The Universe Within (25 page)

Unbeknownst to his friends in Bex, Agassiz set off to test his grand idea. In 1840, he published a book, dedicated to his friends from that fateful summer vacation, called
Studies on Glaciers
. In it he proposed the radical notion that ice at one point in time extended from the
North Pole all the way to the Mediterranean and then retreated, only to extend again. A friend came up with a catchy name for these cold intervals: “
ice ages.”

Agassiz, with his personal charm, set off to convince the great eminences of the time of his notion. He took visitors out in the field as his friends from the summer vacation had done for him, encouraging them to see a past rich in ice. It took many trips, and
even more arguments, but Agassiz succeeded. The ice age theory became widely accepted.

The beauty of this theory was that, like most great scientific ideas, it made specific predictions. Agassiz’s notions could be tested simply by looking at the
rocks in the world. Exotic boulders, mounds, and linear gashes on rocks should be widespread. If it is one thing to find a widespread pattern, then it is the clincher to find the cause.

But a problem for enthusiasts was that Agassiz’s ice ages lacked any plausible mechanism. In fact, the idea even flew in the face of existing dogma that Earth has been cooling over time. If Earth was cooling, then glaciers should not have retreated to where they are today; they should have expanded. Moreover, Agassiz’s layers of gravel and boulders were showing not a single shift but a rise and fall of Earth’s temperatures over time. What caused the waxing and waning of the ice?

Born and raised on a farm in
Scotland,
James Croll (1821–1890) lacked any formal education. Like Agassiz, he lived for the life of the mind: great ideas, puzzles, and intellectual problems. To support himself, he tried selling insurance, but with a natural aversion to people he couldn’t stomach the job. Leaving that, he set up a tea shop. While he still couldn’t manage to avoid people altogether, the shop did offer one salient advantage over the other gig: it left him plenty of time to study. And studying was the one thing he absolutely loved to do.

Croll’s physiognomy, revealed by the best-known picture of him, shows the thousand-mile stare of one whose mind is transported to a faraway place or working on a deep mathematical problem. His mouth, set firm with a Scottish obduracy, also
reveals a decided lack of humor; one can’t imagine many jokes emerged from those lips. By all accounts, Croll had an exceptional focus that, coupled with a passion for learning, would allow him to spend an entire year reading a single book, often lingering on one page for a day or more to digest each idea. His driving passion was to get to the bottom of intellectual problems. Not satisfied with seeing only patterns, he wanted to figure out how the world actually worked.

Agassiz’s
ice ages provided a puzzle ripe for the solving. Croll’s approach was decidedly different from that of Agassiz before him. Thinking of fundamentals, Croll asked, “What was the cause?” He set off with a pad and pen to solve the problem. His search for a cause demanded thinking about the factors that
changed the amount of
heat on Earth. The source for much of that heat is the
sun. Is there some regular variation in heat from the sun that could trigger ice ages?

Soon after launching into this research, Croll read a paper by a brilliant French scientist that set his mind in motion. The idea was that regular variation in Earth’s
orbit could change the amount of heat that hits Earth’s surface. Earth spins around the sun, and its tilt brings the
seasons. The orbit depends on the proximity of other big celestial bodies nearby:
Mars,
Jupiter,
Venus, and
Saturn are all rotating in space as well. As they approach Earth on regular cycles, their large masses warp the orbit and tilt of our
planet. In times on the order of thousands of years, Earth’s orbit will wobble and change, thereby influencing the amount of sunlight that warms the planet. Croll reasoned that ice ages happen during regular intervals when the orbit causes the planet to receive less heat from the sun.

Here was a cause that made a specific prediction: the ice ages should happen at regular intervals defined by the orbit of the planet. Unfortunately for Croll, his theory became just a passing fad. Because he lacked any firm way of matching the timing of the ice ages to orbits, Croll’s theory remained just a good idea.

A few decades after Croll’s death, a young Serbian concrete engineer got the notion that he could use the mathematical talents that were so helpful in designing buildings to uncover how the universe worked. His thinking was revealed in a toast he gave a poet friend after the two shared a bottle of wine in a Belgrade café. The poet had hoisted his glass to proclaim, “I want to describe our society, our country, and our soul.” The concrete engineer countered with the salute, “I want to do more than you. I want to grasp the entire universe and spread light into its farthest corners.”

Soon after the boast, the engineer, Milutin Milankovitch, switched jobs. Leaving his building firm, he took a professorship at the University of Belgrade. Not easily intimidated, he proceeded to announce that he was out to solve the problems of the planet by pure mathematics. Global
climates were his first problem. But not just Earth’s. He wanted to devise a mathematical theory for climate all over the face of Earth and for every other planet in the solar system as well.

This ambition puzzled a few of his colleagues. Why would you need to calculate global temperatures if we can simply set up weather stations to measure them? Milankovitch’s answer revealed his thinking. If, armed with only pencil and paper, he could predict temperatures mathematically, then we would truly
understand their causes. Off he went, looking at the planetary rhythms that so captivated
Croll.

Croll’s ideas were a natural starting point, but Milankovitch brought a huge new twist to the problem. Using
orbital calculations similar to Croll’s, Milankovitch explored how sunlight could change the heat of the planet. To elucidate this relationship, he modeled the different ways that heat gained by the
ocean can be transferred to the atmosphere and back. A brilliant mathematician, he was able to calculate the magnitude of temperature changes during the
seasons, resulting in a remarkably specific set of predictions.

Earth’s orbit changes in three major ways. Over 100,000 years Earth’s orbit goes from the shape of an oval to a more circular pattern. During 41,000 years Earth rocks back and forth about
2 degrees. And in the course of 19,000 years Earth’s tilt
wobbles like a top.

Milankovitch realized that these are not huge changes, and in fact they would not alter the amount of heat received by Earth much. What they could do, as his equations showed beautifully, is change the duration and intensity of the
seasons. And the reason is straightforward: if the seasons depended on the degree Earth is tilted and the manner in which the planet rotates around the sun, then changes to the shape and orientation of the planet and its orbit will affect the heat of summer, the cold of winter, and everything in between.

The
rocks reveal the occurrence of ice ages. Mathematical calculations show that Earth’s climate can change in a cyclic manner, matching the orbital changes of our planet. But do the cycles of ice ages and those of Earth’s orbits march together? Answers would have to wait for new scientific quests—namely, the effort to make the
atom bomb.

The
Manhattan Project was a short-term war effort that pulled together a unique cadre of scientists to focus on a single goal. With the war’s end the U.S. government found itself with a problem, but one of those problems that is good to have. It had teams of scientific geniuses housed in different places, from New Mexico to New York, with no long-term infrastructure to continue their work. To make matters more challenging, no longer was there a single goal to their work, like developing a bomb; there were now many. Not wanting to lose the talent, or the momentum generated from fundamental breakthroughs in physics, the government supported a number of labs around the country, including one at the
University of Chicago. Chicago was home to the group, led by
Enrico Fermi, that launched the first
controlled
nuclear reaction (today the spot is marked by a Henry Moore sculpture across the street from the gym). After the war, the government helped the university establish a number of institutes exploring the big questions of physics and chemistry. One of those big problems was the history of our planet.

Two people who benefited from this transition from war to peace science at Chicago,
Willard Libby and
Harold Urey, shared a passion and a belief. The passion was for expanding knowledge. The belief was that trapped in the dynamics of single
atoms—in their
electrons,
protons, and
neutrons—were clues to the origin and history of the planet and perhaps even the entire
solar system.