reduced the saltiness (and thus density) of northern oceans, causing the Gulf Stream to swerve to the south, like a driver trying to avoid a collision. Deprived of the Gulf Stream’s warmth, the northern latitudes returned to chilly conditions. But this doesn’t begin to explain why a thousand years later when the Earth warmed once again the Gulf Stream didn’t veer as before. Instead, we were given the period of unusual tranquility known as the Holocene, the time in which we live now.
There is no reason to suppose that this stretch of climatic stability should last much longer. In fact, some authorities believe that we are in for even worse than what went before. It is natural to suppose that global warming would act as a useful counterweight to the Earth’s tendency to plunge back into glacial conditions. However, as Kolbert has pointed out, when you are confronted with a fluctuating and unpredictable climate “the last thing you’d want to do is conduct a vast unsupervised experiment on it.” It has even been suggested, with more plausibility than would at first seem evident, that an ice age might actually be induced by a rise in temperatures. The idea is that a slight warming would enhance evaporation rates and increase cloud cover, leading in the higher latitudes to more persistent accumulations of snow. In fact, global warming could plausibly, if paradoxically, lead to powerful localized cooling in North America and northern Europe.
Climate is the product of so many variables-rising and falling carbon dioxide levels, the shifts of continents, solar activity, the stately wobbles of the Milankovitch cycles-that it is as difficult to comprehend the events of the past as it is to predict those of the future. Much is simply beyond us. Take Antarctica. For at least twenty million years after it settled over the South Pole Antarctica remained covered in plants and free of ice. That simply shouldn’t have been possible.
No less intriguing are the known ranges of some late dinosaurs. The British geologist Stephen Drury notes that forests within 10 degrees latitude of the North Pole were home to great beasts, including Tyrannosaurus rex. “That is bizarre,” he writes, “for such a high latitude is continually dark for three months of the year.” Moreover, there is now evidence that these high latitudes suffered severe winters. Oxygen isotope studies suggest that the climate around Fairbanks, Alaska, was about the same in the late Cretaceous period as it is now. So what was Tyrannosaurus doing there? Either it migrated seasonally over enormous distances or it spent much of the year in snowdrifts in the dark. In Australia-which at that time was more polar in its orientation-a retreat to warmer climes wasn’t possible. How dinosaurs managed to survive in such conditions can only be guessed.
One thought to bear in mind is that if the ice sheets did start to form again for whatever reason, there is a lot more water for them to draw on this time. The Great Lakes, Hudson Bay, the countless lakes of Canada-these weren’t there to fuel the last ice age. They were created by it.
On the other hand, the next phase of our history could see us melting a lot of ice rather than making it. If all the ice sheets melted, sea levels would rise by two hundred feet-the height of a twenty-story building-and every coastal city in the world would be inundated. More likely, at least in the short term, is the collapse of the West Antarctic ice sheet. In the past fifty years the waters around it have warmed by 2.5 degrees centigrade, and collapses have increased dramatically. Because of the underlying geology of the area, a large-scale collapse is all the more possible. If so, sea levels globally would rise-and pretty quickly-by between fifteen and twenty feet on average.
The extraordinary fact is that we don’t know which is more likely, a future offering us eons of perishing frigidity or one giving us equal expanses of steamy heat. Only one thing is certain: we live on a knife edge.
In the long run, incidentally, ice ages are by no means bad news for the planet. They grind up rocks and leave behind new soils of sumptuous richness, and gouge out fresh water lakes that provide abundant nutritive possibilities for hundreds of species of being. They act as a spur to migration and keep the planet dynamic. As Tim Flannery has remarked: “There is only one question you need ask of a continent in order to determine the fate of its people: ‘Did you have a good ice age?’ ” And with that in mind, it’s time to look at a species of ape that truly did.
28 THE MYSTERIOUS BIPED
JUST BEFORE CHRISTMAS 1887, a young Dutch doctor with an un-Dutch name, Marie Eugene Francois Thomas Dubois, arrived in Sumatra, in the Dutch East Indies, with the intention of finding the earliest human remains on Earth.[46]
Several things were extraordinary about this. To begin with, no one had ever gone looking for ancient human bones before. Everything that had been found to this point had been found accidentally, and nothing in Dubois’s background suggested that he was the ideal candidate to make the process intentional. He was an anatomist by training with no background in paleontology. Nor was there any special reason to suppose that the East Indies would hold early human remains. Logic dictated that if ancient people were to be found at all, it would be on a large and long-populated landmass, not in the comparative fastness of an archipelago. Dubois was driven to the East Indies on nothing stronger than a hunch, the availability of employment, and the knowledge that Sumatra was full of caves, the environment in which most of the important hominid fossils had so far been found. What is most extraordinary in all this-nearly miraculous, really-is that he found what he was looking for.
At the time Dubois conceived his plan to search for a missing link, the human fossil record consisted of very little: five incomplete Neandertal skeletons, one partial jawbone of uncertain provenance, and a half-dozen ice-age humans recently found by railway workers in a cave at a cliff called Cro-Magnon near Les Eyzies, France. Of the Neandertal specimens, the best preserved was sitting unremarked on a shelf in London. It had been found by workers blasting rock from a quarry in Gibraltar in 1848, so its preservation was a wonder, but unfortunately no one yet appreciated what it was. After being briefly described at a meeting of the Gibraltar Scientific Society, it had been sent to the Hunterian Museum in London, where it remained undisturbed but for an occasional light dusting for over half a century. The first formal description of it wasn’t written until 1907, and then by a geologist named William Sollas “with only a passing competency in anatomy.”
So instead the name and credit for the discovery of the first early humans went to the Neander Valley in Germany-not unfittingly, as it happens, for by uncanny coincidence
Many people refused to accept that the Neandertal bones were ancient at all. August Mayer, a professor at the University of Bonn and a man of influence, insisted that the bones were merely those of a Mongolian Cossack soldier who had been wounded while fighting in Germany in 1814 and had crawled into the cave to die. Hearing of this, T. H. Huxley in England drily observed how remarkable it was that the soldier, though mortally wounded, had climbed sixty feet up a cliff, divested himself of his clothing and personal effects, sealed the cave opening, and buried himself under two feet of soil. Another anthropologist, puzzling over the Neandertal’s heavy brow ridge, suggested that it was the result of long-term frowning arising from a poorly healed forearm fracture. (In their eagerness to reject the idea of earlier humans, authorities were often willing to embrace the most singular possibilities. At about the time that Dubois was setting out for Sumatra, a skeleton found in Perigueux was confidently declared to be that of an Eskimo. Quite what an ancient Eskimo was doing in southwest France was never comfortably explained. It was actually an early Cro-Magnon.)
It was against this background that Dubois began his search for ancient human bones. He did no digging himself, but instead used fifty convicts lent by the Dutch authorities. For a year they worked on Sumatra, then transferred to Java. And there in 1891, Dubois-or rather his team, for Dubois himself seldom visited the sites-found a section of ancient human cranium now known as the Trinil skullcap. Though only part of a skull, it showed that the owner had had distinctly nonhuman features but a much larger brain than any ape. Dubois called it
The next year Dubois’s workers found a virtually complete thighbone that looked surprisingly modern. In fact, many anthropologists think it
