Frozen Earth: The Once and Future Story of Ice Ages

by Doug Macdougall

  Agassiz was fortunate to have Cuvier as a guru, but their work together was short-lived: Cuvier died in May 1832. In that short time—Agassiz had been in Paris for only half a year—Agassiz had already come to regard Cuvier as both mentor and friend, and their brief association would influence him throughout his career. In spite of Cuvier’s death, Agassiz was determined to complete the work on fossil fish that had been entrusted to him, but he was at a loss about how to proceed. His mentor was gone, and his personal funds were all but exhausted. But a guardian angel appeared just when Agassiz needed it the most. Unsolicited, Alexander von Humboldt sent Agassiz a check for a thousand francs so that he could continue the work. More than that, Humboldt was instrumental in securing a position for Agassiz that would, for the next thirteen and a half years, allow him to do his best scientific work—including his seminal studies of glaciers and development of the ice age theory. As fate would have it, the town of Neuchâtel, where Agassiz’s parents had originally wanted him to serve an apprenticeship in business, was about to establish a new academy and a natural history museum. Equally important—at least as far as Agassiz’s career was concerned—the canton’s affairs at that time were governed jointly by Switzerland and the king of Prussia. Humboldt quickly mobilized support for Agassiz among the Prussian authorities, and he also wrote to the local Neuchâtel aristocracy in praise of this native son of Switzerland, the local boy who had already gained international prominence as a naturalist. They had little choice; how could such entreaties be ignored? And wouldn’t Agassiz and his already substantial collections bring fame to their museum and town? Their response was to create a position for Agassiz at the new college—they appointed him professor of natural history and raised money for a modest salary. In addition, Humboldt arranged for the Prussian government to subsidize purchase of Agassiz’s personal collections for the new museum, a move that helped him considerably financially. In the fall of 1832, at the ripe old age of twenty-five, Agassiz returned to Switzerland to take up his professorship. He was brimming with ambitious plans for the new college and museum, and also for his own place in the wider world of science.

  It had always been apparent that Agassiz was a gifted communicator and an engaging companion at the café or pub, but it was in Neuchâtel that his skills as a teacher became obvious to everyone. He was an avid believer in what would be called, in today’s jargon, inquiry-based learning. Within months of arriving at his new post, Agassiz had formed a local natural history society. In the beginning, it consisted mostly of the higher echelons of Neuchâtel society, but soon Agassiz had, it seemed, persuaded half the townspeople that they should be out collecting specimens and learning about zoology, geology, and botany. To be sure, he gave conventional lectures in his role as professor, but learning by doing was what he espoused most enthusiastically. Later, he would transform science education in America using the same approach. But for the moment, the whirlwind that was Agassiz had descended on quiet little Neuchâtel, and at least while he remained, it was never quite the same. He soon became a source of civic pride for many of the town’s prominent citizens, and the success of the man and his museum became their personal concern. For scores more, he was an inspiring leader of field trips and teacher of nature. Not incidentally, the steady stream of fish, fossils, birds, and animals collected by these new nature enthusiasts allowed his small museum to grow rapidly.

  But Agassiz had other things on his mind as well. He married a German sweetheart of many years and settled into a comfortable domestic life. He also threw himself again into the work on fossil fish that had begun with Cuvier in Paris. One of the main reasons he had taken the post in Neuchâtel, far from the great European centers of learning, was that it both offered him the opportunity to spend much of his time on his own research and provided him with a small but dependable income. It was a wise decision. Over the next decade, his research resulted in a series of volumes on fossil fish that were unequalled in their clarity of description and classification, and that were accompanied by beautiful, accurately drawn illustrations. His reputation grew steadily and rapidly, and his work brought widespread acclaim and a series of medals and prizes.

  One summer during his stay in Neuchâtel—the summer of 1836—Agassiz took his family on holiday to a picturesque region of the Swiss alps near the town of Bex. The town was home to a well-known geologist, Jean de Charpentier, who was director of the salt-mining operations there. De Charpentier was a convivial man who frequently hosted scientists, naturalists, and other men of learning at his home, and he had urged Agassiz to visit. The two families got along well; de Charpentier’s wife, like Agassiz’s, was German, and Agassiz had rightly perceived that his own spouse would welcome the company of a compatriot after the relative insularity of Neuchâtel. The decision to spend that summer holiday in Bex proved to be a crucial one in Agassiz’s career—once more serendipity at work. For Charpentier was convinced that the glaciers of the Alps had once been much more extensive, and he was keen to show Agassiz the evidence.

  Charpentier had been brought to this conclusion through the work of a friend and colleague, an engineer named Ignatz Venetz. During his work in the Swiss countryside, Venetz had had ample opportunity to observe the so-called erratic boulders that bore no resemblance to local rocks and were often stranded far up on valley walls. Some of the boulders were scratched and faceted, features reminiscent of those he had observed on rocks at the very margins of active glaciers. He also saw arcuate ridges of boulders and gravel curving across the green Swiss valleys. They were almost identical to the mounds of rock debris—moraines—that marked the sides and ends of contemporary glaciers in the Alps. Venetz concluded that these features could best be explained by glacial action in the past, which meant that the Alpine glaciers must have been much more extensive. He had developed these ideas over a long period of time and had formally proposed them in 1829, some seven years before Agassiz visited Bex. Venetz also knew that similar features had been reported from other parts of Europe, and he concluded that glaciers had probably existed in those regions as well. He convinced his initially skeptical friend de Charpentier of the reality of the proposal by taking him out into the field and showing him the widespread and abundant glacial features. By the time Agassiz visited in 1836, de Charpentier had accumulated and cataloged evidence of extensive past glaciation both in Switzerland and elsewhere. But neither Venetz nor de Charpentier aggressively pushed their ideas about glaciation. Perhaps they simply did not realize the significance of their observations. For whatever reason, they were content to discuss their ideas in a low-key way with other scientists, and, for those willing to make the effort, to show them the field evidence. Many naturalists, especially those interested in natural history, knew about their views but did not give them much credence.

  Agassiz was one of those familiar with the ideas of these two men, but until his summer visit to Bex, he too had dismissed their theory as unlikely. The holiday was a pleasant one—the scenery was idyllic, and the Agassizes found that they had much in common with the de Charpentiers. Most evenings would find Agassiz at de Charpentier’s table with Venetz and others, enjoying their host’s hospitality and engaging in long conversations about natural history and philosophy. We shall never know exactly what transpired during these discussions, but given de Charpentier’s and Venetz’s interests, they must have included debates about glaciers and their past behavior. Agassiz listened to what his colleagues had to say, and undoubtedly these evening brainstorming sessions influenced his thinking. However, with his strong belief in observation and hands-on science, it was almost certainly the visible field evidence that really convinced him that Venetz and de Charpentier had discovered something important. When they took him out into the Alpine valleys and showed him the moraines, erratic boulders, and glacial scratches and grooves, it was a revelation. When he returned to Neuchâtel that autumn, he was like a blind man suddenly given sight: he saw signs of glaciation—especially erratic boulders and glacial scratches
—everywhere around him. And, together with his long-time friend from student days, the botanist Karl Schimper (the same Schimper who coined the phrase “ice age,” and who was now working with Agassiz in Neuchâtel and living in the family home), he synthesized these observations and soon came up with a theory. With the zeal of a convert, Agassiz took up the cause of past glaciation and did his mentors one better: he proposed a period of global frigidity in the past, not just one in which glaciation in the Alps and a few other regions of Europe had been more extensive.

  The announcement of Agassiz’s ice age theory came only a year after his sojourn with de Charpentier in Bex. In 1837, the Natural History Society of Switzerland met in Neuchâtel, and Agassiz, as president of the society and host of the gathering, gave the introductory address. The delegates, who expected that Agassiz would discuss fossil fish or one of his other biological interests, were in for a surprise. After expressing his pleasure in welcoming them to Neuchâtel, and extolling the advances that were occurring in the sciences, Agassiz said that he wished to focus on a topic appropriate to the location: glaciers, moraines, and erratic boulders. Carefully acknowledging his debt to de Charpentier and Venetz, he laid out a comprehensive ice age hypothesis that presaged his book Studies on Glaciers, which would be published three years later. The address was the pivotal event that brought the idea of an ice age to the full attention of scientists. In the context of what had gone before, it was a grandiose scheme, and it generated instant and long-lasting controversy. What was truly new was Agassiz’s proposition that during the ice age, a great sheet of ice had extended from the North Pole to the Mediterranean, before the Alps had even been formed. This was very different from the idea that Alpine glaciers had extended a bit further down their valleys in the past. It took even his friends Venetz and de Charpentier by surprise. Furthermore, Agassiz brought zoology into the picture by proposing that the ice age had extinguished many of the Earth’s living creatures. And implicit in his theory was the idea that there had been significant climatic variations in the Earth’s past. The conventional wisdom at the time was that the Earth had been cooling since its creation. Agassiz suggested instead that each geological period (already geologists had subdivided the Earth’s past into different periods based on the fossil record) had had an equable, stable, climate, but was terminated by a frigid episode, after which temperatures recovered, albeit perhaps not quite to their previous level.

  One imagines that many in the audience rolled their eyes. The scope of this scheme was too much even for de Charpentier, who was the person most responsible for convincing Agassiz that Alpine glaciation had once been much more extensive. Agassiz, even in his enthusiasm for this new (for him) subject, recognized that there was likely to be some adverse reaction. Toward the end of his address (which was later published) he said:

  I am afraid that this approach will not be accepted by a great number of our geologists, who have well-established opinions on this subject, and the fate of this question will be that of all those that contradict traditional ideas. Whatever the opposition to this approach, it is unquestionable that the numerous and new facts mentioned above concerning the transportation of boulders, which may easily be studied in the Rhône valley and in the vicinity of Neuchâtel, have completely changed the context in which the question has been discussed up to the present time.

  And in this respect he was right. His theory was not a flight of fancy; it was carefully based on detailed field observations. Some of the observations he discussed drew on the work of de Charpentier and Venetz, but many were his own. The observational skills he had learned from Cuvier in Paris served him just as well in glaciological as in fossil studies. “Fortunately, in scientific problems, numerical majorities never settled any issue at first glance,” Agassiz told the skeptical delegates, confident of his ability to win over critics in the long run.

  Three years after his lecture at the Neuchâtel meeting, in 1840, Agassiz published his carefully compiled evidence for widespread past glaciation in a large volume written in French and titled Études sur les glaciers—translated as Studies on Glaciers. It was the formal presentation of the ice age theory to the world, and it is a remarkable book, truly a tour de force. Although he never considered studies of glaciers to be his primary scientific focus, in practice, Agassiz devoted a great deal of his time to this work, spending the better part of each summer in the Alps doing glaciological fieldwork. In his book, in engaging language, Agassiz described in great detail the observations that he and his colleagues had recorded during those summer field seasons: the temperatures, the nature of the crevasses, the morphology of moraines, the details of the grooves and scratches on the underlying rock, and much more. He included beautiful, if somewhat unnatural-looking, sketches of many of the glaciers they studied, often with tiny people—walkers, women in peasant dress, picnickers—or farm animals drawn in. After cataloging the field observations, and noting how similar features occur far from the present-day glaciers, Agassiz, in a few short sentences, laid out his revolutionary conclusion:

  In my opinion, the only way to account for all these facts and relate them to known geological phenomena is to assume that . . . the Earth was covered by a huge ice sheet that buried the Siberian mammoths and reached just as far south as did the phenomenon of erratic boulders. . . . It extended beyond the shorelines of the Mediterranean and of the Atlantic Ocean, and even completely covered North America and Asiatic Russia.

  The frozen Siberian mammoths to which Agassiz refers in this passage had caused a great stir in Europe, and they featured significantly in the ideas he developed about the biological effects of the ice ages. Several reports that had filtered out from arctic Siberia described these giant mammals melting out of decomposing ice, almost perfectly preserved. Hair, skin, and flesh were intact—in fact, polar bears fed on the thawing animals and local villagers hacked off meat for their dogs. To Agassiz this indicated that the ice age had begun suddenly and had been a biological catastrophe. He also mentions here erratic boulders, the same kinds of boulders that had played a major role in convincing Venetz and de Charpentier about past glaciation. Erratics had puzzled geologists for decades and, as has already been mentioned, were at the focus of the debate between those who wanted to explain most geological features as originating in the biblical Flood and those who sought more natural explanations. Some of the erratics in the Alps are huge, weighing thousands of tons, and they are unusual because they bear no resemblance to other rock types in their immediate vicinity. Their great importance in Agassiz’s theory was that they are markers of the extent of ice age glaciers.

  Agassiz dedicated his book to Venetz and de Charpentier. Still, they were slighted—Agassiz did not consult them about his ideas, and they felt that his grandiose theory misrepresented some of their ideas. No one before had postulated a truly global cold period, and no one was as enthusiastic or confident about promoting the theory as Agassiz. In addition to showing how important ice is in shaping the landscape, Agassiz also introduced the idea that drastic climate change had occurred in the Earth’s history, and that the cold of the ice age had strongly affected life on Earth. Each of these was a new idea, and each was controversial.

  Today, Agassiz’s logic seems unassailable, and no one doubts the reality of ice ages. To present-day scientists, as to Agassiz, the conclusion that there were great sheets of ice covering the northern continents is a straightforward outcome of the observations. However, at the time it was a radical concept. By the time Agassiz’s book was published, many scientists had come to accept that the Alpine glaciers had once been somewhat more extensive than they were in the 1830s—after all, there were historical accounts as proof. Europe was just then emerging from a period of several hundred years of cool temperatures that would later come to be known as the “Little Ice Age.” The slightly larger Alpine glaciers described in historical accounts could explain some of the geological observations in valleys now free of ice. But an ice age that was global in extent—that
was a different matter altogether.

  Agassiz’s interest in glaciation may have been stimulated in part by his biological interests. Through his work on fossil fish, he was well aware of the paleontological evidence for periods of massive extinction in the Earth’s past. The ice age theory provided a way to understand at least one of these events, and the frozen mammoths confirmed the extreme biological impact. In a passage from his book that is quite poetic, he describes the ice age landscape and the effects he believed the frigid climate must have had on living things:

  The development of these huge ice sheets must have led to the destruction of all organic life at the Earth’s surface. The land of Europe, previously covered with tropical vegetation and inhabited by herds of great elephants, enormous hippopotami, and gigantic carnivora, was suddenly buried under a vast expanse of ice, covering plains, lakes, seas, and plateaus alike. The movement of a powerful creation was supplanted by the silence of death. Springs dried up, streams ceased to flow, and the rays of the sun, rising over this frozen shore (if they reached it at all) were greeted only by the whistling of the northern wind and the rumbling of crevasses opening up across the surface of the huge ocean of ice.

  Like many of his contemporaries, Agassiz equated life with “a powerful creation.” Religion still had a strong influence on thinking about the origin and history of life, even if observation and reasoning had gradually overturned the teachings of the religious authorities on matters such as astronomy and even the Earth’s history. It was to be a topic that dogged Agassiz throughout his career. In spite of his contributions to paleontology and the evolution of fish, he would never accept Darwin’s ideas on evolution.