Читать книгу Extinction: Evolution and the End of Man - Michael Boulter - Страница 6

Travelling between these ancient monuments of nature in the winter of 2000 brought home with great force the horror of the human impact upon the environment. The local newspaper declared it was ‘the wettest weather since records began over a hundred years ago, all brought about by global warming’. There were landslides from new road verges, floods from broken river embankments, fallen trees from old plantations. Land being reclaimed from salt marsh was once again covered by the storming high tides.

It is interesting to note that the damage was restricted to modern features of the environment, artificial landscapes out of balance with the whole system. In contrast, the rocks and soil that had been around for millennia remained intact. These mature structures are part of the enormous system that can survive extreme events because they have been developed within that system through long periods of time. Theirs is a natural peace, a balance within complexity.

We know what the landscape of western Scotland and Ireland was like from the fossil remains that make up the underlying peat. One of the most thorough studies of these environments was conducted by John Birks, a specialist in post-glacial vegetation, on the plants of the Isle of Skye. He reconstructed several different habitats since the last glaciation when the most conspicuous vegetation comprised mixed birch and hazel woodland and shrubby heath. They were grazed by deer, which in turn were kept in check by wolves and foxes. In the cold climate, mammals were best to be smaller, the same species being larger in the warmer south. On Skye, with its bad soil, Birks found pollen and leaves from juniper shrub, while blanket bog and raised bog flourished where water accumulated.

Just as it is shells and bones, the hard parts of animals, that become fossilised, so the lignin in leaves and wood and the resistant walls of pollen grains survive in the suffocating marshes and bogs of these wetlands. Within a few years the fossilised plant parts become peat, then a few million years later, browncoal. With the right temperature and pressure, even greater lengths of time in the hundreds of millions of years turn the organic remains into coal or oil and gas. Pick up a piece of peat between your finger and thumb, throw it into strong acid and then alkali, sieve what’s left, and you will retrieve the broken bits of plants and animals from that wetland grave. Specialists like Birks work at the microscope identifying and counting the bits, finally reconstructing the original biosphere and showing how it changes through different scales of time.

Throughout these northern latitudes evidence is left as pine stumps, pollen, plant and animal fragments preserved in the peat. Rannoch Moor is far up in the Scottish Highlands and still has clumps of natural pine, with lots of heather and bog, building up more peat to record the present environmental and biological changes. You can easily see these rare ecosystems from the train, as it passes slowly from Crianlarich to Fort William along some of the most isolated railway in north-west Europe. There is a long climb up around the deforested mountains, slowly pulling onto raised wetlands of bog and marsh isolated from civilisation and even roads. You are in touch with the wild and exposed spirits of Rannoch Moor and its ancient habitat in the vast isolation of the Highlands.

Those spirits of Rannoch create a sense of another age, the clearances of the eighteenth century when landowners started to burn old heather in ten- or twenty-year cycles to rear pheasant and other game for sport, while also clearing the ground for new growths of the same heath. Such fires still maintain the artificial ecosystem on the mountains, holding back mature growth of the trees that would otherwise resume their dominance. The vestigial pines you see around Rannoch are about the only remnants of natural forest in the British Isles. The complete mixed deciduous conifer forest associated with the pines once covered the lowlands down into England and Wales. All that was taken away when humans wanted shelter, ships and sport, and this occurred hundreds of years before the big twentieth-century environmental tragedies that headline the news of environmental decline.

Would the environment have changed in the same way without humans? The answer is a definitive no. That view may be as obvious as many a verdict in a murder trial, but where is the evidence that the jury must have to make a proper decision?

In the nineteenth century when labourers were making the railway across the Rannoch bog, they sliced through sections of peat that had slowly built up through thousands of years. The broken bits of fossil plants and animals preserved in this suffocating sludge tell us what had been happening during the time of their deposition. In the Scottish bogs it is mainly the plants that tell the story. In other places more romantic creatures such as large mammals have left their remains, especially when the sections go back into previous interglacial intervals, about every 100,000 years.

At about the same time as the Scottish railway was being built, other labourers were digging foundations for Nelson’s Column in Trafalgar Square. The sides of their trench showed more solidly compressed peat, but samples showed up much the same pollen and leaf fragments as at Rannoch. We call it the Trafalgar Square interglacial, the warm interval from 80,000 to 125,000 years ago, before the last glaciation. Although the vegetation had been very similar to the present interglacial, the animals were very different. The labourers were the first to be astonished by the big bones from mammals. The Victorian scientists were the next to be surprised, identifying hippopotamus, an extinct elephant with straight tusks and a weird rhinoceros with a narrow nose. It was hard for Victorian society to believe that in the centre of one of the world’s most splendid metropolises once roamed animals that now could be seen only in Regent’s Park Zoo, captured and transported from Africa. The realisation sent shockwaves along the spine of human civilisation and culture.

Progress was slow with understanding these amazing discoveries until modern dating techniques could give the changes some relative scale. One difficulty is that much of the fossil evidence from the earlier warm intervals gets scraped away by later glaciers. This makes it very difficult to be sure that the grave has not been moved, or to be precise about the age of what little gets left behind. But from the whole of Europe, North America and Asia, evidence of mammal extinctions during these earlier interglacials is becoming clear.

Furthermore, it appears that the cause of the extinctions was due less to the cold – they could mostly migrate south when it got too cold – than to aggressive hunting by ourselves, Homo sapiens. In Africa, new discoveries show that we caused extinctions of almost half the large mammal genera such as giant baboon, three-toed horse, antlered giraffe and many more. In Europe, at the peak of the last glaciation just over 21,000 years ago, we killed off the mammoth, woolly rhino, elk, hyena, lion, bear and tiger.

Scientists and others have been arguing for years about the causes of these ice age extinctions. Several groups with their own special interest have become involved, trying to argue about race and religion, not caring much about the natural processes of change. Some say the large mammals’ immune system broke down because of ‘hyperdisease’ spread by humans. Other scientists see the weather involved with climate change through the ice ages as responsible for the large mammal extinctions.

The aggressive patterns of human behaviour (I dare not call them instincts for lack of clues) appear to have been with us since our inception. Early man migrated out of Africa to central Asia and eastern Europe, then on to China and north-west Europe, and now we are looking for the signs of battle. They are hard to find. Perhaps that’s because the relics have been removed by erosion or glaciation, or even because the battles didn’t happen. However, there are more and more circumstantial details being discovered to suggest that these early migrants killed off many large mammal species from Neanderthal man to the mammoth. And there are new arguments about the history of man entering North America.

Most scientists now agree that vicious events happened more than 11,000 years ago as the ice was retreating from the last polar glaciations. Then our much less civilised ancestors, Siberia Man, were walking across the newly emerging Bering land bridge from Siberia to North America. They were skilled hunters, and within a few thousand years of their migration 70 per cent of the species of large mammals in North America were extinct.

There is also more and more evidence that extinctions over the last one hundred years result from environmental changes caused by us. As my Taipei tearoom conversation showed, our abuse of the planet is gathering pace and there is little that we do to stop it getting worse, scientifically, socially and politically. There are conventions and summits, a permanent United Nations Conference to look after the Biodiversity Convention, as well as regular meetings of environment ministers. But the sales of cars and refrigerators soar in India and China; gasoline stays cheap in North America; Europe consumes timber from dwindling tropical rainforest. The tourist industry booms globally. So we go on living through a catastrophe of a kind that our planet has never experienced. It has suffered major environmental changes before, with a consequent loss in biodiversity, but never have they been caused by a selfish species.

Within a few tens of thousands of years we have progressed from scenes of ice age glaciers to temperate interglacials, no doubt causing the extinction of many mammal species. Then there were aggressive hunts by humans for more mammals in Africa, Europe and Asia, and eventually America. Now we humans direct our aggression to abusing our environment. The importance of this sequence of man-made crises becomes clear when you realise that all these human actions have lasted only a few thousands of years, a quick flash in the 400 million years through which our planet has had life on land.

On the other hand, you can argue that these few thousand years are a long time in comparison to the two hundred or so years since the Industrial Revolution. What we’ve done in our short sojourn on Earth may be comparable to other catastrophic events that happened millions of years ago. It’s 65 million years since the last big catastrophe. It happened in a flash. It took seconds for the meteorite to pass through the Earth’s atmosphere before the impact explosion and then the long environmental recovery.

Of course, what’s happening now is different. The damage we are inflicting has been taking place since the end of the last ice age, about 10,000 years ago, and we are doing it in stages. The most recent stage is dominated by burning oil. Relatively recently, in April 1899, the New York Herald Tribune wrote: ‘Two motor cars will commence to carry Her Majesty’s mails in London itself, the postal authorities having decided to give the new means of locomotion a fair trial. They have quite as great a carrying capacity as the two-horse vans.’ Before this, we burnt another fossil fuel, coal, in quantity from the start of industrialisation. Going back further, wood was the main fuel, bringing about large-scale deforestation, and the whole catastrophe began just a little earlier when we hunted so many mammals to extinction. Ten thousand years seems an age by the scale of a human lifetime, but geologically it is only a flash.