Frozen Earth: The Once and Future Story of Ice Ages (6 page)

In Italy and in France in the eighteenth century, and even earlier, there were men who, usually through their natural curiosity rather than their vocation, made perceptive and prescient observations about the nature of fossils, the existence of extinct volcanoes, and how sedimentary rocks must have formed.
They published their work, but for whatever reason, it was not widely known in Britain, which was to become the acknowledged leader in the development of geology as a modern science in the nineteenth century.
There, especially, religion continued to have a very strong influence on science during this entire period.
But throughout Europe in these early times there was often not much distinction made between the study of nature and theology.
The underlying assumption was that there was a God who had created the Earth and all living things.
That meant that human history and the Earth’s history were coincident.
Observations of the natural world had to fit into this framework.

To a present-day reader, many of the early books about the Earth are fantastical conjectures without much basis in reality.
Some attempted simultaneously to explain facts about the present Earth and still conform to the biblical story of genesis, the details of which were widely known to people of the time.
But the more influential of these accounts were essentially philosophical enquiries, steeped in knowledge of the writings of “the ancients,” especially the Bible, but also seeking “truth” in the spirit of the Age of Reason.
Perhaps the most important of these was written by Thomas Burnet, a British academic who was first and
foremost a theologian—he served for a time as a chaplain to King William III.
His book, written in Latin, appeared in 1681; the English version published a few years later had the title
The Sacred Theory of the Earth,
and it contained chapters dealing with topics such as Paradise, the Flood, and the Conflagration.
Burnet likened the primordial Earth to an egg—slightly oval in shape, with a smooth and “pure” surface, and, in its structure, layered in several “orbs,” which he equated with the yolk, white, and other parts of an egg.
However weird all of this seems to us now, Burnet’s book was a best-seller in England and abroad, and it affected thinking about the Earth for the next century.
Writers and poets—including Coleridge and Wordsworth—acknowledged its influence.
Newton, a contemporary, thought that Burnet gave “the most plausible account” of the presence of seas, mountains, and rocks on the Earth.

Nevertheless, Burnet’s book was controversial.
He tried, he explained, to put some science into his theory.
At the same time, if God had created the Earth, he could rationalize that it was also a theological enquiry, because learning about the Earth was a route to knowledge of God.
Burnet was a philosopher and a theorist, rather than a close observer of nature, but he tried in his writing to bring some sort of order to the often conflicting scenarios that characterized various contemporary ideas about the Earth’s history.
He constructed a theory that could be held up to nature for verification.
However, both scientists and theologians took issue with much of what he wrote.
They paid particular attention to his version of the biblical Flood.
Burnet calculated that there wasn’t enough water in the ocean to cover the land to the prescribed depth, and he concluded that the Flood could not have been caused simply by heavy rains.
And so he devised a different, somewhat more complicated explanation.
The problem for many theologians, however, was that his was a physical explanation, rather than one based on God’s displeasure with man.
Burnet envisioned the early Earth—the paradise phase—not only to be smooth like an egg, but to be blessed with perpetual summer.
For an Englishman, this would surely be a vision of paradise.
Under these conditions,
he wrote, within a few hundred years the Earth’s crust would start to dry out and crack.
Not only that, but the region under the crust—the albumin in Burnet’s egg analogy—was mostly water and would be heated up by the constant sunshine.
The deepening cracks, combined with the expansion of the heated water, would eventually cause the crust to collapse in a violent paroxysm, the interior water shooting high into the air and covering the entire surface.
According to Burnet, the water would have slopped around the Earth’s surface for months, like water in a shaken bucket.

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 was 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.