Frozen Earth: The Once and Future Story of Ice Ages

by Doug Macdougall

  This deluge would have left “ruin” in its wake—that is, the landscape of the seventeenth century familiar to Burnet and his readers; valleys, mountains, and seas replaced the smooth surface of paradise. Rugged topography was imperfection; mountains especially were dark and inhospitable and possibly evil. “Thus perisht the old World, and the present arose from the ruines and remains of it” wrote Burnet. And later in his narrative: “And so the Divine Providence, having prepar’d Nature for so great a change, at one stroke dissolv’d the frame of the old World, and made us a new one out of its ruines.”

  Religion continued to influence investigations of the Earth and its history for the century and a half that would elapse between the publication of Burnet’s book and Agassiz’s theory of ice ages. In Britain, even in the early 1800s, most of the people we now consider early geologists—and all of those who were educating students in geology at the universities—were actually clerics, in the employ of the church, although they probably spent more time on their geological pursuits than their theological ones. But there were other, secular, influences as well. The practical concerns of miners, engineers, and navigators required ever more accurate information about minerals, the nature of coal and metal deposits, and the Earth’s magnetic field. Government funding began to flow into some areas of science as entrepreneurial scientists realized that they could finance their investigations by emphasizing the economic payoffs. The making of precise instruments for measuring physical properties of the Earth became highly developed.

  The earliest geologists naturally enough concentrated most of their attention on the land surface, because it is the most easily accessible part of the Earth. It is also where the evidence that eventually led to the development of the theory of ice ages lay, in the shape and nature of the glaciated landscape. Because the peak of the most recent advance of ice in the Northern Hemisphere occurred only 20,000 years ago—a geological blink of the eye—the evidence is abundant. There has not been time for it to be eroded away or destroyed by the mountain-building forces of plate tectonics. The evidence for more ancient ice ages is much less apparent. Had no ice age occurred on the Earth for hundreds of millions of years, there would have been no glaciers in Switzerland in the nineteenth century, and none of the geologically ephemeral evidence that was used to document the ice age theory would be present. We might even today be puzzling over the significance of the much more cryptic evidence that exists for the Earth’s earlier ice ages.

  Much of the early geological exploration was focused on questions of how the various rock types observed at the Earth’s surface had formed, or how the morphology of the landscape had originated and evolved. As the sway that religion held over explanations for the natural world waned, most of the men taking part in these investigations—they were all men—began to acknowledge that if God were involved at all, it was through the action of secondary agents or processes. Initially, long before there was any hint that ice was important in sculpting the land, the debate centered on whether the rocks at the Earth’s surface were deposited from water or somehow formed in the heat of great fires in the Earth’s interior. At the poles of this debate were three men. Abraham Werner (1749–1817), a Prussian scientist who worked at the Freiberg Mining Academy in Germany for most of his professional life, formulated a comprehensive scheme in which he proposed that virtually all rocks on the Earth had been deposited by the waters of the ocean. In his view, they were either direct chemical precipitates from the sea or mechanical deposits of debris washed in from the land. At the same time, in France, Nicolas Desmarest (1725–1815) realized that, at least in some places, quite different processes had been at work. Desmarest was a remarkable civil servant who traveled widely in France in the course of his government business. He was also obsessed with geology. He knew that there were active volcanoes in some places, and that their molten products cooled to form surface rocks. But as he traveled in the southern and central parts of France, he found volcanic rocks that were very far from any centers of active volcanism and made detailed surveys of them. He realized that they must have been formed at some time in the past, and that the volcanoes responsible for these rocks had since become dormant. Finally, James Hutton (1726–97), a Scottish intellectual who, like Desmarest, was a keen observer, realized that volcanic lavas erupting on the surface aren’t the only rocks produced by great heat. Based on his field observations of granite and related rocks, he concluded that they had once been molten, but that instead of flowing out onto the Earth’s surface from a volcano, these materials had cooled and congealed while still deep within the Earth. Hutton realized that an internal source of heat was required. He was also one of the first to recognize the cyclic nature of geologic processes—hills and mountains are worn down by erosion, the debris produced by this process is deposited as sediments in the sea, buried sediments are heated and fused together to make rocks, and, finally, to complete the process, they are thrust up again by some force to make the hills and mountains of the continents. It was Hutton, contemplating the vast amount of time required for these geological processes, who crystallized for many the immensity of geologic time with his famous line that there is “No vestige of a beginning, no prospect of an end.”

  Although Fire—the Demarest and Hutton views—eventually won out, Werner and his many students, dubbed the Neptunists because of the importance of water in their theories, had a great influence on the young field. A highly respected British cleric and geologist, Adam Sedgwick, writing about the controversy in the nineteenth century and attempting to inject a little humor, said “For a long while I was troubled with water on the brain, but light and heat have completely dissipated it.” And while Werner himself never tried to equate his primordial ocean with the biblical Flood, it was a seductive idea for those who still tried to connect all aspects of the natural world to a strict interpretation of the Bible.

  The ideas of the Neptunists, even though partly discounted by the early 1800s, strongly influenced many of the opponents of Agassiz’s ice age theory. Glacial deposits are often just heaps of boulders and gravel, or sometimes banks of sand and silt, carried away from the front of a retreating glacier by meltwater, and they were invariably interpreted by early observers as water-deposited sediments. Critics of the ice age theory continued to promote this view. They had problems explaining how a flowing stream could leave behind both large boulders and small sand grains simultaneously, but such difficulties were glossed over. They simply discounted Agassiz’s contention that the deposits were the work of glaciers. They bolstered their argument that the glacial sediments must have been deposited in one or more huge floods by pointing to their often chaotic character. When it was shown that many of the boulders were simply too massive to have been carried by water, a new twist was added to the old ideas. Perhaps the boulders had been carried by ice, it was said, but icebergs floating south from the polar region, not solid ice advancing directly over the continents. Sailors, especially fishermen and whalers, were well acquainted with icebergs in the North Atlantic. If sea level had been higher in the past, or if the land had been depressed, one could imagine melting icebergs dropping their rocky burdens onto the submerged English or European countryside.

  Such was the social and scientific backdrop when Agassiz’s theory that there had been a worldwide ice age emerged on the scene. Remnants of Neptunist ideas and thoughts about the biblical Flood still influenced some naturalists. That the debate about large-scale glaciation went on for so long, at least three decades, is a lesson in the durability of ideas—even when there is very strong evidence that they are wrong.

  CHAPTER THREE

  Glaciers and Fossil Fish

  Louis Agassiz grew up in Switzerland, in a village that was almost surrounded by water—two lakes and a river flanked his little town. From the time he was a small boy, he loved to go fishing. Local fishermen would take the parson’s son out in their boats and teach him their secrets. They liked this precocious lad, and they soon realized that he w
as a quick study. Although none of them knew it at the time, fish were to be an important part of Agassiz’s later life. So too were the glaciers of the Alps, looming on the horizon not far from his home.

  Agassiz was to become one of the nineteenth century’s most respected naturalists, a man whose rapid rise to prominence was the result of a unique combination of intelligence, singular determination, force of personality, and perhaps a certain amount of luck. But his personality was certainly central to his accomplishments. The village fishermen who took him out in their boats weren’t the only ones to succumb to Agassiz’s spell. He had an almost instant effect on everyone he met, and throughout his life he was able to persuade people to help him—with money, with sketches of his specimens, or with permission to use their libraries or inspect their fossil collections. Quite often their offers were spontaneous, and even complete strangers did not escape his appeal. When Agassiz was in his late teens studying at Zurich, he and his brother once traveled home on foot, a distance of about a hundred and fifty kilometers—almost a hundred miles—as the crow flies, and much farther for the walkers. Along the way, they were offered a lift by a well-to-do citizen, who, during his brief encounter with the boy, was so impressed that he later wrote to Agassiz’s parents saying that he would be happy to pay for the entire cost of Louis’s education. Although the family didn’t accept this generous offer, the story illustrates just how powerful Agassiz’s enthusiasm and charm could be, even when he was a young man. The incident also foretold a common occurrence in his later life—financial rescue by a wealthy patron. Agassiz paid scant attention to money, and his dreams and ambitions in science often far outstripped the conventionally available resources.

  The Agassiz family envisioned a traditional middle-class life for their son—a profession such as medicine or business that would command respect in the community, marriage into a good family, and a comfortable life at home in Switzerland. But it was not to be. In spite of their best efforts, Agassiz was unwavering in his determination to become a naturalist. He was not a rebel in the conventional sense, and he always had great respect and love for his parents, but he also always managed to persuade them—either himself or through influential relatives or mentors—to do things his way.

  One of the first instances of this characteristic that we know about occurred when Agassiz, at age fifteen, had finished the first stage of his education at a nearby school. He had impressed his teachers with his learning, especially his gift for languages. In his spare time, he fed his insatiable curiosity by collecting and learning about everything he could lay his hands on from the natural world—insects, plants, animals, fish. He seemed to be on an academic trajectory. But his parents had a different plan: now that he had had some education, they would send him to nearby Neuchâtel, where he could serve an apprenticeship with one of his uncles, who ran a business there. Young Louis would thus learn the intricacies of commerce. But in fact he had not the slightest interest in doing so. Although his vision of a career was still hazy, he knew he wanted to continue his education. He wanted to be a “man of letters,” he wrote in a private note to himself; he wanted to “advance in the sciences.” Shrewdly for a lad of fifteen, he enlisted the help of one of his teachers, who spoke to his parents about their son’s future. Before long, they concurred with Agassiz’s wishes, although they may not have realized who was really behind the plan. Louis was sent off for two years of additional schooling in Lausanne—a temporary delay, his parents thought, in his entry into the world of business. The two years in Lausanne, however, only strengthened Agassiz’s resolve to become a man of science. Although he was there ostensibly to study the humanities, he attended lectures on natural history, spent time in the natural history museum, and learned anatomy from a relative who was a physician in the town.

  By then there was no turning back. Agassiz never did return to Neuchâtel to serve an apprenticeship with his uncle; instead, he went on to study in Zurich, and from there to Heidelberg and Munich. It was in Munich that one of his professors asked him to work on a collection of fish from the Amazon that had been collected during an expedition some years before, but never described or cataloged. Louis readily agreed, and with characteristic energy, and in spite of the fact that he was attending lectures and separately doing his own studies of European fish, he completed the work far ahead of schedule. He published a book on his investigation, Brazilian Fishes, in 1829, which was received with considerable acclaim. Agassiz was only twenty-two and still a student. Already he had entered the world of scholarship and had come to the attention of naturalists throughout Europe.

  How, then, did this brilliant young naturalist whose specialty was fish end up being forever identified with the concept of ice ages? More than a little serendipity was required. But it should also be remembered that this was a time long before the era of narrow specialization in the sciences, when “naturalists,” especially, tended to be generalists who could and did pursue any phenomenon that piqued their curiosity. It was a time of exploration, of great general interest in the natural world, of expeditions to unexplored places to collect specimens for Europe’s burgeoning museums. Agassiz’s initial interest in glaciers was almost certainly stimulated partly by the challenge of deciphering the enigmatic landscape features of his native Switzerland but also partly by simple curiosity. (“Among all nature’s phenomena, not a single one seems to me to be more worthy of the interest and curiosity of the naturalist than glaciers,” he wrote in 1840.) His theory of ice ages was, moreover, soon woven into the framework of his ideas about the origin of life on Earth. Eventually, it became one of the pillars of his opposition to the idea of Darwinian-style evolution. It is ironic that this theory, formulated early in his career and truly a triumph of observation and deduction, was later to become an important part of his dogmatic and very nonempirical rejection of the developing ideas about evolution.

  Serendipity, chance observations or opportunities, and unexpected results are common enough in science even today, and they played an important role in Agassiz’s career. His route from being a student of zoology and medicine in Munich to authoring the theory of ice ages was in some ways unremarkable and in others quite amazing. (Notice that Agassiz studied both zoology and medicine. His parents were by this time resigned to the fact that he was destined to be a naturalist, but they urged him to complete a degree in medicine so that he could always work as a physician if a career as a naturalist didn’t work out. Ever dutiful, Agassiz followed their advice—but it was zoology, not medicine, that really captured his heart and mind.) When he had completed his book on Brazilian fish, Agassiz decided to dedicate it to the great French naturalist Baron Georges Cuvier. Agassiz had never met Cuvier, but he idolized him and confessed when he sent him a copy of Brazilian Fishes that “your works have been till now my only guide.” Still, the dedication may have been made with one eye on the future. Agassiz’s letter also laid out his hopes and plans for a career in science. Cuvier replied, which flattered and encouraged the young naturalist. And a few years later, in late 1831, shortly after he had completed both his degree in medicine and a Ph.D. in zoology at Munich, Agassiz was in Paris seeking an audience with the great man. They met, and Cuvier, like so many others, was quickly won over by Agassiz’s intellect, enthusiasm, and complete dedication to his work. So impressed was Cuvier that before long he had turned over to Agassiz one of his own projects, one that seemed tailor-made for the young scientist: a comprehensive examination of the entire fossil fish collection then housed at the French National Museum of Natural History. It was the kind of large, important, and, if done properly, reputation-enhancing study that could fully engage Agassiz’s interest. He waded into it with gusto, and for a short but intense time, he worked together with Cuvier, learning about the importance of careful observation and the intricacies of reconstructing anatomy from fragmentary fossil evidence. He also absorbed Cuvier’s theories about the origin of life, which had been developed from long and careful study of fossils: that an
imals could be divided into several groups with no connections among them; that species were “fixed” and did not change; and that there had been periodic catastrophes in the Earth’s history that had wiped out most living things, with newly emerging species bearing no relationship to those that preceded them. This, of course, was a very different scenario from the one that would soon be proposed by Charles Darwin. However, it was one that undoubtedly played a part in the development of Agassiz’s ideas about a catastrophic ice age. Cuvier was a devout man, and he believed that the conclusions he reached from the study of fossils were simply manifestations of a higher plan, God’s plan. For the rest of his career, Agassiz was to work within a similar framework, believing that he was revealing the creator’s design through his studies of nature.

  Cuvier’s accomplishments and position made him an influential man in France, with important connections in science and government. One of these was Alexander von Humboldt, another great man of the times, who happened to be in Paris on official business for the king of Prussia when Agassiz arrived to begin work with Cuvier. Humboldt was a renowned explorer, and, like Cuvier, a naturalist of high distinction. He was also interested in discovering and encouraging new talent. Humboldt knew of Agassiz’s book on Brazilian fish, and when he learned more about Agassiz’s work from Cuvier and others, he invited the young scientist to his Paris headquarters. Soon he too was charmed by Agassiz’s enthusiasm and impressed with his dedication to science. In turn, Agassiz had his eyes opened to the possibility that distinguished scientists could also move easily in the highest circles of society and government and have influence far beyond their chosen field—a lesson that most probably played a part in his assumption of just such a role many years later when he emigrated to the United States.