Course description

Ageing the Earth

At the very end of the 18th century – in 1797, to be precise – in Edinburgh, capital of Scotland, James Hutton was dying. This was bad news for Hutton, of course, but good news for geology as it cleared the way for a man named John Playfair to re-write Hutton’s classic work without embarrassing the great scientist who had done so much to advance human understanding of Earth sciences. Hutton was, by all accounts, a man of the most brilliant insights and liveliest conversation, a delight to sit next to at the dinner table, and unequalled in understanding the mysterious slow processes that shaped the Earth. Unfortunately, he was unable to write his ideas and discoveries in a way that anyone could understand. 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. Incomprehensible! Yet almost singlehandedly, he created the science of geology and transformed our understanding of the Earth. Hutton was born in 1726 into a rich Scottish family, and could spend his life in light work and intellectual hobbies. He studied medicine, but did not enjoy it and turned instead to farming, which he followed in a relaxed and scientific way on the family land. Tired of fields and sheep, in 1768 he moved to Edinburgh, where he founded a successful business, and busied himself with science. Edinburgh at that time was an intellectual centre. Hutton became a member of the Oyster Club, where he passed his evenings with men such as the economist Adam Smith, the chemist Joseph Black, and the philosopher David Hume, as well as occasional visitors like Benjamin Franklin and James Watt.

Like many gentlemen of that age, Hutton took an interest in nearly everything. He conducted experiments with chemicals, investigated methods of coal mining and canal building, toured salt mines, discussed heredity, collected fossils, and came up with theories on rain, the composition of air, and the laws of motion. But his particular interest was geology. A question that attracted interest in that fantastically curious age was why ancient sea shells and other marine fossils were so often found on mountaintops. How did they get there? Those who thought they had a solution were on two opposing sides. One group, known as the Neptunists, was sure that everything on Earth, including seashells in impossibly high 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, but were changed when water surrounded them during periods of global flooding. Against them were the Plutonists, who noted that volcanoes and earthquakes continually changed the face of the planet but clearly owed nothing to seas. The Plutonists also raised difficult questions about where all the water went when it wasn’t flooding. If there was enough of it at times to cover mountains, then where was it during calmer times? They believed that there were huge internal forces as well as surface ones acting on the Earth. However, they couldn’t explain how all those shells got up mountains. Hutton had a series of exceptional insights. From looking at his own farm, he could see that soil was created by the erosion of rocks and that particles were continually washed away by streams and rivers and re-deposited elsewhere. He realized that if this process continued to its natural conclusion then Earth would eventually be smooth. Yet there were hills everywhere around him. Clearly there was another process, some kind of renewal and uplift that created new hills and mountains to keep the cycle going. The marine fossils on mountaintops, he decided, did not come from floods, but had risen with the mountains themselves. He also deduced it was heat within the Earth that created new rocks and continents and pushed up mountains. Above all, what Hutton’s theories suggested was that Earth processes required huge amounts of time, far more than anyone had ever dreamed.

(512×659)In 1785, Hutton worked his ideas into a long paper, which was read at meetings of the Royal Society of Edinburgh. It attracted almost no notice at all. Nobody in the audience had any idea what he was talking about. Encouraged by his friends to expand his theory in book form, Hutton spent the next ten years preparing his life’s work, published in two volumes in 1795. Together the two books were nearly a thousand pages and were worse than even his most pessimistic friends had feared. Apart from anything else, nearly half the completed work now was quotations still in the original French. A third volume was so boring that it wasn’t published until 1899, more than a century after Hutton’s death, and the fourth and last was never published at all. Luckily Hutton had John Playfair, a professor of mathematics at the University of Edinburgh and a close friend, who could not only write but, thanks to many years with Hutton, actually understood what the great man was trying to say. In 1802, five years after Hutton’s death, Playfair produced a simplified book of Hutton’s principles, Illustrations of the Huttonian Theory of the Earth. The book was appreciated by those with an active interest in geology, which in 1802 was not a large number. That, however, was about to change.

In the winter of 1807, thirteen interested friends in London got together at a pub in Covent Garden, to form a club called the Geological Society. The idea was to meet once a month to exchange geological ideas over dinner. The price was set very high to discourage those with qualifications and interest but who were not gentlemen. It soon became clear, however, that there was demand for an institution, with a headquarters, where people could discuss new findings. In a decade, membership grew to four hundred – still all gentlemen, of course – and the Geological looked like getting bigger than the Royal as the premier scientific society in the country. The members met twice a month from November until June, when almost all of them went off to do fieldwork. These weren’t people with a financial interest in minerals or even academics, but simply gentlemen with the wealth and time for a hobby at a more or less professional level. By 1830, there were 745 of them. It’s hard to imagine now, but geology excited the nineteenth century in a way that no science ever had before or would again. In 1839, when Roderick Murchison published The Silurian System, a thick and difficult 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 unreadable. And when, in 1841, the great Charles Lyell traveled to America to give lectures in Boston, sellout audiences of three thousand packed in to hear his sleepy descriptions of marine zeolites in Campania. William_Buckland_detail.png (130×160)Charles 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, because his mother was sure that Scots were drunks. Like so many other great scientific minds of that age, Lyell came from a background of comfortable wealth and intellectual energy. From his father Lyell gained an interest in natural history, but it was at Oxford, where he was taught by Reverend William Buckland, that the young Lyell began his lifelong interest in geology. Buckland had some real intellectual achievements, but he is remembered as much for his eccentricities. He was especially famous for the wild animals, some large and dangerous, allowed to walk through his house and garden, and for eating every animal on Earth. Guests at Buckland’s house might eat baked mice, roasted hedgehog, or boiled sea slug. He became an expert on coprolites – fossilized toilet – and had a table made of them. Charles Darwin thought Buckland a fool, but Lyell liked him enough to go touring with him in Scotland in 1824. It was soon after this trip that Lyell decided to leave a career in law and turn his attention to geology full-time. Lyell was extremely short-sighted and eventually would go blind. His other strange habit, when thinking, was lying across two chairs at once or resting his head on the seat of a chair, while standing up. 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, which in many ways explained Hutton’s thoughts a generation earlier.

Between Hutton’s age and Lyell’s there was another geological fight. The new battle became an argument between catastrophism and uniformitarianism, unattractive terms for an important and very long-running disagreement. Catastrophists believed the Earth was shaped by sudden disasters – floods principally. Catastrophism was comforting to Christians like Buckland because it allowed them to include Noah’s flood in serious scientific discussions. Uniformitarians by contrast believed that changes on Earth were gradual and that nearly all Earth processes happened over immense periods of time. Hutton was more father of the idea than Lyell, but it was Lyell most people read, and so he became in most people’s minds the father of modern geological thought. Lyell believed the Earth’s shifts were steady, that everything that had ever happened in the past could be explained by events still going on today. Lyell didn’t just disagree with catastrophism, he hated it. Catastrophists believed that a series of extinctions repeatedly wiped animals out and replaced them with new ones. It was too convenient as a way to explain the unknown. It’s impossible to overestimate Lyell’s influence. The Principles of Geology went through twelve editions in Lyell’s lifetime and included notions that shaped geological thinking into the 20th century. Meanwhile, geology had much sorting out to do, and not all of it went smoothly. From the start, 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. This wasted a huge amount of time.

Nowadays, very generally, geological time is divided first into four great eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic. These four eras are then divided into a dozen to twenty subgroups, usually called ‘periods’ though sometimes ‘systems’. Most of these are also well known: Cretaceous, Jurassic, Triassic, and so on. 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 finer subdivisions known as stages or ages. Fortunately, you’re unlikely ever to hear about any of them again. Further confusing the matter is that the stages or ages in North America have different names from those in Europe and often only roughly intersect in time. Also, all this changes from textbook to textbook and from person to person, so that some authorities describe seven recent epochs, while others are happy with four. It can all get very confusing to non-specialists, but to a geologist these can be matters of passion. At least today we can use some advanced dating techniques. For most of the nineteenth century geologists had only 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 estimated the age 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 were many people willing to try. The best-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 that the Earth was created at midday on October 23, 4004 B.C. There is a myth, incidentally, that Ussher’s views dominated scientific beliefs into the nineteenth century, and that it was Lyell who showed it was not true. In fact, no. No geologist of any nationality suggested a Biblical timescale. Even Buckland, a very serious Christian, noted that the Bible never said God made Heaven and Earth on the first day, but only “in the beginning.” That beginning may have lasted “millions upon millions of years.” Everyone agreed that the Earth was ancient. The question was how ancient.

The first scientific attempt at measurement was made by the Frenchman Georges-Louis Leclerc, Count of Buffon, in the 1770s. It was known that the Earth radiated large amounts of heat – that was clear to anyone who went down a coal mine – but there wasn’t any way of estimating how fast it disappeared. Buffon’s experiment was heating spheres until they glowed white hot and then estimating the rate of heat loss by touching them (probably 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 huge underestimate, but still radical, and Buffon was threatened with being thrown out of the Catholic Church because of it. A practical man, he apologized at once, then repeated it in all his later writings. By the middle of the 19th century most people thought the Earth was at least a few million years old, perhaps tens of millions, 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 an area of southern England, had taken, he calculated, 306,662,400 years to complete. (Darwin loved exact numbers!) This was remarkable for rejecting accepted wisdom about the age of the Earth. It was so problematic that Darwin took it out of his book. The problem remained, however. Darwin 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, one of the most extraordinary figures of the nineteenth century – indeed of any century. Kelvin really was a kind of Victorian superman. In the course of a long career (he lived till 1907 and the age of eighty-three), he wrote 661 papers, received 69 patents (which made him very wealthy), and became famous in nearly every branch of the physical sciences. Here are just a few examples: he suggested the method of refrigeration; he devised the scale of absolute temperature that still has his name; he invented boosting devices that allowed telegrams to travel across oceans; and made uncountable improvements to shipping and navigation. And those were just his practical achievements. His theoretical work in electromagnetism, thermodynamics, and the wave theory of light, was equally revolutionary. There was only one problem with him 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, 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 time, Kelvin became more decided and less correct.

He continually revised his estimates downward, from a maximum of 400 million years, to 100 million years, to 50, and finally, in 1897, to just 24 million years. You see: there was nothing in physics that could explain how something the size of the Sun could burn continuously for more than a few tens of millions of years without using all its fuel. Therefore the Sun and its planets were relatively, but inescapably, young. The problem was that nearly all the fossil evidence contradicted this, and suddenly in the nineteenth century there was a lot of fossil evidence. If you want to watch some videos on this topic, you can click on the links to YouTube videos below. If you want to answer questions on this article to test how much you understand, you can click on the green box: Finished Reading?

Videos :

1. James Hutton (4:00)

2. Neptunism (5:00)

3. Plutonism (00:14)

4. Roderick Murchison (10:00)

5. Charles Lyell and Geologic Time (3:30)

6. William Buckland (20:00)

7. Uniformitarianism Vs Catastrophism (17:00)

8. Precambrian Era (2:00)

9. Paleozoic Era (6:00)

10. Mesozoic Era (4:00)

11. Cenozoic Era (2:00)