A Little History Of Science: The History of Our Planet
Uncovering the bones of ancient beasts is only part of the story. Walking in the country, you must have noticed that a valley often has a river or stream running down the middle of it. Hills and mountains, too, will surround the valleys. In some parts of the world, say, the Alps of Switzerland, it is striking how the mountains are very high and the valleys are very deep.
How were the earth’s features formed? Mountains and valleys could not have always been the way they are now, since the land- scape is changed every year by earthquakes, volcanic eruptions, rivers and glaciers. The change in any one year may be slight, but even in your lifetime, visible differences occur. Coastlines wear away and houses sometimes fall into the sea. Multiply that by several, or many, generations, and the changes are even larger. Violent earthquakes, volcanoes and tsunamis are nothing new.
Mount Vesuvius, near Naples in Italy, erupted in ad 79. It buried the town beneath it, Pompeii, killing many people, and the volcanic ash and lava changed the coastline dramatically. Today you can walk along the streets of Pompeii, which have been excavated from the ash and pumice that settled there.
Many people wondered about what these kinds of dramatic happenings meant. Some thought they were supernatural acts. But from the late 1600s, observers began to study the earth as an object of natural history. Modern geology was born when they grappled with three problems. The first was a new way of understanding ‘history’. In earlier times, ‘history’ really meant ‘description’. Natural history was simply a description of the earth and the things on it.
Gradually, ‘history’ acquired its modern meaning of change through time. We are used to things changing quickly: clothes, music, hairstyles, slang, and anything to do with computers and mobile phones. We see photographs of people in the 1950s and think how different they looked then. This is not really new – the Romans dressed differently than the ancient Greeks, for instance – but the pace of change is much faster now. So, we accept change as natural. History is the study of that change.
The second problem was that of time. Aristotle assumed that the earth is eternal, and had always been much as it was when he lived.
Ancient Chinese and Indian scientists also believed that the earth was very old. With the coming of Christian and Islamic views of the earth, time shrank. ‘Time we may comprehend, ’tis but five days older than ourselves,’ said the writer Sir Thomas Browne in 1642. What he meant was that the Book of Genesis tells the story of Creation, in which God created Adam and Eve on the sixth day.
During the previous five days the earth, sky, stars, sun, moon and all the plants and animals were created. For Christians like Browne, our planet, the earth, was created only shortly before Adam and Eve saw the first dawn in the Garden of Eden.
If you read the Bible carefully, and add up all the ages of the descendants of Adam and Eve mentioned in the Old Testament, that gives an approximate date for the first couple. In the mid- 1600s, an Irish archbishop did just that. His addition told him that the earth was created on 22 October 4004 bc, in the early evening, to be precise! Archbishop Ussher’s calculations were not accepted by many Christians in the 1650s. But for people wanting to know how the geological features of the earth were formed, it was difficult to explain how, say, river valleys could have gradually come about if the earth was less than 6,000 years old.
This limited period of time also created difficulties explaining how shells could be found on mountain tops, far above the present oceans and seas. What geologists needed above all was to find more time for the earth to have been in existence. Then the things they were observing could be put into some kind of sensible perspective. And this they did. Beginning in the late seventeenth century, naturalists began to argue that the world must be older than the few thousand years allowed by Ussher.
Several decades later, the Comte de Buffon (the pioneering natural historian we met in Chapter 19) worked out a scheme that combined cosmology and geology. His cosmology had the earth as originally a very hot ball, flung off from the sun. It gradually cooled down, and life became possible. He tentatively put the date of the separation of the earth from the sun at about 80,000 years ago, being careful with his exact language so as not to offend the Church.
The third problem was to understand the nature of rocks and minerals. All rocks are not the same. Some are hard, some soft and crumbly, and they are made up of different kinds of materials.
They also seemed to be of different ages. Naming and analysing rocks and minerals allowed the geologists who studied them to put together a picture of the earth’s history. Abraham Werner (1749–1817) in Germany did a lot of this early work. He worked in a university, but he was actively involved in mining. Mines deep under the earth helped scientists by providing samples of materials not easily obtained on the earth’s surface. Werner based his classification of rocks not simply on their composition, but also on their relative ages. The oldest ones were very hard and never contained fossils.
Thus the kinds of rocks found in a given place provided a clue to the age of the place, relative to other places. Digging downwards, where the layers of rocks and earth (the strata, as geologists call them) contained fossils, these too provided clues to the relative ages of both the fossils and the strata in which they were found.
The man who showed that the fossils were very important in this dating process was a surveyor, William Smith (1769–1839). Smith helped build Britain’s canals in the early nineteenth century. Before railways, water was the best way to transport goods, particularly heavy things like coal. Smith measured many miles of land, helping to decide the best route for a new canal. What he gradually realised, as he created a geological map of England and Wales, was that the most important characteristic of a layer of the earth’s crust was not simply the kind of rock it contained, but also the fossils that could be found within it.
With an expanded timescale for the earth’s history, an under- standing of the different kinds of rocks, and Smith’s insight into the importance of the fossils, geologists could try to ‘read’ the earth’s history. In the early 1800s, most geologists were ‘catastrophists’.
Piecing together the record uncovered through mining, canal building, and then railway building, they found many instances where volcanoes and earthquakes had thrown up layers previously buried deep in the earth’s crust. So it seemed to most naturalists that the history of the earth had been one of periods of stability separated by periods of violent events – catastrophes – across the globe. Floods counted as catastrophes, so as geologists tried to fit their findings with the Bible, they were happy that there seemed to be evidence of massive and widespread flooding in the past, including a recent one (in geological terms) that could be the universal flood in which Noah took the animals two by two into his ark.
The catastrophists found a lot of evidence to support their view of the earth’s history. The fossils in any of the various layers showed obvious differences from those below or above. The newer strata had fossils that were more like present-day living plants and animals than did the ones in the older layers. In Paris, Georges Cuvier (whom we met in the last chapter) was using ‘comparative anatomy’ and reconstructing vivid pictures of the animals of bygone ages. One of his followers was William Buckland (1784– 1856), a liberal English clergyman who taught geology at Oxford University. Buckland was especially energetic in his search for geological evidence for the biblical flood. He found lots of things that he thought were obviously caused by water: debris washed into caves, and rocks and even huge boulders spread over the fields. In the 1820s, he was very sure that these were the result of Noah’s flood; by the 1840s, as geological investigations had revealed more detail, he became less sure. Glaciers (huge rivers of ice) could have had an effect even in Britain, he realised. They provided a more convincing explanation of things like the scattered boulders, which could have been left behind as the ice moved slowly onwards.
In the 1820s and 1830s, most geologists believed that these ancient catastrophes coincided with new geological strata. Because the fossils in the layers were generally slightly different, they concluded that the earth’s history consisted of a series of cataclysmic events – massive floods, violent earthquakes – followed by the creation of new plants and animals that were adapted to the new conditions that had come into being. The earth, it seemed, had undergone a progressive history in preparation for its crowning glory: the creation of mankind. This scheme fitted with the account of Creation in the Book of Genesis, either by assuming that its six days of creation were actually six long periods, or that the Bible only described the last creation, the age of human beings.
In 1830, Charles Lyell (1797–1875), a young lawyer-turned- geologist, challenged this general account. Lyell had looked at rocks and fossils in France and Italy. He was studying geology at Oxford and his teacher was William Buckland, the catastrophist.
Lyell was dissatisfied with Buckland’s geological vision. What could we show, Lyell asked, if we assumed that the geological forces that operated on the earth had actually always been uniform (the same)? He became the leader of the ‘uniformitarians’, who grew to be opposed to the ‘catastrophists’. Lyell wanted to see how much of the whole geological history of the earth he could explain by using his principle of uniformity. He could see that at the present time the earth was very active geologically; there were still volcanoes, floods, erosion and earthquakes. If the rate of these changes was the same as long ago, was that enough to explain all the evidence of periods of ancient violent catastrophes?
Yes, he said, and set out his reasons in a three-volume work, The Principles of Geology (1830–33). He would revise it for the next forty years, carefully taking into account his own and other geologists’ research.
Lyell’s uniformitarianism was a bold attempt to get rid of catastrophes and the reliance on miracles such as Noah’s flood. He wanted to set geologists free to interpret the earth’s history without interference from the Church. Lyell was a deeply religious man who held that mankind was a unique, moral creature, with a special position in the universe. And he saw more clearly than most that the catastrophists’ idea of successive creations of plants and animals, approaching ever nearer those living in the present day, looked very much like evolution. Where the catastrophists compared deep fossils with shallow ones and saw progress, Lyell argued instead that fossils displayed no overall development. He was very excited when a fossil mammal was uncovered in an old layer, deep underground. Mammals were generally found only in recent strata, so this suggested to him that there was no real progress in the history of plants and animals, except for humans. If it looked like progress, that was only a fluke. No more than a tiny number of the species that existed in prehistoric times had been preserved as fossils.
Charles Lyell helped create modern geology. The way he thought about geology, and his extensive fieldwork, were both outstanding. He showed that, if our earth had a long enough history, much could be explained by simply observing what was going on now and using present-day geological events or forces to explain the past. A young naturalist, Charles Darwin, was much impressed with Lyell’s Principles of Geology. He took the first volume with him (and had the other two sent out to him) when he set off on his travels around the globe on the Beagle. Darwin said that he looked with Lyell’s eyes at the geological world – the world of earthquakes, rocks and fossils – during his voyage. But he came to very different conclusions about what the fossil record actually meant.