Aerial photograph of receding glacier, braided Delta River, and mountain peaks in Alaska.
Taken from U.S. Fish and Wildlife Service (National Image Database).
Aerial photograph of receding glacier, braided Delta River, and mountain peaks in Alaska.
Taken from U.S. Fish and Wildlife Service (National Image Database).
Although many past scientists had made discoveries involving how glaciers shape the land, the real impetus toward a cohesive theory began inauspiciously in 1815,
when a chamois-hunter was intrigued by boulders perched on a hilltop. Although not a scientist by trade, Jean-Pierre Perraudin knew that a great deal of
work would be involved in placing a boulder so high, and it seemed unreasonable to him to suppose that a flood could have done it. He believed glaciers
were the most likely culprits. He appealed to a foremost
scientist of the region, Jean de Charpentier. Charpentier was unimpressed with Perraudin’s reasoning, but another naturalist, Ignace Venetz, was. In 1821, at
a Swiss natural history meeting, he expounded on the idea that many features of the Swiss landscape could be explained by glaciers. In fact, they were recorded
in 14th century painting of Alpine scenery (Rance). Eventually things came full circle, when in 1829 a lecture by Venetz convinced even the skeptical de Charpentier.
An enthusiastic convert, de Charpentier began his own line of inquiry. He was met by resistance from a leading scientist of the day, Jean Louis Rodolphe Agassiz.
Agassiz had gained renown through his study of ancient fish, and it was critical to win his support if the theory was to prevail.
In 1836, the pivotal moment came when de Charpentier went with Agassiz to the Alps, ostensibly to be convinced that glaciation had not occurred. But it was Agassiz
who recanted when presented with the evidence, and he became convinced that the Alps were once
a sea of ice. Although a firm believer in the Biblical flood, Agassiz was obsessed with this new notion. He conducted several years of research in the
Alps, discovering that the boulders in the area were consistent with Scandanavian origin. This led him to a theory even more radical than de Charpentier's: a vast portion of Europe had been covered with a blanket of ice.
This neatly merged with his
belief in a the fixity of species. It was not necessary for life to adapt to the changes. It was simply wiped out, and created anew at the end of the ice age (Rance).
A precedent was set. To convince others of the veracity of an ice age, simply take them out
to the field. Agassiz used the technique to convince a prominent British scientist, William Buckland, in 1868. Although a devout diluvalist, Buckland could not deny the evidence before him. And as a catastrophist, he
found that an ice age wasn't so unpalatable after all. Buckland's reputation greatly aided in the battle to establish the validity
of glacial theory.
Agassiz first made public his beliefs at a Presidential address to the Société Helvétique de Sciences Naturelles in Neuchâtel on July 24th, 1837.
The Earth was once covered in ice from the North pole to the Mediterranean, he conjectured, to the shock of his audience. Ice age theory fit in well with the catastrophist view of the world. It was less appealing to those who favored
uniformitarianism. For this reason many of the leading scientists of the day,
who understood the implications of embracing catastrophism, were less than enthusiastic. Earth science had been legitimized as an empirical system by uniformitarianism,
and they would not abandon it easily, believing that to do so would render the world once again at the mercy of forces they could not see or study.
J.W. Dawson, in particular, was determined to remedy what he saw as the error of glacial theory, and wrote at length in Acadian Geology against it.
Another group, favoring the belief that a flood was the more logical (and Biblical)
explanation for the landforms in question, were equally opposed. Among the most vociferous of these was Sir Henry Howorth.
Even as late as 1893, Howorth wrote in favor of diluvialism in The Glacial Nightmare and the Flood.
As mentioned before, large boulders, consisting of material foreign to their surroundings, were puzzling to geologists of the
18th century. Geologists dubbed them 'erratics' in keeping with their odd character. As early as 1795 James Hutton had recognized the fact that boulders in the Jura mountains contained material
consistent with origin in the Alps, and his explanation was expectedly uniformitarian. Erosion wore away the valley between
the Jura and the Alps, and wore away the Alps as well, causing ice to slide downhill, carrying boulders with it (Williams).
Other strange evidence also presented itself. In 1820, John Playfair, Hutton's illustrious biographer, visited the Jura himself, finding there polished bedrock and ridges and mounds of
poorly sorted sediments. He suggested they were evidence of glaciation, but was not taken seriously, as such features
were considered irrefutable evidence of a global flood (Rance).
The idea that a vast flood had created much of the terrain was indeed difficult to eradicate.
It was seen even in the naming of various deposits. "Diluvium" was the name given to loose accumulations of unsorted rocks.
In 1833 Charles Lyell published Principles of Geology, in which we can today seen numerous misinterpretations due to
the widespread lack of glacial understanding at the time. In it Lyell proposed that icebergs could the means of transport
for erratics. During periods of global warming, ice breaks off the poles and floats across submerged continents,
carrying debris with it, he conjectured. When the iceberg melts, it rains down sediments upon the land. Because this theory could account
for the presence of diluvium, the word "drift" became the preferred term for the loose, unsorted material, today called "till."
Furthermore, Lyell believed that the accumulation of fine angular particles covering much of the world (today called loess) was a deposit settled from
mountain flood water (Rance).
A decade would pass before a challenge to iceberg theory was in the offing. But when Agassiz began to focus his attention
on a global ice age, things began to fall into place. In 1840 he published Études Sur les Glaciers wherein he lucidly
explained many of the confusing landforms that geologists had puzzled over for so long. Agassiz argued convincingly that
the position of the striated rocks upon which till rests is consistent only with a large mass of ice, such as glacier, moving
across the land (Rance).
Loess, however, was not addressed by Agassiz's work. It remained a mystery for several more decades. Its fine grain size
and lack of coarse material was deceptively consistent with lacustrine, or lake, deposits.
Orestes Hawley St. John in 1870 questioned this explanation, but it wan't until 1877 that an alternate means for
its transport was suggested by Ferdinand Baron von Richthofen: wind. However his idea was still considered less appealing
than the lacustrine hypothesis. To maintain it, geolgists appealed to the absurd: Thomas Chrowder Chamberlin and Rollin D.
Salisbury in 1885 published a discussion that included a
lengthly explanation of how a lake could cover almost the whole of North America (Totten and White, 1985). Among those unsatisfied with this
explanation was Frank Leverett, who
pointed out that the occurrence of loess at all elevations made deposition by flooding ludicrous, and that thicker loess
on the east side of valley could best be explained by eolian deposition (Totten and White, 1985). In the end
these observations convinced the geological community that loess was indeed a windblown
deposit, associated with the margins of glaciers (Britannica).
Glacial lakes were another source of angst, and an explanation for their existence was formed only after many years after
glacial theory was widely accepted. John Strong Newberry and Charles Whittlesey between the years 1862 and 1870 proposed that glaciers had
formed the Great Lakes (Totten and White, 1985). Fierce opposition from many other geologists, who proposed the alternate mechanisms of
erosion and tectonics for their formation, did not prevail; Newberry and Whittlesey's hypothesis was eventually accepted.
Glaciers are mysterious, creeping slowly along through the ages, then retreating just as slowly, razing the landscape and
leaving only obscure traces of themselves. Their abstruse nature was the cause of a
a dispute so bitter and public that it became known as “the Great Glacier Controversy.”
Like many disputes, this one had a prosaic beginning. As a guest of Agassiz in 1841, James David Forbes, a leading figure
in the scientific world, casusally
mentioned that he had noticed a characteristic vertical stratification in the ice of glaciers. Intrigued, Agassiz began independently to measure ice flow;
Forbes was doing likewise, and concluded his
study only weeks prior to Agassiz. Agassiz found this utterly unconscionable, and the two became lifelong antagonists (Aber). But this rancorous dispute
was not the event that became known as "the Great Glacier Controversy." The next chapter in the story came when Forbes published his findings, boldly
asserting that ice, under enough pressure, can behavior plastically. This drew the attention of
a leading scientist of the day, John Tyndall. He found them inconsistent with the most respected new theory of the time,
Faraday's principle of relegation. He insisted
that glaciers are not subject to plastic behavior, but would instead move by fracture and regelation, or alternate thawing and refreezing. (Britannica).
The debate was further complicated by the contribution of James Thomson, who insisted on a thermodynamic explanation.
The debate grew so heated that
it drew the public's interest. Ironically, current theory incorporates both Forbes and Tyndall's views of ice flow (Selby, 1985).
This scientific clash led to even more disharmony further down the road, when P.G. Tait, in
writing Forbes’ biography, gave credit for the discovery of glacial movement entirely to Forbes. Tyndall saw this as unjust and sought to redress it, to
the irritation of Tait. Their dispute erupted in a series of acrimonious letters to Nature magazine (Booth, 1999).
In 1879 Gerhart de Geer devised a method by which to test Agassiz's theory. In spite of the great conjecture surrounding ice ages, no one had yet designed a
scientific procedure by which to prove their existence. With a group of students from the University of Uppsala, de Geer
remedied this omission. His plan to find an annual record left by glaciers in Sweden resulted in the discovery of varves.
When the weather warms in the summer, silt accumluates in lakes fed by glaciers, forming a light gray layer. In the winter,
only clay-sized material settles, forming a dark gray layer. By counting these couplets of dark and lightmaterial,
a date can be established for the timing of glaciation of the area. At the end of his study, de Geer had composed a varve
chronology dating back almost 17,000 years. He presented his findings to the International Geological Congress in Stockholm in 1910 (Rance). Varve
sequences have proven an exceedingly useful tool, and are utilized by geologists even today.
Explorers as well as scientists played a role in these arctic discoveries. From 1893 to 1896, Fridtjof Nansen sailed to Greenland and found a
vast sheet of ice. This discovery led him the the hypothesis that deep convection, or mixing, of North Atlantic ocean water occurred in
this area. Only a few years ago this idea was revived and it now appears that Nansen's ideas will be proved correct 100 years after
first proposed (WHOI, 2003).
Once widespread acceptance of the concept of ice ages was in place, the stage was set for a remarkable discovery:
the Earth has been subject to numerous ice ages
over the course of its existence. In England, James Geikie theorized five interglacial periods had occurred in Britain (Britannica).
In Europe, Albrecht Penck and E. Bruckner, in 1909, noted remnants of four sets of river terraces in the outwash gravels in the northern foothill valleys of the
Alps. Newberry, however, was at first resistant to the
idea of multiple glaciations. He preferred one event, from which great numbers of icebergs were emitted, explaining all
drift deposits. He was confronted by the work of
G.J. Hinde, who found evidence for two interglaical periods in Ohio in 1878. Newberry accordingly modified his views (Totten and White, 1985).
And Chamberlin, in spite of his initial reluctance to accept the glacial origin of the Great Lakes, was among the pioneers in
the area of ice ages, noting that drift in Ohio correlated with his studies in Wisconsin, which suggested multiple glaciations. Early Glacial Theory
The Objectors
The Evidence
The Controversy
Testing the Theory
Evidence for Numerous Ice Ages