Something else conjectured by Newton in the Principia was that a plumb bob hung near a mountain would incline very slightly toward the mountain, affected by the mountain’s gravitational mass as well as by the Earth’s. This was more than a curious fact. If you measured the deflection accurately and worked out the mass of the mountain, you could calculate the universal gravitational constant—that is, the basic value of gravity, known as G—and along with it the mass of the Earth.

Bouguer and La Condamine had tried this on Peru’s Mount Chimborazo, but had been defeated by both the technical difficulties and their own squabbling, and so the notion lay dormant for another thirty years until resurrected in England by Nevil Maskelyne, the astronomer royal. In Dava Sobel’s popular book Longitude, Maskelyne is presented as a ninny and villain for failing to appreciate the brilliance of the clockmaker John Harrison, and this may be so, but we are indebted to him in other ways not mentioned in her book, not least for his successful scheme to weigh the Earth. Maskelyne realized that the nub of the problem lay with finding a mountain of sufficiently regular shape to judge its mass.

At his urging, the Royal Society agreed to engage a reliable figure to tour the British Isles to see if such a mountain could be found. Maskelyne knew just such a person—the astronomer and surveyor Charles Mason. Maskelyne and Mason had become friends eleven years earlier while engaged in a project to measure an astronomical event of great importance: the passage of the planet Venus across the face of the Sun. The tireless Edmond Halley had suggested years before that if you measured one of these passages from selected points on the Earth, you could use the principles of triangulation to work out the distance to the Sun, and from that calibrate the distances to all the other bodies in the solar system.

Unfortunately, transits of Venus, as they are known, are an irregular occurrence. They come in pairs eight years apart, but then are absent for a century or more, and there were none in Halley’s lifetime.*5 But the idea simmered and when the next transit came due in 1761, nearly two decades after Halley’s death, the scientific world was ready—indeed, more ready than it had been for an astronomical event before.

With the instinct for ordeal that characterized the age, scientists set off for more than a hundred locations around the globe—to Siberia, China, South Africa, Indonesia, and the woods of Wisconsin, among many others. France dispatched thirty-two observers, Britain eighteen more, and still others set out from Sweden, Russia, Italy, Germany, Ireland, and elsewhere.

It was history’s first cooperative international scientific venture, and almost everywhere it ran into problems. Many observers were waylaid by war, sickness, or shipwreck. Others made their destinations but opened their crates to find equipment broken or warped by tropical heat. Once again the French seemed fated to provide the most memorably unlucky participants. Jean Chappe spent months traveling to Siberia by coach, boat, and sleigh, nursing his delicate instruments over every perilous bump, only to find the last vital stretch blocked by swollen rivers, the result of unusually heavy spring rains, which the locals were swift to blame on him after they saw him pointing strange instruments at the sky. Chappe managed to escape with his life, but with no useful measurements.

Unluckier still was Guillaume Le Gentil, whose experiences are wonderfully summarized by Timothy Ferris in Coming of Age in the Milky Way. Le Gentil set off from France a year ahead of time to observe the transit from India, but various setbacks left him still at sea on the day of the transit—just about the worst place to be since steady measurements were impossible on a pitching ship.

Undaunted, Le Gentil continued on to India to await the next transit in 1769. With eight years to prepare, he erected a first-rate viewing station, tested and retested his instruments, and had everything in a state of perfect readiness. On the morning of the second transit, June 4, 1769, he awoke to a fine day, but, just as Venus began its pass, a cloud slid in front of the Sun and remained there for almost exactly the duration of the transit: three hours, fourteen minutes, and seven seconds.

Stoically, Le Gentil packed up his instruments and set off for the nearest port, but en route he contracted dysentery and was laid up for nearly a year. Still weakened, he finally made it onto a ship. It was nearly wrecked in a hurricane off the African coast. When at last he reached home, eleven and a half years after setting off, and having achieved nothing, he discovered that his relatives had had him declared dead in his absence and had enthusiastically plundered his estate.

In comparison, the disappointments experienced by Britain’s eighteen scattered observers were mild. Mason found himself paired with a young surveyor named Jeremiah Dixon and apparently they got along well, for they formed a lasting partnership. Their instructions were to travel to Sumatra and chart the transit there, but after just one night at sea their ship was attacked by a French frigate. (Although scientists were in an internationally cooperative mood, nations weren’t.) Mason and Dixon sent a note to the Royal Society observing that it seemed awfully dangerous on the high seas and wondering if perhaps the whole thing oughtn’t to be called off. In reply they received a swift and chilly rebuke, noting that they had already been paid, that the nation and scientific community were counting on them, and that their failure to proceed would result in the irretrievable loss of their reputations. Chastened, they sailed on, but en route word reached them that Sumatra had fallen to the French and so they observed the transit inconclusively from the Cape of Good Hope. On the way home they stopped on the lonely Atlantic outcrop of St. Helena, where they met Maskelyne, whose observations had been thwarted by cloud cover. Mason and Maskelyne formed a solid friendship and spent several happy, and possibly even mildly useful, weeks charting tidal flows.

Soon afterward, Maskelyne returned to England where he became astronomer royal, and Mason and Dixon—now evidently more seasoned—set off for four long and often perilous years surveying their way through 244 miles of dangerous American wilderness to settle a boundary dispute between the estates of William Penn and Lord Baltimore and their respective colonies of Pennsylvania and Maryland. The result was the famous Mason and Dixon line, which later took on symbolic importance as the dividing line between the slave and free states. (Although the line was their principal task, they also contributed several astronomical surveys, including one of the century’s most accurate measurements of a degree of meridian—an achievement that brought them far more acclaim in England than the settling of a boundary dispute between spoiled aristocrats.)

Back in Europe, Maskelyne and his counterparts in Germany and France were forced to the conclusion that the transit measurements of 1761 were essentially a failure. One of the problems, ironically, was that there were too many observations, which when brought together often proved contradictory and impossible to resolve. The successful charting of a Venusian transit fell instead to a little-known Yorkshire-born sea captain named James Cook, who watched the 1769 transit from a sunny hilltop in Tahiti, and then went on to chart and claim Australia for the British crown. Upon his return there was now enough information for the French astronomer Joseph Lalande to calculate that the mean distance from the Earth to the Sun was a little over 150 million kilometers. (Two further transits in the nineteenth century allowed astronomers to put the figure at 149.59 million kilometers, where it has remained ever since. The precise distance, we now know, is 149.597870691 million kilometers.) The Earth at last had a position in space.

As for Mason and Dixon, they returned to England as scientific heroes and, for reasons unknown, dissolved their partnership. Considering the frequency with which they turn up at seminal events in eighteenth-century science, remarkably little is known about either man. No likenesses exist and few written references. Of Dixon the Dictionary of National Biography notes intriguingly that he was “said to have been born in a coal mine,” but then leaves it to the reader’s imagination to supply a plausible explanatory circumstance, and adds that he died at Durham in 1777. Apart from his name and long association with Mason, nothing more is known.

Mason is only slightly less shadowy. We know that in 1772, at Maskelyne’s behest, he accepted the commission to find a suitable mountain for the gravitational deflection experiment, at length reporting back that the mountain they needed was in the central Scottish Highlands, just above Loch Tay, and was called Schiehallion. Nothing, however, would induce him to spend a summer surveying it. He never returned to the field again. His next known movement was in 1786 when, abruptly and mysteriously, he turned up in Philadelphia with his wife and eight children, apparently on the verge of destitution. He had not been back to America since completing his survey there eighteen years earlier and had no known reason for being there, or any friends or patrons to greet him. A few weeks later he was dead.

With Mason refusing to survey the mountain, the job fell to Maskelyne. So for four months in the summer of 1774, Maskelyne lived in a tent in a remote Scottish glen and spent his days directing a team of surveyors, who took hundreds of measurements from every possible position. To find the mass of the mountain from all these numbers required a great deal of tedious calculating, for which a mathematician named Charles Hutton was engaged. The surveyors had covered a map with scores of figures, each marking an elevation at some point on or around the mountain. It was essentially just a confusing mass of numbers, but Hutton noticed that if he used a pencil to connect points of equal height, it all became much more orderly. Indeed, one could instantly get a sense of the overall shape and slope of the mountain. He had invented contour lines.

Extrapolating from his Schiehallion measurements, Hutton calculated the mass of the Earth at 5,000 million million tons, from which could reasonably be deduced the masses of all the other major bodies in the solar system, including the Sun. So from this one experiment we learned the masses of the Earth, the Sun, the Moon, the other planets and their moons, and got contour lines into the bargain—not bad for a summer’s work.

Not everyone was satisfied with the results, however. The shortcoming of the Schiehallion experiment was that it was not possible to get a truly accurate figure without knowing the actual density of the mountain. For convenience, Hutton had assumed that the mountain had the same density as ordinary stone, about 2.5 times that of water, but this was little more than an educated guess.

One improbable-seeming person who turned his mind to the matter was a country parson named John Michell, who resided in the lonely Yorkshire village of Thornhill. Despite his remote and comparatively humble situation, Michell was one of the great scientific thinkers of the eighteenth century and much esteemed for it.

Among a great deal else, he perceived the wavelike nature of earthquakes, conducted much original research into magnetism and gravity, and, quite extraordinarily, envisioned the possibility of black holes two hundred years before anyone else—a leap of intuitive deduction that not even Newton could make. When the German-born musician William Herschel decided his real interest in life was astronomy, it was Michell to whom he turned for instruction in making telescopes, a kindness for which planetary science has been in his debt ever since.*6

But of all that Michell accomplished, nothing was more ingenious or had greater impact than a machine he designed and built for measuring the mass of the Earth. Unfortunately, he died before he could conduct the experiments and both the idea and the necessary equipment were passed on to a brilliant but magnificently retiring London scientist named Henry Cavendish.

Cavendish is a book in himself. Born into a life of sumptuous privilege—his grandfathers were dukes, respectively, of Devonshire and Kent—he was the most gifted English scientist of his age, but also the strangest. He suffered, in the words of one of his few biographers, from shyness to a “degree bordering on disease.” Any human contact was for him a source of the deepest discomfort.

Once he opened his door to find an Austrian admirer, freshly arrived from Vienna, on the front step. Excitedly the Austrian began to babble out praise. For a few moments Cavendish received the compliments as if they were blows from a blunt object and then, unable to take any more, fled down the path and out the gate, leaving the front door wide open. It was some hours before he could be coaxed back to the property. Even his housekeeper communicated with him by letter.

Although he did sometimes venture into society—he was particularly devoted to the weekly scientific soirées of the great naturalist Sir Joseph Banks—it was always made clear to the other guests that Cavendish was on no account to be approached or even looked at. Those who sought his views were advised to wander into his vicinity as if by accident and to “talk as it were into vacancy.” If their remarks were scientifically worthy they might receive a mumbled reply, but more often than not they would hear a peeved squeak (his voice appears to have been high pitched) and turn to find an actual vacancy and the sight of Cavendish fleeing for a more peaceful corner.

His wealth and solitary inclinations allowed him to turn his house in Clapham into a large laboratory where he could range undisturbed through every corner of the physical sciences—electricity, heat, gravity, gases, anything to do with the composition of matter. The second half of the eighteenth century was a time when people of a scientific bent grew intensely interested in the physical properties of fundamental things—gases and electricity in particular—and began seeing what they could do with them, often with more enthusiasm than sense. In America, Benjamin Franklin famously risked his life by flying a kite in an electrical storm. In France, a chemist named Pilatre de Rozier tested the flammability of hydrogen by gulping a mouthful and blowing across an open flame, proving at a stroke that hydrogen is indeed explosively combustible and that eyebrows are not necessarily a permanent feature of one’s face. Cavendish, for his part, conducted experiments in which he subjected himself to graduated jolts of electrical current, diligently noting the increasing levels of agony until he could keep hold of his quill, and sometimes his consciousness, no longer.

In the course of a long life Cavendish made a string of signal discoveries—among much else he was the first person to isolate hydrogen and the first to combine hydrogen and oxygen to form water—but almost nothing he did was entirely divorced from strangeness. To the continuing exasperation of his fellow scientists, he often alluded in published work to the results of contingent experiments that he had not told anyone about. In his secretiveness he didn’t merely resemble Newton, but actively exceeded him. His experiments with electrical conductivity were a century ahead of their time, but unfortunately remained undiscovered until that century had passed. Indeed the greater part of what he did wasn’t known until the late nineteenth century when the Cambridge physicist James Clerk Maxwell took on the task of editing Cavendish’s papers, by which time credit had nearly always been given to others.

Among much else, and without telling anyone, Cavendish discovered or anticipated the law of the conservation of energy, Ohm’s law, Dalton’s Law of Partial Pressures, Richter’s Law of Reciprocal Proportions, Charles’s Law of Gases, and the principles of electrical conductivity. That’s just some of it. According to the science historian J. G. Crowther, he also foreshadowed “the work of Kelvin and G. H. Darwin on the effect of tidal friction on slowing the rotation of the earth, and Larmor’s discovery, published in 1915, on the effect of local atmospheric cooling . . . the work of Pickering on freezing mixtures, and some of the work of Rooseboom on heterogeneous equilibria.” Finally, he left clues that led directly to the discovery of the group of elements known as the noble gases, some of which are so elusive that the last of them wasn’t found until 1962. But our interest here is in Cavendish’s last known experiment when in the late summer of 1797, at the age of sixty-seven, he turned his attention to the crates of equipment that had been left to him—evidently out of simple scientific respect—by John Michell.

When assembled, Michell’s apparatus looked like nothing so much as an eighteenth-century version of a Nautilus weight-training machine. It incorporated weights, counterweights, pendulums, shafts, and torsion wires. At the heart of the machine were two 350-pound lead balls, which were suspended beside two smaller spheres. The idea was to measure the gravitational deflection of the smaller spheres by the larger ones, which would allow the first measurement of the elusive force known as the gravitational constant, and from which the weight (strictly speaking, the mass)*7 of the Earth could be deduced.

Because gravity holds planets in orbit and makes falling objects land with a bang, we tend to think of it as a powerful force, but it is not really. It is only powerful in a kind of collective sense, when one massive object, like the Sun, holds on to another massive object, like the Earth. At an elemental level gravity is extraordinarily unrobust. Each time you pick up a book from a table or a dime from the floor you effortlessly overcome the combined gravitational exertion of an entire planet. What Cavendish was trying to do was measure gravity at this extremely featherweight level.

Delicacy was the key word. Not a whisper of disturbance could be allowed into the room containing the apparatus, so Cavendish took up a position in an adjoining room and made his observations with a telescope aimed through a peephole. The work was incredibly exacting and involved seventeen delicate, interconnected measurements, which together took nearly a year to complete. When at last he had finished his calculations, Cavendish announced that the Earth weighed a little over 13,000,000,000,000,000,000,000 pounds, or six billion trillion metric tons, to use the modern measure. (A metric ton is 1,000 kilograms or 2,205 pounds.)

Today, scientists have at their disposal machines so precise they can detect the weight of a single bacterium and so sensitive that readings can be disturbed by someone yawning seventy-five feet away, but they have not significantly improved on Cavendish’s measurements of 1797. The current best estimate for Earth’s weight is 5.9725 billion trillion metric tons, a difference of only about 1 percent from Cavendish’s finding. Interestingly, all of this merely confirmed estimates made by Newton 110 years before Cavendish without any experimental evidence at all.

So, by the late eighteenth century scientists knew very precisely the shape and dimensions of the Earth and its distance from the Sun and planets; and now Cavendish, without even leaving home, had given them its weight. So you might think that determining the age of the Earth would be relatively straightforward. After all, the necessary materials were literally at their feet. But no. Human beings would split the atom and invent television, nylon, and instant coffee before they could figure out the age of their own planet.

To understand why, we must travel north to Scotland and begin with a brilliant and genial man, of whom few have ever heard, who had just invented a new science called geology.

5 The Ston-breakers

AT JUST THE time that Henry Cavendish was completing his experiments in London, four hundred miles away in Edinburgh another kind of concluding moment was about to take place with the death of James Hutton. This was bad news for Hutton, of course, but good news for science as it cleared the way for a man named John Playfair to rewrite Hutton’s work without fear of embarrassment.

Hutton was by all accounts a man of the keenest insights and liveliest conversation, a delight in company, and without rival when it came to understanding the mysterious slow processes that shaped the Earth. Unfortunately, it was beyond him to set down his notions in a form that anyone could begin to understand. He was, as one biographer observed with an all but audible sigh, “almost entirely innocent of rhetorical accomplishments.” Nearly every line he penned was an invitation to slumber. Here he is in his 1795 masterwork, A Theory of the Earth with Proofs and Illustrations, discussing . . . something:

 

The world which we inhabit is composed of the materials, not of the earth which was the immediate predecessor of the present, but of the earth which, in ascending from the present, we consider as the third, and which had preceded the land that was above the surface of the sea, while our present land was yet beneath the water of the ocean.

Yet almost singlehandedly, and quite brilliantly, he created the science of geology and transformed our understanding of the Earth. Hutton was born in 1726 into a prosperous Scottish family, and enjoyed the sort of material comfort that allowed him to pass much of his life in a genially expansive round of light work and intellectual betterment. He studied medicine, but found it not to his liking and turned instead to farming, which he followed in a relaxed and scientific way on the family estate in Berwickshire. Tiring of field and flock, in 1768 he moved to Edinburgh, where he founded a successful business producing sal ammoniac from coal soot, and busied himself with various scientific pursuits. Edinburgh at that time was a center of intellectual vigor, and Hutton luxuriated in its enriching possibilities. He became a leading member of a society called the Oyster Club, where he passed his evenings in the company of men such as the economist Adam Smith, the chemist Joseph Black, and the philosopher David Hume, as well as such occasional visiting sparks as Benjamin Franklin and James Watt.

In the tradition of the day, Hutton took an interest in nearly everything, from mineralogy to metaphysics. He conducted experiments with chemicals, investigated methods of coal mining and canal building, toured salt mines, speculated on the mechanisms of heredity, collected fossils, and propounded theories on rain, the composition of air, and the laws of motion, among much else. But his particular interest was geology.

Among the questions that attracted interest in that fanatically inquisitive age was one that had puzzled people for a very long time—namely, why ancient clamshells and other marine fossils were so often found on mountaintops. How on earth did they get there? Those who thought they had a solution fell into two opposing camps. One group, known as the Neptunists, was convinced that everything on Earth, including seashells in improbably lofty places, could be explained by rising and falling sea levels. They believed that mountains, hills, and other features were as old as the Earth itself, and were changed only when water sloshed over them during periods of global flooding.

Opposing them were the Plutonists, who noted that volcanoes and earthquakes, among other enlivening agents, continually changed the face of the planet but clearly owed nothing to wayward seas. The Plutonists also raised awkward questions about where all the water went when it wasn’t in flood. If there was enough of it at times to cover the Alps, then where, pray, was it during times of tranquility, such as now? Their belief was that the Earth was subject to profound internal forces as well as surface ones. However, they couldn’t convincingly explain how all those clamshells got up there.

It was while puzzling over these matters that Hutton had a series of exceptional insights. From looking at his own farmland, he could see that soil was created by the erosion of rocks and that particles of this soil were continually washed away and carried off by streams and rivers and redeposited elsewhere. He realized that if such a process were carried to its natural conclusion then Earth would eventually be worn quite smooth. Yet everywhere around him there were hills. Clearly there had to be some additional process, some form of renewal and uplift, that created new hills and mountains to keep the cycle going. The marine fossils on mountaintops, he decided, had not been deposited during floods, but had risen along with the mountains themselves. He also deduced that it was heat within the Earth that created new rocks and continents and thrust up mountain chains. It is not too much to say that geologists wouldn’t grasp the full implications of this thought for two hundred years, when finally they adopted plate tectonics. Above all, what Hutton’s theories suggested was that Earth processes required huge amounts of time, far more than anyone had ever dreamed. There were enough insights here to transform utterly our understanding of the Earth.

In 1785, Hutton worked his ideas up into a long paper, which was read at consecutive meetings of the Royal Society of Edinburgh. It attracted almost no notice at all. It’s not hard to see why. Here, in part, is how he presented it to his audience:



In the one case, the forming cause is in the body which is separated; for, after the body has been actuated by heat, it is by the reaction of the proper matter of the body, that the chasm which constitutes the vein is formed. In the other case, again, the cause is extrinsic in relation to the body in which the chasm is formed. There has been the most violent fracture and divulsion; but the cause is still to seek; and it appears not in the vein; for it is not every fracture and dislocation of the solid body of our earth, in which minerals, or the proper substances of mineral veins, are found.

Needless to say, almost no one in the audience had the faintest idea what he was talking about. Encouraged by his friends to expand his theory, in the touching hope that he might somehow stumble onto clarity in a more expansive format, Hutton spent the next ten years preparing his magnum opus, which was published in two volumes in 1795.

Together the two books ran to nearly a thousand pages and were, remarkably, worse than even his most pessimistic friends had feared. Apart from anything else, nearly half the completed work now consisted of quotations from French sources, still in the original French. A third volume was so unenticing that it wasn’t published until 1899, more than a century after Hutton’s death, and the fourth and concluding volume was never published at all. Hutton’s Theory of the Earth is a strong candidate for the least read important book in science (or at least would be if there weren’t so many others). Even Charles Lyell, the greatest geologist of the following century and a man who read everything, admitted he couldn’t get through it.

Luckily Hutton had a Boswell in the form of John Playfair, a professor of mathematics at the University of Edinburgh and a close friend, who could not only write silken prose but—thanks to many years at Hutton’s elbow—actually understood what Hutton was trying to say, most of the time. In 1802, five years after Hutton’s death, Playfair produced a simplified exposition of the Huttonian principles, entitled Illustrations of the Huttonian Theory of the Earth. The book was gratefully received by those who took an active interest in geology, which in 1802 was not a large number. That, however, was about to change. And how.

In the winter of 1807, thirteen like-minded souls in London got together at the Freemasons Tavern at Long Acre, in Covent Garden, to form a dining club to be called the Geological Society. The idea was to meet once a month to swap geological notions over a glass or two of Madeira and a convivial dinner. The price of the meal was set at a deliberately hefty fifteen shillings to discourage those whose qualifications were merely cerebral. It soon became apparent, however, that there was a demand for something more properly institutional, with a permanent headquarters, where people could gather to share and discuss new findings. In barely a decade membership grew to four hundred—still all gentlemen, of course—and the Geological was threatening to eclipse the Royal as the premier scientific society in the country.

The members met twice a month from November until June, when virtually all of them went off to spend the summer doing fieldwork. These weren’t people with a pecuniary interest in minerals, you understand, or even academics for the most part, but simply gentlemen with the wealth and time to indulge a hobby at a more or less professional level. By 1830, there were 745 of them, and the world would never see the like again.

It is hard to imagine now, but geology excited the nineteenth century—positively gripped it—in a way that no science ever had before or would again. In 1839, when Roderick Murchison published The Silurian System, a plump and ponderous study of a type of rock called greywacke, it was an instant bestseller, racing through four editions, even though it cost eight guineas a copy and was, in true Huttonian style, unreadable. (As even a Murchison supporter conceded, it had “a total want of literary attractiveness.”) And when, in 1841, the great Charles Lyell traveled to America to give a series of lectures in Boston, sellout audiences of three thousand at a time packed into the Lowell Institute to hear his tranquilizing descriptions of marine zeolites and seismic perturbations in Campania.

Throughout the modern, thinking world, but especially in Britain, men of learning ventured into the countryside to do a little “stone-breaking,” as they called it. It was a pursuit taken seriously, and they tended to dress with appropriate gravity, in top hats and dark suits, except for the Reverend William Buckland of Oxford, whose habit it was to do his fieldwork in an academic gown.

The field attracted many extraordinary figures, not least the aforementioned Murchison, who spent the first thirty or so years of his life galloping after foxes, converting aeronautically challenged birds into puffs of drifting feathers with buckshot, and showing no mental agility whatever beyond that needed to read The Times or play a hand of cards. Then he discovered an interest in rocks and became with rather astounding swiftness a titan of geological thinking.

Then there was Dr. James Parkinson, who was also an early socialist and author of many provocative pamphlets with titles like “Revolution without Bloodshed.” In 1794, he was implicated in a faintly lunatic-sounding conspiracy called “the Pop-gun Plot,” in which it was planned to shoot King George III in the neck with a poisoned dart as he sat in his box at the theater. Parkinson was hauled before the Privy Council for questioning and came within an ace of being dispatched in irons to Australia before the charges against him were quietly dropped. Adopting a more conservative approach to life, he developed an interest in geology and became one of the founding members of the Geological Society and the author of an important geological text, Organic Remains of a Former World, which remained in print for half a century. He never caused trouble again. Today, however, we remember him for his landmark study of the affliction then called the “shaking palsy,” but known ever since as Parkinson’s disease. (Parkinson had one other slight claim to fame. In 1785, he became possibly the only person in history to win a natural history museum in a raffle. The museum, in London’s Leicester Square, had been founded by Sir Ashton Lever, who had driven himself bankrupt with his unrestrained collecting of natural wonders. Parkinson kept the museum until 1805, when he could no longer support it and the collection was broken up and sold.)

Not quite as remarkable in character but more influential than all the others combined was Charles Lyell. Lyell was born in the year that Hutton died and only seventy miles away, in the village of Kinnordy. Though Scottish by birth, he grew up in the far south of England, in the New Forest of Hampshire, because his mother was convinced that Scots were feckless drunks. As was generally the pattern with nineteenth-century gentlemen scientists, Lyell came from a background of comfortable wealth and intellectual vigor. His father, also named Charles, had the unusual distinction of being a leading authority on the poet Dante and on mosses. (Orthotricium lyelli, which most visitors to the English countryside will at some time have sat on, is named for him.) From his father Lyell gained an interest in natural history, but it was at Oxford, where he fell under the spell of the Reverend William Buckland—he of the flowing gowns—that the young Lyell began his lifelong devotion to geology.

Buckland was a bit of a charming oddity. He had some real achievements, but he is remembered at least as much for his eccentricities. He was particularly noted for a menagerie of wild animals, some large and dangerous, that were allowed to roam through his house and garden, and for his desire to eat his way through every animal in creation. Depending on whim and availability, guests to Buckland’s house might be served baked guinea pig, mice in batter, roasted hedgehog, or boiled Southeast Asian sea slug. Buckland was able to find merit in them all, except the common garden mole, which he declared disgusting. Almost inevitably, he became the leading authority on coprolites—fossilized feces—and had a table made entirely out of his collection of specimens.

Even when conducting serious science his manner was generally singular. Once Mrs. Buckland found herself being shaken awake in the middle of the night, her husband crying in excitement: “My dear, I believe that Cheirotherium’s footsteps are undoubtedly testudinal.” Together they hurried to the kitchen in their nightclothes. Mrs. Buckland made a flour paste, which she spread across the table, while the Reverend Buckland fetched the family tortoise. Plunking it onto the paste, they goaded it forward and discovered to their delight that its footprints did indeed match those of the fossil Buckland had been studying. Charles Darwin thought Buckland a buffoon—that was the word he used—but Lyell appeared to find him inspiring and liked him well enough to go touring with him in Scotland in 1824. It was soon after this trip that Lyell decided to abandon a career in law and devote himself to geology full-time.

Lyell was extremely shortsighted and went through most of his life with a pained squint, which gave him a troubled air. (Eventually he would lose his sight altogether.) His other slight peculiarity was the habit, when distracted by thought, of taking up improbable positions on furniture—lying across two chairs at once or “resting his head on the seat of a chair, while standing up” (to quote his friend Darwin). Often when lost in thought he would slink so low in a chair that his buttocks would all but touch the floor. Lyell’s only real job in life was as professor of geology at King’s College in London from 1831 to 1833. It was around this time that he produced The Principles of Geology, published in three volumes between 1830 and 1833, which in many ways consolidated and elaborated upon the thoughts first voiced by Hutton a generation earlier. (Although Lyell never read Hutton in the original, he was a keen student of Playfair’s reworked version.)

Between Hutton’s day and Lyell’s there arose a new geological controversy, which largely superseded, but is often confused with, the old Neptunian–Plutonian dispute. The new battle became an argument between catastrophism and uniformitarianism—unattractive terms for an important and very long-running dispute. Catastrophists, as you might expect from the name, believed that the Earth was shaped by abrupt cataclysmic events—floods principally, which is why catastrophism and neptunism are often wrongly bundled together. Catastrophism was particularly comforting to clerics like Buckland because it allowed them to incorporate the biblical flood of Noah into serious scientific discussions. Uniformitarians by contrast believed that changes on Earth were gradual and that nearly all Earth processes happened slowly, over immense spans of time. Hutton was much more the father of the notion than Lyell, but it was Lyell most people read, and so he became in most people’s minds, then and now, the father of modern geological thought.

Lyell believed that the Earth’s shifts were uniform and steady—that everything that had ever happened in the past could be explained by events still going on today. Lyell and his adherents didn’t just disdain catastrophism, they detested it. Catastrophists believed that extinctions were part of a series in which animals were repeatedly wiped out and replaced with new sets—a belief that the naturalist T. H. Huxley mockingly likened to “a succession of rubbers of whist, at the end of which the players upset the table and called for a new pack.” It was too convenient a way to explain the unknown. “Never was there a dogma more calculated to foster indolence, and to blunt the keen edge of curiosity,” sniffed Lyell.

Lyell’s oversights were not inconsiderable. He failed to explain convincingly how mountain ranges were formed and overlooked glaciers as an agent of change. He refused to accept Louis Agassiz’s idea of ice ages—“the refrigeration of the globe,” as he dismissively termed it—and was confident that mammals “would be found in the oldest fossiliferous beds.” He rejected the notion that animals and plants suffered sudden annihilations, and believed that all the principal animal groups—mammals, reptiles, fish, and so on—had coexisted since the dawn of time. On all of these he would ultimately be proved wrong.

Yet it would be nearly impossible to overstate Lyell’s influence. The Principles of Geology went through twelve editions in Lyell’s lifetime and contained notions that shaped geological thinking far into the twentieth century. Darwin took a first edition with him on the Beagle voyage and wrote afterward that “the great merit of the Principles was that it altered the whole tone of one’s mind, and therefore that, when seeing a thing never seen by Lyell, one yet saw it partially through his eyes.” In short, he thought him nearly a god, as did many of his generation. It is a testament to the strength of Lyell’s sway that in the 1980s when geologists had to abandon just a part of it to accommodate the impact theory of extinctions, it nearly killed them. But that is another chapter.

Meanwhile, geology had a great deal of sorting out to do, and not all of it went smoothly. From the outset geologists tried to categorize rocks by the periods in which they were laid down, but there were often bitter disagreements about where to put the dividing lines—none more so than a long-running debate that became known as the Great Devonian Controversy. The issue arose when the Reverend Adam Sedgwick of Cambridge claimed for the Cambrian period a layer of rock that Roderick Murchison believed belonged rightly to the Silurian. The dispute raged for years and grew extremely heated. “De la Beche is a dirty dog,” Murchison wrote to a friend in a typical outburst.

Some sense of the strength of feeling can be gained by glancing through the chapter titles of Martin J. S. Rudwick’s excellent and somber account of the issue, The Great Devonian Controversy. These begin innocuously enough with headings such as “Arenas of Gentlemanly Debate” and “Unraveling the Greywacke,” but then proceed on to “The Greywacke Defended and Attacked,” “Reproofs and Recriminations,” “The Spread of Ugly Rumors,” “Weaver Recants His Heresy,” “Putting a Provincial in His Place,” and (in case there was any doubt that this was war) “Murchison Opens the Rhineland Campaign.” The fight was finally settled in 1879 with the simple expedient of coming up with a new period, the Ordovician, to be inserted between the two.

Because the British were the most active in the early years, British names are predominant in the geological lexicon. Devonian is of course from the English county of Devon. Cambrian comes from the Roman name for Wales, while Ordovician and Silurian recall ancient Welsh tribes, the Ordovices and Silures. But with the rise of geological prospecting elsewhere, names began to creep in from all over. Jurassic refers to the Jura Mountains on the border of France and Switzerland. Permian recalls the former Russian province of Perm in the Ural Mountains. For Cretaceous (from the Latin for “chalk”) we are indebted to a Belgian geologist with the perky name of J. J. d’Omalius d’Halloy.

Originally, geological history was divided into four spans of time: primary, secondary, tertiary, and quaternary. The system was too neat to last, and soon geologists were contributing additional divisions while eliminating others. Primary and secondary fell out of use altogether, while quaternary was discarded by some but kept by others. Today only tertiary remains as a common designation everywhere, even though it no longer represents a third period of anything.

Lyell, in his Principles, introduced additional units known as epochs or series to cover the period since the age of the dinosaurs, among them Pleistocene (“most recent”), Pliocene (“more recent”), Miocene (“moderately recent”), and the rather endearingly vague Oligocene (“but a little recent”). Lyell originally intended to employ “-synchronous” for his endings, giving us such crunchy designations as Meiosynchronous and Pleiosynchronous. The Reverend William Whewell, an influential man, objected on etymological grounds and suggested instead an “-eous” pattern, producing Meioneous, Pleioneous, and so on. The “-cene” terminations were thus something of a compromise.

Nowadays, and speaking very generally, geological time is divided first into four great chunks known as eras: Precambrian, Paleozoic (from the Greek meaning “old life”), Mesozoic (“middle life”), and Cenozoic (“recent life”). These four eras are further divided into anywhere from a dozen to twenty subgroups, usually called periods though sometimes known as systems. Most of these are also reasonably well known: Cretaceous, Jurassic, Triassic, Silurian, and so on.*8

Then come Lyell’s epochs—the Pleistocene, Miocene, and so on—which apply only to the most recent (but paleontologically busy) sixty-five million years, and finally we have a mass of finer subdivisions known as stages or ages. Most of these are named, nearly always awkwardly, after places: Illinoian, Desmoinesian, Croixian, Kimmeridgian, and so on in like vein. Altogether, according to John McPhee, these number in the “tens of dozens.” Fortunately, unless you take up geology as a career, you are unlikely ever to hear any of them again.

Further confusing the matter is that the stages or ages in North America have different names from the stages in Europe and often only roughly intersect in time. Thus the North American Cincinnatian stage mostly corresponds with the Ashgillian stage in Europe, plus a tiny bit of the slightly earlier Caradocian stage.

Also, all this changes from textbook to textbook and from person to person, so that some authorities describe seven recent epochs, while others are content with four. In some books, too, you will find the tertiary and quaternary taken out and replaced by periods of different lengths called the Palaeogene and Neogene. Others divide the Precambrian into two eras, the very ancient Archean and the more recent Proterozoic. Sometimes too you will see the term Phanerozoic used to describe the span encompassing the Cenozoic, Mesozoic, and Paleozoic eras.

Moreover, all this applies only to units of time. Rocks are divided into quite separate units known as systems, series, and stages. A distinction is also made between late and early (referring to time) and upper and lower (referring to layers of rock). It can all get terribly confusing to nonspecialists, but to a geologist these can be matters of passion. “I have seen grown men glow incandescent with rage over this metaphorical millisecond in life’s history,” the British paleontologist Richard Fortey has written with regard to a long-running twentieth-century dispute over where the boundary lies between the Cambrian and Ordovician.

At least today we can bring some sophisticated dating techniques to the table. For most of the nineteenth century geologists could draw on nothing more than the most hopeful guesswork. The frustrating position then was that although they could place the various rocks and fossils in order by age, they had no idea how long any of those ages were. When Buckland speculated on the antiquity of an Ichthyosaurus skeleton he could do no better than suggest that it had lived somewhere between “ten thousand, or more than ten thousand times ten thousand” years earlier.

Although there was no reliable way of dating periods, there was no shortage of people willing to try. The most well known early attempt was in 1650 when Archbishop James Ussher of the Church of Ireland made a careful study of the Bible and other historical sources and concluded, in a hefty tome called Annals of the Old Testament, that the Earth had been created at midday on October 23, 4004 B.C., an assertion that has amused historians and textbook writers ever since.*9

There is a persistent myth, incidentally—and one propounded in many serious books—that Ussher’s views dominated scientific beliefs well into the nineteenth century, and that it was Lyell who put everyone straight. Stephen Jay Gould, in Time’s Arrow, cites as a typical example this sentence from a popular book of the 1980s: “Until Lyell published his book, most thinking people accepted the idea that the earth was young.” In fact, no. As Martin J. S. Rudwick puts it, “No geologist of any nationality whose work was taken seriously by other geologists advocated a timescale confined within the limits of a literalistic exegesis of Genesis.” Even the Reverend Buckland, as pious a soul as the nineteenth century produced, noted that nowhere did the Bible suggest that God made Heaven and Earth on the first day, but merely “in the beginning.” That beginning, he reasoned, may have lasted “millions upon millions of years.” Everyone agreed that the Earth was ancient. The question was simply how ancient.

One of the better early attempts at dating the planet came from the ever-reliable Edmond Halley, who in 1715 suggested that if you divided the total amount of salt in the world’s seas by the amount added each year, you would get the number of years that the oceans had been in existence, which would give you a rough idea of Earth’s age. The logic was appealing, but unfortunately no one knew how much salt was in the sea or by how much it increased each year, which rendered the experiment impracticable.

The first attempt at measurement that could be called remotely scientific was made by the Frenchman Georges-Louis Leclerc, Comte de Buffon, in the 1770s. It had long been known that the Earth radiated appreciable amounts of heat—that was apparent to anyone who went down a coal mine—but there wasn’t any way of estimating the rate of dissipation. Buffon’s experiment consisted of heating spheres until they glowed white hot and then estimating the rate of heat loss by touching them (presumably very lightly at first) as they cooled. From this he guessed the Earth’s age to be somewhere between 75,000 and 168,000 years old. This was of course a wild underestimate, but a radical notion nonetheless, and Buffon found himself threatened with excommunication for expressing it. A practical man, he apologized at once for his thoughtless heresy, then cheerfully repeated the assertions throughout his subsequent writings.

By the middle of the nineteenth century most learned people thought the Earth was at least a few million years old, perhaps even some tens of millions of years old, but probably not more than that. So it came as a surprise when, in 1859 in On the Origin of Species, Charles Darwin announced that the geological processes that created the Weald, an area of southern England stretching across Kent, Surrey, and Sussex, had taken, by his calculations, 306,662,400 years to complete. The assertion was remarkable partly for being so arrestingly specific but even more for flying in the face of accepted wisdom about the age of the Earth.*10 It proved so contentious that Darwin withdrew it from the third edition of the book. The problem at its heart remained, however. Darwin and his geological friends needed the Earth to be old, but no one could figure out a way to make it so.

Unfortunately for Darwin, and for progress, the question came to the attention of the great Lord Kelvin (who, though indubitably great, was then still just plain William Thomson; he wouldn’t be elevated to the peerage until 1892, when he was sixty-eight years old and nearing the end of his career, but I shall follow the convention here of using the name retroactively). Kelvin was one of the most extraordinary figures of the nineteenth century—indeed of any century. The German scientist Hermann von Helmholtz, no intellectual slouch himself, wrote that Kelvin had by far the greatest “intelligence and lucidity, and mobility of thought” of any man he had ever met. “I felt quite wooden beside him sometimes,” he added, a bit dejectedly.

The sentiment is understandable, for Kelvin really was a kind of Victorian superman. He was born in 1824 in Belfast, the son of a professor of mathematics at the Royal Academical Institution who soon after transferred to Glasgow. There Kelvin proved himself such a prodigy that he was admitted to Glasgow University at the exceedingly tender age of ten. By the time he had reached his early twenties, he had studied at institutions in London and Paris, graduated from Cambridge (where he won the university’s top prizes for rowing and mathematics, and somehow found time to launch a musical society as well), been elected a fellow of Peterhouse, and written (in French and English) a dozen papers in pure and applied mathematics of such dazzling originality that he had to publish them anonymously for fear of embarrassing his superiors. At the age of twenty-two he returned to Glasgow University to take up a professorship in natural philosophy, a position he would hold for the next fifty-three years.

In the course of a long career (he lived till 1907 and the age of eighty-three), he wrote 661 papers, accumulated 69 patents (from which he grew abundantly wealthy), and gained renown in nearly every branch of the physical sciences. Among much else, he suggested the method that led directly to the invention of refrigeration, devised the scale of absolute temperature that still bears his name, invented the boosting devices that allowed telegrams to be sent across oceans, and made innumerable improvements to shipping and navigation, from the invention of a popular marine compass to the creation of the first depth sounder. And those were merely his practical achievements.

His theoretical work, in electromagnetism, thermodynamics, and the wave theory of light, was equally revolutionary.*11 He had really only one flaw and that was an inability to calculate the correct age of the Earth. The question occupied much of the second half of his career, but he never came anywhere near getting it right. His first effort, in 1862 for an article in a popular magazine called Macmillan’s, suggested that the Earth was 98 million years old, but cautiously allowed that the figure could be as low as 20 million years or as high as 400 million. With remarkable prudence he acknowledged that his calculations could be wrong if “sources now unknown to us are prepared in the great storehouse of creation”—but it was clear that he thought that unlikely.

With the passage of time Kelvin would become more forthright in his assertions and less correct. He continually revised his estimates downward, from a maximum of 400 million years, to 100 million years, to 50 million years, and finally, in 1897, to a mere 24 million years. Kelvin wasn’t being willful. It was simply that there was nothing in physics that could explain how a body the size of the Sun could burn continuously for more than a few tens of millions of years at most without exhausting its fuel. Therefore it followed that the Sun and its planets were relatively, but inescapably, youthful.

The problem was that nearly all the fossil evidence contradicted this, and suddenly in the nineteenth century there was a lot of fossil evidence.