T he success of Lyell's Principles of Geology was so pronounced that the biblical geologists and catastrophists finally threw in the towel. By the mid-1830s, Buckland had dropped his dependence on the Deluge as an explanation for the earth's geologic formations. Even Jameson softened his positions, and his later papers reflected his acceptance of the Hutton-Lyell view. The Huttonian revolution was won, and the discipline of geology, finally freed from the blinkers of catastrophes, deluges, and universal oceans, could now get on with the difficult task of determining just what had occurred over the incredible expanse of geologic time.

If the earth was not young, and if catastrophes did not mask the past, was it possible to arrive at a figure for the earth's age? James Hutton never attempted an estimate. He knew that the means for projecting an accurate date did not exist; therefore to venture a guess was irresponsible. Besides, he was critical of theorists who tried to calculate the beginning of time, and he was determined not to fall into the same trap.

Charles Lyell followed his lead and steadfastly refused to commit himself.

However, Lyell's friend Charles Darwin did venture something that was perceived as a guess, and it caused him much more trouble than it was worth. In the first edition of The Origin of Species, while making a point about the vast amount of time needed for even the most subtle of geologic changes, Darwin gave as an example his calculation for how long it took to form the Weald Valley in the south of England. He incautiously wrote that the valley took approximately 300 million years to form. With armies of critics biting at Darwin's heels, any assertion less than completely supported by hard facts was seized on as a weakness in Darwin's thinking. Several scholars felt that 300 million years was an absurdly high number, and they criticized Darwin for soft thinking. Because this point was not essential to his arguments, Darwin dropped the estimate by the third edition of his book.

Just a few years after the initial publication of Darwin's Origin, the first genuine attempt to calculate the age of the earth was undertaken. Lord Kelvin, whose real name was William Thomson (1824-1907), was the most famous and established physicist in the United Kingdom in the second half of the nineteenth century. He was born in Glasgow, where his father was a professor of mathematics, and he studied math and physics at the University of Glasgow while still quite young. By the age of twenty he had finished his education and was already performing serious science. One of his main interests was heat transfer, which caused him to investigate the exchange of heat between the Sun and the earth. He also became curious about the propagation of heat from the center of the earth to the surface.

Kelvin had a physicist's arrogance, especially toward the other sciences, and he found the thinking of the geology community to be less than rigorous. He especially objected to Hutton and Lyell's conception of a steady-state, recycling earth, which was buttressed by unspecified chemical reactions in the core of the planet. Exhaustively studying the laws of thermodynamics, he was convinced that the Sun and the earth were cooling at a rate that was constant, though currently unknowable, in direct opposition to what the geology community believed. If the earth was cooling, then geologic processes would necessarily have been different in the past, with, for example, greater rates of volcanism and more intense winds and storms. Thus, Hutton and Lyell's belief in the constancy of geologic processes would be wrong. As early as 1844, Kelvin had decided to try to determine the age of the earth. In essence, he revisited Buffon, starting with the Frenchman's idea that the earth had begun as a mass of molten rock, and that the heat from that original molten state was slowly dissipating.

Working on other projects for years, Kelvin was finally able to announce his findings in 1862. He chose a locale guaranteed to ensure notice—the very scene of one of James Hutton's triumphs, the Royal Society of Edinburgh (which by now had moved from the university to a beautiful building in New Town). In April of that year, Kelvin, now the physics professor at the University of Glasgow, addressed the society, reading his paper "On the Secular Cooling of the Earth." The thirty-eight-year-old aggressively criticized the Huttonian view because it did not allow for his contention that the earth was cooling. After calculating a rate of cooling and then extrapolating, Kelvin presented an age of between 20 million and 400 million years. Though the speech was impressively technical, and the geologists in the audience may have felt chastised, the wide range of ages did not prove persuasive. Revisiting the issue periodically, Kelvin consistently brought his estimate down, so that by the end of the 1880s, the bottom number, 20 million, had become Kelvin's official calculation. Kelvin was such a scientific titan that 20 million years became the accepted age of the earth. Twenty million became the new 6,000—the age of the earth recognized by popular culture.

Everything changed when Henri Becquerel discovered radiation in his Paris lab in 1896. In an ingenious experiment, he took sealed, unexposed photographic film and put it in a room with uranium, a mineral known to exhibit unusual properties. When the film was checked after several hours, it was completely exposed, as if it had been left in the sunshine. Becquerel, and his lab assistants Marie and Pierre Curie, next sought to understand what had happened. They realized that certain elements are fundamentally unstable, and this instability leads their isotopes (different species of an element, the difference being the number of neutrons) to undergo spontaneous decay, to break apart, and to ultimately produce stable atoms, along with energy. This action is known as radioactive decay, and a by-product is the escape of the energy. It was this energy that caused the exposure of the film.

The discovery of radioactivity galvanized the world of science, and ambitious scientists everywhere began working in the field. The next big breakthrough occurred in 1902, when Ernst Rutherford and his colleague Frederick Soddy showed that radioactive decay of a given element occurs at a constant rate, one that can be measured. It was not long before they realized that the steady rate of radioactive decay could be used as a geologic clock to determine the age of the earth. In 1905, Rutherford delivered the Silliman Lectures at Yale, and used the forum to challenge the science community to try to date the age of the earth using this new natural clock.

A chemist soon took up the Rutherford-Soddy challenge. In 1907, Bertram Boltwood used the known rate of decay of radium, combined with his discovery that uranium decays to lead, to come up with a range of 400 million to 2,200 million years for the age of the earth.

The next push to date the earth moved back to the United Kingdom in the person of Arthur Holmes (1890-1965). Holmes was a gifted student who had won a science scholarship to study physics at Imperial College in London. When his talents were recognized by the physicist R. J. Strutt, Holmes was urged to stay on as a graduate student to work on the "age of the earth problem." Holmes followed Boltwood's insight into the relationship between uranium and lead, and came up with more refined numbers. In 1913, and again in 1927, he published a popular book on the age of the earth, in which he presented his calculation that the earth was 1.6 billion years old.

Through the 1930s and 1940s the work of Holmes, Alfred Nier, E. Gerling, and F. Houtermans became more rigorous and precise. These men, and many others, were now working primarily with common lead, and by the beginning of World War II, "isotope geologists" had now calculated the age of the earth to be at least 3.3 billion years.

The final breakthrough came in the 1950s, when Claire Patterson, of Caltech, realized that the only way to get a completely accurate measurement of common lead decay was to leave the planet, since the complicated mix of other elements in the earth distorted any measurement attempt. He and his colleagues decided to focus on objects that were the same age as all the planets in the solar system, including the earth, but allowed for more accurate lead decay calculations—meteorites. As Claire Patterson later related:

Lead in iron meteorites was the kind of lead that was in the solar system when it was first formed, and ... it was preserved in iron meteorites without change from uranium decay, because there is no uranium in iron meteorites. ... If we only knew what the isotopic composition of primordial lead was in the earth when formed, we could take that number and stick it into this marvelous equation that the atomic physicists had worked out. And you could turn the crank and blip—out would come the age of the earth.

By 1956, Patterson had calculated the age of the earth to be 4.6 billion years, which remains the accepted age of our planet. James Hutton was right—the earth is unfathomably old.

Why is it that James Hutton, the man who proved the earth's antiquity and made it possible for Claire Patterson to complete his work, is essentially unknown to all but geologists? One reason for his relative invisibility is that geology has never been a partic ularly flashy discipline. And it seems to have done an especially poor job of publicizing its founding fathers, whereas other scientific fields have somehow pushed their pioneers into the popular consciousness: Lavoisier in chemistry, Galileo and Newton in physics, Darwin and Gregor Mendel in biology. However, that cannot be the whole story because most people have at least heard of Charles Lyell, the discipline's other trailblazer.

Another reason is that the world's attention was certainly focused elsewhere when Hutton was first presenting and then defending his theory. The American War of Independence ended in 1783, and the French Revolution began in 1789—two galvanizing events that changed world history forever, and certainly preoccupied the people who lived through the last decades of the eighteenth century, as well as future historians. Still, these two conflagrations did not prevent Adam Smith from gaining the recognition he deserved.

One is left with the fact that James Hutton was not a gifted communicator. Indeed, just about the only negative passage in Playfair's biography concerns Hutton's writing: "The reasoning is sometimes embarrassed by the care taken to render it strictly logical; and the transitions, from the author's peculiar notions of arrangement, are often unexpected and abrupt. These defects run more or less through all Dr. Hutton's writings, and produce a degree of obscurity astonishing to those who knew him, and heard him everyday converse with no less clearness and precision than animation and force."

The defective writing, coupled with the great pain Hutton was suffering while working on his book, caused it to be put together in a hurried way. Not just long (approximately 1,200 pages over two volumes), The Theory of the Earth also contained turgid passages from other works in other languages. A book that unwieldy simply would not be read today, and it was not widely read then. One historian has determined that the first printing was just 500 copies (not an unusual first printing for the time; the first printing for Origin of Species was just 1,250 copies), but it was never reprinted. The long article from 1788 was a solid piece of scientific writing, but it was available only in a volume containing several other papers, and it was not broadly distributed.

That Hutton's book was virtually ignored by readers in 1795, and thereafter, seemed to seal his fate as a member of the legion of forgotten scientists. In fact, one might argue that the key to being remembered by posterity is to write a popular book. The works of Charles Lyell and Charles Darwin are regarded as masterpieces, still wonderfully interesting and insightful over 100 years after their publication. Adam Smith's Wealth of Nations carries a similar status. David Hume's books, though less widely read now, were best-sellers 200 years ago, and are actively perused by philosophy students today. Newton's Principia, though technical, is still read by most serious students of physics. John Playfair's own book, unlike Hutton's, was well written and popular at the time, but perhaps it was prevented from remaining visible over the decades because he was explaining another's work.

Steno, Werner, Black, and Hall also did not write books that resonated across a broad spectrum of readers, and their fates have been similar to Hutton's. But the lack of recognition for the doctor is an enormous oversight: James Hutton's brilliant insights forever changed how we think about our planet and our place on it. The man who found time has hopefully been found at last.

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