowball episodes firmly ties our own origins to the Supercontinent Cycle, because it was the chance siting of continents around the Equator 1000 million years ago that made those all-important snowball events possible.

Life itself probably owes its origin to the geology of ocean-floor hydrothermal vents. But that part of it that isn’t slime may owe its brief 580-million-year tenure of this planet to nothing more than random turbulence within the Earth’s convecting mantle, which once swept the continents to the tropics. There, far from stopping a runaway snowball, their fragmentation from maximum packing enhanced weathering, created volcanic cooling and multiplied the length of shallow, lasagne-covered sea floor, just at the time when a billion and a half years of photosynthesis and carbon sequestration had already made the Earth System especially vulnerable.

Out of this catastrophe came glorious, complex life. And now, we are blessed (or cursed) with the brains to work it all out for ourselves. The question then becomes: will we bother, or will we sit, like Albrecht Dürer’s
Melancholy
, surrounded by the tools that can help us explain the world, but too indolent to use them?

Melancholia
by Albrecht Dürer. Hapless Melancholy lies surrounded by the untouched tools of science and art. Reproduced by permission of the Mary Evans Picture Library.

 

On the morning of Sunday, 26 December 2004 about 1300 tourists and pilgrims crowded on to Kanyakumari rock, a charnockite islet 200 metres or so off the southernmost tip of India. Geologists call the islet ‘Gondwana junction’ because it marks the 550-million-year-old suture where India, Madagascar, Sri Lanka, East Antarctica and Australia once joined together to build the eastern portion of Suess’s Gondwanaland. But to followers of Vedantist spiritual philosopher Swamy Vivekananda (1863–1902), the rock is remarkable for being the foundation for his memorial, which opened to visitors in 1970. This was the impressive structure that drew them to Kanyakumari as the sun came up over the Bay of Manar that morning.

Mr G. Ramalingam of the Port Authority remembered afterwards that they had sold 3469 tickets for sailings between 8am and 9.45am, though they had suspended sailings to another outlying rock, Valluvar, at 9am – a decision that probably saved about 500 lives because the monument to the great Tamil poet, a forty-metre-high statue on a square plinth, offers no shelter. For 26 December would prove to be a much more memorable day than anyone expected.
Although not one of the tourists and pilgrims would die at Kanyakumari, some 230,000 others around the Indian Ocean would lose their lives before the day was out.

Perhaps as they were preparing for their expedition, some of those pilgrims may have been aware of a slight earth tremor; but most of them either didn’t notice or slept through it. Yet even as that distant seismic shock rumbled through India and around the world, slower and much more deadly waves began spreading across the Indian Ocean. By the time the pilgrims climbed aboard the ferry of the Poompuhar Shipping Corporation that would take them to the island, tens of thousands were already dead in Indonesia. Thousands more lives were being lost in Sri Lanka, just over the horizon. Soon the wave would turn the corner and sweep up Sri Lanka’s west coast and bear down upon Kanyakumari.

The deep ocean trench that skirts the Indonesian Archipelago on the other side of the ocean, marks the contact between two of the tectonic plates making up the cracked eggshell of the Earth’s crust. One is the Australian Plate, consisting of Australia and the floor of the Indian Ocean, and the other, to the north, carries Europe and Asia and is called the Eurasian Plate. At this trench the floor of the Indian Ocean is subducting, sinking down into the mantle, beneath the island arc of Indonesia. This is but one small part of the long process of building the next supercontinent, piece by piece, each fragment edging into place, just as India has already been annealed to Asia in the collision that is today creating the Himalayas and the Tibetan Plateau.

In many ways the earthquake that caused the 26 December tsunami should have taken nobody by surprise. There are known to have been
two great earthquakes of over magnitude 8 along this part of the Indonesian Arc: in 1833 and 1861. The zones of rupture that caused these two events sit along adjoining, non-overlapping parts of the same plate boundary, adjoining the Batu Islands. No quake of similar size happened during the twentieth century, until June 2000, when a 7.9 quake struck near Enggano at the extreme south-eastern end of the 1833 rupture zone. The 26 December event extended movement along the plate boundary from the island of Simeulue, at the other end of the chain, almost to the coast of Myanmar (Burma). This left a gap of a few hundred kilometres between Banyak and Simeulue over which no movement at all had taken place in historical time. The omission was rectified on 28 March 2005, when the last ‘stuck’ part of the fault gave way in an 8.6 magnitude tremor that thankfully produced no very serious widespread tsunami.

The processes of plate movement are not smooth at our human timescale; the heat engine of the Earth is no perfectly oiled machine. So while the average rate of convergence between South-East Asia and the floor of the Indian Ocean may be 5.2 centimetres per year, unlike your growing toenails, these figures represent the averages of many sudden discrete movements, some of which, especially when long delayed, can be very large and very sudden indeed.

On 26 December 2004 stress that had built up over hundreds, perhaps thousands, of years was finally released along a 1200-kilometre stretch of plate boundary to the north-west of Simeulue. This stupendous quantity of energy, stored as though in a giant leaf-spring, was liberated in seconds as the crust of the overriding plate (which had been bent downwards by the pressure of the sinking ocean floor beneath) bounced back, flinging the ocean up by as much as ten metres.

At a magnitude of 9.3 (on a scale whose every increment denotes a quake thirty times larger than the one below), this was the largest quake unleashed by the Earth for half a century, the second strongest ever recorded, and the first true ‘Global Geophysical Event’ since Krakatoa erupted in 1883. Its seismic waves, travelling quickly through the Earth’s crust, crossed the Indian Ocean and passed through the Vivekananda Memorial almost instantaneously, as the whole planet reverberated like a bell struck with a massive hammer.

The Sumatra subduction system, showing the dates of known historical earthquakes and the sections that moved during each. First published in
Geoscientist
15, 8 p. 4. Reproduced courtesy of Dr John Milsom.

 

The tsunami meanwhile rolled outwards from where the ocean floor had been uplifted. In deep water, travelling at the speed of a jumbo jet, its waves were only a few centimetres high, passing unnoticed beneath the hulls of container ships crossing the Bay of Bengal, stacked and sleeping in the morning light. But in the shallows, the waves slowed and bunched together, piling up huge cliffs of surging, turbid water that rushed inland like supercharged high tides, sometimes tens of metres tall, razing all before them, scouring the coastline of an entire ocean.

The tourists and pilgrims, now disembarked at the Vivekananda Memorial, watched as the horror unfolded. The morning was calm and the sky clear and blue. The first thing the visitors noticed was the withdrawing roar of a false tide, as though someone had pulled a plug on the ocean. Dark, wet rocks at the foot of the many islets, and finally the seabed in between, were suddenly exposed. It was as though the sea had inhaled. In the eerie quiet, which had almost silenced the chatter on the Memorial, the visitors could hear the hiss of air being sucked into the pore spaces of the draining sand and the flapping of a few stranded fish. Then, just as the onlookers had begun to shrug their shoulders at the sight, a series of huge waves, each several metres high, rushed in, crashing over the sunstruck promenades
surrounding the Vivekananda Memorial. The great statue of Tiru Valluvar was engulfed in spray, like a deep-sea light breasting an Atlantic storm, but on a cloudless morning.

How many of the visitors to that tiny outcrop of charnockite thought at that moment about Katalakōl, of the lost books, and the palaces of the great scholar kings who, in the dreamtime of Tamil myth, held benevolent sway over the lost lands of Ilemuriakkantam? Perhaps many thanked the gods, because they had indeed made a
life-saving
choice that morning. All three boats of the Poompuhar Shipping Corporation were washed ashore by the tsunami; but after a long wait all the visitors were rescued, not by the Indian Air Force helicopter, which found it could not land, but by local fishermen whose boats survived the tsunami and who made several sorties to pluck the visitors to safety.

Over the days and weeks that followed, many stories emerged about how, here and there around the ocean, a little learning had been a life-saving thing; tales of the teacher who saw the tide go out unexpectedly and shooed all her pupils upstairs just in time. They served to show the life-saving power of knowledge; knowledge that most simply didn’t have. But it became clear that, given the right combination of technology and education, many might have enjoyed a fate like that of the lucky fishermen of Nallavadu, on India’s eastern coast.

The story goes that the son of one Nallavadu fishing family was on holiday in Singapore when he saw a news report of a massive earthquake and rumours of a terrible wave. He telephoned his sister and told her to spread the word and leave home immediately for high ground. This small community had for several years benefited from the presence of a small Internet-linked communications centre, set up by the M. S. Swaminathan Research Centre in Chennai to provide information to fishermen about weather in the Bay of Bengal. Armed
with the news, villagers broke into the centre’s telecoms facility and, using its public-address system, told the village’s 500 families to run for their lives. And in the end, not one life was lost from Nallavadu’s population of 3500; though 150 houses and 200 boats were reduced to rubble and matchwood.

For scientists, especially those working at the Pacific Tsunami Warning Centre in Hawaii, the unfolding situation was immensely frustrating. Together with seismologists all over the world, they had detected the massive quake and knew that a tsunami was a likely consequence. But there is no regular correlation between earthquake magnitude and tsunamis; and without any tsunami sensors in the Indian Ocean, still less any established lines of communication with the countries bordering it, it was impossible for them to get any warning to those who might have benefited (except, finally, to the Horn of Africa, where casualties were low as a result).

But it was not long before the political will arising from the disaster began to take effect. On Monday 10 October 2005 a German research vessel set sail from Jakarta to place the first of fifteen earthquake sensors on the seabed some 620 miles offshore. Attached by ties to large buoys at surface, their signals are now being continuously beamed to the offices of Indonesian government geologists, and warnings can be relayed to the media and the public via SMS, fax and email. For its part, India decided to set up a tsunami warning centre in Hyderabad at an estimated cost of $27 million, and by December 2005 an interim Indian Ocean tsunami early-warning system costing $53 million, tying together seabed earthquake sensors and tide gauges, was nearing completion thanks to the United Nations Intergovernmental Oceanographic Commission (IOC).

As usual, because such warning systems involve links at all levels stretching from international to local, coordination will be the biggest
problem. Emergency preparedness planning, awareness campaigns, drills and local evacuation plans, educational programmes, and installing emergency operational capability – all these need to be present across a vast area that pays no heed to national boundaries. But without these things, none of the new technology will prove to be any use at all.

Science historian Naomi Oreskes has written: ‘Scientists are interested in truth. They want to know how the world really is, and they want to use that knowledge to do things in the world.’ It was this same impulse that drove Eduard Suess to design and build his clean-water scheme for Vienna, or Henno Martin and Hermann Korn to find water for Namibia, or John Joly to apply radiotherapy to the treatment of cancer.

Earth scientists often complain, with reason, that politicians underuse the full potential of their subject, especially for the benefit of vulnerable (for which read ‘poor’) people living in unsafe housing in unstable places. But, in times like the tsunami’s aftermath, this feeling rises to a pitch higher than mere frustration. That feeling is
despair
: that the world is still so ruled by the short-term, by superstition, inertia and irrationality, and that their humane, possibilist long-term view of the world is not only ignored but even denied.

If today there is fresh water on Namibian farms and in Vienna, and an emerging tsunami early-warning system in the Indian Ocean, it is because geologists in the past have done the science that brings a closer understanding of deep time and the inner workings of the Earth. You cannot pick and choose with science. A seemingly rarefied geology that reconstructs the lost supercontinents of Earth’s deep
past is the same science that (with political will) can save hundreds of thousands of lives in the Indian Ocean when the next tsunami strikes. The arcane business of how our Earth’s atmosphere evolved during the Precambrian under the influence of evolving life is the same science that now helps us understand the massive, uncontrolled climate experiment in which the human race is currently engaged. But to deny one part of science is to deny it all. Science hangs together. It is a supercontinent.

It is also progressive, as its ideas approach ever more closely the actual truth of nature as revealed in the great palimpsest of the geological record. ‘Progress’ may be an unfashionable Enlightenment notion, but in science it is real; and the test of that progress’s reality is the ever-increasing power that science puts in our hands. Just as the history of the Earth is made up of both repetitive cycles and directional arrows, as the wheels of science turn, throwing up the same ideas time and again throughout intellectual history, the train to which they are fixed moves forward.