Life

by Tim Flannery

  This was an impact so intense it could send portions of the Earth spinning into space, coat the globe with iridium and, on the micro-scale, change the structure of grains of sand. How could such awesome forces have been generated, and what were the implications for Ground Zero America? If the location of the strike was unfortunate for North America, the angle of the blow was nothing short of catastrophic. Seismic studies of the crater indicate that the asteroid made a low swipe from the south-east that—like a golfer’s chip shot—generated tens to hundreds of times more heat than a vertical strike would have done. It literally fried America, the heat generated by the impact reaching 1000 times that provided by the sun. And the result would have been particularly severe within 7000 kilometres of the impact point, an area that effectively covers the continent.6

  The atmospheric shock wave must have flattened trees all over North America, creating great piles of timber. There is convincing evidence that the Earth’s atmosphere was then about ten per cent richer in oxygen than it is today. With oxygen levels at about twenty-three per cent this was a flammable world—when oxygen comprises twenty-four per cent of the atmosphere, even damp timber will burn. Not surprisingly, evidence has been discovered of vast forest fires following the impact, and a global soot layer has been identified. It appears that much of the northern hemisphere was carbonised by the impact.7

  The celestial chip shot had other unfortunate consequences, for it took a huge divot of molten rock and debris and propelled it straight up the Bearpaw seaway. Evidence of the result is found in the distinctive sediments that formed as a result of the catastrophe. These rocks differ from similar-aged deposits elsewhere on Earth in that they have two distinct layers. The lower one is a chaotic mixture of materials and may represent part of the ‘divot’ dumped unceremoniously by the shock wave. The upper layer is better sorted and has thinner layers within it, as if it were laid down by water. Such rocks have been found all along the southern margin of North America, for example on the Brazos River, Texas, and near Braggs, Alabama, as well as the Caribbean and Mexico. The exact nature of the upper layer is still debated, but many researchers postulate that they resulted from titanic tsunamis that raked the land a few hours after the asteroid hit.8

  Scientists think that the sea along the southern coast of North America withdrew as it poured into the crater, only to return a few hours later as an enormous tsunami, or more likely a series of them. Were the waves a kilometre high ‘the largest in the history of the world’ as some claim?9 Whatever the case, I cannot imagine them as being anything but titanic, devastating all that remained standing in interior North America.

  No humans have ever experienced anything comparable to the asteroid impact, but once—just once in written history—a faint echo of the great impact was directly experienced by a small section of humanity. On 27 August 1883 the island of Krakatoa, lying in the strait between Sumatra and Java, blew apart, releasing as much energy as 10,000 Hiroshima-sized bombs. A vast cloud of pulverised rock blocked out the sun for fifty-six hours. Villagers reported that the darkness was more profound than that of the blackest night, for it was palpable, like a blanket, and it cut off not only sight, but sound as well. In the terrible silence that reigned, they did not hear the explosion that 3000 kilometres away in central Australia was mistaken for the report of distant cannon. They did not even hear the tsunami, as tall as a seven-storey building and travelling as fast as a train, which was to obliterate their world. Thirty-six thousand people met death in that dark, silent instant.10

  Given the stupendous power of the many violent forces released by the impact of the asteroid it is difficult to imagine any life, except perhaps seeds and microscopic species, surviving in the more exposed parts of North America. Certainly the forests were devastated. The emergent conifers were all destroyed, never to return to the continent, and along with them went nearly eighty per cent of the flowering plant species, including, it seems, almost all of the trees. The destruction off the southern coast was similarly extreme, with even such hardy and uncomplicated creatures as shellfish suffering massive extinctions. Indeed the effect was so profound that even three million years later the fifty-eight species of mollusc then living were but a shadow of their pre-impact diversity.11

  Further north, in Canada’s Alberta province, the evidence left in the rocks is less suggestive of catastrophe, as befits its location near the Arctic Circle of the day. On a cold June afternoon I went to examine the boundary as it is exposed in the badlands along Alberta’s Red Deer River. With horizontal rain blowing in my face I trudged through a field of newly sown wheat towards the edge of a precipice. The wind blew like the exhaust from a jet engine as it rose over the rim of the cliff, and I had to force myself to look down at the crumbling unstable-looking slope that dropped away into the stream below. Some years earlier a team from the Royal Tyrrell Museum in Drumheller had discovered a near-complete skeleton of a tyrannosaurus at the base of the cliff. The neck unfortunately disappeared into the rock face and just as they reached the spot where the skull should lie the situation became too perilous even for this resolute and experienced team of excavators. They decided to quit for the season and try to figure out some way to recover the all-important skull. Soon after the entire bluff collapsed, irretrievably burying the skull. The tyrannosaurus had died before Chicxulub and was entombed in a layer around seven metres below that marking the asteroid impact that I had come to see.

  As I crossed the slope in search of the boundary layer the ground crumbled under my feet, sending small landslides cascading off the abrupt drop. After some minutes edging my way along I reached the site. The impact horizon was marked by a seam of whitish clay just two centimetres thick. Below it was a narrow band of coal, then the sands of the Alberta badlands that stretched to the level of the tyrannosaurus tomb, and way below that.

  As my legs straddled this evidence of catastrophe I wondered at the layers below the clay. The now-vanished creatures entombed there lived in ignorance of an event that would, like an eraser, put an end to their world. What was it like to stand in what is now Canada as the dust that composed the clay layer rained down out of the sky, coating an entire landscape in ghostly, pale grey? Perhaps it was the great breakaway yawning below me, or the dismal weather, but a distinct feeling of the transience of life stole over me as I peered at that thin line that separated two very different worlds.

  North America bore the brunt of the impact because it lay in the direct line of the chip shot. Elsewhere, the immediate impact effects were lessened, though the asteroid would unleash a second generation of consequences that would be global in their effects, and which would last not minutes or hours, but months.

  Despite all its attendant drama, the direct effects of the asteroid collision cannot account for the massive global extinctions that finished the age of dinosaurs. For that, one must poison the atmosphere. Just how that happened and how long it lasted are issues of intense debate. Some researchers suggest that a vast amount of sulphur entered the atmosphere from the Earth’s crust under the impact site. For a few weeks or months this may have created acid rain, particularly in the northern hemisphere. A number of scientists even speculate that the rain acidified the top 100 metres of the world’s oceans.12

  More likely is an idea preferred by Carl Sagan, who coined the term ‘impact winter’ to explain it. Sagan suggested that the ejecta from the impact made the atmosphere opaque, preventing energy from reaching the Earth’s surface. Just how much of the sun’s energy was lost is difficult to estimate, but a loss of one-fifth for a decade seems reasonable. This would have produced ten years of freezing or near-freezing temperatures across the globe. Even if it did not become that cold, the rock ejected into the atmosphere may have created a twilight sufficiently dim to prevent photosynthesis. In effect, the whole world may have been plunged into a long polar night, thereby starving its plants.13

  While the immediate effects of the Chicxulub impact on North America are widely accepted by the
scientific community, there is less agreement upon the nature of these global, medium-term consequences and how they affected the dinosaurs and other creatures. Recent research in North America points to a sudden extinction of the eight families and fourteen genera of dinosaurs, including such favourites as triceratops and tyrannosaurus, at about the time of the impact, rather than the gradual decline over millions of years that many earlier researchers believed had occurred. Despite such findings, some scientists still maintain that the asteroid had nothing to do with the extinction of the dinosaurs. Nevertheless, the reality of the asteroid impact is now securely established, and I believe that its medium-term consequences best explain the global extinction of the dinosaurs and many other living things.14

  The great divide in this impact-dominated world was the equator. To its north the consequences of Chicxulub were extreme and palpable, while southward ramifications appear not to have occurred, or at least were much attenuated there. The result is that species that vanished from the north survived in southern lands, for the south suffered no tsunami, no huge shock wave and, perhaps, no fires. This difference was to have ongoing repercussions for life on the various continents. Indeed it can still be discerned in their present faunas and floras, for vegetable dinosaurs still haunt southern forests.

  Seymour Island, lying off the Antarctic Peninsula, collected sediment right through the time of the great catastrophe, but these sediments tell a very different story from those of North America. Before the asteroid impact the dominant tree in this Antarctic forest was a relative of Tasmania’s Huon pine (Lagarostrobos). Looking at the pollen and leaf remains of these trees in the sediments, you would never guess that an asteroid struck the planet at the time they grew. For they, along with the other dominant plants of these southern forests—relatives of the king billy, celery top and other southern pines, the bright-flowered members of the Protea family such as mountain rocket, and the stately southern beeches—sailed right through the crisis unaffected. You can still see their descendants living today, growing in communities that the dinosaurs would have recognised, in parts of Tasmania’s south-west.15

  Anyone fortunate enough to travel to Tasmania will find that a great tradition of timber-working has developed among the inhabitants of that isolated isle. Breathtaking works of art, forged from a timber the colour of rich butter, across which play lustrous rays of light that seem to penetrate deep into the wood, are to be found in the workshops of many small towns. This luminous timber is Huon pine. Count the densely packed growth rings and you’ll find that the backrest of a chair took 500 years to grow broad enough to support you, and that a tabletop is the gift of 2000 years of history. Such trees cannot be planted for harvest, except perhaps for a people as distant from us as we are from King Canute or Julius Caesar, and they are now so rare, growing in just a few remote valleys, that the living trees can no longer be cut. The wood you see before you is from a tree that grew before Columbus—maybe even before the pyramids.

  The furniture is there because Huon pine does not rot. A log will sit in a cold Tasmanian swamp for 10,000 years and, when you pull it out and mill it, will still exude that inexpressible odour that this one tree possesses. Yet Huon pine is even more miraculous, for it survived the Chicxulub impact while its northern relatives perished. It is thus a living vegetable dinosaur, making a last stand in the wettest part of one of the world’s most distant islands.

  Other vegetable dinosaurs have survived throughout much of Australasia. The rainforests of New Zealand and New Caledonia are still overtopped by magnificent kauri and araucaria pines, trees that once shaded and possibly fed America’s dinosaurs. New Caledonia has no fewer than twelve species of Araucaria and eight of Agathis, in all about half the world’s total. All grow as emergents, below which thrive communities of broadleaved flowering plants of an ancient hue, just as they did in North America during the age of dinosaurs. It is difficult not to overstate just how much these southern forests are direct survivors of the age of reptiles.

  Australia is the only place on Earth where all three genera of those magnificent emergent araucarians still grow today: the araucarias themselves, those great columnar trees with their impossibly symmetrical growth patterns, the magnificent squat kauri, their bark twisted as if covering sinews and, the most remarkable of all, Wollemia nobilis.

  When Wollemia was found in 1994 the discovery was hailed as being every bit as remarkable as discovering a small living dinosaur. A highly distinctive tree growing forty metres tall, just forty individuals were found growing in a deep canyon about one hundred kilometres from Sydney—a city of four million people. They are the most elegant of trees, pencil thin with bark that looks like Coco Pops, and their male cones actually ejaculate great clouds of pollen into the still canyon air. I was in New Orleans when the discovery was announced. ‘Jurassic Bark!’ the Picayune Tribune proclaimed on page one. I opened the paper expecting to read of a discovery in distant central Asia or Africa, only to find that it had been made an hour’s drive from my house in Sydney!

  Even if the southern hemisphere evaded tsunamis, fires and other abrupt and fatal catastrophes, something malevolent clearly did happen there. A few species of flowering plants vanished, and of course all the dinosaurs were plucked from the forest, their likes never to be seen again. The dinosaurs, though, were not the only creatures to suffer, for some researchers have suggested that the asteroid left the land bereft of every living creature weighing more than twenty-five kilograms at sexual maturity and certainly the majority of survivors were far smaller—rat- or lizard-sized.

  By sweeping away almost all of the larger organisms the asteroid had reset the evolutionary clock, allowing a few humble if not meek survivors to inherit the Earth. The mammals, which had evolved at the same time as the dinosaurs, had until now played the underdog, for despite more than 100 million years of evolutionary change they had been unable to evolve into creatures larger than a domestic cat. Now all that would change, for the age of mammals—the Cenozoic era—was at hand.

  The Fatal Impact

  2001

  IN THE 1820S Fanny Trollope, that perceptive, sharp-tongued traveller, described North America as ‘a vast continent, by far the greater part of which is still in the state in which nature left it, and a busy, bustling, industrious population, hacking and hewing their way through it’.1 That hewing, hacking and shooting was to cause a lot of environmental damage.

  The extermination of American species at the hands of Europeans began, and with luck will end, in the north Atlantic. Its first victim was the great auk or garefowl. The original penguin (though not related to the southern hemisphere birds of that name), the great auk was a flightless black and white bird that stood taller than your knee. Its breeding colonies had been pillaged since prehistory but it was the French explorer Jacques Cartier, during his 1534 exploration of the Gulf of St Lawrence, who discovered its last stronghold—a vast, hidden breeding ground on Funk Island.2 In the centuries that followed, the huge aggregations that came to nest on the island were ravaged by one boatload of visitors after another. The birds fuelled European explorations, baited cod-hooks and, in their dying days, supported taxidermists eager to turn a profit from selling stuffed and mounted specimens. The last two documented individuals were killed in Iceland and sold to a taxidermist in June 1844.

  One hundred and fifty-four years later on 31 July 1998, the journal Science published an article sternly warning the world that a large member of the stingray family, the barn-door skate (Raja radiata), could become the first marine fish to be made extinct by humanity. The skate, whose size is reflected in its common name, lives only on the Grand Banks and adjacent areas of New England. Forty-five years ago fishermen working its territory on St Pierre Bank hauled it up in about ten per cent of their trawls, yet not a single creature has been seen there in over twenty years. This is hardly surprising, for in the last years before the the Atlantic cod fishery closed every area of the banks was trawled on average every four month
s. Skates breed slowly and have few young and the cod nets appear to have caught every barn-door skate on the banks. They were, incidentally, a mere by-catch in the industry—hauling them up was a waste of time. Today the last few barn-door skates hold out in water a kilometre deep off Newfoundland. This area has been recently designated to support a new fishery—based on Greenland halibut. Unless something is done very soon the gigantic barn-door skate will certainly join the original penguin as another victim of the great North American expansion.3

  In between these oceanic bookends of fish and fowl lies a history of ruthless environmental exploitation, the audacity and imbecility of which leaves one gasping for breath. In the words of Henry Fairfield Osborn, president of the New York Zoological Society in the early twentieth century, ‘nowhere is Nature being destroyed so rapidly as in the United States…an earthly paradise is being turned into an earthly Hades; and it is not savages nor primitive men who are doing this, but men and women who boast of their civilisation’. It was a cry heard over and over throughout North America, yet for a century it seemed as if nothing could stop the slaughter. This is the sad story of the economic machine that ate the life of a continent, and it was not just animals that were fed into its maw, but people and cultures too.4

  When the Pilgrim Fathers stepped ashore at New Plymouth they imagined that they were entering a new and virginal land, yet in 1621 New England was, some writers have said, more like a widow than a virgin. Three years earlier her native peoples had been visited by a terrible pestilence, possibly the plague or smallpox. The Patuxet plague ensured that for some years there would be no real competition for land between new colonists and old. In such circumstances the greatest benefit to either group was to be had from honourable trade. The Indians benefited from the trade goods brought by the Europeans while, at least at first, the Europeans were dependent upon the Indians for their survival.